WO2016062554A1

WO2016062554A1 - Method for operating a spark-ignition, direct-injection internal combustion engine

Info

Publication number: WO2016062554A1
Application number: PCT/EP2015/073313
Authority: WO
Inventors: Matthias Thewes
Original assignee: Fev Gmbh
Priority date: 2014-10-21
Filing date: 2015-10-08
Publication date: 2016-04-28
Also published as: DE112015004778A5

Abstract

The invention relates to a method for operating a spark-ignition, direct-injection internal combustion engine, wherein a pilot injection quantity of fuel is injected and is ignited for a pre-combustion 3 and, in the same cycle, a main injection quantity of fuel is injected and is ignited for a main combustion 4.

Description

Method for operating a spark-ignited direct injection internal combustion engine

description

The invention relates to a method for operating a spark-ignited direct-injection internal combustion engine, preferably a four-stroke gasoline engine, wherein the method is used in particular for operating the internal combustion engine under cold start conditions.

The cold start behavior, or the ability to start at low temperatures at all, can be known to be improved in internal combustion engines in that an increased amount of fuel is injected into the cylinder. Especially for fuels with poor evaporation behavior at low temperatures, eg. As alcohol fuels, or in their mixtures with petroleum-based fuels, can reach a high-pressure pump for conveying the fuel their delivery limits.

To address the problem of limited flow rates, DE 10 2009 037 294 A1 proposes a method for starting a multi-cylinder direct injection internal combustion engine, in which at least in groups independently controllable injection valves are provided in the cylinders, wherein fuel from at least one injection pump via at least one fuel rail to Is made available. When starting the internal combustion engine under cold start conditions, the injectors of a starter cylinder group inject an increased starting amount of fuel into the starter cylinders. The injectors of a shutdown cylinder group inject no or less than the increased starting amount of fuel into the shutdown cylinders. This means that essentially the fuel provided by the at least one injection pump can be injected into the starter cylinder group and not distributed to all the cylinders of the internal combustion engine. This is to achieve that a higher amount of fuel can be provided for each cylinder of the starter cylinder group.

DE 10 2006 025 920 A1 proposes to improve the cold start behavior, in addition to the normal operating fuel, a starting fuel, which has a sufficient flammability to allow a cold start of the internal combustion engine to inject. The disadvantage here is the increased construction costs for storage and for the supply of a second fuel for the internal combustion engine.

Under cold start conditions in the context of the invention, in particular those conditions are to be understood in which the internal combustion engine has not reached the operating temperature, in particular when low ambient temperatures, eg. B. temperatures below minus 10 degrees Celsius, prevail. Cold start conditions are present in particular when, in the case of a main injection of a maximum available fuel quantity, an insufficient amount of fuel can be vaporized and vaporized in order to allow safe ignition of the fuel-air mixture. Here, the type and quality of the fuel, or the alcohol, in particular ethanol content influence the evaporation properties and thus also determine the cold start conditions. The object of the invention is to provide a method which contributes in a simple way to improving the cold start behavior of spark-ignited internal combustion engine with direct injection.

The object is achieved by a method for operating a spark-ignited direct-injection internal combustion engine, in which a pilot injection quantity of fuel is injected and ignited for pre-combustion and then a main injection quantity of fuel is injected in the same work cycle and ignited for a main combustion. In contrast to conventional combustion processes in which a single combustion, a main combustion, takes place, in the method according to the invention in a working cycle, a further combustion, the pre-combustion, is provided. One working cycle comprises four process steps, namely suction, compaction, working and discharging. Pre-combustion of a lower fuel quantity near the bottom dead center than the main combustion pre-heats the gas in the combustion chamber prior to the initiation of the main combustion. If the working cycle is a four-stroke cycle, as in gasoline engines, the two burns take place within half a cycle, possibly even within a cycle, namely the compression stroke instead. The inventive method ensures that the cylinder charge is preheated early in the process, so that due to the subsequent compression results in a significant increase in temperature to top dead center.

In this case, the pre-injection quantity can preferably be injected in the compression phase, but it is also conceivable that the injection of the pre-injection quantity starts already in the intake phase and extends into the compression stroke or is already completed before this. The later the pre-combustion takes place, the more the temperature is reduced when the top dead center is reached. A very early pre-combustion, for example already in the intake phase, causes a part of the charge to be pushed out again as a result of the expansion of the combustion gases. As a result, the filling decreases, so that by the subsequent main combustion a lower indicated mean pressure can be achieved.

The pilot injection quantity is injected near bottom dead center, preferably between 270 ° before top dead center and 90 ° before top dead center. More preferably, the injection of the pilot injection takes place between 180 ° before top dead center and 135 ° before top dead center.

The pilot injection quantity of fuel is preferably injected in a layered manner, so that a stratified charge is achieved. Thus, despite the injection of a small amount of fuel, a layer of ignitable fuel-air mixture in the region of the spark plug can be achieved. The pilot injection quantity can be divided into a plurality of pilot injections, that is, several partial pilot injections take place in rapid succession, which are subsequently ignited. By injecting a plurality of partial pilot injection quantities, the time duration for which an ignitable fuel-air mixture is present in the form of a stratified charge is increased in order to enable reliable ignition and combustion.

Furthermore, it can be provided that is ignited multiple times for the pre-combustion, so take place several ignitions. Multiple ignitions increase the likelihood that ignition will occur in any event at a time when an ignitable fuel-air mixture predominates on the spark plug.

The main injection amount is preferably injected in the compression phase, with the main injection amount near the top dead center injected between 90 ° before top dead center and top dead center. Preferably, the injection of the main injection amount takes place between 45 ° before top dead center and top dead center. The main combustion preferably takes place with as homogeneous a charge as possible, ie a homogeneous distribution of the fuel-air mixture in the combustion chamber. Combustion burns the largest amount of fuel in the main combustion, so the work is done during the main combustion cycle. Since the pre-combustion only serves to heat the combustion chamber and the gas therein, a small pre-injection amount of fuel is sufficient. Preferably, the pilot injection quantity of fuel is less than 10%, preferably less than 5%, of the total injection quantity of pilot injection quantity and main injection quantity. Particularly advantageous is a pre-injection amount of about 2% of the total injection has been found.

The invention will be explained in more detail below with reference to FIGS. 1 shows the sequence of ignition and injection at the start of the combustion engine with a pre-injection and an ignition for pre-combustion,

FIG. 2 shows the sequence of ignition and injection at the start of the internal combustion engine with a plurality of partial pilot injections,

3 shows the sequence of ignition and injection at the start of the internal combustion engine with multiple ignitions for the precombustion, and Figure 4 shows the idealized pressure and temperature profile in the combustion chamber at the start of the internal combustion engine according to the inventive method.

Figures 1 to 3 show three different processes of ignitions and injection according to the inventive method for a four-stroke gasoline engine. Figures 1 to 3 show diagrams in which the abscissa of the crank angle (KW) in degrees before the dead center in the region of the ignition, the ignition TDC (ZOT), is removed. Far left begins the illustrated part of the four-stroke cycle in the middle of the third clock, the power stroke, at 630 ° before the ignition TDC (ZOT). On the extreme right, the illustrated part of the four-stroke duty cycle ends with the completion of the fourth stroke, the compression stroke, at the ignition TDC (ZOT) at 0 °.

On the ordinate, the valve lift of the intake valve and the exhaust valve is shown schematically. The movements or the valve lift of the exhaust valve is represented by the curve 1 and that of the intake valve by the curve 2.

The diagrams show a total of three and a half cycles of the four-stroke process. From the third clock, only the second half is shown, namely the crank angle range from 630 ° to 540 ° before the ignition TDC (ZOT). During the third cycle, the work is carried out, whereby the combustion of the fuel-air mixture, the gas mixture expands and moves the piston down. Shortly before reaching the bottom dead center (UT) at 540 ° before the ignition TDC (ZOT), the exhaust valve is gradually opened. The exhaust valve continues to open during the fourth stroke to approximately half of the fourth stroke. At the end of the fourth cycle at 360 ° before ignition TDC (ZOT), the exhaust valve is almost completely exhausted again. concluded. During the fourth stroke, the fuel gases are expelled from the combustion chamber by the movement of the piston from bottom dead center (UT) to top dead center (TDC). During the first cycle from 360 ° to 180 ° before ignition TDC (ZOT), the inlet valve is opened so that fresh air is sucked in by movement of the piston from top dead center (TDC) to bottom dead center (TDC). In most of the second stroke, the compression stroke, the gas in the combustion chamber is compressed by the movement of the piston from bottom dead center (UT) to ignition TDC (ZOT). During the second cycle from 180 ° to 0 ° before ignition TDC (ZOT) is a first execution of the method shortly after the bottom dead center (UT) at 180 ° before ignition TDC (ZOT) a pre-combustion

3 performed. Shortly before reaching the ignition TDC (ZOT) becomes a main combustion

4 performed.

In the variant of the method according to FIG. 1, the pre-combustion 3 comprises a pre-injection 5 and a pre-ignition 6, which takes place shortly after the pre-injection 5. The pre-injection 5 takes place in the first half of the second cycle, shortly after reaching bottom dead center (UT), so that the entire pre-combustion 3 is completed within the first half of the second cycle. The pre-combustion 3 is used to heat the gases in the combustion chamber before the main combustion takes place 4 to significantly increase the temperature when reaching the ignition TDC (ZOT) compared to a four-stroke process without pre-combustion. The pre-combustion 3 is not used to generate a torque of the internal combustion engine. Since the pre-combustion 3 in the area of bottom dead center (UT) takes place at 180 ° before ignition TDC (ZOT) or shortly before or after, it should be noted that the forces acting on the piston by the pre-combustion 3, not are large so as not to decelerate the piston in its upward movement toward the ignition TDC (ZOT).

Since the pre-combustion 3 only serves to heat the combustion chamber, very small quantities of fuel are sufficient. The amount of fuel is indicated by the length of the beam representing the pilot injection 5 along the abscissa. The length of the beam of the pilot injection 5 corresponds to the duration of the pilot injection 5 and thus the injection quantity. The same applies to the injection quantity of the main injection 7. The lengths of the bars are not in the illustrated figures scale. The amount of fuel of the pilot injection 5 is preferably about

2% of the total injection quantity. The total injection quantity includes all injections of a complete four-stroke process, that is to say in the present case the injection quantity of the pilot injection 5 and the injection quantity of the main injection 7.

The main combustion 4 is divided into a main injection 7 and a main ignition 8, which take place shortly before reaching the ignition TDC (ZOT). The main combustion 4 is used to generate torque of the internal combustion engine.

1 shows an embodiment of the method in which the pre-combustion 3 is divided into a pre-injection 5 and a pre-ignition 6. As shown in Figure 2, the pre-injection 5 can also be divided into partial pre-injections 5, 5 ', 5 ", wherein the Total amount of partial pilot injections 5, 5 ', 5 "of the total amount of the pilot injection 5 may correspond according to Figure 1. The individual partial pilot injections 5, 5 ', 5 "are followed by a single preignition 6. By injecting a plurality of partial pilot injection quantities, the time duration for which an ignitable fuel-air mixture in the form of a stratified charge is present at the spark plug is increased in order to ensure reliable ignition and To allow burning.

In the embodiment of the method according to FIG. 3, the pre-combustion is subdivided

1, and in three pre-ignitions 6, 6 ', 6 ". A variant in which a plurality of partial pre-injections take place and several pre-ignitions is also conceivable. in any event, ignition occurs at a time when an ignitable fuel-air mixture predominates on the spark plug.

FIG. 4 shows the temperature profile 9 and the pressure curve 10 within the combustion chamber via the crank angle (KW). Furthermore, the valve lift of the intake valve and the exhaust valve is shown schematically. It can be seen that at the time shortly after reaching bottom dead center (UT) at 180 ° before ignition TDC (ZOT), that is, in the field of pre-combustion 3 according to one of the embodiments of Figures 1 to 3, a significant increase in temperature 9 to is recorded. The pressure but at the same time is relatively low, indicating that the force on the piston is low in its direction of travel and has little effect on the efficiency of the internal combustion engine.

LIST OF REFERENCE NUMBERS

1 valve lift of the exhaust valve

2 Valve lift of intake valve

3 pre-combustion

4 main combustion

5, 5 ', 5 "pilot injection

6, 6 ', 6 "pre-ignition

7 main injection

8 main ignition

9 temperature profile

10 pressure course

KW crank angle

OT top dead center

UT bottom dead center

ZOT ignition TDC

Claims

claims

1 . A method of operating a spark-ignited direct-injection internal combustion engine in which a pilot injection amount of fuel is injected and ignited for pre-combustion (3) and then a main injection amount of fuel is injected in the same work cycle and ignited for a main combustion (4).

2. The method according to claim 1, characterized in that the pre-injection quantity is injected in the intake phase and / or the compression phase.

3. The method according to any one of the preceding claims, characterized in that the pre-injection amount near the bottom dead center (UT) between 270 ° before top dead center (ZOT) and 90 ° before top dead center (ZOT), preferably between 180 ° before the top Dead center (ZOT) and 135 ° before top dead center (ZOT) is injected.

4. The method according to any one of the preceding claims, characterized in that the pre-injection amount of fuel is injected in a layered manner.

5. The method according to any one of the preceding claims, characterized in that the pre-injection amount to a plurality of pilot injections (5, 5 ', 5 ") is divided.

6. The method according to any one of the preceding claims, characterized in that for the pre-combustion (3) is ignited several times.

7. The method according to any one of the preceding claims, characterized in that the pre-injection amount of fuel is injected layered.

8. The method according to any one of the preceding claims, characterized in that the main injection quantity is injected in the compression phase.

9. The method according to any one of the preceding claims, characterized the main injection quantity is close to top dead center (ZOT) between 90 ° before top dead center (ZOT) and 0 ° before top dead center (ZOT), preferably between 45 ° before top dead center (ZOT) and 0 ° before top dead center (ZOT) ZOT), is injected.

10. The method according to any one of the preceding claims, characterized in that the main combustion (4) takes place at homogeneous charge.

1 1. Method according to one of the preceding claims, characterized in that the pilot injection quantity of fuel is less than 10%, preferably less than 5%, of the total injection quantity of pilot injection quantity and main injection quantity.