DE10153629A1 - Fuel injection method - Google Patents

Abstract

A method for injecting fuel directly into a combustion chamber (2) of an internal combustion engine, the fuel injection system (1) comprising a fuel injection valve (12) which injects fuel directly into the combustion chamber (2) during an injection cycle, which is injected from a cylinder wall (3) is formed, in which a piston (5) is guided, the fuel injection valve (12) generating a mixture cloud (13) in the combustion chamber (2), has the following method steps: DOLLAR A - opening the fuel injection valve (12) and injecting a first one Mixture cloud (13a) in a first injection interval; DOLLAR A - closing the fuel injector (12); DOLLAR A - reopening the fuel injection valve (12) and injecting at least one second mixture cloud (13b; 13c) in at least one further injection interval during the same injection cycle of the internal combustion engine.

Description

State of the art

The invention is based on a method for injection of fuel in the combustion chamber of an internal combustion engine according to the genus of the main claim.

DE 198 27 219 A1 describes a fuel injection system known for an internal combustion engine, which has an injector with a fuel jet adjustment plate, which has first nozzle holes that run along a first circle are arranged, and second nozzle holes that run along a second circle are arranged. The second circle has one Diameter larger than that of the first circle is. The circles are coaxial to a central axis of the Adjustment plate arranged. Each hole axis of the second Nozzle holes form an acute angle with one Reference plane that is perpendicular to the central axis of the Valve body is. The angle is smaller than the one through each hole axis of the first nozzle holes with the Reference plane is formed. Therefore can Atomizing fuel through the first nozzle holes be injected away from fuel atomization directed through the second nozzle holes be injected. As a result, they interfere Atomizing fuel through the first nozzle holes are injected, not the fuel atomizers that what it is injected through the second nozzle holes allows to inject fuel appropriately atomize.

DE 196 42 653 C1 describes a method for forming a ignitable fuel / air mixture known. In the Cylinders of direct injection internal combustion engines an ignitable fuel / air mixture can be formed by in each combustion chamber delimited by a piston by means of a Injector when a nozzle opening is released by lifting it off of a valve member from a one comprising the nozzle opening Valve seat fuel is injected. To among all Operating conditions of the internal combustion engine, especially in Stratified charge operation, a consumption and emission-optimized inner mixture formation in everyone To enable the operating point of the entire map provided that the opening stroke of the valve member and the Injection time are variably adjustable.

DE 198 04 463 A1 describes a fuel injection system for mixture-compressing, spark ignition internal combustion engines known, which with an injection valve, the fuel into one formed by a piston / cylinder arrangement Injected combustion chamber, and with one in the combustion chamber protruding spark plug is provided. The injection valve is with at least one row across the circumference of the injector distributed injection holes provided. By a targeted fuel injection via the Injection holes become a jet-guided combustion process realized by forming a mixture cloud, where at least one beam of ignition towards the Spark plug is directed. More rays are provided through which an at least approximately closed or coherent mixture cloud is formed.

A disadvantage of the from the above publications known methods for mixture formation or Fuel injection systems are particularly lacking Homogeneity of the mixture cloud as well as the problem that ignitable mixture in the area of the spark gap Transport spark plug. To achieve a low-emission, To enable fuel-efficient combustion, in complicated combustion chamber geometries, swirl valves or swirl mechanisms can be used on the one hand fill the combustion chamber with the fuel / air mixture and on the other hand to lead the ignitable mixture to the spark plug.

The spark plug is usually molded directly. This leads to heavy sooting of the spark plug and frequent Thermal shocks, which makes the spark plug a shorter one Has lifespan.

A disadvantage of the known from DE 196 42 653 C1 Process for forming an ignitable fuel / Air mixture is also impossible, especially in Stratified charge operation small amounts of fuel precisely to be measured since the times for opening and closing the Fuel injector is not controlled precisely enough can be.

Another disadvantage is that complicated Combustion chamber geometries and fuel injectors with Twist preparation difficult to manufacture and costly in of production.

Advantages of the invention

The inventive method for injecting Fuel in the combustion chamber of an internal combustion engine with the has characteristic features of the main claim in contrast the advantage that by several, or at least two injection phases in a row in any selectable Intervals a mixture cloud can be formed that the Operating parameters of the internal combustion engine for Injection time is optimally adjusted.

By the measures listed in the subclaims advantageous developments of the main claim specified method for injecting fuel possible.

The injection phases are advantageously the same in each case long to form a mixture cloud with rich and lean areas to build.

It is also advantageous that the intervals between the individual injection phases can be selected as desired, preferably can be of equal length, so that the mixture cloud in their Shape and penetration length is deformable.

drawing

Embodiments of the invention are in the drawing, shown in simplified form and in the following Description explained in more detail. Show it:

Fig. 1 shows a schematic section through a fuel injection system with a suitable for use with the inventive method, fuel injection valve,

Fig. 2A-D highly schematic representations of a mixture cloud that is injected by the inventive method into the combustion chamber, and

Fig. 3 is a schematic sectional view of a fuel injector suitable for carrying out the method according to the invention.

Description of the embodiments

Fig. 1 shows a schematic section through a fuel injection system which is suitable for applying the method described below. The fuel injection system 1 has a combustion chamber 2 which is delimited by a cylinder wall 3 , a cylinder head 4 and a piston 5 . A combustion chamber trough 6 is formed in the piston 5 . In a ridge 7 of the combustion chamber 2 is a spark plug 8 with two electrodes 15 z. B. centrally located. An inlet valve 9 and an outlet valve 10 are indicated on ridge slopes 11 of the combustion chamber 2 . A fuel injector 12 arranged laterally between the cylinder wall 3 and the cylinder head 4 injects a conical mixture cloud 13 into the combustion chamber 2 . The geometry of the combustion chamber trough 6 and the shape of the mixture cloud 13 determine the path of the mixture cloud 13 into the region of a spark gap 14 which extends between the electrodes 15 of the spark plug 8 . The mixture cloud 13 is ignited by the electrical spark of the spark plug 8 .

The mixture cloud 13 is only partially stoichiometric in conventional fuel injection systems 1 due to the injection behavior of the fuel injection valves 12 . The jet front, that is to say the area of the mixture cloud 13 that is furthest away from the fuel injection valve 12 and was injected first in terms of time, is determined by the largest droplet size in the spray, while the jet end, that is to say the area of the mixture cloud 13 , that of the fuel injection valve 12 closest and last injected is determined by the smallest droplets. The distribution of the fuel between these two areas is not such that a uniform, stoichiometric mixture can arise. On the one hand, the mixture contains significantly more medium-sized droplets than large or small in Gaussian distribution. B. when opening and closing the fuel injector 12 and fluid dynamic phenomena affect the stoichiometry of the mixture cloud 13 .

So that the above-mentioned disadvantages of the mixture cloud 13 can be eliminated, a method for injecting fuel into the combustion chamber 2 is provided according to the invention, which influences the shape and the stoichiometry of the mixture cloud 13 in such a way that an optimal combustion process can take place.

The fuel injector 12 can be controlled such that a mixture cloud 13 injected from the fuel injector 12 into the combustion chamber 2 of the internal combustion engine can be adapted to the current operating state, for example full load or part load operation, and to the position of the piston 5 . In particular, the penetration of the mixture cloud 13 and its stoichiometry can be influenced in a targeted manner by generating several, at least two, in the exemplary embodiment three mixture clouds 13 a, 13 b and 13 c by at least two, in the exemplary embodiment three, injection intervals separated from one another before the ignition process. The mixture clouds 13 a, 13 b and 13 c partially penetrate each other or influence each other so that the penetration, the droplet size and the shape of the resulting mixture cloud 13 can be adjusted to the operating state.

Figs. 2A to 2D show, respectively, thereby a highly schematic mixture cloud 13 which each of three mixture clouds 13 a, 13 b and 13 c exists. The individual mixture clouds 13 a, 13 b and 13 c are injected into the combustion chamber 2 by means of the method according to the invention, the injection intervals and the intervals between them each having a different duration.

FIG. 2A shows the simplest case of a mixture cloud 13 injected in three injection phases. The injection intervals each have the same length and are separated from one another by equally long intervals. This results in three separate mixture clouds 13 a, 13 b and 13 c, which do not penetrate or overlap each other. As a result, a resulting mixture cloud 13 can be generated, which is particularly advantageous in jet-guided combustion processes, since the individual mixture clouds 13 a, 13 b and 13 c can be swirled separately from one another.

If a mixture cloud 13 with a richer jet front is to be generated, then, as shown in FIG. 2B, the first mixture cloud 13 a, which expands most spatially, is injected into the combustion chamber 2 with an extended injection interval and a shorter second injection interval. A mixture cloud 13 constructed in this way has a large penetration length and a rich beam front. Alternatively, a very lean jet front can also be generated by a very short first injection interval.

To generate a mixture cloud 13 with a shorter penetration length, it is advisable to let the injection intervals follow one another quickly, as shown in FIG. 2C, so that the individual mixture clouds 13 a, 13 b and 13 c partially overlap. In this way, for example, undesired wetting of the piston 5 during a late injection can be avoided.

If the injection intervals, as shown in FIG. 2D, are carried out even faster and at even shorter intervals in succession, the mixture cloud 13 is widened in edge regions 16 , so that the mixture cloud 13 is deformed as a whole. As a result, both the penetration and the stoichiometry of the mixture cloud 13 can be influenced.

The different penetration of the mixture clouds 13 a, 13 b and 13 c can also be achieved by heating the fuel while it is flowing through the fuel injection valve 12 . The heating of the fuel increases the evaporation rate, which has a positive effect on the mixture formation. The heating can, for example, by the waste heat of an actuator 17 of the fuel injector 12 , the z. B. can be designed as a piezoelectric actuator 17 take place. As described below Fig. 3 an embodiment of a fuel injection valve 12 is illustrated which is suitable for the abovementioned heating of the fuel.

Fig. 3 shows, in a partial sectional view of an outwardly opening fuel injection valve 12, which has an already-mentioned piezoelectric actuator 17 for actuating the fuel injection valve 12. The piezoelectric actuator 17 is enclosed in air and is supported on the one hand on a first housing component 18 and on the other hand on a shoulder 19 of a valve needle 20 . The valve needle 20 is operatively connected to a valve closing group 21 , which need not be discussed in more detail in this context. The valve needle 20 is urged by a spring 22 so that the fuel injection valve 12 is held in the rest state of the piezoelectric actuator 17 in the closed state. If the piezoelectric actuator 17 is excited by an electrical voltage, it expands against the force of the spring 22 , as a result of which the valve needle 20 moves in an opening direction and the fuel injection valve 12 is opened.

The fuel is fed to the fuel injection valve 12 centrally, for example, through a fuel supply 23 in the first housing component 18 and flows around an actuator housing 24 which is arranged in a second housing component 25 . The actuator 17 , which heats up due to the rapidly changing voltages during operation, dissipates its waste heat to the actuator housing 24 , which in turn is at least partially flowed around by the fuel, so that the heat is given off to the fuel.

The invention is not limited to the exemplary embodiments shown and can be used for fuel injection valves 12 of any design in various fuel injection systems 1 .

Claims (7)

1. A method for the direct injection of fuel into a combustion chamber ( 2 ) of an internal combustion engine with a fuel injection valve ( 12 ), which injects fuel during an injection cycle directly into the combustion chamber ( 2 ), which is formed by a cylinder wall ( 3 ) in which a Piston ( 5 ) is guided, the fuel injection valve ( 12 ) generating a mixture cloud ( 13 ) in the combustion chamber ( 2 ), with the following method steps: - Opening the fuel injector ( 12 ) and injecting a first mixture cloud ( 13 a) in a first injection interval; - closing the fuel injector ( 12 ); - Reopening the fuel injection valve ( 12 ) and injecting at least one second mixture cloud ( 13 b; 13 c) in at least one further injection interval while the same injection cycle of the internal combustion engine. 2. The method according to claim 1, characterized, that the time intervals between the injection intervals are the same length. 3. The method according to claim 1 or 2, characterized, that the injection intervals are the same length. 4. The method according to any one of claims 1 to 3, characterized in that the mixture clouds injected during the injection intervals ( 13 a; 13 b; 13 c) overlap. 5. The method according to any one of claims 1 to 4, characterized in that the fuel pressures prevailing during the injection intervals in the fuel injection valve ( 12 ) are of different heights. 6. The method according to any one of claims 1 to 5, characterized in that the fuel in the fuel injection valve ( 12 ) is heated before the injection. 7. The method according to claim 6, characterized in that the waste heat of an actuator ( 17 ) of the fuel injector ( 12 ) is used for heating the fuel.