WO2004101972A1

WO2004101972A1 - Method for operating an internal combustion engine

Info

Publication number: WO2004101972A1
Application number: PCT/EP2004/004929
Authority: WO
Inventors: Jürgen Ringler; Wolfgang Strobl; Andreas SCHÜERS; Helmut Eichlseder; Andreas Wimmer; Thomas Wallner
Original assignee: Bayerische Motoren Werke Aktiengesellschaft
Priority date: 2003-05-14
Filing date: 2004-05-06
Publication date: 2004-11-25
Also published as: DE10321794A1

Abstract

The invention relates to a method for operating a gas-operated, particularly hydrogen-operated, internal combustion engine, comprising a device for injecting the fuel into the combustion chamber and a device for igniting the fuel/air mixture, during which at least one first quantity of fuel is injected into the combustion chamber whereby forming a fuel/air mixture. This fuel/air mixture is ignited and at least one second quantity of fuel is injected into the combusting fuel/air mixture.

Description

Method for operating an internal combustion engine

The invention relates to a method for operating a gas-operated, in particular hydrogen-powered, internal combustion engine with a device for injecting the fuel into the combustion chamber and a device for igniting the fuel-air mixture.

In the context of the present invention, a gas-fueled internal combustion engine, in contrast to a gasoline or diesel-fueled internal combustion engine, means an operation with a fuel which has comparatively wide ignition limits, such as hydrogen or hydrogen-containing gas mixtures, which in particular also include carbon monoxide and / or dioxide and / or Nitrogen and / or methane include, with hydrogen not necessarily having the largest share.

Such a method is known from DE 37 31 986 A1. Based on the problem of operating an internal combustion engine with hydrogen (H ₂ ) so that on the one hand, the nitrogen oxide emission (NOχ emission) is reduced as much as possible and on the other hand, a simple power control is possible, proposes DE 37 31 986 A1, the outer mixture formation,

in which the fuel is supplied to the intake air and thus a fuel-air mixture is formed outside the combustion chamber to combine in a hybrid process with the internal mixture formation, in which the fuel is injected directly into the combustion chamber. According to DE 37 31 986 A1, a second injector is provided for fuel injection into the intake line with external mixture formation and for fuel injection into the combustion chamber with internal mixture formation, a control of the injectors by means of the engine control.

Although a number of advantages of a two-stage fuel injection before and after ignition are achieved with the method according to DE 37 31 986 A1, resulting from the external mixture formation many disadvantages. For example, considerable performance losses due to the displacement effect must be expected. The - significant - volume H ₂ , which is introduced by external mixture formation, displaces a corresponding volume of air, so that in the filled combustion chamber correspondingly less oxygen is available. Furthermore, uncontrolled pre-ignition of the fuel-air mixture can occur at the hot residual gas or at hot spots in the combustion chamber, especially at high compression and charge. To optimize the combustion, the amount of fuel supplied via external mixture formation can only be changed within limits. Influencing the combustion management via injection time and pressure of the first injection quantity is not possible. Furthermore, two mixture formation / injection systems are required.

The invention is therefore based on the object to provide an aforementioned method, which combines the advantages of a multi-stage fuel injection before and after the ignition while avoiding the disadvantages of an external mixture formation in itself. The object is achieved by the features of claim 1, wherein according to the underlying idea at least a first amount of fuel is injected into the combustion chamber, forming a fuel-air mixture, the fuel-air mixture is ignited and at least a second amount of fuel is blown into the burning fuel-air mixture.

Particularly preferred embodiments and further developments of the method according to the invention are the subject of the dependent claims.

According to a particularly advantageous embodiment, the fuel-air mixture formed with the at least one first amount of fuel has an excess of air, so that with the first amount of fuel, a fuel-air mixture with an air ratio λ> 1 is formed.

In a method in which during the combustion of the fuel-air mixture, the profile of the nitrogen oxide (NOχ) emissions as a function of the air ratio (λ), starting from a stoichiometric air ratio (λ = 1) increases in the direction of larger λ values, reaches a maximum value and subsequently decreases to a negligible level, expediently the fuel-air mixture formed with the at least one first fuel quantity has an air ratio (λ) which lies at least approximately in the region of the transition to the negligible level.

According to a particularly preferred embodiment of the method, the fuel-air mixture formed with the at least one first fuel quantity has an air ratio (λ) in the range 1, 5 <λ, in particular in the range 1, 8 <λ. It is regarded as very advantageous if the determination of the injection parameters such as time, duration or quantity / time of the at least one first fuel quantity takes place with a view to optimized homogenization of the fuel-air mixture.

Appropriately, the injection of the at least one first amount of fuel after closing the intake valve and / or the ignition of the fuel-air mixture begins at least approximately in the region of top dead center (TDC), wherein according to another, also preferred embodiment, the ignition of the fuel Air mixture can also be done before reaching the top dead center (TDC).

Furthermore, it is considered to be particularly advantageous if the injection of the at least one second quantity of fuel depends on the burning rate and / or the course of combustion of the fuel-air mixture, for example -10-30 ° crankshaft angle, in particular 0-20 ° crankshaft angle, after TDC, he follows. In addition, the dependence of the at least one second injection quantity on the load lever is preferred, whereby an increasing amount of fuel is injected only from a load lever of approximately 50% in the direction of the 100% load lever.

According to a preferred embodiment of the method according to the invention, the injection end of the at least one first fuel quantity correlates at least approximately with the start of injection of the at least one second fuel quantity.

With the solution according to the invention in particular the high ignitability of the fuel is used at very wide ignition limits, the combustion is initiated by means of spark ignition and a pressure / Brennverlaufsformung about the Einblasestrategie, ie via the regulation the amount of fuel before and after ignition takes place without the formation of soot occurs.

In the partial load, a very homogeneous combustion with excess air and thus a quality-controlled operation of the engine are still possible. The efficiency advantage through operation at high air ratio and without throttle losses remains.

The ignition timing can be chosen arbitrarily to optimize efficiency and performance.

It is a high diesel-like compression to further increase the engine efficiency feasible after knocking phenomena on the injection strategy in full load are manageable. By introducing only a subset before ignition the knocking behavior is significantly improved because a reduced ignitability in lean mixtures with the listed fuels, such as hydrogen, is present and required for full load additional amount is only introduced directly into the combustion.

For the same reason, a charging of the engine to increase the power density as in diesel engines and an implementation of downsizing approaches to further fuel consumption can be represented, without that low-efficiency ignition to avoid knocking phenomena in full load must be taken into account.

Compared to conventional diesel engines, this combustion process, despite being injected into the combustion and thus the short period for fuel injection, mixture preparation and combustion without the formation of soot allows similar speeds as in a gasoline engine, since the proportion of fuel to be supplied directly into the

Combustion is not as big as conventional diesel engines and there already present a very willing to ignite and Verbrennungsfördemdes homogeneous fuel / air mixture in the combustion chamber by the pre-introduced amount of fuel.

Furthermore, the ignitability and combustion characteristics, for example the higher burning speed, of the stated fuels allow a faster conversion even with non-premixed combustion and the turbulent flow conditions in the combustion chamber can be explicitly optimized for the combustion of the amount of fuel introduced after ignition, so that high from this side Speeds are possible.

About the combustion control extreme diesel-like pressure increases and peak pressures in the combustion chamber can be prevented. The more moderate pressure gradients are, for example, in the range dp / dα = 4-6 bar; p _max = 100-125 bar and have a much better engine acoustics result.

By the combustion control, the peak temperature level in the combustion chamber can be significantly reduced. In this way, the characteristic of hydrogen engines exponentially below an air ratio of λ = 2 increasing NOx formation is prevented by excessive combustion chamber temperatures. Measurements have already resulted in a reduction of nitrogen oxide emissions at selected operating points of more than 90%.

The lower pressure and temperature-side load on the combustion control allows a component design similar to the gasoline engine. Despite high compression therefore occur for the diesel engine higher friction losses and the associated reduction of the effective efficiency does not occur. The combustion control can also reduce wall heat losses.

In summary, it can be stated that the method according to the invention has a specific influence on the combustion process, in particular on the start of combustion and the pressure waveform, so that both a high power density, corresponding to a high rotational speed, a low friction power and due to lower pressure increases and peak pressures softer engine noise and due to the high compression ratio high efficiency and high torque can be achieved and at the same time the formation of nitrogen oxides at high engine loads can be significantly reduced.

Hereinafter, with reference to figures, a particularly preferred embodiment of the method according to the invention is explained in more detail, show schematically and by way of example

FIG. 1 shows a pressure curve during two-stage fuel injection before and after spark ignition,

Figure 2 Pressure curves for single and multiple injection in

Comparison,

Figure 3a shows a discrete two-stage injection as well

FIG. 3b shows a transitional two-stage injection.

Figure 1 relates to a hydrogen-powered four-stroke multi-cylinder internal combustion engine not shown here with internal mixture formation and spark ignition, the invention of course also in another internal combustion engine, such as Wankel engine or Two-stroke internal combustion engine, can be used. The combustion chambers of the cylinders can be filled with air in each case via at least one inlet valve, wherein the supplied air may optionally contain recirculated exhaust gas and / or alternatively or additionally further admixtures and / or with increased pressure (charging) can be supplied. For injecting the fuel at a pressure of about 100 to 300 bar, an injector is provided which can be controlled by means of the internal combustion engine control including a plurality of parameters; the spark ignition in the power stroke is also controlled by the engine control in the present case by means of a spark plug, wherein in another embodiment, another ignition device may be used. The burned mixture is ejected via at least one exhaust valve and possibly fed to an exhaust aftertreatment system, wherein in the present case, an exhaust gas after-treatment with respect to the emitted nitrogen oxides (NO _x ), for example by means of a three-way catalyst or a NOχ storage catalytic converter takes place. The hydrogen is entrained cryogenic and liquid in a cryogenic tank on board the vehicle and injected after evaporation in the gaseous state into the combustion chamber, wherein it is emphasized that the invention of the storage type of hydrogen is independent, so stored according to another embodiment, the hydrogen also differently and can be fed ..

FIG. 1 shows, in a diagram 100, a pressure profile 102 in the case of two-stage fuel injection before and after spark ignition plotted against the crankshaft angle α and illustrates the arbitrary influenceability of the combustion process with the method according to the invention.

About the introduced before ignition first fuel amount of the

Pressure increase at combustion start, the maximum pressure increase dp / dα and determines the maximum cylinder pressure p _ma χ, set the ignition timing (ZZP) of the combustion start and then the duration of the diesel-like combustion (constant pressure combustion) or width of the cylinder pressure curve .DELTA..alpha. influenced by the second, directly fed to the combustion amount of fuel. The smaller the first amount of fuel, the greater the air ratio λ, with the result that the combustion after ignition runs colder and slower and less nitrogen oxides (NO _x ) are formed. In the present case, the first amount of fuel is such that a fuel-air mixture with 1, 5 <λ, in particular 1, 8 <λ, results. The increase dp / dα is flatter with a larger λ and a lower maximum cylinder pressure p _{max is} achieved. The ignition takes place in the present embodiment, a few degrees crank angle before reaching the top dead center (ZOT).

FIG. 2 shows in a diagram 200 pressure curves for single injection 202 and multiple injection 204 for a hydrogen-operated internal combustion engine with direct injection in comparison. The illustration relates to the crankshaft angle α and includes a single-injection and multiple-injection 208 and single-injection 210 and multiple-injection 212; ZOT marks top dead center, UT indicates bottom dead center.

Considering the single injection 202, 206, 210 in which the total amount of hydrogen is introduced after the inlet closing, but before ignition of the mixture, so the much higher pressure rise and the higher maximum pressure is noticeable. The multiple injection of hydrogen 208 not only before, but also after the ignition 212 directly into the combustion, a more moderate pressure curve 204 is achieved with reduced pressure increases and peak pressure cylinder. In the case of multiple injection, the ignition 212 takes place earlier than a single injection, in this case significantly before reaching the top dead center. To a combustion control over In order to be able to carry out an injection of hydrogen directly into the flame, hydrogen supply pressures above the combustion chamber pressure present during the injection are required. In order to ensure supercritical injection at any time, the pressure ratio of combustion chamber pressure and hydrogen supply pressure must be below the critical pressure ratio of about 0.5, which corresponds to a hydrogen supply pressure of about 200 to 300 bar. In this way, independent of the combustion chamber pressure fuel metering can be realized. Incidentally, the high injection pressures can have a positive effect not only on the mixture formation / homogenization process of the second injection, but also on the first injection.

FIGS. 3a and 3b show various injection strategies 300 and 350 for realizing a combustion control, with the injected fuel quantity (n) m in each case being shown as a function of the crankshaft angle α. The top dead center in the charge cycle cycle is WOT, the top dead center in the power stroke is designated ZOT, UT marks the bottom dead center. The cylinder inlet opens at EO and closes at ES

Both strategies 300, 350 have in common that after ignition, a subset of hydrogen is injected directly into the combustion. While, however, in FIG. 3 a, a first amount of hydrogen is supplied during Δi via an early internal mixture formation and a second amount of hydrogen is blown in during Δα ₂ after ignition and in the present case also after ZOT, the introduction of the first and second quantities of H ₂ occurs according to FIG before and after ignition via an injection process .DELTA.α-ι, so that even a single injection with intermittent ignition can be spoken. Both in the strategy 300 and in the strategy 350, the parameters α-i, Δα-ι, α ₂ , Δα ₂ freely selectable depending on the speed and load lever, where i and α ₂ each mark the beginning of injection.

Claims

Claims: Method of operating an internal combustion engine

1 . Method for operating a gas-powered, in particular hydrogen-powered, internal combustion engine with

- A device for injecting the fuel into the combustion chamber and

- A device for igniting the fuel-air mixture, characterized in that - at least a first amount of fuel (208 a, Δα- in the

Combustion chamber is blown, forming a fuel-air mixture,

- The fuel-air mixture is ignited (ZZP, 212) and

- At least a second amount of fuel (208 b, Δα ₂ ) is injected into the burning fuel-air mixture.

2. The method according to claim 1, characterized in that with the at least one first amount of fuel (208a, Δα- formed fuel-air mixture has an excess of air (λ> 1).

3. The method of claim 1 or 2, wherein in the combustion of the fuel-air mixture, the course of nitrogen oxide emissions (NOχ emissions) as a function of the air ratio (λ), starting from a stoichiometric air ratio (λ = 1) towards larger λ values increases, reaches a maximum value and subsequently decreases to a negligible level, characterized in that the at least a first amount of fuel (208a, Δα-ι) formed fuel-air mixture has an air ratio (λ), which at least is close to the transition to negligible level.

4. The method according to claim 3, characterized in that the at least one first fuel quantity (208a, Δαi) formed fuel-air mixture an air ratio (λ) in the range 1, 5 <λ, in particular in the range 1, 8 <λ , having.

5. The method according to any one of the preceding claims, characterized in that the determination of the injection parameters such as time, duration or amount / time of at least a first amount of fuel with regard to an optimized homogenization of

Fuel-air mixture takes place.

6. The method according to any one of the preceding claims, characterized in that the injection of the at least one first amount of fuel (208a, Δαi) after closing the inlet valve

(It begins.

7. The method according to any one of the preceding claims, characterized in that the ignition of the fuel-air mixture at least approximately in the region of top dead center (ZOT) takes place.

8. The method according to any one of the preceding claims, characterized in that the ignition of the fuel-air mixture takes place before reaching the top dead center (ZOT).

9. The method according to any one of the preceding claims, characterized in that the injection of the at least one second amount of fuel (208b, Δα ₂ ) is carried out depending on the burning rate and / or the combustion profile of the fuel-air mixture.

10. The method according to any one of the preceding claims, characterized in that the injection of the at least one second amount of fuel (208b, Δα ₂ ) -10-30 ° crankshaft angle, in particular 0-20 ° crankshaft angle, takes place after ZOT.

1 1. Method according to one of the preceding claims, characterized in that the amount of at least one second injection (208b, Δα ₂ ) is dependent on the load lever.

12. The method according to any one of the preceding claims, characterized in that the Einblasende the at least one first amount of fuel and the Einblasbeginn the at least one second amount of fuel at least approximately correlate (Fig. 3b, Δα-ι).