DE102016219152B4 - Internal combustion engine for a bi-fuel motor vehicle - Google Patents

Abstract

Internal combustion engine for a bi-fuel motor vehicle with at least one combustion chamber (70) and a fuel injection rail (40) for direct injection of gaseous fuel into the combustion chamber (70) by means of at least one injection nozzle (60; 61) on the fuel injection rail (40), characterized that the fuel injection rail (40) is connected to two tanks (10;20) for gas fuel, in which respectively liquefied petroleum gas (LPG) and compressed natural gas (CNG) are located, the fuel injection rail (40) and thus the combustion chamber (70 ) a gaseous fuel can optionally be supplied from one of the two tanks (10; 20), and the fuel injection rail (40) has for each gaseous fuel type at least one injection nozzle (60; 61) designed for this gaseous fuel type, by means of which the combustion chamber (70) the respective type of gas fuel can be supplied by direct injection, the two injection nozzles (60; 61) differing in their injection angle are arranged in a straight line and an injector (61) for the liquefied petroleum gas (LPG) has a lateral injection position, while an injector (60) for the compressed natural gas (CNG) has a central injection position.

Description

The invention relates to an internal combustion engine for a bi-fuel motor vehicle according to the preamble of claim 1.

So-called bi-fuel motor vehicles or multi-fuel or multi-fuel engines are known in automotive engineering, which can be operated with different fuels such as petrol (or diesel) and natural gas. Gasoline is typically used as a reserve fuel so that the engine can continue to run when the natural gas is exhausted. A vehicle can also be operated with petrol (or diesel) and a gas such as LPG (Liquefied Petroleum Gas) or CNG (Compressed Natural Gas).

In such bi-fuel vehicles, switching between the types of fuel often entails problems that have to be solved for safe and comfortable vehicle operation. For example, the U.S. 6,591,817 B2 a method and a system for the operation of a bi-fuel motor vehicle, designed in particular to enable a smooth switch between the two types of fuel. In such a change, a valve for the supply of a second fuel such as LPG is activated by measuring and evaluating the oxygen content in the exhaust gas after the fuel change. A filtered signal is generated from this, on the basis of which the valve is controlled. The valve is opened when the filtered signal decreases after switching to the second fuel, while the valve is closed when the filtered signal increases after switching to the first fuel.

the U.S. 9,046,049 B2 also discloses a method of operating an engine alternately with gasoline and LPG. When changing fuel, the injection quantity, injection ratio and injection time are adjusted in order to keep the air-fuel ratio as constant as possible when changing fuel. A control unit can control the injection of both types of fuel. Also from the U.S. 5,450,832 a method and a system for operating a motor vehicle with gasoline and an alternative fuel such as liquid gas are known. An existing electronic injection system for petrol is also to be used to supply the liquid gas.

However, running a vehicle on LPG can also cause problems. A method and a system for controlling the fuel supply of a bi-fuel motor vehicle are known from US 2015/0 047 590 A1, in which petrol and LPG are used depending on the operating mode of the vehicle. Gasoline is usually used to start the vehicle and then switched to LPG for driving. In order to prevent serious safety problems when driving due to malfunctions, provision is made for a switchover to emergency operation in the event of such a malfunction. In this emergency mode, for example, the vehicle speed is limited and the engine speed is kept in a specific range that is above an idle speed. However, this will affect the ride. Provision can therefore be made for a control unit to switch to operating the vehicle with petrol in emergency operation if a malfunction in the LPG fuel system has been detected.

US 2015/0 159 570 A1 discloses a method and a system for safety control of bi-fuel vehicles in the event of an accident. For example, if a vehicle uses gasoline and LPG, liquefied LPG is vaporized inside a container to be burned in the engine. However, in the event of an accident, a very high or very low pressure can occur in this evaporator, which poses a safety hazard. Therefore, the pressure in the evaporator is monitored in gas mode and if this is too high or too low and at the same time an airbag of the vehicle has been inflated, the system switches from gas mode to petrol mode.

WO 2003/036 073 A1 discloses a fuel distribution system with an injection device which is suitable for injecting LPG, for example, into an engine. An injection ramp is provided, which communicates with at least one injection element through a passage opening for the fuel with a fuel supply line, through a first opening and with a fuel return line and through a second opening. Furthermore, an expansion element is provided in the injection ramp, which in an active expansion position

Opening and / or the other two openings closed. In this way, in particular, leakage of the LPG should be avoided.

Furthermore, the different fuels in bi-fuel motor vehicles have different anti-knock properties, which must be taken into account. In particular, power losses usually occur in such motor vehicles, since the engine of the vehicle has to deliver acceptable power levels even with the respective “poorer” fuel. For example, the compression ratio cannot be increased on bi-fuel vehicles using CNG or LPG because gasoline, as a reserve fuel, is significantly more prone to engine knock than the two gases. The engine can therefore not be optimally designed and adjusted for one fuel. One possible solution to the problem are mono-fuel vehicles that only run on one type of gas. Realistically, however, such vehicles cannot be sold because the availability of the gases varies greatly in different regions.

It has therefore already been proposed in the prior art to adjust a fuel metering system as a function of the fuel type in order to be able to operate an engine with different fuels with different anti-knock properties. For example, to determine the type of fuel, the DE 10 2010 045 593 A1 proposes a system for detecting the nature of a gaseous fuel and a method for controlling an internal combustion engine that can be operated with different fuels. A gaseous fuel is used to operate an internal combustion engine with an intake manifold and at least one cylinder. At least two different gaseous fuels can be combusted in the cylinder to operate the engine. A sensor system can be used to determine parameters of the respective gaseous fuel, from which the type of gaseous fuel that is in the intake manifold of the engine is determined. The mixing ratio of two gaseous fuels can also be determined in this way. The system does not have to know the type of gaseous fuel currently being used, but if a fuel is no longer available, it can be switched to another fuel without having to first adjust the internal combustion engine and/or its control system to the new fuel. Consequently, combustion in the engine can be continuously controlled and optimized during operation. In particular, the air mass flow in the intake manifold, the lambda value and/or the fuel injector pressure can be used as parameters.

US 2014/0 034 023 A1 relates to an internal combustion engine for a bi-fuel motor vehicle in which both a gaseous and a liquid fuel can be burned. Two separate fuel rails are provided for this purpose, one for the gaseous fuel and one for the liquid fuel. Each combustion chamber connected to these fuel rails has a single injection nozzle which injects centrally into the respective combustion chamber from above. Gaseous fuel is thus injected exclusively into the cylinders of one fuel rail, while liquid fuel is injected exclusively into the cylinders of the other fuel rail.

the DE 10 2004 043 143 A1 discloses a device for igniting fuel-air mixtures in a gas internal combustion engine with pre-chamber ignition, with fuel being injected from the side into a combustion chamber via a valve.

In view of the state of the art shown, however, the field of bi-fuel vehicles still offers room for improvement.

The object of the invention is to provide an internal combustion engine for a bi-fuel motor vehicle with which the problems mentioned can be avoided.

The object is achieved by an internal combustion engine with the features of claim 1. An internal combustion engine for a bi-fuel motor vehicle is disclosed with at least one combustion chamber and a fuel injection rail for direct injection of gaseous fuel into the combustion chamber by means of at least one injection nozzle on the combustion chamber.

According to the invention, the fuel injection rail is connected to two tanks for gaseous fuel, in each of which liquid gas (LPG) and compressed natural gas (CNG) are located, with the fuel injection rail and thus the combustion chamber being able to be supplied with a gaseous fuel from one of the two tanks, and the fuel injection rail has for each type of gas fuel at least one injection nozzle designed for this type of gas fuel, by means of which the respective gas fuel type can be supplied to the combustion chamber by direct injection, the two injection nozzles being arranged differently in their injection angle and one injection nozzle for the liquid gas ( LPG) has a side injection position, while a compressed natural gas (CNG) injector has a center injection position.

Further, particularly advantageous configurations of the invention are disclosed in the dependent subclaims.

It should be pointed out that the features and measures listed individually in the following description can be combined with one another in any technically meaningful way and show further refinements of the invention. The description additionally characterizes and specifies the invention, in particular in connection with the figure.

The internal combustion engine for a bi-fuel motor vehicle has at least one combustion chamber and a fuel rail for injecting fuel directly into this combustion chamber. At the combustion chamber it is the combustion chamber adjacent to a piston within a cylinder where combustion begins. The engine can have different numbers of cylinders and thus also of combustion chambers. The fuel injection rail is connected to two tanks, each containing different gas fuels. A gaseous fuel can be supplied to the combustion chamber from one of the two tanks, with the fuel injection rail having at least one injection nozzle designed for this gaseous fuel type for each gaseous fuel type. The two gaseous fuels are preferably liquefied petroleum gas (LPG) and compressed natural gas (CNG).

With the internal combustion engine according to the invention it is thus possible to operate a vehicle with two different gaseous fuels such as LPG and CNG, the two gaseous fuels both being fed directly to a combustion chamber. This allows the compression ratio to be increased without increasing the risk of knocking. It is therefore not a bifuel vehicle, which is operated with either petrol (or diesel) and one gaseous fuel, but rather the vehicle is operated with one of two gaseous fuels. If the vehicle carries both gaseous fuels in different tanks, the supply situation improves considerably, because when refueling is required, both LPG and CNG filling stations can be used. Furthermore, both gaseous fuels can be used as reserve fuel if one of the two gaseous fuels is no longer available. This also reduces the operating costs of the vehicle.

Furthermore, the internal combustion engine according to the invention has the advantage that its starting can be guaranteed under any condition. This is usually a problem for direct injection of LPG, but since CNG is also available as an alternative fuel and CNG injectors are also available, there are no problems with hot starts, for example. In addition, high inlet pressures of the LPG direct injectors are not required in front of a high-pressure pump, since the engine also runs under gas conditions. The CO ₂ emissions are also reduced compared to engines that use petrol as reserve fuel, for example.

In order to enable direct injection of both gaseous fuels, the internal combustion engine can have a special fuel injection system. For this purpose, a common fuel injection rail is provided, via which both types of gaseous fuel can be supplied to the combustion chambers of the engine. In this case, special injection nozzles are used for each type of gas fuel, with at least the positions of the injection nozzles differing from one another.

In an inventive embodiment of the invention, at least one compressed natural gas (CNG) injector has a central injection position, i. H. the compressed natural gas CNG is supplied to a combustion chamber of the engine from above at a central position. An LPG injector, on the other hand, can have a lateral injection position, i.e. H. the liquid gas is fed to a combustion chamber from the side. This respective position represents the ideal configuration. Ideally, the compressed natural gas CNG is introduced centrally from above into the combustion chamber, since this is fed in via an injector type that opens to the outside, with the resulting cone jet being ideal for this central location. The injector for liquid gas LPG is or can be designed as a multi-hole nozzle and can therefore also be used for the lateral position. A combustion chamber thus has at least two different injection nozzles in order to be able to selectively supply both gas fuels, the two injection nozzles being arranged differently in their injection angle. Of course, the respective injection nozzles are connected via control lines to a control unit, ideally to a central control unit (CPU) of the vehicle, so that the injection nozzles are controlled by the relevant fuel, i.e. LPG or CNG.

In order to be able to selectively supply both types of gaseous fuel to the fuel injection rail, the two tanks for the gaseous fuels can also be connected to a 2-way valve. Depending on the activation of this 2-way valve, one or the other gaseous fuel is supplied to the fuel injection rail, in order to then be injected into the combustion chambers of the engine with the respectively assigned injection nozzle. The two tanks for the gaseous fuels are connected to the 2-way valve via respective feed lines, with the 2-way valve in turn being connected to the fuel injection nozzle via a feed line.

The tank with the compressed natural gas is preferably connected to the fuel injection rail via a pressure relief valve. Furthermore, the tank with liquid gas is connected to the fuel injection rail via a high-pressure pump. Above a certain pressure, the gaseous liquid gas can be transferred between its tank and the 2-way valve into the compressed natural gas supply line. In one embodiment of the invention, therefore, there is a supply line between the tank with liquid gas and the fuel injection rail and a supply line between the tank with compressed natural gas and the fuel injection rail are connected to each other via a connecting pipe, a valve being provided in the connecting pipe. In this way, the LPG can be transferred to the CNG supply line if required.

Sensor means for detecting parameters of the respective gaseous fuel are preferably provided on at least one feed line from a tank to the fuel injection rail. The detected parameters include at least the pressure and the temperature of the gaseous fuel. A sensor means for detecting parameters of the respective gaseous fuel can also be provided on the common fuel injection rail. The sensed parameters also include at least the pressure and temperature of the gaseous fuel.

It is expedient if the control unit or the central control unit is supplied with data from the elements mentioned, so that the corresponding parameters are also available for controlling them. For this purpose, control or connecting lines can be provided, which can also be designed to be wireless.

• 1 zeigt ein Kraftstoffsystem für einen Verbrennungsmotor eines Kraftfahrzeugs.

Further advantageous refinements of the invention are contained in the subclaims and the following description of the only ones 1 disclosed.

• 1 shows a fuel system for an internal combustion engine of a motor vehicle.

The internal combustion engine is only shown schematically with four cylinders, i. H. there are four combustion chambers 70 in which a mixture of fuel and air is combusted. The combustion chambers 70 are connected to a common fuel rail 40 through which fuel is supplied to all of the combustion chambers 70 . For this purpose, several injection nozzles 60, 61 are each provided for direct injection.

The fuel system also has two tanks 10 and 20, which can be filled with two different gaseous fuels. The tank 10 is provided in particular for LPG, while the second tank 20 is provided for CNG. The two tanks 10, 20 are connected to the fuel injection rail 40 via respective feed lines and a 2-way valve 30.

A first supply line 11 from the LPG tank 10 to the 2-way valve 30 has a high-pressure pump 14 . Sensor means 13 for detecting the pressure and/or the temperature of the LPG are also provided in or on this supply line 11 . A second supply line 21 from the CNG tank 20 to the 2-way valve 30 has a pressure-limiting valve 22 .

Appropriate activation of the 2-way valve 30 allows the fuel injection rail 40 to be supplied either with LPG or CNG. For this control, the 2-way valve is connected to a control unit (not shown). Above a certain pressure, gaseous LPG can also be transferred from the feed line 11 via a connecting line 12 into the feed line 21 for CNG. A further valve 15 is provided in the connecting line 12 for this purpose.

After the respective gaseous fuel has been supplied to the fuel injection rail 40, the gaseous fuel is supplied to the associated injection nozzles 60, 61 for this type of fuel. There are several direct injection nozzles 61 for the LPG and several direct injection nozzles 60 for the CNG. The direct injectors 60 for the CNG are arranged to inject the fuel centrally into a combustion chamber 70 from above, while the direct injectors 61 for the LPG are arranged to inject the fuel into a combustion chamber 70 from the side.

In 1 control or connecting lines 80 are also indicated, which lead from the respective element to the control unit or to the central control unit, so that parameters of the corresponding elements can also be recorded, with the corresponding elements being controllable in this way. The control or connecting lines 80 can also be wireless. A sensor means 50 for detecting parameters of the respective gaseous fuel can also be provided on the common fuel injection rail 40 . The sensed parameters also include at least the pressure and temperature of the gaseous fuel.

Reference List

10

Tank with liquefied petroleum gas (LPG)

11

LPG supply line

12

connection line

13

sensor means

14

high pressure pump

15

Valve

20

Compressed natural gas (CNG) tank

21

Supply CNG

22

pressure relief valve

30

gas switching valve

40

fuel rail

50

sensor means

60

Injector CNG

61

Injector LPG

70

combustion chamber, cylinder

80

Control or connecting lines

Claims (7)

Internal combustion engine for a bi-fuel motor vehicle with at least one combustion chamber (70) and a fuel injection rail (40) for direct injection of gaseous fuel into the combustion chamber (70) by means of at least one injection nozzle (60; 61) on the fuel injection rail (40), characterized that the fuel injection rail (40) is connected to two tanks (10;20) for gas fuel, in which respectively liquefied petroleum gas (LPG) and compressed natural gas (CNG) are located, the fuel injection rail (40) and thus the combustion chamber (70 ) a gaseous fuel can optionally be supplied from one of the two tanks (10; 20), and the fuel injection rail (40) has for each gaseous fuel type at least one injection nozzle (60; 61) designed for this gaseous fuel type, by means of which the combustion chamber (70) the respective type of gas fuel can be supplied by direct injection, the two injectors (60; 61) differing in their injection angle are arranged neatly and an injector (61) for the liquefied petroleum gas (LPG) has a lateral injection position, while an injector (60) for the compressed natural gas (CNG) has a central injection position. combustion engine after claim 1 , characterized in that the two tanks (10; 20) are connected to a 2-way valve (30) with which the gaseous fuels can be supplied to the combustion chamber (70) selectively. Internal combustion engine according to one of Claims 1 and 2 , characterized in that a supply line (11) between the tank (10) with liquid gas and the fuel injection rail (40) and a supply line (21) between the tank (20) with compressed natural gas and the fuel injection rail (40) via a connecting line (12 ) are connected to one another, a valve (15) being provided in the connecting line (12). Internal combustion engine according to one of the preceding claims, characterized in that the tank (20) with compressed natural gas is connected to the fuel injection rail (40) via a pressure-limiting valve (22). Internal combustion engine according to one of the preceding claims, characterized in that the tank (10) with liquid gas is connected to the fuel injection rail (40) via a high-pressure pump (14). Internal combustion engine according to one of the preceding claims, characterized in that sensor means (13) for detecting parameters of the respective gaseous fuel are provided on at least one supply line (11; 21) from the tank (10; 20) to the fuel injection rail (40). combustion engine after claim 6 , characterized in that the detected parameters include at least the pressure and the temperature of the gaseous fuel.

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