WO2009053160A2

WO2009053160A2 - Method and device for operating an internal combustion engine with two types of fuel

Info

Publication number: WO2009053160A2
Application number: PCT/EP2008/062091
Authority: WO
Inventors: Juergen Foerster; Thorsten Allgeier; Juergen Raimann; Winfried Langer
Original assignee: Robert Bosch Gmbh
Priority date: 2007-10-22
Filing date: 2008-09-11
Publication date: 2009-04-30
Also published as: DE102007050305A1; WO2009053160A3

Abstract

The invention relates to a method for operating an internal combustion engine. Said internal combustion engine can be operated in a first operating mode wherein a first fuel is injected into a suction pipe (5) and a mixture of a first fuel and air is supplied to a combustion chamber (3), in order to operate the internal combustion engine (1) according to a pre-defined nominal moment. In a valve protection operating mode, the quantity of the first fuel is reduced by a certain amount and a quantity of a second fuel is injected by means of a direct injection valve (9) arranged directly on the combustion chamber (3). The quantity of the second fuel is selected in such a way that the nominal moment is maintained.

Description

description

title

Method and apparatus for operating an internal combustion engine with two types of fuel

Technical area

The invention generally relates to internal combustion engines which can be operated in alternation with a plurality of fuel types, and more particularly to a method of operating such an internal combustion engine.

State of the art

Vehicle manufacturers increasingly want to offer natural gas (CNG: compressed natural gas) as an alternative fuel for their vehicles. Since the supply of natural gas is not yet comprehensively possible, one approach is to design internal combustion engines so that they can be operated in a conventional manner with gasoline as well as with natural gas as an alternative fuel. The internal combustion engines for driving these vehicles then provide, for example, a direct gasoline injection and a gas port injection. That is, in a gasoline operation, the fuel is injected directly into the cylinders before ignition, while in a gas operation, the gas is injected into the intake manifold. The injected into the intake manifold gas is swirled there, and the resulting gas-air mixture is passed through the inlet valve in the cylinder. However, such an arrangement has the disadvantage that in the gas operation of the internal combustion engine direct injection valve, which is located directly on the combustion chamber, the hot combustion gases is directly exposed to the gas gases in the gas operation, without cooling by a fuel flow, which is normally present in a direct injection in gasoline operation , to experience. In addition, minimal leakage of the direct injectors can lead to coking of gasoline, which significantly reduces the life of these valves.

It is therefore an object of the present invention to avoid damage to the direct injection valves due to excessive temperature and / or by coking in the gas operation of the internal combustion engine.

This object is achieved by the method according to claim 1 and by the device according to the independent claim.

Further advantageous embodiments of the invention are specified in the dependent claims.

According to a first aspect, a method for operating a combustion engine is provided. In the method, the internal combustion engine is operable in a first mode in which a first fuel is injected into a suction pipe and a mixture of first fuel and air is supplied to a combustion chamber to operate the internal combustion engine according to a predetermined target torque. In a valve protection mode, the amount of first fuel is reduced by a proportion and an amount of second fuel is injected via a direct injection valve located immediately adjacent to the combustion chamber, the amount of second fuel being selected to maintain the desired torque.

The method has the advantage that overtemperature and coking of the direct injection valves can be avoided by adding, in addition to supplying the Mixture of first fuel and air via the intake manifold in the first mode second fuel is injected via the direct injection valve directly into the cylinder. As a result, cooling of the injection valves can be achieved and coking avoided.

Furthermore, it can be provided that the internal combustion engine can be operated in a second operating mode, in which only the second fuel is injected directly via a direct injection valve.

According to one embodiment, the valve protection mode is taken at predetermined times or at periodic or regular time intervals each for a predetermined period of time. In particular, the valve protection mode can be adopted depending on an operating parameter of the internal combustion engine, in particular a rotational speed and / or a torque.

Furthermore, depending on the operating parameter of the internal combustion engine, the valve protection mode may be taken either at regular or periodic intervals or permanently.

According to a further embodiment, the amount of the second fuel may be injected immediately before the ignition timing, for the most part during a compression period of the combustion chamber and / or up to crankshaft angles between 5 ° and 10 ° before the ignition timing.

In another aspect, there is provided an engine controller for operating an internal combustion engine, wherein the engine controller is configured to operate the internal combustion engine in a first mode, wherein in the first mode the engine controller drives an injector disposed on an intake manifold of the internal combustion engine to operate in accordance with a predetermined operating condition Sollmo- ment inject the first fuel, so that via the intake manifold, a mixture of the first fuel and air is supplied to a combustion chamber. The engine control may further be configured so that in a valve protection mode, the injection valve is driven to inject a proportion of the first fuel reduced by a proportion and inject a quantity of a second fuel via a direct injection valve, which is arranged directly on the combustion chamber, wherein the amount of the second fuel is selected so that the desired torque is maintained.

In another aspect, an engine system is provided with an engine controller above and the engine operated by the engine controller.

In another aspect, a computer program containing program code that, when executed on a computing device, executes one of the above methods.

Brief description of the drawing

Preferred embodiments of the invention are explained below with reference to the accompanying drawings.

Figure 1 shows an engine system with an internal combustion engine according to an embodiment of the invention.

Embodiments of the invention

The sole FIGURE shows an internal combustion engine 1 for operation with several types of fuel. For simplified representation of the internal combustion engine 1 is shown only with a cylinder 2. However, the internal combustion engine 1 may include any number of cylinders. The cylinder 2 comprises a combustion chamber 3 with a piston 4. The combustion chamber 3 is supplied via a suction pipe 5 air for combustion. In the suction pipe 5, a throttle valve 6 is arranged to adjust the amount of air introduced into the combustion chamber. The cylinder 2 is also connected to an exhaust pipe 7, can be derived from the combustion chamber 3 via the combustion gases.

The internal combustion engine 1 is formed with both a first fuel, e.g. compressed natural gas (CNG), to be operated as well as with a second fuel, e.g. Gasoline and the like. In the following example, natural gas is assumed to be the first fuel and gasoline the second fuel. However, the invention is not limited to the use of these fuels.

Such an internal combustion engine 1 can be operated both with natural gas and with gasoline. In a gas operation, the natural gas can be injected into the suction pipe 5, so that it is mixed with the air located there and fed to the combustion chamber 3 of the cylinder 2 as a gas-air mixture via the suction pipe 5. In a gasoline operation of the internal combustion engine 1 is operated via a direct injection valve 8, via which the gasoline is injected directly into the combustion chamber 3.

The direct injection valve 8 is controlled via a motor control unit 10. The engine control unit 10 further controls the position of the throttle valve 6 and the injection valve 9 in the intake manifold 5 for injecting natural gas. Further, the engine control unit 10 determines the timing of ignition of the air-fuel mixture in the combustion chamber 3 by means of an ignition unit such as an ignition unit. a spark plug 11.

When operating with natural gas, the direct injection valves 8 for injecting gasoline in conventional internal combustion engines are usually inactive. However, they are directly exposed to the heat of combustion in the combustion chamber 3 and are therefore strongly heated in a corresponding manner. As opposed to Gasoline operation in the gas mode no or substantially no fuel flows through the direct injection valves, eliminating thereby caused cooling of the direct injection valves 8, so that they heat up significantly more in gas operation than in gasoline direct injection in gasoline mode. The increased heating can lead to damage or destruction of the direct injection valves 8. Due to unavoidable low leakage of gasoline through the direct injection valves 8 into the combustion chamber even in pure gas operation, coking of the gasoline can additionally take place.

To avoid the above drawbacks, it is envisaged to lower the temperature of the direct injection valves 8 by providing additional injection of gasoline during gas operation, i. There is provided an operation in which both a gas-air mixture from the suction pipe 5 is passed into the combustion chamber, as well as a predetermined amount of gasoline is injected via the direct injection valves. It is provided to reduce the proportion of natural gas in the combustion chamber and inject a corresponding amount of gasoline through the direct injection valves 8 in the combustion chamber. The amount by which the natural gas introduced into the combustion chamber 3 is reduced, and the amount of gasoline which is injected into the combustion chamber 3 before ignition are coordinated with one another such that the same torque is obtained without adjusting the ignition angle as in FIG results in pure gas operation or results in a torque that substantially corresponds to the desired torque. For example, the proportion by which the amount of the first fuel is reduced while maintaining the torque is between 5% to 30%, preferably between 10% and 20%.

The additional injection of gasoline via the direct injection valves 8 leads to a cooling of the direct injection valves by the lower temperature of the gasoline and by cooling due to the evaporation of the gasoline.

In particular, the injection of the gasoline should take place immediately before the ignition, ie with a crank angle 5 ° to 10 ° before the ignition, so that the injected amount of gasoline is heated only minimally by the heated by the compression gas-air mixture. By evaporating the gasoline, a low temperature of the gasoline content is additionally supported. A possible cool portion of the gasoline-air mixture in the cylinder is particularly important in this type of combustion in order not to increase the tendency to knock due to the gasoline content. This makes it possible that the high knock resistance of the natural gas-air mixture is not reduced. This also gives the advantage of increased efficiency due to higher compression and / or charge. A Zündwinkelspätverstellung due to the injection of gasoline in the gas mode is not necessary.

The additional injection of gasoline via the direct injection valves 8 can be started when the internal combustion engine 1 or the direct injection valves 8 reaches a first temperature threshold, and be terminated accordingly when falling below the same or an underlying second temperature threshold. Alternatively, if no temperature sensing is provided immediately proximate the direct injectors 8, it is possible to inject the gasoline fraction in gas mode at regular intervals, i. in accordance with a periodic operation, e.g. at intervals in a range of 30 seconds to 3 minutes, preferably at intervals of 1 minute to 2 minutes. The distances may be adjusted according to operating parameters, such as Torque or speed of the internal combustion engine 1 vary. The duration during which the gasoline injection takes place in the gas mode depends on the proportion of the natural gas which is replaced by the gasoline in the gas mode, and is e.g. between 10 seconds and 30 seconds.

Also, depending on the operating parameters, a switchover from the above-described periodic operation to a continuous operation can be carried out in which a portion of the first fuel, ie the natural gas, is permanently replaced by a second fuel, ie by gasoline. In particular, if the operating parameters on increased heat in the Close gas operation, such as under full load, can permanently replace a portion of the natural gas by gasoline.

The additional injection of gasoline in the gas mode has the further advantage that the direct injection valves 8 can be regenerated, since deposits formed by coking can be eliminated. Furthermore, this method has no effect on the efficiency, the fuel consumption or the engine noise and there are no additional components required because this mode can be realized by an appropriate programming as an additional function of the engine control unit 10.

Claims

Claims:

A method for operating an internal combustion engine (1), wherein the internal combustion engine (1) is operable in a first mode in which a first fuel is injected into a suction pipe (5) and a

Mixture of first fuel and air is supplied to a combustion chamber (3) to operate the internal combustion engine (1) according to a predetermined target torque; characterized in that in a valve protection mode, the amount of the first fuel by one

Proportion is reduced and an amount of a second fuel via a direct injection valve (8), which is arranged directly on the combustion chamber (3) is injected, wherein the amount of the second fuel is selected so that the desired torque is maintained.

2. The method according to claim 1, characterized in that the internal combustion engine (1) is operable in a second operating mode, in which only the second fuel directly via a direct injection valve (8) is injected.

3. The method according to claim 1 or 2, characterized in that the valve protection mode is taken at predetermined times or at periodic or regular time intervals each for a predetermined period of time.

4. The method according to claim 3, characterized in that the valve protection mode is occupied depending on an operating parameter of the internal combustion engine (1), in particular a rotational speed and / or a torque.

5. The method according to claim 4, characterized in that the valve protection mode depending on the operating parameters of the internal combustion engine (1) and / or depending on a temperature of the direct injection valve (8) is taken either at regular intervals or at periodic intervals or permanently.

6. The method according to any one of claims 1 to 5, characterized in that the amount of the second fuel immediately before the ignition, mostly during a compression period of the combustion chamber (3) and / or up to crankshaft angles between 5 ° and 10 ° before the ignition Time is injected.

7. engine controller (10) for operating an internal combustion engine (1); wherein the engine control unit (10) is designed to operate the internal combustion engine (1) in a first operating mode, wherein in the first operating mode the engine control unit (10) has an injection valve (9) arranged on a suction pipe (5) of the internal combustion engine (2) ) is actuated in order to inject first fuel in accordance with a predetermined desired torque, so that a mixture of first fuel and air is fed to a combustion space (3) via the intake manifold (5); characterized in that the engine controller (10) is further configured to control the injector (9) in a valve protection mode to inject a reduced amount of the first fuel and an amount of second fuel via a direct injector (8) is arranged directly on the combustion chamber (3), inject, wherein the amount of the second fuel is selected so that the desired torque is maintained.

8. Engine system with a motor controller according to claim 7 and the internal combustion engine (1), which is operated by means of the engine control.

A computer program containing program code which, when executed on a data processing unit, executes a method according to any one of claims 1 to 6.