GB2530085A

GB2530085A - An internal combustion engine with a novel 4-stroke cycle and optional compressed air energy storage

Info

Publication number: GB2530085A
Application number: GB1416194.7A
Authority: GB
Inventors: Michael Willoughby Essex Coney; Karim Wazni
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-09-12
Filing date: 2014-09-12
Publication date: 2016-03-16
Also published as: WO2016038384A1; GB201416194D0

Abstract

An internal combustion engine 4 is configured to operate in an unconventional 4-stroke cycle, which incorporates two cooling strokes and can operate using stored or externally supplied compressed air. During starting and if the compressed air store 15 is depleted, the engine 4 can operate with a conventional 4-stroke cycle. When used in a vehicle, the stored compressed air may be provided by an external compressor and external renewable power source. The vehicle system may incorporate regenerative braking and provide motive power even when the compressed air store 15 is depleted. The disclosed power system may also operate in a low emissions mode suitable for urban motoring by burning fuel in a low pressure duct burner or catalytic combustor 35. In one embodiment of the power system, there is both a high pressure adiabatic expander 1 and a low pressure expander 4 with internal combustion. A coupled internal air compressor 8 may provide compressed air for the engine.

Description

PATENT APPLICATION

An Internal Combustion Engine with a Novel 4-Stroke Cycle and Optional Compressed Air Energy Storage

DESCRIPTION

BACKGROUND

[0001] It is well known that compressed air may be used as a means of storing energy for later use in power generation or for the purpose of recovering braking energy in moving vehicles.

[0002] The use of gas turbines in combination with compressed air energy storage is well-known and two such plants have been built and operated.

[0003] The use of fuelled reciprocating engines in combination with compressed air energy storage is also known. The so-called split cycle engine is an example of this. In these systems, the intake and compression strokes are performed in different cylinders from the combustion and exhaust strokes.

[0004] Split cycle engines generally also have the ability to run with or without using stored compressed air, which is useful when the compressed air store is depleted.

[0005] The recuperation of exhaust heat after compression in order to heat the air before combustion is also known. Recuperation is particularly useful if the stored air is relatively cool, for example if compression is performed either with intercooling or quasi-isothermally with direct water spray injection into the compression cylinder.

[0006] Practical experience has shown problems with the cooling of cylinders which are used only for combustion and expansion, without intake and compression. This is a disadvantage of split-cycle engines. Also the absence of in-cylinder compression can cause difficulties in achieving reliable ignition and combustion of the fuel-air mixture, particularly when the engine is being started or is being operated at low power levels.

[0007] The use of compressed air storage as a means to provide a regenerative braking system to a road vehicle is known in the literature and developments of such systems are in progress. However, most of these systems are not capable of utilizing compressed air supplied from an external source such as mains electric power.

[0008] Also most of these vehicle-based compressed air storage systems do not make use of the potential to substantially increase the amount of recovered energy by adding heat to the air before expansion.

[0009] Full electric vehicle systems, which can utilize mains electric power and store it in batteries, have effectively zero emissions, but suffer from various disadvantages including high cost and weight, short lifetime, availability of materials, undesirable by-products of manufacture, a fixed relationship between power output and storage capacity, long battery charging times and no fall-back motive power if the battery energy is exhausted.

[00010] Hybrid electric vehicles can overcome some, but not all of the disadvantages of a pure electric vehicle. For instance, they have longer ranges because they can run on fuel and have a lower battery capacity, which decreases the initial battery cost and its replacement costs. On the other hand, they have a disadvantage in that they carry the size, weight, complexity and cost of two motive power systems.

BRIEF DESCRIPTION

[00011] The present invention concerns a reciprocating internal combustion engine with a novel 4-stroke cycle, which also has the capability to run as a conventional 4-stroke engine. The waste heat of the engine is recovered and used to pre-heat the air before combustion, which reduces fuel consumption. The engine has the capability to run with an external supply of compressed air or with air supplied from a compressed air storage vessel. The ability to run as a conventional 4-stroke engine is most useful during starting and when the supply of compressed air is exhausted or cut off.

[00012] The invention is distinguished from the prior art in that the combustion and expansion process includes two additional strokes for the purpose of providing internal cooling and in order to facilitate ignition and combustion particularly during starting and low power operation.

[00013] The present invention allows the storage of energy which can be supplied by renewable sources such as a remote wind farm, solar energy farm, or by nuclear or fossil-fired power stations operating at off-peak times. The externally supplied energy is used to compress air which may be stored in static compressed air storage tanks or stored directly in on-board air tanks in the case of a vehicle.

[00014] The invention may be applied to power a road, rail or a marine vehicle, such as a ship. If the vehicle is a small road vehicle such as a passenger automobile, then the compressor delivering the compressed air may be installed in a commercial garage or a garage at a private house, or a network of air charging stations, where compressors are either used to refill the on-board air tanks directly or to recharge large stationary air tanks used to fill the vehicles' on-board tanks. In this case, the compressed air is then transferred to the vehicle.

[00015] II the vehicle is a large road or rail vehicle or a ship for example it may carry its own compressor which can be powered by connecting the vehicle to an external source of mains electricity. Alternatively a large vehicle could carry a supplementary source of power such as a photovoltaic system or a wind turbine system. Such power sources could also be used to produce and store compressed air.

[00016] The present invention has the capacity to make use of regenerative braking, in which the kinetic energy of the decelerating vehicle may be stored in the form of additional compressed air.

[00017] A first embodiment of the invention refers to a power system with two stages of expansion. There is a high pressure adiabatic expander and a combustion expander operating at lower pressure. The system also includes storage vessels containing compressed air at an upper and a lower pressure.

[00018] In the case of a vehicle with regenerative braking, the drive system of the first embodiment also has an on-board air compressor which is used to compress air from the lower to the upper air storage pressures. This on-board compressor is generally separate and distinct from the compressor used to supply the main charge of stored compressed air.

[00019] In the first embodiment there are three different modes of operation, which are; firstly normal operation involving consumption of stored compressed air, secondly extended range operation and thirdly operation with low emissions, which could be used when the vehicle is within an area of high environmental sensitivity, such as an urban area.

[00020] The term "extended range" is taken here to mean continued operation of the energy system even when the compressed air store is depleted, whether or not the energy system is installed in a vehicle.

[00021] Stored compressed air is not consumed in extended range operation or in low emission operation. In these two operational modes, the operation of the system is limited only by the availability of fuel.

[00022] All three modes of operation involve some consumption of fuel. In the case of normal operation some of the fuel is burned by internal combustion and some of it may be burned continuously in one or two duct burners. In the case of the extended range mode of operation, all the fuel is burned in the cylinders using internal combustion. In the case of low emission operation, all the fuel is burned continuously using a low pressure duct burner or catalytic combustor.

[00023] The normal mode of operation is expected to give the best fuel economy in terms of output drive energy per unit of input fuel energy. The normal mode is also expected to give the highest engine power, when it is needed. However, the normal mode is only available as long as the stored compressed air is available. When the pressure in the compressed air storage vessel falls to a certain minimum, it is necessary to switch to either the extended range mode or the low emissions mode.

[00024] The low emissions mode is expected to give the lowest emissions of carbon monoxide and nitrogen oxides, since the combustion temperature and pressure are much lower. Particulate emissions should also be very low. If catalytic combustion is used rather than a duct burner, then even lower emissions of carbon monoxide, NOx and particulates should be possible.

[00025] Regenerative braking is available during all three modes of operation.

[00026] A second embodiment is described in which the adiabatic expander and the combustion expander is coupled to the drivetrain via an electric generator and motor in a similar way to that used in conventional hybrid electric vehicles, such as the Chevrolet Volt. Energy may be stored for short periods for example by means of an electrochemical battery or a flywheel.

[00027] The second embodiment is similar to the first embodiment with regard to normal operation and extended range operation, but regenerative braking is provided by the battery or other short-term energy storage device.

[00028] If the battery or other energy storage device has sufficient capacity it may also be used for low or zero emission motoring.

[00029] A third embodiment is also described which is a simplified version of the first embodiment. In the third embodiment, there is only a single pressure of compressed air storage and single expansion stage, which involves internal combustion. The high pressure adiabatic expander is absent. The air storage pressure of the third embodiment is expected to be lower than in the first embodiment, and the duration of normal operation is expected to be less. The third embodiment retains the capacity for normal operation, extended range operation and low emissions operation, all with regenerative braking.

[00030] A fourth embodiment is also described which is applicable to a static fuel-assisted energy storage system. In this case, the regenerative braking capability is unnecessary and is removed. It is assumed that the static plant is sited remote from an urban area, so that the low emissions capability may also be removed. However the ability to continue operation when the compressed air energy store is depleted is retained. This type of system could be applied to a remote site, such as an island without a grid connection. For example, such a site could have a renewable power source such as wind or solar, which can provide the energy to produce compressed

S

air on an intermittent basis. The proposed system of the fourth embodiment could utilise the stored compressed air when it is available, but still provide security of supply when it is not available.

[00031] A fifth embodiment is also described in which the novel 4-stroke cycle with two cooling strokes is applied as a recuperated split-cycle engine with one or more compression cylinders, which are directly driven by one or more combustion cylinders. This engine may be used for power generation, mechanical drive or as the motive power for a vehicle. This engine may be connected to a generator and battery or other energy storage device either in a static power generating system or as a hybrid electric drive system for a vehicle.

[00032] A common rail fuel injection system may be used for injection of fuel in the combustion expanders of any or all of the described embodiments.

PRIOR ART

[00033] US patent 1932698 by Robert B Jose describes a vehicle drive system in which an internal combustion engine is mechanically connected to a compressor via a crankshaft. The internal combustion engine has an intake valve admitting atmospheric air. The air compressor supplies air to a compressed air store. Air from the compressed air store passes through a heat exchanger, where it is heated by the exhaust heat of the combustion engine. Thus this type of engine does have recuperation of waste heat. The heated compressed air then flows to a separate air motor, which is an air expander. The air motor drives a crankshaft which is mechanically connected to the road wheels of the vehicle.

[00034] US patent 1932698 does not disclose the use of the air storage vessel for the storage of externally supplied compressed air. All the power delivered in this system derives from fuelling the internal combustion engine. Therefore it is not an energy storage system as far as externally supplied energy is concerned.

[00035] Furthermore, US patent 1932698 does not disclose the use of stored compressed air for the combustion of fuel in the internal combustion engine. Thus, there is no attempt to reduce the work of compression of the internal combustion engine by modifying the operating cycle.

[00036] us patent 1932698 does not disclose any form of regenerative braking system.

[00037] us patent application publication 2013/0269632 by Meldolesi et al discloses a split cycle engine working as a compressed air energy storage system. This system can operate with or without stored compressed air. The system is described as operating on a 4-stroke cycle, with the intake and compression stroke in one cylinder and the combustion and exhaust stroke in another cylinder. Thus each type of cylinder operates on a 2-stroke cycle. In particular, the expansion cylinder is not cooled by the intake air and is totally reliant on external cooling.

[00038] US patent application publication 2013/0269632 does not disclose any form of regenerative braking and there is no recuperation of waste heat.

[00039] US patent number 6817185 by Coney et al describes a split cycle engine in which the compression is performed quasi-isothermally using water sprays inside the compression cylinder. This invention also discloses a recuperator which uses heat from the exhaust gases of the combustion cylinders to pre-heat the compressed air prior to combustion. One embodiment of the invention describes the application of the invention in combination with a compressed air energy storage system.

[00040] US patent 6817185 describes a 2-stroke cycle for the cylinders which perform the combustion and expansion, with no internal cooling provided by the inlet air.

Although the invention can operate with or without stored compressed air, no system of regenerative braking is proposed.

[00041] Paper 170 by Sugiura et al published at the 2007 CIMAC conference in Vienna and entitled "Isoengine test experience and proposed design improvements" describes test work performed on a prototype version of the engine disclosed in US patent 6817185. This paper describes difficulties with the design of the cooling system of the 2-stroke combustion cylinders and with the method of starting and raising power.

BRIEF DESCRIPTION OF THE DRAWINGS

[00042] Figure 1 is a diagram of a vehicle power and drive system including an adiabatic expander, a combustion expander and regenerative braking using compressed air according to the first embodiment.

[00043] Figure 2 is a diagram of a vehicle power and drive system according to the second embodiment, including both compressed air energy storage and a short-term energy storage system such as a battery, which provides regenerative braking capability.

[00044] Figure 3 is a diagram of a vehicle power and drive system according to the third embodiment, in which there is no adiabatic expander [00045] Figure 4 is a diagram showing an application of the invention to a static power generation and energy storage system according to the fourth embodiment.

[00046] FigureS is a diagram of the fifth embodiment showing the application of the invention to an engine which produces its own compressed air and does not have compressed air storage.

[00047] Figure 6 shows a 2-way exhaust gas separation valve, which is integrated with the exhaust valve of a combustion engine.

[00048] Figure 7 shows a compressed air inlet valve with variable closing time.

DETAILED DESCRIPTION OF THE FIRST EMBODIMENT

[00049] The vehicle power and drive system of the first embodiment shown in Figure 1 will now be described in detail.

[00050] Referring to Figure 1, the power and drive system has a high pressure air storage tank 15 equipped with a first pressure transducer 51 and a medium pressure air storage tank 25 equipped with a second pressure transducer 24. Both storage tanks are also equipped with safety valves (not shown). The high pressure air storage tank would normally be charged overnight or before a journey to its maximum pressure of 200 bars or more. The medium pressure storage tank may also be charged to a pressure of about 50 bars.

[00051] The power and drive system has one or more high pressure adiabatic expansion stage(s) 1, which do not have fuel injection, and a low pressure expansion stage 4, into which fuel may be injected and burned. For example there could be two high pressure adiabatic expansion stages at different pressures, with the exhaust of first adiabatic stage feeding into the inlet of the second adiabatic stage. Each expansion stage may consist of just one cylinder as shown in Figure 1, or some or all expansion stage may consist of more than one cylinder.

[00052] The power and drive system also includes a compressorS which is used for regenerative braking.

[00053] During normal operation air from the high pressure tank 15 is admitted to a first air heater 18 via a valve 16 and a pipe 17. The high pressure air enters the first heating element 19 within the air heater 18. The heating element may consist of a tube shaped as a coil, a serpentine or other shape within the casing of the 1S air heater 18.

[00054] Hot high pressure air exits the air heater 18 via a pipe 20 which leads to the high pressure adiabatic expander 1. The hot high pressure air is periodically admitted to the adiabatic expander 1 by an inlet valve 48.

[00055] The timing of closing of inlet valve 48 is controllable so that the amount of air entering cylinder 1 is adjustable according to the conditions.

[00056] The inlet valve or inlet valves 48 may be a poppet valve or other suitable valve which can be rapidly opened and closed according to the crank-angle of the crank 3, which is connected to the piston and piston rod 2 of the expander 1.

[00057] The inlet valve or valves 48 opens when the piston and piston rod 2 is at or near top dead centre. Hot high pressure air is admitted to the cylinder or cylinders of the expander 1. The valve closes again at a variable crank position after top dead centre. Typically the valve 48 may close at a crank angle of about 45° after top dead centre. The crank angle at which the inlet valve 48 closes is adjustable while the system is running.

[00058] After the inlet valve 48 closes, the air within the cylinder undergoes an approximately adiabatic expansion to a lower pressure and in doing so it performs work against the piston 2. The piston 2 transmits the work to the crankshaft 3, which is connected to the gearbox 46 via the clutch 43.

[00059] The exhaust valve 49 opens when the piston 2 is at or near bottom dead centre and the partially expanded air, which is at a lower temperature and pressure than the inlet air, is vented from the cylinder ito an exhaust pipe 21.

[00060] The high pressure adiabatic expander 1 operates on a 2-stroke cycle. Thus, following the venting of the cylinder 1 to the exhaust pipeline 21 during the piston up-stroke, another cycle begins involving a further admission of high pressure air into the cylinder and a further adiabatic expansion.

[00061] The first exhaust pipeline 21 contains a branch connection to another pipe 22 which leads to the medium pressure air storage tank 25 equipped with a pressure transducer 24. The medium pressure storage tank 25 also acts as an accumulator which can reduce the pressure fluctuations in pipe 21.

[00062] After the branch connection to pipe 22, the first exhaust pipeline 21 leads to a 2nd air heater 27. The first exhaust pipeline 21 is connected to the second heating element 28 which is within the 2nd air heater 27. The 2nd heating element may consist of a tube shaped as a coil, a serpentine or other shape within the casing of the 2 air heater 27.

[00063] After passing through the second heating element 28, the exhaust air from cylinder 1 passes along the pipeline 29 leading to the inlet valve 50 of the second expander 4. The inlet valve 50 may be a poppet valve or other suitable valve which can be rapidly opened and closed according to the crank-angle of the crank 6, which is connected to the piston and piston rod 5 of the expander 4.

[00064] The timing of the closing of the inlet valve 50 on the expander 4 is also controllable in a similar way to that of inlet valve 48 on expander 1. This allows control of the amount of air entering expander 4 at each cycle.

[00065] The inlet valve or valves 50 opens when the piston and piston rod 5 is at or near top dead centre. Hot high pressure air is admitted to the cylinder or cylinders of the expander 4.The valve 50 closes again at a variable crank position after top dead centre. The crank angle at which the inlet valve 50 closes is adjustable while the system is running.

[00066] Unlike the adiabatic expander 1, the second expander 4 operates on a 4-stroke cycle and is equipped with the means to inject fuel and to burn it. The fuel may be injected via a fuel injector 30 within a period beginning shortly before the piston and piston rod 5 reaches top dead centre and ending near the time at which the air inlet valve 50 closes. The fuel ignites and burns in the hot air which is still at a relatively high pressure.

[00067] The ignition may occur spontaneously due to the high pressure and temperature of the air within the cylinder or an ignition aid such as a spark plug or glow plug may be used.

[00068] During the first piston down-stroke, the combustion gases in the cylinder 4 expand doing work against the piston and piston rod 5. This work is transmitted to the crankshaft 6, which is connected to the gearbox 46 via the clutch 44 and the pair of gears 53 and 9.

[00069] During the first piston up-stroke, which follows combustion of the fuel, the exhaust valve 31 opens. There is an initial blow-down as the cylinder 4 depressurizes.

Then the exhaust gases are expelled via the valve 31 and the exhaust pipe 32 during the up-stroke of the piston and piston rod 5.

[00070] Valve 31 is a 2-way valve, which can connect the cylinder 4 either to the exhaust pipe 32 or to a short air pipe 42.

[00071] When the piston S reaches top dead centre following the exhaust stroke, the 2-way valve 31 is switched so that cool air can be drawn into the cylinder 4 during the second piston down-stroke.

[00072] The 2-way valve remains in the same position during the second piston up-stroke, so that the cool air which was drawn in is expelled again via the short air pipe 42. The short air pipe 42 is joined to an air duct 40 through which a flow of cold atmospheric air is blown continuously by a fan 39.

[00073] Table 1 summarizes the sequence of events in the 4-stroke combustion expander during normal operation with diesel fuel which is ignited by compression ignition.

TABLE 1

Approx Fuel Via 2-way valve Hot HP Description of process crank injection Exhaust Cold LP air air inlet angle ° gas outlet inlet/outlet __________ _____________________________________ 0° Off Closed Opening Closed Cold LP air intake begins Cold LP air intake for cooling, followed by partial air expulsion 2700 Off Closed Closing Closed Cold LP air expulsion ends __________ __________ ___________ ____________ _________ Compression of residual air 355° Starts Closed Closed Closed Fuel injection begins; compression _________ _________ __________ ___________ ________ ignition of fuel in residual air Fuel burns in residual air 370° On Closed Closed Opens Hot HP air is admitted, more fuel is ___________ __________ ____________ _____________ __________ injected.

Isobaric combustion in hot HP air "420° Ends Closed Closed Closing End of fuel injection Variable ___________ __________ ____________ _____________ __________ Expansion of hot combustion gases 540° Off Opening Closed Closed Exhaust of combustion gas begins Exhaust of combustion gases continues 715° Off Closing Closed Closed Exhaust of combustion gas ends 720° Off Closed Opening Closed As shown at 0° crank angle; 4-stroke __________ __________ ___________ ____________ _________ cycle is repeated [00074] In this mode of operation, one purpose of the additional 2-strokes of expander 4 is to provide cooling to the cylinder. This cooling can be supplemented by conventional water cooling which may be provided to the cylinder 4 and the cylinder head.

[00075] In addition, the additional 2-strokes allow for the compression of a fraction of the intake cooling air, which is trapped in the cylinder when the 2-way valve closes.

[00076] The air pipe 42 should be as short as possible and preferably less than about 0.1 m in length since there is a flow reversal in the pipe between the second piston down-stroke and the second piston up-stroke. If the pipe is too long, then too much hot air will be left in the pipe and not enough cooling air will be drawn in at each cycle.

[00077] The exhaust gas passing along the exhaust pipe 32 during the first piston upstroke continues to the second air heater 27 via a duct burner or catalytic combustor 33, which may be equipped with a fuel injector 34. The second air heater 27 is able to increase the temperature of the air which may come from the first expander via pipe 21 or from the medium pressure air tank 25 via the pipe 22.

[00078] The exhaust gas which leaves the 2 air heater through pipe 52 goes to the duct burner or catalytic combustor 35, which is equipped with a fuel injector 36. The duct burner or catalytic combustor 35 raises the temperature of the exhaust gas prior to entry into the first air heater 18. After exchanging heat with the incoming compressed air by flowing inside heating element 19, the exhaust gas exits the air heater 18 and flows to the atmosphere through the exhaust pipe 37.

[00079] During normal operation in which stored compressed air is consumed, the power delivered to crank 3 by the adiabatic expander 1 is transmitted to the crank 6 via a first clutch 43. The power provided by the combustion expander 4is transmitted by the piston and piston rod 5 to the crank 6, which is connected to a gear 53 via a clutch 44. The gear 53 drives another gear 9 which is mounted on the main drive shalt through the gear box 46.

[00080] The arrangement of clutches 43, 44 and 45 and gears 9, 10 and 53 shown in Figure 1 allows the mechanical connection or disconnection of either of the two expanders or of the compressor used for regenerative braking.

OPERATION OF THE FIRST EMBODIMENT IN LOW EMISSIONS MODE

[00081] When the first embodiment shown in Figure 1 operates in low emissions mode, the internal combustion expander 4 is disconnected from the drive system by disengaging clutch 44. The high pressure air inlet valve 50 on the combustion expander 4 is kept closed. The fan 39 operates with valve 54 closed and valve 55 open in order that atmospheric air flows along pipe 56 to the junction 60 at the air heater 27. Also valve 58 is closed and valve 59 is opened.

[00082] Clutch 45 is permanently engaged during operation in low emissions mode in order that air is taken from the medium pressure storage vessel 25 via pipe 26 and cooler 23 to the compressor 8, where it is compressed to the higher pressure prevailing in the high pressure air storage tank 15. The high pressure air is delivered by the compressor 8 along pipe 12 via cooler 13 and check valve 14.

[00083] Meanwhile, cold high pressure compressed airflows from the storage vessel or from pipe 12 through valve 16 and pipe 17 and through the heater coil 19 in the air heater 18. The high pressure compressed air is heated in the heater 18 and then flows via pipe 20 to the inlet valve 48 on the high pressure adiabatic expander 1.

[00084] The hot high pressure air is partially expanded adiabatically in expander 1 down to a medium pressure imparting power to the crankshaft 3 in the process. The partially expanded air, which is still hot then flows from the expander exhaust valve 49 along pipe 21 to the heater coils 28 within heater 27. In low emissions operation, this heater is used to cool the partially expanded air and transfer heat to the incoming cool atmospheric air which has entered the system at junction 60. The partially expanded air passes out of the heater coils along pipe 29 and then along pipe 57 and valve 59 to the medium pressure storage vessel 25.

[00085] The cool atmospheric air which is blown by the fan 39 is thereby pre-heated in heater 27 and then flows along pipe 52 to the duct burner or catalytic combustor 35, where fuel is injected and burned. The combustion gases entering the low pressure side of the heater 18 are hot enough to heat the high pressure air inside the heater coil 19 to a temperature of about 700 C. [00086] The combustion gases finally exit the heater 18 to the atmosphere via pipe 37, having heated the high pressure air from near ambient temperature to about 700 C. The flow rate of air coming from fan 39 is controlled at a level such that the final exhaust temperature of the combustion gases in pipe 37 is preferably in the region of 100 C so as to maximize the efficiency of the system.

[00087] As described above, the low emissions mode involves combustion with a continuously fired duct burner or catalytic combustor. Intermittent firing at high pressure and temperature as in a spark-ignited or compression ignition internal :ii combustion engine is absent. The low emissions mode is a closed Brayton cycle, with the rejected heat used to preheat the air supplying the duct burner or catalytic combustor. The combustion of fuel at moderate temperature and low pressures minimizes the production of polluting gases such as NOx and CO. Particulate emissions are also minimized.

REGENERATIVE BRAKING SYSTEM OF THE FIRST EMBODIMENT

[00088] When driving a conventional gasoline or diesel-powered vehicle, a driver often decelerates by partially lifting his/her foot on the accelerator pedal, without touching the brake pedal. The kinetic energy of the vehicle is absorbed in friction and in pumping air through the engine. This process is known as "engine braking", which can be very effective particularly if the driver changes into a lower gear, which causes the engine speed to increase relative to the vehicle speed. The deceleration is controlled by slight adjustments of the accelerator pedal. The frictional power dissipation is approximately linear with engine speed at low engine speeds, but varies approximately with the square of the engine speed when the engine speed is increased. Therefore engine braking is an effective method of reducing speed, particularly if the engine speed is relatively high.

[00089] The driver may also use the foot-brake, particularly if the vehicle is required to stop or reduce speed suddenly. In this case, the vehicle kinetic energy is absorbed by friction and generation of heat in the brake pads or brake discs. Both during engine braking and when the foot-brake is used, the excess kinetic energy of a conventional gasoline or diesel-powered vehicle is dissipated as heat and is not recovered.

[00090] As shown in Figure 1, the shaft of the gearbox 46 is connected to a gear 9, which drives another gear 10. Gear 10 is connected to a crank 11 and a compressor 8 via a third clutch 45. One purpose of the compressor 8 is to allow regenerative braking of the vehicle. When clutch 45 is engaged, compressor 8 begins to operate, drawing air at medium pressure from the storage vessel 25 via a cooler 23.

[00091] The cooling of cooler 23 may be provided by the natural flow of air over a tube coil caused by motion of the vehicle, or the air cooling may be enhanced by the use of a fan, such as fan 39 which may be used to provide more than one cooling function.

[00092] The air entering compressorS via cooler 23 is compressed in a 2-stroke cycle.

The compressor 8 is equipped with valves (not shown) at the point of entry to the cylinder and at the point of discharge. These valves can be poppet valves or plate valves acting under the effect of differential air pressure alone. Compressor plate valves do not require active timing by mechanical or other means.

[00093] The compressorS increases the air pressure from the medium pressure of storage vessel 25 to the high pressure of storage vessel 15. The air discharged from the compressor 8 may pass through another cooling coil 13 and a check valve 14 before entering the high pressure storage vessel 15.

[00094] The purpose of the cooler 23 is to maximise the amount of air which is compressed by a given amount of mechanical energy. This allows optimum use of the energy of braking.

[00095] The purpose of cooler 13 is to maximise the mass of air which can be stored in the high pressure air storage vessel 15. The heat which is rejected in cooler 13 cannot be used to improve performance, since if it were not rejected it would simply displace other heat which is available from the exhaust gas in heat exchanger 18 and the temperature of the exhaust gas at 37 would rise.

[00096] When the vehicle decelerates by engaging the clutch 45, the compressorS starts to operate and pumps air from the medium pressure storage vessel 25 to the high pressure storage vessel 15. This process can replenish air which has been expanded in expander 1, thereby utilizing the excess kinetic energy of the vehicle during deceleration or when the vehicle is going downhill.

[00097] In the case of a road vehicle, the regenerative braking system is envisaged as additional to the brake discs or pads, which would be operated hydraulically by a foot brake and mechanically by a handbrake in the conventional way. These conventional systems will allow the vehicle to be stopped very quickly in an emergency. Also a road vehicle can conveniently be brought to a complete halt and parked safely on a slope.

[00098] The maintenance of a suitable pressure ratio between the storage vessels 15 and 25 can be achieved by adjusting the flow of compressed air through the inlet valve 48 to the expander 1 relative to the flow through valve 50 to the combustion expander 4. The difference between these flow rates corresponds to the flow into the medium pressure storage vessel 25. It is expected that these flow rates will be adjusted automatically by the engine control system.

[00099] The proposed regenerative braking system effectively replaces the engine braking of a conventional road vehicle, but it is expected to be rather more powerful so the brake discs or pads would be used less often than is the case with conventional vehicles.

[000100] The regenerative braking system could be brought into operation when the driver depresses the brake pedal by a short distance. The clutch 45 would be designed so that it is gradually engaged by light pressure on the brake pedal. If the vehicle needs to stop quickly, then the driver would depress the brake pedal past the initial movement, so that the regenerative braking is supplemented by the friction in the brake pads or discs.

[000101] An alternative method of operation of the regenerative braking system is to automatically engage the clutch C3 if the driver lifts his/her foot on the accelerator pedal, but only when the engine speed is above a certain threshold speed. This would allow the engine to tick over at slow speed without bringing the regenerative braking system into operation.

OPERATION OF THE FIRST EMBODIMENT DURING EXTENDED RANGE MOTORING

[000102] Operation of the system during extended range motoring is now described. In this situation, the vehicle is powered by the combustion expander operating in a similar way to a conventional 4-stroke internal combustion engine. However, in this operating mode, the compressed air inlet valve 50 shown in Figure 1 is kept shut and the 2-way valve is used both for intake of atmospheric air and the discharge of hot exhaust gas.

[000103] During the intake stroke, the 2-way valve allows fresh air to enter the cylinder via the short air pipe 42. The intake stroke is followed by a compression stroke during which the 2-way valve 31 is shut so that the cylinder is sealed. Fuel is injected into the cylinder via injector 30 either during the compression stroke or around the time when the piston reaches top dead centre. The fuel may be ignited either by compression ignition or a spark plug or glow plug may be used. The fuel burns and the hot combustion products are expanded as the piston performs the power stroke. Finally, during the exhaust stroke the expanded gases are expelled from the cylinder via the 2-way valve 31 and the exhaust pipe 32.

[000104] During extended range operation, the exhaust gases pass through the two air heaters 27 and 18, but since there is no flow within the heating coils 28 and 19, no heat is transferred.

[000105] During extended range motoring, the air which is used to support combustion is limited to that which is trapped in the cylinder when the 2-way valve closes. The mass of trapped air is determined by the timing of the valve closing and by the volume of dead space when the piston is at top dead centre. This dead space volume and the timing of valve closing can be determined by the engine designer, but it is also necessary to limit the maximum pressure in the cylinder.

[000106] For the purpose of extended range motoring, a relatively large dead space may be preferred, similar to that in conventional engines. For the purpose of normal operation in which stored compressed air is being consumed, a smaller dead space is desirable. Ideally, the volume of the dead space may be variable, and this option is considered later in this document. However, if the volume of the dead space is fixed, then a suitable compromise between the requirements of normal operation and the requirements of extended range motoring must be found.

[000107] The mass of air which is used for the combustion of fuel at each cycle essentially determines the fuel energy which can be utilized in each cycle. This in turn is closely related to the maximum torque of the engine. The engine power is the product of the torque and the rotational speed. It is therefore clear that if the dead space in the cylinder is small, then the maximum power of the engine during extended range operation will be low.

[000108] The disadvantage of having too large a dead space in the combustion cylinder is that the engine becomes too much like a conventional internal combustion engine and that relatively little benefit is obtained from having stored compressed air.

[000109] The optimum choice of dead space volume therefore depends on the expected utilization of the vehicle.

Regenerative braking can also be applied during extended range operation of the system.

The vehicle might be switched from normal operation to extended range operation when the pressure in the HP compressed air store falls from an initial pressure of bar to a lower pressure of 50 bar. When the vehicle brakes or goes downhill, air is pumped from the medium pressure compressed air store 25 to the HP compressed air store 15. When braking stops, air can be admitted to the 2-stroke expander 1 via the heating coil 19, the air pipe 20 and the air inlet valve 48 to recover the stored energy. Since the air is heated prior to expansion by hot exhaust gases, it may be possible to recover more energy in expansion than is consumed during braking. Thus the operation of the regenerative braking system within extended range mode recovers braking energy and reduces the consumption of fuel.

[000110] When starting from cold, it may be advantageous to start the engine in the extended range mode, which will allow the engine and the heat exchangers to heat up. Initial rotation of the engine may be achieved using a battery as in a conventional internal combustion engine. Alternatively stored compressed air can be used to provide the initial rotation in order to begin the firing of the engine. In this case, the air inlet valve SOon the combustion expander would be kept closed but inlet valve 48 would be operated to allow a controlled amount of compressed air into the 2-stroke expander. Clearly clutch 43 needs to be engaged to transmit the movement to the combustion expander 4.

[000111] The vehicle may be driven as soon as firing begins in the combustion expander, just like a vehicle powered by a conventional internal combustion engine.

However, the engine power will initially be limited to the design power of the engine in the extended range mode.

[000112] If necessary, the duct burners or catalytic combustors 33 and 35 may be used to shorten the time required to achieve the desired operating temperature of the heat exchangers 27 and 18, so that lull engine power can be achieved if required.

POSSIBLE MODIFICATIONS OF THE FIRST EMBODIMENT

[000113] There are various possible modifications of the system shown in Figure 1, some of which are described below.

[000114] The gearbox 46 may be replaced by an automatic transmission system, which may have a continuously variable ratio of input and output speeds.

[000115] A different method of mechanically connecting the compressor 8, the adiabatic expander land the combustion expander 4 may be employed. For example, the gear 9 could be placed on the crankshaft 6 or on the crankshaft 3. The arrangement shown in Figure 1 has the advantage that the regenerative system is brought into action when clutch 45 is engaged and is not dependent on the positions of clutches 44 or 43.

[000116] The system shown in Figure 1 may be applied to different fuels and different ignition methods. The sequence described in Table 1 focusses on the use of diesel fuel which is ignited by compression ignition. Gasoline is an alternative fuel which may be injected directly into the combustion cylinder as in conventional engines equipped with gasoline direct injection (GDI). In this case a spark plug would be used to achieve ignition. Another fuel option is to use natural gas injection. A spark plug may be used in this case also.

[000117] The system shown in Figure 1 employs a 2-way valve which allows both atmospheric air intake and exhaust outflow at different stages of the cycle as described in Table 1. Instead of using a 2-way valve, an alternative embodiment could separate the atmospheric air intake from the exhaust outflow and have different valves for each. A separate high pressure air intake valve would still be needed. Such a system would avoid the need for a short air pipe 42 supplied by a fan 39. On the other hand, it may be difficult to find sufficient space on the cylinder head for all the valves. Also the cooling of the exhaust valve may be more difficult.

[000118] A means of adjusting the dead volume at top dead centre may be provided.

This would allow a reduction of dead volume during operation with stored compressed air or in the low emissions mode and an increase of dead volume when the system is in extended range mode. The adjustment means may involve relative movement of the cylinder 64 relative to the crankshaft 66. Alternatively there could be an adjustment of the length of piston or piston rod 65. Another method of adjustment is to have a moveable plug in the cylinder head. The plug can be partially withdrawn in order to form a cavity in the cylinder head.

[000119] A means of adjusting the timing of the closing of the exhaust valve may be provided so that the compression pressure of the residual air can be adjusted.

[000120] The application of the coolers 23 and 13 may also be varied from that shown in Figure 1. An alternative option is to apply the cooling directly to vessels 25 and 15.

[000121] An alternative arrangement of the heat exchangers 27 and 18 could be to install the two heating coils 28 and 19 inside a single heat exchanger with a single duct burner. The two heating coils could be arranged in parallel with respect to the gas flow outside the tubes. Such an arrangement could be appropriate if the amount of atmospheric air used for combustion of fuel is similar to the amount of stored compressed air which is used.

[000122] Another possible variation on the arrangement shown in Figure 1 is to dispense with one of the burners 33 or 35.

[000123] Suitable filters or catalytic converters may be fitted to the exhaust system to minimize emissions of NOx, CO and particulates. These are not shown in Figure 1.

DESCRIPTION OF THE SECOND EMBODIMENT WITH AIR-FUEL-ELECTRIC

HYBRIDIZATION

[000124] In the second embodiment, which is illustrated in Figure 2, the mechanical power provided by the expansion of compressed air stored in 15 through expanders 1 and 4 is converted to electrical power by the motor/generator 153 and can be either stored in electricity storage equipment 154 and/or fed directly to an electric motor/generator 155 coupled to the drivetrain through a gearbox 46.

[000125] The electricity storage equipment 154 may incorporate power conditioning equipment such as a rectifier and inverter to convert from AC current to DC and vice versa.

[000126] Regenerative braking can be achieved by operating 155 as a generator to produce electricity which is stored in 154. Therefore the medium pressure air store and the compressor 8, which were shown in Figure 1, are absent in Figure 2. The amount of energy recovered is limited by the state of charge of 154.

[000127] The electricity storage equipment 154 can be an electrochemical battery, a flywheel, a super-capacitor, or any other electricity storage system that can provide a high amount of power but does not necessarily need to hold a lot of energy.

[000128] In this second embodiment, which is shown in Figure 2, the normal mode and the extended range motoring modes described in connection with the first embodiment are still available. Regenerative braking is done differently as described.

[000129] Low or zero emission motoring is possible if the battery or other storage device 154 has sufficient capacity.

[000130] An energy management system, in the form of an electronic controller manages the state of charge of 154 within certain limits, partly to account for the electricity storage technology limitation, but mostly to ensure that both sufficient energy is available to the driver and that some capacity is left to store energy recovered during regenerative braking.

[000131] In this embodiment, the driver's commands are directly implemented by the electric motor/generator 155, which is capable of a very fast response. This considerably simplifies the command and control of the air energy recovery system (expanders 1 and 4 and associated valves), resulting in a cheaper and more efficient system. It also provides the driver with a greater driving experience, typical of pure electric vehicles.

[000132] Electric motor/generator 155 is sized according to the vehicle power requirements, typically in a range of 50-300kw, while electric motor/generator 153 is much less powerful, in the range of 2-10kw, since it only needs to provide the average power necessary to move the car. It may be run at variable or fixed speed.

[000133] When the vehicle is stopped, the air energy recovery system can be completely turned off as soon as the state of charge of 154 is within acceptable limits. This allows for a fuel free idling mode.

[000134] The compressed air store 15 can be recharged when the vehicle is stopped or when the electricity storage device 154 is too full by using 153 as an electric motor and by operating the expanders 1 and 4 as compressors. when the vehicle is parked, 153 can be powered by the electric mains through a wall socket connection or a fast charger such as those used for conventional battery plug-in electric vehicles, when 154 is reaching its maximum capacity and the vehicle is still moving and needs to be slowed down, for instance when braking or going downhill, the excess electricity being generated by 155 can be used to power 153 and compress the air.

[000135] In the recharging mode, 153 operates as a motor to power the air energy system in reverse. Clutch 43 is engaged, valve 54 is closed and valve 55 is open. The air flow in and out of the expanders land 4 is reversed and the expanders now operate as a 2-stage adiabatic compressor with inter-stage cooling. No fuel is injected in 4. This involves changing the timing of the valves 48, 49, 50 and 31. The 2-way valve 31 opens towards the pipe 42 and valve 50 is closed. The air is drawn into 4 through 41 during the piston down stroke. At bottom dead centre, valve 31 closes while valve 50 is maintained in a closed position. The air is compressed during the piston up-stroke and hot, compressed air is exhausted through valve 50. The hot air is then cooled by flowing through heat exchanger 27, using cool ambient air blown by fan 39. The medium pressure air exits 27 through pipe 21 and is drawn into cylinder 1 through valve 49. After being compressed in 1, it is exhausted at high pressure and high temperature through valve 48 then along pipe 20 and into heat exchanger 18, where it is after-cooled before being stored in 15. After-cooling in 18 occurs through a similar mechanism as the cooling of the medium pressure air in 27: a fan blows cool ambient air into the low pressure side of 18.

DESCRIPTION OF THE THIRD EMBODIMENT WITHOUT 2-STROKE ADIABATIC

EXPANDER

[000136] A simplification of the first embodiment may be achieved by dispensing with the 2-stroke adiabatic expander and its associated heater and duct burner as shown in Figure 3. The medium pressure compressed air storage vessel is also removed.

This third embodiment also has a normal operating mode, extended range mode and a low emissions mode. Regenerative braking is possible in all these modes.

[000137] In this simplified embodiment high pressure compressed air is stored in the vessel 81. During normal operation the compressed air flows through valve 82 and pipe 83 to the heating coil or serpentine 85 which is situated inside the heater 84.

The heated compressed air then flows along pipe 88 to the controllable air inlet valve 89 on the combustion expander 64.

[000138] During normal operation, the combustion expander 64 operates on a 4-stroke cycle in the same way to that described in connection with Figure land summarized in TABLE 1. Referring to Figure 3, the 2-way valve, which is used to intake atmospheric air and to exhaust the spent combustion products, is indicated by 91 and the fuel injector is indicated by 90. The piston and piston rod 65 transmits power to the crank 66 which is connected to the gearbox 70 by a clutch 93.

[000139] The exhaust gases from the combustion process flow through the 2-way valve to the exhaust pipe 99 and onward to the duct burner or catalytic combustor 87 which has a fuel injector 86. The burner 87 may be used to raise the temperature of the exhaust gases during starting or during normal operation in order to increase the temperature of the compressed air in the heating coil 85. After passing through the heater 84, the exhaust gases flow to the atmosphere through the pipe 101.

[000140] The omission of the adiabatic expander and its associated heater from the simplified embodiment shown in Figure 3 has certain consequences concerning the operating pressures of the system. Since there is only one stage of expansion, this implies a large expansion ratio of the combustion expander 64 and a reduction in the range of pressures used for air storage in the vessel 81.

[000141] For example the range of air storage pressures could be from about 80 bars when fully charged down to a lower limit of about 20 bars. The expansion ratio of the combustion cylinders 64 could be increased by having a small bore/stroke ratio.

The expansion ratio can also be varied by allowing the 2-way exhaust valve to discharge exhaust gas when the cylinder pressure is still significantly above atmospheric pressure. This implies an enhanced blowdown phase. The compressed air leaving the tank 81 could be throttled at valve 82 to reduce the air pressure prior to expansion, but this is inefficient compared to allowing enhanced blowdown.

[000142] Another consequence of the simplification of the third embodiment relative to the first embodiment is that a low pressure compression stage is required in addition to the high pressure compression stage. The low pressure compression stage needs to be physically larger than the high pressure compression stage.

[000143] The operation of the system of Figure 3 during extended range motoring is essentially the same as described in connection with the first embodiment shown in Figure 1. In this case, the combustion expander 64 is operated in the same way as a conventional diesel or gasoline engine, but with the 2-way valve admitting fresh air and exhausting the spent combustion products.

[000144] The regenerative braking system of Figure 3 is modified relative to that shown in Figure 1. In Figure 3 the air to be compressed is drawn from the atmosphere through pipe 76 into a first compression stage 74. The piston 75 of this compression stage is connected to the crankshaft 72. After compression in the first stage, the air is discharged via a cooler 77 to the second compression stage 100, where it is further compressed by the piston 73 and then discharged via the cooler 78 to the storage vessel 81. The reason for having 2 (or more) compression stages as shown in Figure 3 is that the pressure ratio between the atmospheric pressure and the storage vessel 81 is expected to be too large for a single stage.

[000145] Operation of the regenerative braking system shown in Figure 3 allows the partial replenishment of stored compressed air with freshly compressed air from the atmosphere. During normal operation this additional compressed air can be consumed at any time, without changing the engine operating mode.

[000146] lIthe vehicle is operating in the extended range mode, then the stored compressed air is not being used at that time. Therefore the regenerative braking system continues to recharge the storage vessel 81 and after a time, there may be sufficient stored air in vessel 81 to allow the vehicle to operate in the normal mode again.

[000147] A low emissions mode is also possible with the third embodiment illustrated in Figure 3. In this mode, no fuel is injected into to the expander 64. Instead, fuel is burned in the duct burner or catalytic combustor 87. Either of these forms of continuous external combustion at low pressure can be performed with much lower emissions than with cyclic internal combustion at high pressure. Compressed air arriving at the heater 84 through pipe 83 is heated and supplied to the expander 64, which acts as an adiabatic expander in this mode of operation. The expanded air, which is still hot, is fed along pipe 99 to the burner or catalytic combustor 87, where fuel is added. The exhaust gases, which contain very low levels of pollutant, exchange heat with the incoming air in heater 84 and exhaust to the atmosphere at 101. The compressed air is supplied by the multistage compressor illustrated by the cylinders 74 and 100 in Figure 3. Clutch 69 is engaged to enable this. Intercooling is performed in the cooler 77. After-cooling is provided by cooler 78, which assists the storage of any surplus compressed air in vessel 81. This mode of operation, which is a form of open Brayton cycle, is not dependent on the availability of stored compressed air and can continue until the supply of fuel is exhausted.

[000148] The multistage compressor shown in Figure 3 can be used to recharge the air in the system as well as for the purpose of regenerative braking and low emission motoring. For example, as shown in Figure 3, an electric motor 157 can be mechanically connected to the crankshaft 72 via a clutch 158 in order that an external source of electric power could be used to recharge the vessel 81 with compressed air. Alternatively the electric motor 157 could be external to the vehicle and coupled via a mechanical drive connection.

[000149] The method of starting the engine shown in Figure 3 is essentially the same as that for the engine shown in Figure 1. Basically the engine is started in the extended range mode using battery power to provide the initial rotation. When the temperature of the air heater coils 85 has increased sufficiently then the engine can begin to operate using stored compressed air. The burner or catalytic combustor 87 may be used to shorten the time required to achieve operation at full power.

[000150] There are various possible modifications of the system shown in Figure 3, which are described as follows.

[000151] The gearbox 70 may be replaced by an automatic transmission system which may have a continuously variable ratio of input and output rotational speeds.

[000152] A different method of mechanically connecting the crankshafts 66 and 72 with gearbox 70 may be used.

[000153] Different fuels and ignition systems may be used as described in connection with Figure 1.

[000154] A separate valve may be provided for the intake of low pressure air into the combustion expander 64 instead of having a 2-way valve 91. This may avoid the need for the short pipe 92 and the fan 96.

[000155] A means of adjusting the dead volume at top dead centre may be provided as described in connection with Figure 1.

[000156] A means of adjusting the closing time of the 2-way valve 91 or of an exhaust valve may be provided as described in connection with Figure 1.

[000157] The separate cooler 78 could be replaced by a method of cooling the vessel 81.

[000158] The burner or catalytic combustor 87 could be omitted, but in this case the low emissions mode would not be possible [000159] Suitable filters or catalytic converters could be included to reduce emissions of CO, NOx and particulates.

THE FOURTH EMBODIMENT: A STATIC FUEL-ASSISTED ENERGY STORAGE SYSTEM

WITH CAPACITY TO RUN WITHOUT AN EXTERNAL SUPPLY OF COMPRESSED AIR

[000160] Figure 4 shows a fourth embodiment of the invention consisting of a static fuel-assisted energy storage system supplied with compressed air by a compressor 108 powered by an external source of power, such as a wind turbine or solar power installation. However, the energy storage system can also produce power at a lower level when the external power required to drive the compressor 108 is not available and the compressed air energy store 15 is depleted.

[000161] The system shown in Figure 4 is derived from the arrangement shown in Figure 1, but without the regenerative braking system and without the low emissions capability. This means that the compressor 8, medium pressure air storage vessel 25 and duct burner 33, which are present in Figure 1 are omitted in Figure 4. The gears 9, 10 and 53 and clutches 43 and 45 which are present in Figure tare also omitted in the embodiment shown in Figure 4.

[000162] Figure 4 shows atmospheric air 107 being compressed by a compressor 108 and stored in a compressed air storage vessel 15 which is equipped with a pressure transducer 51 and a pressure relief valve (not shown). The compressed air flows via a valve 16 along a pipe 17 into a heating coil 19 within a first air heater 18. Heated compressed air then flows along pipe 20 to an adiabatic expander 1, which it enters via valve 48. The adiabatic expander 1 expands the hot compressed air performing work on a piston and piston rod 2, which transmits power to a crankshaft 3.

[000163] The expanded air exhausts from the adiabatic expander 1 via exhaust valve 49 and flows via pipe 21 to a heating coil 28 within a second air heater 27. The reheated partially expanded air then flows along pipe 29 to a combustion expander 4, which operates on the novel 4-stroke cycle previously described in connection with Figure 1. The exhaust gases of the combustion expander 4 exit via the 2-way valve 31 along pipe 32 to the 2 air heater 27 and then to a duct burner 35, in which fuel is added via injector 36. The reheated exhaust gases then pass through the first air heater 18 to the atmosphere via exhaust pipe 37.

[000164] The fourth embodiment shown in Figure 4 shows a generator 102 which is connected to the crankshaft 6, which is driven by the combustion expander via the piston and piston rod 5.

[000165] When the compressed air store 15 is depleted and no external power is available to drive the compressor 108, then the system shown in Figure 4 may still operate at a reduced power level by shutting the valve 16, disengaging the clutch 44 and fixing the compressed air inlet valve 50 of the combustion expander in the closed position. The combustion expander 4 is then run as a conventional 4-stroke engine, using the 2-way valve 31 both for the intake of atmospheric air and for the removal of the exhaust gases, as previously described in connection with Figure 1.

THE FIFTH EMBODIMENT: A SPLIT CYCLE ENGINE INCORPORATING THE NOVEL 4-

STROKE CYCLE WITH OPTIONAL COMPRESSED AIR STORAGE

[000166] FigureS illustrates a fifth embodiment of the invention. This embodiment may be considered as being derived from the third embodiment, which is shown in Figure 3, but the combustion expander 64 now drives two compressor stages 74 and via a crankshaft 66, with no intervening clutch. The crankshaft 66 also drives a motor-generator 138.

[000167] The system shown in Figure 5 may be configured as a pure engine without any energy storage or energy storage capability may be provided.

[000168] lIthe engine is configured without energy storage, atmospheric air enters the system at 132 and passes through the turbo-compressor 133 of a turbo-charger 131.

The turbocharged air passes along pipe 135 to a pipe junction 140. Some of the air is intermittently drawn into the combustion expander 64 via the short pipe 92 and the 2-way valve 91. This air cools the inside of the combustion expander 64 and is then discharged again back through the 2-way valve 91 and into the pipe 94, where it re-joins the main flow of air coming from pipe 135. This air flow now passes along pipe 94 to the intercooler 136, which may be cooled by water or by direct air cooling.

Leaving the intercooler along pipe 141, the turbocharged air enters a first stage reciprocating compressor 74 via inlet valve 142 and is compressed further by piston 75. The compressed air then passes out through valve 143 to a second intercooler 77 and then to a second stage reciprocating compressor 100 via inlet valve 144. The reciprocating compressor 100 performs the final stage of compression and discharges the air through valve 145 to pipe 137.

[000169] The compressed air passes along pipe 137 to the heating coil 85 within an air heater 84. The hot compressed air then passes out of the air heater 84 along pipe 88 to the compressed air inlet valve 89 of the combustion expander 64.

[000170] Fuel is injected via injector 90 and is burned. The combustion gases are expanded doing work against the piston and piston rod 65, which imparts energy to the crankshaft 66. The combustion expander operates on the novel 4-stroke cycle with two cooling strokes as described in all the embodiments of this invention. The expanded gases exhaust via the 2-way valve 91 and flow along the pipe 99 to the air heater 84. After transferring heat to the incoming air, the exhaust gases pass out of the air heater 84 via pipe 101 to the turbocharger turbine 134. Finally, the exhaust gases leave the turbocharger turbine at 139, where they are exhausted to the atmosphere.

[000171] For the purpose of starting, initial rotation of the engine shown in FigureS can be provided by the motor-generator 138 powered by a battery or by mains power. The compressor inlet valves 142 and 144 and the vent valve 146 may be held open during starting so that negligible compression work is performed by compressors 74 and 100. Valve 145 is kept shut. The combustion expander 64 is set to operate as a conventional 4-stroke engine, with the 2-way valve both admitting the intake air and allowing the exhaust gases to be vented from the cylinder. The exhaust gases flow along pipe 99 to the air heater and heat the heating coil 85 within the air heater 84. When the pressure and temperature of the air in the pipework 137, 21.

83, 85 and 88 reaches suitably high values, the combustion expander is then switched over to operate with compressed air supplied by pipe 88 via valve 89.

[000172] The engine shown in Figure 5 may also be equipped with compressed air energy storage. In this case a compressed air storage volume 149 is connected to the pipe 137 by means of another pipe 148 and a valve 147. The compressed air storage volume 149 may optionally be supplied with compressed airfrom an external source by means of the pipe connection 152 and the valve 151. In addition a vent pipe 150 and a vent valve 146 are provided.

[000173] lIthe engine is storing compressed air, the combustion expander 64 may be isolated from the air flow path by setting the 2-way valve 91 so that the flow path to pipe 92 is open and the flow path to pipe 99 is closed. No fuel is injected into the injector 90 and valve 89 is closed, so that no high pressure air is admitted. Vent valve 146 is open so that air may flow freely in or out of the vent pipe 150. The turbocharger 131 is inactive in this mode of operation since there is no exhaust gas flow in pipe 101. The two stage reciprocating compression system consisting of compressors 74 and 100 provide all the necessary compression without the assistance of the turbocharger. The compressed air passes through the open valve 147 and the pipe 148 to air storage volume 149.

[000174] The system shown in Figure 5 recovers stored energy with the assistance of fuel combustion so that the ratio of energy produced to energy stored is more than unity and may be a factor of 2 or more. In this mode, the vent valve 146 is open and the discharge valve 145 on the high pressure compressor 100 is kept shut. Valve 144 on the same compressor 100 is kept open. Valves 142 and 143 on the low pressure compressor 74 are both kept open. In this way air at near atmospheric pressure is able to flow freely in and out of both the compressors 74 and 100 as the pistons 73 and 74 move up and down. Stored compressed air from the vessel 149 passes through the open valve 147 and flows into the heating coil 85 of the air heater 84.

From this point, the process of pre-heating, combustion, expansion and exhaust is the same as that previously described for the system shown in Figure 5 when it is operating without using stored compressed air.

[000175] The motor-generator 138 of the system shown in Figure Scan be connected to a battery or other energy storage device. In a static power generating system, this could provide a fast response capability for grid stabilisation. If the battery is large enough, then it could also provide a few hours of energy storage, in which the compressed air storage vessel would not be required.

[000176] Alternatively, the engine shown in Figure 5 without the compressed air storage vessel 149 could be combined with a battery and electric motor to form a novel hybrid electric drive system for a vehicle.

[000177] It can be seen that the 5th embodiment shown in Figure 5 has some similarities to the "isoengine" which is described for example by Sugiura et al in the 2007 CIMAC conference paper number 170. However, that system involves a combustion expander which operated on a 2-stroke cycle, not the novel 4-stroke cycle described here.

[000178] The isoengine incorporates a quasi-isothermal compressor with water spray injection directly into the compressor cylinder, which is of course different from the arrangement shown in Figure 5. In this case it is necessary to include a separator and water injection equipment.

[000179] The embodiment shown in Figure Scan of course be modified to include a quasi-isothermal compressor with water spray injection and separation rather than the 2-stage intercooled compressor which is shown in Figure 5.

[000180] Figure 5 shows a turbocharger which is used to boost the pressure level and therefore the power output of the engine. This is not an essential part of the system and it would be possible to have such an engine without a turbocharger. In this case, a fan would be used to blow atmospheric air along pipe 135 to junction 140 and from there back to the atmosphere in a similar manner to that shown in Figure 3.

A 2-WAY VALVE FOR INTAKE OF COOL AIR AND EXHAUST OF HOT GASES [000181] A 2-way exhaust gas separation valve has been described byTakahashi, Tanaka and Ohtsu in a paper entitled "Study of Exhaust Gas Separation System (EGS) on 2-stroke engine", which was published as paper No. 108 at the 2010 CIMAC Congress in Bergen, Norway. The application of this valve was intended as a means of separating the hot exhaust gas, which flows immediately after the exhaust valve opens, from the cooler exhaust gas and scavenging air, which is exhausted after the hot exhaust gas.

[000182] The 2-way valve shown in Figure 6 is integrated into the body of the exhaust valve and consists of a main valve 103 and a sub-valve 104 in series. Access to the cylinder is controlled by a poppet valve which is similar to a conventional cylinder exhaust valve. This is the main valve 103. The sub-valve 104 controls which of two possible paths the exhaust gases can take. With the sub-valve in one position, the exhaust gases flow into the high temperature region 105. With the sub-valve in the other position, the exhaust gases flow into the low temperature region 106.

[000183] The application of such a valve in the present invention is different to that envisaged by Takahashi et al. Here we wish to allow intake of cool atmospheric air and outflow of hot exhaust gas at different times through the same port. The same type of valve may be used, but the timing of the main valve and sub-valve is different.

[000184] When the main valve 103 is open and the piston is advancing in the cylinder during the exhaust stroke, the sub-valve 104 allows exhaust gas to flow from the cylinder to the exhaust pipe. The valve position is shown on the left side of Figure 6, where the flow path is to the high temperature region 105.

[000185] Immediately after the exhaust stroke, when the piston begins to recede, the main valve 103 remains open, but the sub-valve 104 changes position and allows cool air to be drawn into the cylinder. Then when the piston is advancing again during the following up-stroke, the main valve 103 and sub-valve 104 allow most of the cool air to return to its source, but a certain fraction of the inlet air is trapped in the cylinder and compressed. The sub-valve 104 position is shown on the right side of Figure 6, where the flow path is into the low temperature region 106.

[000186] An important advantage of using a 2-way valve in the present application is that the valve is cooled by the passage of cool air during part of the 4-stroke cycle.

Another advantage is that the available space in the cylinder head is used more efficiently, so that a larger total valve area can be accommodated.

CONTROLOFTHE HIGH PRESSUREAIR INLET VALVE

[000187] The valves 48 and 50 which allow high pressure air to enter the adiabatic expander land the combustion expander 4 shown in Figure 1 need to be controlled so that the correct mass of air enters at each stroke. The same requirement applies to the combustion expander 64 shown in Figure 3. In particular, the closing time of the valve needs to be variable.

[000188] One possible way of achieving this is to have a poppet valve which is opened by a mechanical cam, but to use a hydraulic system to allow the valve to close earlier than the cam would otherwise allow. A system of this type is described by Matthey in paper 298 of the 2010 Cl MAC Congress in Bergen, Norway. However, in that system the poppet valve opened inwards towards the piston, whereas in the present application it is desirable that the poppet valve should open in the direction away from the piston. There are two reasons for this. Firstly, the present poppet valve normally has a higher pressure in the air supply pipe than in the cylinder. If the poppet valve opens away from the piston, then this high pressure acts to improve the sealing of the valve. If the poppet valve opens towards the piston, then a powerful spring will be needed to keep the valve closed and there will be an increased danger of leakage. Another reason for opening the valve away from the piston is that there may be a danger of the valve hitting the piston, since the valve is opened when the piston is near top dead centre.

[000189] In the present system, it is desirable that the valve should be driven by an overhead camshaft rather than by a camshaft at a low position and connected to the valve by means of a push rod and rocker arm. The reason for this is that the air inlet valves must open and close very quickly and it is important to minimize the inertia of the moving assembly and to make it as stiff as possible. This is another difference between the system proposed here and that considered by Matthey in paper 298 of the 2010 CI MAC conference.

[000190] Figure 7 shows a rotating cam 118, which acts on a cam follower 117 to move the piston 116 of the hydraulic pump 114. If the solenoid valve 123 is shut, the hydraulic fluid is trapped between the pump piston 116 and the actuator piston 113, so the fluid acts like a solid rod to move the actuator piston. The actuator piston 113 pushes the upper bracket 111 which is rigidly connected to the lower bracket 119 by tie rods 114 and 124. The lower bracket pulls the poppet valve 121 open compressing the valve spring 120 at the same time. If the solenoid valve 123 is kept shut, then the valve spring 120 acts to compress the hydraulic fluid, but since this fluid is incompressible, it continues to act as a solid rod and both the opening and closing motion of the valve is governed by the shape of the cam.

[000191] If the solenoid valve 123 is opened when the poppet valve 121 is open, then the hydraulic fluid is forced into the accumulator 122 and the force of the valve spring 120 closes the poppet valve 121 at an earlier time. The speed at which the poppet valve contacts its seat must be controlled so that any damage to the valve and to the seat is avoided. This can be achieved by suitable design of the actuator piston 113, including the diameter of the piston, the diameter of the connecting pipe between the actuator 112 and the pump 115 and the minimum clearance under the actuator piston 113. If these dimensions are chosen appropriately, then a strong damping effect can be produced when the poppet valve is close to its seat.

[000192] An important feature of this system is the fact that the early release of hydraulic fluid through the solenoid valve 123 causes a transfer of energy from the spring 120 to the hydraulic accumulator 122. When the cam 118 is on its downward slope, the accumulator 122 pushes hydraulic fluid back to the pump 115 and the cam follower 117 applies a force to the cam 118, which returns energy to the cam 118 and restores the system to the correct state for the next cycle. Although there are clearly energy losses in the system, a significant fraction of the energy can be recovered for the next cycle. Thus we can expect that the overall energy losses of the combined hydraulic and cam system should be significantly less than would be the case for a hydraulic system with no cam.

[000193] By sending an electrical signal to the solenoid at the appropriate time it is possible to vary the opening time of the solenoid valve 123, which in turn determines the closing time of the poppet valve 121. Thus the system allows control of the duration of the valve opening.

Claims

CLAIMS1. A 4-stroke reciprocating internal combustion engine comprising a combustion expander in which: o a quantity of air at low pressure is drawn by a piston into one or more combustion cylinders through a low pressure air intake valve in the first stroke o most of the air drawn in on the first stroke is expelled again during the first part of a second stroke thus providing a cooling effect to the cylinder o a fraction of the low pressure air drawn in on the first stroke is retained and compressed to a high pressure within the cylinder during the second part of the second stroke o a high pressure air inlet valve allows the admission of a controlled amount of pre-compressed pre-heated air, which mixes with the retained compressed air while the piston is near the top of the cylinder o fuel is injected into the cylinder before, during or after the air mixing takes place o the air and fuel mixture is ignited and expansion of the gases takes place during the third stroke imparting powerto a mechanical piston and crankshaft o an exhaust valve opens at the end of the third stroke and stays open during the fourth stroke, expelling the expanded but still hot exhaust gases through an exhaust valve to an air heater, which is used to pre-heat the pre-compressed air before it enters the combustion cylinder o and the high pressure air inlet valve of the combustion cylinders can optionally be kept closed while there is a conventional 4-stroke sequence of intake, compression, combustion with expansion and finally exhaust of the combustion products of fuel with the original low pressure inlet air.
2. A 4-stroke internal combustion engine as in claim 1, which is equipped with a compressed air storage volume and valve means to connect the engine to this storage volume and to connect the storage volume to an external source of compressed air.
3. A 4-stroke internal combustion engine as in claim 1 in which the piston or pistons of the combustion cylinders provide power to the pistons of one or more compression cylinders via a common crankshaft or via separate crankshafts which are mechanically connected.
4. A 4-stroke internal combustion engine as in claim 1 in which the air heater is equipped with a duct burner or catalytic combustor which can burn fuel to increase the temperature of the hot exhaust gases entering the air heater.
5. A 4-stroke internal combustion engine as in claim 3 in which the compression cylinders compress air which is then pre-heated in the air heater prior to passing to the high pressure air intake valve of the combustion cylinder.
6. A 4-stroke internal combustion engine as in claim 3 in which electrical energy storage is provided by a generator connected to a battery or other energy storage device.
7. A 4-stroke internal combustion engine as in claim 6 combined with a battery or other energy storage device and an electric motor is applied to power a hybrid electric vehicle.
8. A 4-stroke internal combustion engine as in claim S in which there is intercooling of air between the stages of compression.
9. A 4-stroke internal combustion engine as in claim S in which a water spray is injected into one or more compression cylinders in order to achieve quasi-isothermal compression.
10. A 4-stroke internal combustion engine as in claim 5, which is turbocharged.
11. A 4-stroke reciprocating engine as in claim 5 which is installed in a vehicle and in which the crankshaft of the combustion cylinders and the crankshaft of the compression cylinders are separate but may be connected via a clutch mechanism in order to recover surplus kinetic energy of the vehicle and re-charge the compressed air storage vessel, thus providing regenerative braking.
12. A 4-stroke internal combustion engine as in claim 11 which includes a duct burner or catalytic combustor in which fuel may be burned with low emissions and which can be operated as an open or closed Brayton cycle using the combustion expander as an adiabatic expander.
13. A 4-stroke internal combustion engine as in claim 11 with an external mechanical coupling to allow recharging of the compressed air store by an external mechanical drive.
14. A 4-stroke internal combustion engine as in claim 11 including an electric motor, clutch and external electrical connection point to allow an external source of electric power to drive the internal compressor to recharge the compressed air storage vessel.
15. A 4-stroke reciprocating engine as in claim 2 in which the engine installed in a vehicle operates a conventional 4-stroke cycle in order to produce power during start-up and when no stored compressed air is available.
16. A 4-stroke reciprocating engine as in claim 2 in which there is an additional high pressure air heater equipped with a duct burner or catalytic combustor and there is an additional high pressure adiabatic expander with a crankshaft that can be connected to the crankshaft of the combustion expander by means of a clutch mechanism.
17. A 4-stroke reciprocating engine as in claim 16 in which the engine operates at a relatively even power level to drive a first motor-generator supplying power to an electrical storage device and to a second motor-generator of higher power capacity, which provides more variable motive power to a vehicle.
18. A 4-stroke reciprocating engine as in claim 17 in which the vehicle can perform regenerative braking by operating the second motor-generator as a generator and storing the electrical energy in the electrical storage device.
19. A 4-stroke reciprocating engine as in claim 17 in which the vehicle is fitted with an external electrical connection point to allow the electrical storage device to be recharged from an external source of electric power.
20. A 4-stroke reciprocating engine as in claim 19 in which the timing of the valves in the high pressure adiabatic expander and the combustion expander can be changed so that they can operate as compressors to compress and store air, with the air heaters also configured to act as air coolers to provide intercooling and after-cooling to the air.
21. A 4-stroke reciprocating engine as in claim 20 in which the external electrical connection point is used to power the first motor-generator so that it drives the expanders when they are operating as compressors.
22. A 4-stroke reciprocating engine as in claim 16 in which there is an additional air storage volume at an intermediate pressure and valve connections to allow air which has been partially expanded in the high pressure adiabatic expander to be cooled, rather than heated, in the lower air pressure heater before the partially expanded air enters the said additional storage volume at intermediate pressure.
23. A 4-stroke reciprocating engine as in claim 22 which allows the high pressure adiabatic expander to work with a high pressure compressor to perform a low emissions Brayton cycle operating between the pressures of the intermediate and high pressure storage volumes and burning fuel in a duct burner or catalytic combustor.
24. A 4-stroke reciprocating engine as in claim 22 which recovers surplus kinetic energy of the vehicle by using a high pressure compressor to compress air from the intermediate pressure storage tank and deliver it to the high pressure air storage tank.
25. A 4-stroke reciprocating engine as in claim 23 and in claim 24 in which the same high pressure compressor is used for kinetic energy recovery and for low emissions motoring.
26. A 4-stroke reciprocating engine as in claim 1 in which the controllable high pressure air inlet valve is opened by a mechanical cam but may be closed at variable times using a hydraulic system involving a solenoid valve.
27. A 4-stroke reciprocating engine as in claim 1 in which the low pressure air inlet valve and the exhaust valve are integrated into a single 2-way valve.
28. A 4-stroke reciprocating engine installed in a vehicle as in claim 11 in which either a manual gearbox, or automatic transmission with fixed or continuously variable gear ratios, is used to connect the engine to the drive wheels.
29. A 4-stroke reciprocating engine installed in a vehicle as in claim 11 in which the regenerative braking capability as applied to road vehicles is supplemented with a conventional friction braking system using discs or pads and a mechanical handbrake.
30. A 4-stroke reciprocating engine installed in a vehicle as in claim 29 in which the initial movement of the brake pedal activates the regenerative braking, followed by friction braking as the brake pedal is depressed further.
31. A 4-stroke reciprocating engine installed in a vehicle as in claim 29 in which the regenerative braking is activated when the driver takes his/her foot off the accelerator pedal, but only if the engine speed is higher than the tick-over speed.
32. A 4-stroke reciprocating engine as in claim 1 in which the combustion expander has a variable dead space volume at top dead centre and variable timing of closing of the exhaust valve, which may be adjusted according to the current mode of operation of the system.