EP1671022A1

EP1671022A1 - Method for operating a combustion engine

Info

Publication number: EP1671022A1
Application number: EP04764785A
Authority: EP
Inventors: Michael Scherrieble; Siegfried Weber
Original assignee: DaimlerChrysler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2003-09-25
Filing date: 2004-09-03
Publication date: 2006-06-21
Also published as: DE10344423A1; US20060201477A1; US7305964B2; WO2005038213A1

Abstract

The invention relates to a method during which fuel is directly injected into a combustion chamber by means of an injection nozzle, whereby during a working cycle, a portion of the fuel is injected in the form of a pre-injection into the combustion chamber, and the remaining fuel is injected in the form of a main injection at a later point in time. The pre-injection forms a homogeneous pre-mixture, with which a homogeneous combustion phase is initiated in the form of a low-temperature phase and a high-temperature phase. The main injection is carried out in such a manner that the self-ignition thereof occurs during the high-temperature phase of the pre-injection. The injection time of the main injection is selected or set so that the ignition of the main injection occurs after the start and preferably before the end of the high-temperature phase.

Description

Method for operating an internal combustion engine

The invention relates to a method for controlling the combustion of a self-igniting internal combustion engine according to claim 1.

When operating internal combustion engines with direct injection, an attempt is made to influence the combustion and the emission formation by varying the course of the injection. In particular in the case of direct-injection internal combustion engines with auto-ignition, injection strategies are proposed for optimizing the combustion, which are intended to increase the output while at the same time reducing the exhaust gas emissions. A substantial increase in performance is usually made more difficult by excessive soot particle formation, especially in full-load operation.

From DE 19953932 AI a method is known in which a combined homogeneous / heterogeneous mode of operation of an internal combustion engine is proposed for achieving medium and higher powers. An injection strategy is intended to enable both early homogeneous mixture formation in the compression stroke and subsequent heterogeneous mixture formation around top dead center. Here, fuel injection takes place with homogeneous mixture formation with a lower injection pressure than with heterogeneous mixture formation in order to avoid the application of fuel to the cold combustion chamber walls. It has nevertheless been shown that, despite the measures proposed above, exhaust gas emissions continue to increase, particularly in full-load operation occur. Further measures must therefore be taken to minimize exhaust emissions.

The invention has for its object to provide a method for an internal combustion engine with auto-ignition, with which an increase in load is achieved with a simultaneous reduction in exhaust gas emissions.

According to the invention, this is solved by the features of claim 1.

According to the method according to the invention, fuel is injected directly into a combustion chamber by means of an injection nozzle, part of the fuel being injected into the combustion chamber as a pre-injection and the remaining fuel as a main injection at a later time during a work cycle. The pre-injection forms a homogeneous premix, with which a homogeneous combustion phase in the form of a low-temperature phase and a high-temperature phase is initiated. The main injection is carried out in such a way that its auto-ignition takes place during the high-temperature phase of the pre-injection. The injection time of the main injection is selected or set so that the ignition of the main injection takes place after the start and preferably before the end of the high temperature phase. The aim of this is to start a main combustion phase of the main injection within the combustion phase of the high-temperature phase of the pre-injection, also known as a “Ho flame”. In this way, a higher burning rate is achieved in the combustion of the main injection, which leads to a reduction in the formation of soot particles with a simultaneous increase in performance, in particular at high speeds in the full branch range. The fact that the start of the heterogeneous combustion phase of the main injection takes place within the hot flame combustion phase of the pre-injection results in a faster conversion of the main injection quantity. The faster combustion results in an increase in the burning rate and a high rise in the exhaust gas temperature is avoided.

The method according to the invention is particularly suitable for full-load operation and in particular for full-load operation at high speeds, e.g. at speeds greater than 3000 rpm. Accordingly, the introduction of the main injection into the combustion chamber according to the invention brings about an increase in performance, in particular at high speeds and high load in diesel engines, the soot particle formation being minimized.

In one embodiment of the invention, the duration and start of the homogeneous combustion phase are regulated in a load-dependent manner by changing the pre-injection quantity, the compression and / or a temperature of the premix. This enables the homogeneous combustion phase to be set depending on the operating point, for example in order to to perform a corresponding main injection according to the invention in the event of a load change. The temperature of the premix is preferably changed by an adjustable exhaust gas recirculation rate.

In a further embodiment of the invention, the pre-injection is injected into the combustion chamber in a clocked manner. Accordingly, the pre-injection is carried out in several subsets, it being possible for the number of clockings and the time of injection of the first subset to be varied depending on the load. In this way, an optimal homogenization of the pre-injected fuel components can be achieved by the clocked pre-injection, so that those injected first Evaporate fuel jets in the combustion chamber and then mix with air before the next batches follow.

According to a further embodiment of the invention, the pilot injection is started in a range from the time the exhaust valve closes to 50 ° K before an ignition dead center. Pre-injection is preferably carried out in a range from 370 ° KW to 300 ° KW before an ignition dead center or in a range from 140 ° KW to 50 ° K before an ignition dead center. This prevents the injected fuel from striking the combustion chamber walls.

Further advantages result from the following description of the drawing. Exemplary embodiments of the invention are shown in the drawing. The description and claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them into useful further combinations. Show it:

1 shows a heating curve of a combustion of a homogenized fuel / air mixture in a self-igniting internal combustion engine,

2 shows a heating curve of a combustion according to the invention with pre-injection and main injection in a self-igniting internal combustion engine, and

3 shows the heating curve of the combustion according to FIG. 2 and a schematic curve of the injection times of the pre-injection and main injection.

A self-igniting internal combustion engine has a combustion chamber formed between a cylinder head and a piston, which shrinks during a compression stroke, compressing the air trapped in it. Furthermore, the internal combustion engine has an injection device, preferably a common rail system, which is controlled by a control device. As a result, fuel is conveyed under high pressure to an injection nozzle arranged in the cylinder head, so that a specific quantity of fuel is then metered into the combustion chamber as a function of the load by means of the injection nozzle. The injection nozzle preferably has a plurality of injection bores which are distributed in one or two rows of holes over the circumference of the injection nozzle.

The internal combustion engine preferably works on the four-stroke principle. In a first cycle of a work cycle, combustion air is supplied to the combustion chamber via inlet ducts, the piston moving in a downward movement to a bottom dead center. In a further compression stroke, the piston moves in an upward movement from bottom dead center to an upper ignition dead center ZOT. The conversion of the fuel mainly takes place around the top ignition dead center ZOT. After combustion, the piston expands downward to a bottom dead center. In a last stroke, the piston moves in an upward movement to a top dead center and pushes the exhaust gases out of the combustion chamber via outlet channels. The current position of the piston relative to the cylinder head is determined or specified by a crank angle ° iC in relation to the top dead center ZOT.

1 shows a heating curve of a self-igniting internal combustion engine, in which a homogenized fuel / air mixture is formed by an early fuel injection, which first has a low-temperature combustion phase, known as Cool-Flame CF, during the combustion. and undergoes a high temperature combustion phase known as hot flame HF.

The present invention aims to combine the combustion process of the homogeneous premix described in FIG. 1 in connection with a targeted main injection in such a way that an increase in performance is achieved in particular in the full load range. Accordingly, according to the present invention, in particular at high speeds in the full load range, the total amount of fuel is divided into a pre-injection and a main injection during a work cycle. With the pre-injection, a homogeneous premix is formed. This initiates a homogeneous combustion phase in the form of a low temperature phase and a high temperature phase in accordance with the combustion process shown in FIG. 1.

In the area of the ignition dead center ZOT, the temperature and pressure rise so much that the homogeneous mixture begins to burn. The start of injection of the main injection HE is then selected so that the combustion of the HE begins during the homogeneously burning pre-injection according to FIG. 2 or FIG. 3. Accordingly, the main injection is carried out in such a way that its auto-ignition takes place after the low-temperature phase of the pre-injection, preferably during the high-temperature phase. The injection timing of the main injection is set so that an ignition delay of the main injection continues until after the end of the low temperature phase or at least until the beginning or before the end of the high temperature phase, so that the auto-ignition of the main injection is initiated during the high temperature phase.

The duration of the ignition delay is preferably determined both by the injection timing of the pre-injection and the main injection or by varying the closing and opening times of the intake and exhaust valves. These are matched to each other in a load-dependent manner in such a way that the corresponding ignition delay is set for the fuel quantity of the main injection associated with the operating point.

According to the invention, a higher burning rate is achieved in the combustion of the main injection, which in particular at high speeds in the full load range leads to a reduction in the formation of soot particles with a simultaneous increase in performance, since the faster combustion achieved by the method according to the invention brings about an increase in the burning rate. The method according to the invention is therefore particularly suitable for full-load operation at high speeds, since increased soot particle formation is generally expected there. The heating curve shown in FIG. 2 according to the invention shows a clear increase in performance compared to conventional combustion. The main combustion starts shortly before the hot flame phase HF of the pre-injection.

According to the invention, the time and duration of the fuel injection and thus the fuel injection quantity can be set as a function of the load. Precise control is made possible by means of the common rail injection device, as a result of which optimized combustion and thus a higher power yield and significantly lower pollutant emissions can be achieved. The common rail injection device enables several injection processes with different injection quantities per cycle.

3 shows the start of activation of the injection nozzle. The pre-injection VE takes place between 10 ° KW and 110 ° KW before the ignition dead center ZOT, the main injection injection HE in a range between 155 ° KW before ZOT and about 5 ° KW after the ignition dead center ZOT.

The pre-injection VE ensures a gentle increase in pressure in the combustion chamber and reduces the typical diesel combustion noise to a minimum. Furthermore, the pilot injection VE, which ignites automatically in the region of the ignition dead center ZOT and burns homogeneously according to FIG. 1, provides optimum ignition conditions for the main injection according to the invention.

2 shows the combustion chamber pressure in conventional diesel combustion without pre-injection and in the case of partially homogeneous combustion when pre-injection VE has been carried out at 90 ° KW before TDC. The combustion of the pre-injection with Cool-Flame CF and Hot-Flame HF can be seen here. The main combustion begins in the area of the burning hot flame HF. The heating curve in the case of partially homogeneous combustion is in many areas above that of the usual application. For comparison, the heating curve for application without pre-injection is also shown in Fig. 2. According to the present invention, an increase in performance under the same boundary conditions, e.g. Cylinder peak pressure, exhaust gas temperature, boost pressure and charge air temperature achieved. An air / fuel ratio can be reduced here. Despite the lower air / fuel ratio, smaller soot emissions are achieved than with conventional applications.

The pre-injection VE can preferably be divided into several smaller pre-injections, ie it can be carried out in a clocked manner. A clocked pre-injection VE can be carried out from closing the exhaust valve up to 50 ° KW before the ignition dead center ZOT. To prevent the injected fuel from hitting the combustion chamber wall, The pre-injection VE can alternatively be carried out in a range from 370 ° KW to 300 ° KW before the ignition dead center ZOT or during the compression stroke between 140 ° KW and 50 ° KW before the ignition dead center ZOT.

3, the more favorable combustion conditions can be used for faster combustion of the HE, which are achieved by the homogeneously burning pre-injection VE. Due to the faster combustion, more fuel can be converted without an increase in the exhaust gas temperature.

Claims

claims

Method for operating a self-igniting internal combustion engine, in which fuel is injected directly into a combustion chamber by means of an injection nozzle, part of the fuel being injected into the combustion chamber as a pre-injection and the remaining fuel as a main injection at a later time during an operating cycle, and wherein the pre-injection forms a homogeneous premix with which a homogeneous combustion phase in the form of a low-temperature phase and a high-temperature phase is initiated, characterized by a main injection, the auto-ignition of which takes place after the start and before the end of the high-temperature phase of the pre-injection.

The method of claim 1, d a d u r c h g e k e n n e e e c h n e t, d a s s duration and start of the homogeneous combustion phase by changing the pre-injection quantity, the compression and / or a temperature of the pre-mixture are controlled depending on the load.

A method according to claim 1 or 2, characterized in that the temperature of the premix is changed by an adjustable exhaust gas recirculation rate.

4. The method according to any one of the preceding claims, that the pre-injection is injected clocked into the combustion chamber.

5. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that starts with the pre-injection in a range from 140 ° KW to 50 ° KW before an ignition dead center.

6. The method according to any one of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that starts with the pre-injection in a range from 370 ° KW to 300 ° KW before the ignition dead center.

7. The method according to any one of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that starts with the pre-injection in a range between a time of closing an exhaust valve and 50 ° KW before an ignition dead center.