WO2005100767A1

WO2005100767A1 - Method for operating an internal combustion engine with direct fuel injection

Info

Publication number: WO2005100767A1
Application number: PCT/EP2005/003413
Authority: WO
Inventors: Bernd Köhler; Christoph Lux; Michael Oechsle; Oliver Platzek
Original assignee: Daimlerchrysler Ag
Priority date: 2004-04-14
Filing date: 2005-04-01
Publication date: 2005-10-27
Also published as: DE102004017988B4; DE102004017988A1

Abstract

The invention relates to a method for operating a spark-ignition internal combustion engine (10) with direct fuel injection. After a cold start of the internal combustion engine (10), a first amount of fuel is pre-injected (MH) into the combustion chamber (18) in an induction stroke of the internal combustion engine (10), enabling a homogeneous, lean fuel-air mixture (λ > 1) to be formed essentially inside the entire combustion chamber (18), and a second amount of fuel is injected into the combustion chamber (18) in the form of a main injection (MS) in a working stroke of the internal combustion engine directly before the moment of ignition (ZT) enabling a layered fat fuel-air mixture (λ < 1) to be formed in the region of the spark plug (26). The main injection (MS) is carried out in the form of a multiple injection with several layered injections over a short time interval. This enables the emission of noxious substances and fuel consumption to be reduced after a cold start and makes it possible to avoid a constructively complex secondary air injection.

Description

Method for operating an internal combustion engine with direct fuel injection

The invention relates to a method for operating a spark-ignited internal combustion engine, in particular for operating a spark-ignited internal combustion engine after the cold start.

In a conventional internal combustion engine arise after

Cold start due to poor mixture preparation in the cold

Combustion chamber high hydrocarbon and

Carbon monoxide emissions. In order to fall below the emission limit values prescribed by law, the catalytic converter has to be switched on as soon as possible after a cold start

Reach temperature at which sufficient

Pollution conversion is guaranteed. This temperature is commonly referred to as the light-off temperature.

In order to solve this problem, a rich charge mixture is conventionally made available to the combustion chamber in order to ensure sufficient flame resistance of the mixture formed in the combustion chamber and to heat up the catalyst for the exhaust gas aftertreatment. In addition, a secondary air injection is often provided in order to enable post-oxidation of the combustion gas in the exhaust duct or in the catalytic converter. A disadvantage of these approaches, however, is an increased fuel consumption due to the rich charge mixture and the various design measures in connection with the secondary air injection. It is therefore an object of the invention to provide a method for operating an internal combustion engine with which the pollutant emissions and the fuel consumption after the cold start can be reduced and at the same time secondary air injection can be dispensed with.

This object is achieved by a method for operating a spark-ignition internal combustion engine

Direct fuel injection with the features of claim 1 solved. Advantageous refinements and developments of the invention are the subject of subclaims 2 to 13.

In the method according to the invention for operating a spark ignition internal combustion engine with

Direct fuel injection after the cold start delivers combustion air to a combustion chamber; fuel is injected into the combustion chamber by means of a fuel injector; and a fuel-air mixture formed in the combustion chamber is ignited by means of a spark plug at a predetermined ignition timing. The method according to the invention is characterized in that a pre-injection of a first fuel quantity in an intake stroke of the internal combustion engine is injected into the combustion chamber, with which a homogeneous, lean fuel-air mixture (λ> 1) is essentially formed in the entire combustion chamber; and that a main injection of a second fuel quantity is then injected into the combustion chamber in a working stroke of the internal combustion engine immediately before the ignition point, with which a stratified, rich fuel-air cloud (λ <1) is formed in the region of the spark plug, the main injection being Multiple injection with multiple stratified injections is carried out in short succession. After the cold start of the internal combustion engine, the fuel quantity to be injected into the combustion chamber is divided into two injection quantities. The pre-injection takes place in the intake stroke of the internal combustion engine in order to form a homogeneous, lean fuel-air mixture in the entire combustion chamber. With the main injection in the working stroke of the internal combustion engine, a stratified, rich fuel-air mixture is formed in the area of the spark plug immediately before the ignition point, so that a reliable ignition of this charge cloud is made possible even at very late ignition points. The late ignition timing creates a high exhaust gas temperature, which favors the post-oxidation of hydrocarbons, carbon monoxide and nitrogen oxides in the exhaust system. This high exhaust gas temperature and the post-oxidation of the pollutants in the catalytic converter itself accelerate the heating of the (bulkhead) catalytic converter, which thus reaches its light-off temperature after a few seconds, which means that overall pollutant emissions can be significantly reduced. By dividing the second fuel quantity into several stratified injections, better mixing of the fuel vapor with fresh air is achieved, which allows a larger injected second fuel quantity without the combustion of this rich charge leading to an excessively high carbon monoxide emission.

In one embodiment of the invention, the main injection is carried out as a double injection with two stratified injections. In this case, the ignition timing can lie either after the second stratified injection of the main injection or between the first and second stratified injection of the main injection. In an alternative embodiment of the invention, the main injection is carried out as a triple injection with three stratified injections. In this case, the ignition timing can lie after the third stratified injection of the main injection or optionally between the first and the second or between the second and the third stratified injection of the main injection.

In a preferred embodiment of the invention, the fuel-air mixture after the second stratified injection is slightly lean averaged over the entire combustion chamber, the average fuel-air ratio in the entire combustion chamber preferably being approximately λ = 1.05. This excess of oxygen enables a complete oxidation of the total injected fuel quantity without additional secondary air injection.

With the method according to the invention, late ignition times of up to 30 ° KW or 35 ° KW after an upper ignition dead center can be achieved with sufficient smooth running of the internal combustion engine.

In a further embodiment of the invention, the ignition point is approximately 2 ° KW to 10 ° KW after the end of the first stratified injection of the main injection.

In a still further embodiment of the invention, the pilot injection is also carried out as a multiple injection with a plurality of homogeneous injections. This measure further improves the homogeneity of the fuel-air mixture in the entire combustion chamber.

In a preferred embodiment of the invention, after the stratified fuel-air mixture is ignited, a further post-injection with a third quantity of fuel injected into the combustion chamber. As a result of this additional fuel injection, which takes place in the working stroke of the internal combustion engine, additional chemical energy is supplied to the exhaust gas, as a result of which the exhaust gas temperatures are increased even further due to complete post-oxidation of hydrocarbons, carbon monoxide and nitrogen oxides.

According to a further embodiment of the invention, a torque output of the internal combustion engine can be regulated by the second fuel quantity of the main injection and the ratio of the second fuel quantity of the main injection to the total fuel quantity of the pre-injection and the main injection. Alternatively, the torque output of the internal combustion engine can also be regulated by the second fuel quantity of the main injection, corrected by the proportion of the first fuel quantity of the pre-injection participating in the combustion.

Further features and combinations of features result from the description and the drawings. concrete

Exemplary embodiments of the invention are shown in simplified form in the drawings and are explained in more detail in the description below. Show:

Figure 1 is a schematic cross-sectional view through a cylinder of a spark-ignition internal combustion engine with direct fuel injection, in which the method according to the present invention can be used.

FIG. 2 shows a schematic diagram of a comparative example of an injection profile of the internal combustion engine of FIG. 1 after a cold start, plotted over the Crank angle, to explain the basic principle of the present invention;

3 shows a schematic diagram of the temperature profile over time of an oxidation catalytic converter of the internal combustion engine from FIG. 1 for an injection profile according to FIG. 2;

Fig. 4 a. 1 shows a schematic diagram of the emission curve over time of the internal combustion engine from FIG. 1 for an injection curve according to FIG. 2;

FIG. 5 shows a schematic diagram of a first exemplary embodiment of an injection profile of the internal combustion engine from FIG. 1 after a cold start, plotted against the crank angle, according to the present invention;

6 shows a schematic diagram of a second exemplary embodiment of an injection profile of the internal combustion engine from FIG. 1 after a cold start, plotted against the crank angle, according to the present invention;

7 shows a schematic diagram of a third exemplary embodiment of an injection profile of the internal combustion engine from FIG. 1 after a cold start, plotted against the crank angle, according to the present invention;

8 shows a schematic diagram of a fourth exemplary embodiment of an injection profile of the internal combustion engine from FIG. 1 after a cold start, plotted against the crank angle, according to the present invention; and

FIG. 9 shows a schematic diagram of a fifth exemplary embodiment of an injection profile of the internal combustion engine from FIG. 1 after a cold start, plotted against the crank angle, according to the present invention.

1 shows, in a highly simplified manner, a cylinder 12 of an externally ignited internal combustion engine 10

Direct fuel injection. In the cylinder 12, a combustion chamber 18 is delimited by a piston 14 and a cylinder head 16 closing the cylinder 12. A fuel injector 20 is arranged centrally in the cylinder head 16, with which fuel can be injected into the combustion chamber 18 through a nozzle opening 22. A control device (not shown) determines, among other things, during a starting phase of the internal combustion engine 10. the injection times of the fuel with the associated fuel quantities and an ignition time at which a fuel-air mixture formed in the combustion chamber is ignited by means of a spark plug 26 or the like.

When the nozzle opening 22 of the fuel injector 20 is released, the fuel is injected into the combustion chamber 18 in the form of a cone jet 24 with an opening angle between 70 ° and 110 °. The positioning of the spark plug 26 in the combustion chamber 18 is selected such that the electrodes 28 of the spark plug 26 are not wetted by the injected fuel cone 24.

The internal combustion engine 10 shown in FIG. 1 preferably works according to the four-stroke principle. In a first bar of a working cycle of the internal combustion engine 10, the so-called intake stroke, combustion air is supplied to the combustion chamber 18 through an inlet duct (not shown). The piston 14 moves in a downward movement to a bottom dead center UT. In a further compression stroke of internal combustion engine 10, piston 14 moves in an upward movement from bottom dead center UT to top ignition dead center ZOT. In a subsequent expansion stroke, the piston 14 moves downward again to a bottom dead center UT; and in a fourth extension stroke, the piston 14 moves in an upward movement to an upper dead center TDC, in order to push out the exhaust gases from the combustion chamber 18.

The aim of the method according to the invention is to reduce the pollutant emissions and the fuel consumption after the cold start, while at the same time dispensing with an additional secondary air injection. This is achieved in that a very late ignition point ZT is made possible with a reliable ignition of the fuel-air mixture in the combustion chamber 18 and the internal combustion engine running smoothly. 2 to 4, the principle on which the invention is based will first be explained in more detail.

2, the injection processes ES after the cold start of the internal combustion engine 10 are plotted over the crank angle ° KW. An essential point of the method according to the invention is the division of the injected fuel into two parts, namely a homogeneous pre-injection M _H and a stratified main injection M _s .

First, in the intake stroke of the internal combustion engine 10, a first amount of fuel in a pilot injection M _H injected so that a homogeneous fuel-air mixture with a fuel-air ratio λ _> 1, preferably λ & 1, 6 is formed in the entire combustion chamber 18. This provides a sufficient supply of hydrocarbon molecules for post-oxidation. A second fuel quantity in a main injection M _{s is then} injected into the combustion chamber 18 as a stratified injection in the working stroke of the internal combustion engine 10 immediately before the ignition point ZT, so that in the area of the spark plug 26 a stratified charge cloud 30 with λ <1, for example λ <0.8 , which is located on the spark plug 26 at the ignition point ZT. Thus, even at very late ignition times ZT of up to 30 ° KW or 35 ° KW after the top ignition dead center ZOT, a reliable ignition of the charge present in the combustion chamber 18 is guaranteed. The combustion of the stratified charge cloud 30 is completed by the rapid combustion of the rich charge mixture until the outlet valve opens.

The charge stratification is given by the beam formation in a jet-guided combustion process. Injection at a certain piston position, such as in a wall-guided combustion process, is not necessary here. This enables stable charge stratification at all injection times and thus greater freedom in the choice of the ignition and injection timing.

After the second stratified injection, the fuel-air mixture is preferably slightly lean averaged over the entire combustion chamber 18, ie the average fuel-air ratio in the entire combustion chamber 18 is preferably approximately λ = 1.05. This excess of oxygen enables a complete oxidation of the total injected fuel quantity without additional secondary air injection. The following catalyst heating strategy enables freedom in the selection of the ignition timing ZT in connection with the given ignition safety and smooth running at extremely late ignition timing.

The pre-injection M _H in the intake stroke generates a lean fuel-air mixture in the entire combustion chamber 18. This provides a sufficient supply of hydrocarbon molecules for post-oxidation. The stratified main injection M _s in the area of the spark plug 26 generates a charge cloud with a rich fuel-air mixture, which ensures reliable ignition. The combustion of the stratified charge is completed by the rapid combustion of the rich mixture until the exhaust valve opens.

The flame front of the combustion continues in the further course of the working cycle into the areas of the combustion chamber 18 in which the lean mixture is present. However, the burning rate is significantly reduced in the area of lean combustion, which is why the combustion is not yet complete when the exhaust valve is opened. As a result, very high exhaust gas temperatures are reached in the exhaust duct and in front of the bulkhead catalytic converter.

The combustion of the rich charge mixture of the stratified main injection M _s produces a large amount of carbon monoxide. This carbon monoxide is reoxidized in the exhaust phase together with partially unburned hydrocarbons from the lean areas.

The graph of FIG. 3 shows measured exhaust gas temperatures upstream or in the bulkhead catalytic converter at Cold start emission measurement for the injection process of Fig. 2. The measurement sequence corresponds to the first seconds of the EU98A cycle. It can be clearly seen that the late ignition timing ZT in conjunction with the effective post-oxidation of the carbon monoxide from the rich charge cloud 30 and the hydrocarbons from the areas with a lean fresh mixture provide very high exhaust gas heat flows for heating the bulkhead catalytic converter. Compared to homogeneous catalyst heating (curves d, e and f) with a late ignition point ZT, this results in a considerable reduction in the time until the catalyst light-off temperature is reached.

4 shows an associated measurement of the pollutant emissions, measured with a CVS measuring system used for exhaust gas tests. The low hydrocarbon emissions immediately after the cold start (curve A) are particularly evident here. The hydrocarbons from the lean areas of the combustion chamber 18 are almost completely oxidized. Most of the carbon monoxide emissions from the rich charge areas are oxidized (curve C). The high carbon monoxide emissions from a purely homogeneous catalyst heating (curve D) are caused by the enrichment required in the cold start; this is necessary in a purely homogeneous injection process in order to achieve a satisfactory smooth running of the internal combustion engine. The end wall catalytic converter, which is ready for operation very quickly (e.g. after about 11 seconds), shows a significant reduction in emissions, especially in the first acceleration phase, with a homogeneously stratified injection process.

Various preferred exemplary embodiments of the injection method according to the invention after the cold start are explained in more detail below with reference to FIGS are based on the basic principle of the invention described above.

In the first exemplary embodiment of FIG. 5, the pre-injection M _H takes place in the intake stroke of the internal combustion engine 10 as a simple homogeneous injection into the combustion chamber 18. The stratified main injection M _s takes place in the working stroke of the internal combustion engine 10 immediately before the ignition point ZT as a double injection with a first and a first second layer injection within a few milliseconds. The formation of the stratified main injection M _s as a multiple injection further improves the mixture formation of the rich charge cloud 30 in the area of the spark plug 26 due to better mixing of the fuel vapor with the fresh air.

Due to the late ignition timing ZT of about 30 ° KW to 35 ° KW according to ZOT, a high exhaust gas temperature is generated, since the late ignition timing ZT results in a late center of gravity and a late burning end. These boundary conditions of the high exhaust gas temperature and the slight excess of oxygen favor the post-oxidation of CO and HC in the exhaust system, both in the exhaust duct and exhaust manifold as well as in the bulkhead catalytic converter. The heat of reaction released thereby causes a further rise in the exhaust gas temperature. This high exhaust gas temperature and the oxidation of CO and HC in the catalytic converter itself accelerate the heating of the bulkhead catalytic converter, which therefore reaches its light-off temperature after only a few seconds, so that pollutant emissions can be reduced.

In the embodiment of FIG. 5, the ignition point is

Sometimes only after the second layer injection of the

Main injection M _s . However, the ignition timing is like also in all other exemplary embodiments preferably coupled to the end of the first stratified injection of the main injection M _s , the distance angle Δ depending on the operating point preferably being about 2 ° KW to about 10 ° KW. Therefore, the main injection M _s takes place at very late ignition times ZT in the working stroke.

As illustrated in FIG. 6, the ignition timing ZT can alternatively also lie between the first and the second stratified injection of the main injection M _s , which is designed as a double injection. The other aspects of the injection method of FIG. 6 correspond to those of the first embodiment of FIG. 5.

While in the first and the second exemplary embodiment the main injection M _{s is carried out} as a double injection with a first and a second stratified injection, the main injection M _{s is carried out} in the third exemplary embodiment of FIG. 7 as a triple injection with a first, a second and a third stratified injection. The spacing angle Δ between the end of the first layer injection and the ignition point ZT is also in this case preferably about 2 ° KW to about 10 ° KW.

As shown in FIG. 7, the ignition ZT takes place between the first and the second stratified injection of the stratified main injection M _s . Alternatively, the ignition timing ZT can also lie between the second and the third stratified injection of the main injection M _s , as indicated in FIG. 7, or even only after the third stratified injection of the main injection M _s .

The fourth exemplary embodiment of the invention shown in FIG. 8 differs from the third Embodiment of FIG. 7 in that the homogeneous pilot injection M _{H is carried out} as a multiple injection, in the embodiment shown as a double injection. This homogeneous double injection further improves the homogeneity of the fuel-air mixture in the entire combustion chamber.

At this point, it should be expressly pointed out that this homogeneous multiple injection M _H from FIG. 8 can also be combined with all the other exemplary embodiments shown, without this being explicitly shown.

Finally, FIG. 9 shows a fifth exemplary embodiment of the injection method according to the invention, which represents a further development of the second exemplary embodiment from FIG. 6. In this injection method, an additional injection M _{N takes place} with a third fuel quantity after the ignition ZT or the stratified main injection M _s . This post-injection M _N takes place in the hot combustion gas in the work cycle, whereby additional chemical energy is supplied. As a result of the ambient conditions prevailing in the outlet duct, the amount of post-sprayed fuel is completely re-oxidized, provided there is a sufficient excess of oxygen.

The present injection method also provides that the torque output of the internal combustion engine by the second fuel quantity of the main injection M _s and the ratio (M _s / M _H + M _S ) of the second fuel quantity of the main injection M _s to the total fuel quantity of the homogeneous pilot injection M _H and the stratified main injection M _{s are} regulated. As an alternative, the torque output of the internal combustion engine can also be corrected by the second fuel quantity of the main injection M _s , corrected for that at the combustion Participating portion of the first fuel quantity of the pre-injection M _{H can be} regulated.

The present invention is particularly suitable for a spark ignition internal combustion engine

Direct fuel injection. The advantages of the present invention are, in particular, the lower pollutant emissions after the cold start by rapid heating of the bulkhead catalytic converter and by effective post-oxidation of the raw emissions which arise; in fuel savings through the omission of a mixture enrichment in the after-start and the shortening of the catalyst heating-up time; and in doing without auxiliary units and saving space and costs in connection with the unnecessary secondary air injection.

Claims

claims

Method for operating a spark-ignition internal combustion engine (10) with direct fuel injection after the cold start, in which combustion air is supplied to a combustion chamber (18); fuel is injected into the combustion chamber (18) by means of a fuel injector (20); and a fuel-air mixture formed in the combustion chamber (18) is ignited by means of a spark plug (26) at a predetermined ignition point (ZT), a pilot injection (M _H ) of a first fuel quantity in an intake stroke of the internal combustion engine (10) into the Combustion chamber (18) is injected, with which a homogeneous, lean fuel-air mixture (λ> 1) is essentially formed in the entire combustion chamber (18); and then a main injection (M _s ) of a second amount of fuel in one working stroke

The internal combustion engine is injected into the combustion chamber (18) immediately before the ignition point (ZT), with which a stratified, rich fuel-air mixture (λ <1) is formed in the area of the spark plug (26), the main injection (M _s ) is carried out as a multiple injection with several stratified injections in a short time sequence.

2. The method according to claim 1, characterized in that the main injection (M _s ) is carried out as a double injection with two stratified injections and the ignition point (ZT) is after the second stratified injection of the main injection.

3. The method according to claim 1, characterized in that the main injection (M _s ) is carried out as a double injection with two stratified injections and the ignition point (ZT) is between the first and the second stratified injection of the main injection.

4. The method according to claim 1, characterized in that the main injection (M _s ) is carried out as a triple injection with three stratified injections and the ignition point (ZT) is after the third stratified injection of the main injection.

5. The method according to claim 1, characterized in that the main injection (M _s ) is carried out as a triple injection with three stratified injections and the ignition timing (ZT) is between the first and the second or between the second and the third stratified injection of the main injection.

6. The method according to any one of claims 1 to 5, characterized in that the fuel-air mixture after the second stratified injection (M _s ) averaged over the entire combustion chamber (18) is slightly lean.

7. The method according to claim 6, characterized in that the average fuel-air ratio in the entire combustion chamber (18) after the second stratified injection (M _s ) is approximately λ = 1.05.

8. The method according to any one of claims 1 to 7, characterized in that the ignition point (ZT) takes about 10 ° KW to 35 ° KW after an upper ignition dead center (ZOT).

9. The method according to any one of claims 1 to 8, characterized in that the ignition point (ZT) is about 2 ° KW to 10 ° KW after the end of the first stratified injection of the main injection (M _s ).

10. The method according to any one of claims 1 to 9, characterized in that the pilot injection (M _H ) is carried out as a multiple injection with a plurality of homogeneous injections.

11. The method according to any one of claims 1 to 10, characterized in that after the ignition (ZT) of the stratified fuel-air mixture, a post-injection (M _N ) with a third quantity of fuel is injected into the combustion chamber (18).

12. The method according to any one of claims 1 to 11, characterized in that a torque delivery of the internal combustion engine (10) is regulated by the second fuel quantity of the main injection (M _s ) and the ratio of the second fuel quantity of the main injection (M _s ) to the total fuel quantity of the pre-injection and the main injection (M _H , M _s ).

13. The method according to any one of claims 1 to 11, characterized in that a torque delivery of the internal combustion engine (10) by the second fuel quantity of the main injection (M _s ), corrected by the proportion of the first fuel quantity of the pre-injection (M _H ) participating in the combustion. is regulated.