DE10033597C2 - Method for operating a diesel engine - Google Patents

Description

The invention relates to a method for operating a die selmotors.

In modern diesel engines, the improvement of Ver combustion process is becoming increasingly important this is due to the increasingly fierce environmental protection is subject to conflicting requirements. at For example, achieving an improved impact grades and, concomitantly, a reduced strength fuel consumption by increasing the combustion temperature be achieved. However, this is disadvantageous increase an emission of nitrogen oxides. Next to a we Improvement in the degree of efficiency can also be achieved by exhaust gas purification be provided for example by means of a catalyst. to Achieving a lasting high impact of such a kata However, this lysator is at times a Reinigungsbe subjected to operation, in which the diesel engine unteröchio metric is operated with excess fuel in the Follow unburned fuel components of the exhaust gas in Kataly afterburning. From the associated Although increasing the catalyst temperature follows a Freibren NEN of residues and thus a regeneration of Kataly However, this method also leads to a Verrin efficiency. Also, this can be an increase associated with the emission of soot particles.  

From DE 32 45 780 C1 is a spark ignited airver sealing internal combustion engine known in the piston rotating body-shaped combustion chamber with constricted over has flow opening, wherein the injection nozzle in Zylin derkopf is located near the edge of the combustion chamber and the Injector opposite ignition device in upper Dead center position of the piston is immersed in the combustion chamber and in the mixture formation mainly by fuel wall order takes place. Furthermore, the highly variable Flow in the vicinity of the combustion chamber wall evened out so like a completely safe ignition and optimal combustion can be achieved in all operating areas, although doing so for reasons of wear a drastic shortening of the ignition device electrodes is made.

From EP 0 967 380 A2 a diesel engine is known, in to improve fuel economy or Ver Reduction of pollutant emissions during the intake stroke a short-term pilot injection takes place. The Vorein injection quantity is about 50% of the per stroke spraying total amount of fuel. Towards the end of the comm Pressionstaktes is the main injection with the rest 50% of the fuel quantity to be injected. By the Pre-injection is intended to improve the mixture formation and, consequently, an improvement in the efficiency or pollutant emissions are achieved. The procedure is only within a limited operating range settable. In particular, there is a risk that the preset splashed amount not ignited by the main injection becomes. For complete combustion of the total fuel amount must possibly about 30 ° after top dead center a white Tere injection done.

The invention has for its object to provide a method for Operation of a diesel engine to develop such that in a wide operating range the pollutant emissions ver reduces and the efficiency is improved.

This task is performed by a procedure with the characteristics of claim 1.

According to the inventive method is provided, the Main quantity of the force to be burnt in one working cycle fabric in a terminating during the compression stroke Homogenization period distributed in time. The temporal distribution avoids that part the injected fuel quantity to the cylinder wall ge reaches and dilutes the oil film adhering there. In the front the homogenization period lying in the ignition period  There is a relatively low pressure in the cylinder; in spite of This low pressure can be due to the temporal Ver Distribution of the homogenization injection into the Kom Pressing into the formation of a very homogeneous Achieve fuel-air mixture. This is on the one hand an improvement in efficiency and a reduction the pollutant emissions achievable. On the other hand, the Mixture formation during the homogenization injection such that a non-auto-ignitable fuel-air Ge mixed. This gives the opportunity to one particularly high fuel quantity of well over 50% of Total amount during the homogenization period splash, without an uncontrolled auto-ignition be must be feared. In support of security against Uncontrolled self-ignition is the homogenization Injection such that there is essentially no heat is released. During the subsequent ignition period then a controlled ignition of the fuel Air mixture by adding an additional ignition energy, whereby the ignition depends on the gentleman shearing operating condition can be selected precisely. Due to the homogeneous mixture formation of the main injection amount during the homogenization period is a si chere ignition of the total simplified.

In a preferred embodiment, the ignition energy is elek For example, by means of a spark or glow plug added. In a further embodiment of the method is the ignition energy by injecting an additional Zündflstoffmenge added by means of an ignition injection adds, creating a secure auto-ignition without additional Device expenditure is achievable. In particular, this is Procedure for existing diesel engines without modes fikation of the cylinder head applicable. The homogenization period  can ge depending on the operating conditions be selected and preferably begins during the intake tes. Depending on the type of injector used, it may be expedient, the main injection quantity during Homo genisierungszeitraumes in individual partial injection quantities inject. When using an injector with a di rectified nozzle needle can be a continuous homo genisierunginspritzung be advantageous. The injection the fuel is carried out in particular in the seat throttle area of the injector, causing a low jet penetration depth can be achieved. Due to the low beam Dringtiefe the risk is reduced, that fuel to settles the cylinder walls, so that overall a good Ho mogenisierung the fuel-air mixture even at a large injection quantity can be achieved.

In an advantageous embodiment of the method takes place in one between the homogenization period and the ignition period pre-injection period a Vorein injection, in which a heat release without ignition of the Fuel-air mixture takes place. By this Voreinsprit tion and heat release associated with it in the fuel-air mixture is an energy level This is only slightly below the energy requirement for a self-ignition lies. This is next to a ge Increase sparkle also a favorable Verringe tion of ignition required to be added energy given.

In an advantageous embodiment of the method takes place after the ignition period, a post-injection such that a substoichiometric air ratio arises. Thereby If necessary, the combustion chamber temperature can be increased. The usually associated soot formation is included  by the improved mixture formation in the homogenization period dammed. The operation with a post-injection may be appropriate in the context of exhaust gas recirculation be used, wherein a part of the exhaust gas stream with un burned fuel components of the combustion air supplied leads. As a result, a reduction of the nitrogen oxide Output achievable. Furthermore, the post-injection If necessary, take place for the purification of a catalyst, where at the concomitant increase in the Katalysatortempe a burning of the same produced and thus the Ver improving its effect. At the same time is a ü excessive emissions of soot particles avoided.

Depending on the operating conditions of the diesel engine can it may be appropriate to be the homogenization injection be may turn off and the diesel engine in previously known Way to operate.

Embodiments of the invention will be described below hand of the drawing explained in more detail. Show it:

Fig. 1 shows a schematic representation of a diesel engine for implementing the method according to the invention,

FIG. 2 shows a schematic time diagram with the sequence of the individual time intervals, FIG.

Figure 3 is a schematic timing diagram approximately period. With a sequence of partial injections during the homogenisation,

Fig. 4 shows a variant of the injection sequence of Fig. 3 with a continuous Homogenisierungseinspritzung and a pilot injection,

Fig. 5 shows a further variant of the injection sequence with an additional post-injection,

Fig. 6 is a schematic timing diagram with the Energieauf come in the cylinder.

In the schematic representation of FIG. 1 is a sel engine with a cylinder 1 and a crankcase 2 ge shows. In the cylinder 1 , a longitudinally displaceable piston 3 is held, which is connected via a connecting rod 6 articulated with a belgehäuse 2 in the cure stored crankshaft. The cure belwelle 4 is rotatable about a crank axis 5 . The longitudinal movement of the piston 3 is limited by a top dead center OT and a bottom dead center UT. In a downward movement from the top dead center OT to bottom dead center UT, the piston 3 performs an indicated by the arrow A intake stroke and in the reverse direction indicated by the arrow K compression stroke. During the intake stroke A to combustion air 12 is passed through a fresh air line 7 into the cylinder 1 and compressed in the subsequent sequent compression stroke K. Through an injector 8 fuel 15 is injected into the cylinder 1 . The resulting during combustion exhaust 13 is discharged through an exhaust pipe 10 and an arrange in the exhaust pipe 10 th catalyst 11 . The exhaust pipe 10 and the fresh air line 7 are connected via a valve 14 , where required by a subset of the exhaust gas 13 of the United combustion air 12 can be supplied. In the area near the injector 8 , a spark plug 16 is arranged.

In the timing diagram of FIG. 2, an intake stroke A is shown depending on the time t, which ends when reaching the lower dead point UT. This is followed between the bottom dead center BDC and the top dead center OT sion clock a Kompres K. It is a Homogenisierungszeitraum t see _H provided that begins during the intake stroke A and ends during the compression stroke K. Towards the end of the compression clock K in the area of the top dead center OT is an ignition period t _Z. Between the homogenization period t _H and the ignition period t _Z , a pre-injection period t _{V is} arranged. Subsequent to the ignition period t _Z is a post-injection period t _N. The time periods shown can be arranged at a distance from one another or directly following one another. In the illustrated embodiment, they are overlapping each other.

In the diagram shown schematically in FIG. 3, the fuel quantity M injected per unit time is plotted over time t. The homogenization injection H takes place by means of a fast-switching injector 8 in a plurality of partial injections T and is distributed over the homogenization time t _H. The Homogenisierungseinspritzung H follows in Zündzeitraum t _{Z is} an ignition injection Z. The total amount M of injected fuel 15 (FIG. 1) is divided into the bulk of M _H and the smaller Zündeinspritzmenge M _Z.

In the variant of the method shown in FIG. 4, the homogenization injection _H takes place during the homogenization period t _H continuously by means of an injector 8 with a direct-controlled nozzle needle. Subsequently, during a pre-injection period t _V, a pre-injection V takes place. The ignition in the ignition period t _Z he follows by an electrically operated actuator 16 of FIG. 1st

Fig. 5 shows yet another variant of the method, in which after a continuous main injection H, a pre-injection V and an ignition Z takes place. At a time interval there is a post-injection period t _N within which a post-injection quantity M _{N is} injected during a post-injection N. In the other features and reference numerals, Fig. 5 is consistent with Figs. 2 to 4 previously shown. In particular, in the variants of the method shown in FIGS . 3 to 5, the homogenization injection of the fuel 15 into the cylinder 1 takes place in the seat throttle region of the injector 8 , whereby a particularly small penetration depth of the fuel 15 is achieved.

Beyond the exemplary embodiments shown, further combinations of the homogenization injection H with an ignition injection Z, a pre-injection V or a post-injection N may be expedient. The amount of fuel M to be burned is composed of the quantities (M _H , M _V , M _Z ) injected during the homogenization injection H, the pilot injection V and the ignition injection _Z ; the additional post-injection amount M _N generates a stoichiometric air ratio during combustion. The resulting exhaust gases 13 are passed as shown in FIG. 1 by a catalyst 11 for its purification and can be supplied via a valve 14 of the combustion air 12 for Fül treatment of the cylinder 1 .

The schematic diagram shown in FIG. 6 shows the energy content E in the cylinder 1 ( FIG. 1) plotted over a time axis t in the region of the compression stroke K. During the homogenization period t _{H, there} is no heat release in the fuel air Mixture 9 ( FIG. 1), so that in this time range the energy content E is determined by the compression energy E _K. The energy required for auto-ignition is marked by the line E _S. The compression energy E _K remains below the line E _S ; the fuel-air mixture 9 is therefore not self-igniting. In the pre-injection period t _V , a pre-injection V ( Fig. 4, Fig. 5) takes place with a heat release E _V , whereby the energy content E is slightly below the energy requirement for the auto-ignition E _S , without self-ignition takes place. In the ignition period t _Z to an additional ignition energy E _{Z is} added, whereby the Energiege stop E is greater than the energy requirement for auto-ignition E _S and ignition of the fuel-air mixture 9 takes place. The addition of the ignition energy E _Z can be done by an ignition injection Z, for example, according to FIG. 5, electrically, for example, according to FIGS . 1 and 3 or in combina tion.

Claims (13)

A method of operating a diesel engine comprising the following steps:

• a) in an intake stroke (A), a cylinder ( 1 ) is filled with combustion air ( 12 );
• b) in a subsequent to the intake stroke (A) compression stroke (K), the combustion air ( 12 ) is compressed;
• c) in a homogenization period (t _H ) ending during the compression stroke (K), in a homogenization injection (H), a main amount (M _H ) of the quantity (M) of fuel ( 15 ) to be burnt is injected by means of an injector ( 8 ) injected into the cylinder ( 1 ), forming a non-auto-ignitable fuel-air mixture;
• d) in the subsequent ignition period (t _Z ) is an ignition of the fuel-air mixture ( 9 ) by adding an additional ignition energy (E _Z ).

2. The method according to claim 1, characterized in that in the homogenization Injection (H) substantially no heat release he follows.   3. The method according to claim 1 or 2, characterized in that the ignition energy (E _Z ) is added by means of an electrically operated actuator ( 16 ). 4. The method according to any one of claims 1 to 3, characterized in that the ignition energy (E _Z ) by injecting an additional Zündkraftstoffmenge (M _Z ) in an ignition injection (Z) is added. 5. The method according to any one of claims 1 to 4, characterized in that the homogenization period (t _H ) during the intake stroke (A) begins. 6. The method according to any one of claims 1 to 5, characterized in that the homogenization injection (H) takes place continuously. 7. The method according to any one of claims 1 to 6, characterized in that the homogenization injection (H) in several partial injections (T) he follows. 8. The method according to claim 6 or claim 7, characterized in that in the homogenization injection ( 4 ), the supply of the fuel ( 15 ) into the cylinder ( 1 ) in the seat throttle region of the injector ( 8 ). 9. The method according to any one of claims 1 to 8, characterized in that in a between the Homo genisierungszeitraum (t _H ) and the ignition period (t _Z ) lying pre-injection period (t _V ) a Vorein injection (V) of a pilot injection (M _V ) of fuel ( 15 ), wherein in the pilot injection (V) heat release (E _V ) takes place without ignition of the fuel-air mixture. 10. The method according to any one of claims 1 to 9, characterized in that after the ignition period (t _Z ) in a post-injection period (t _N ) a Nachein injection ( _N ) of a Nacheinspritzungsmenge (M _N ) of fuel ( 15 ) is such that a substoichi trisches air ratio arises. 11. The method according to claim 10, characterized in that the combustion of the fuel ( 15 ) resulting exhaust gas ( 13 ) is partially the combustion air ( 12 ) for filling the cylinder ( 1 ) is supplied. 12. The method according to claim 10, characterized in that the post-injection (N), if necessary, for the purification of a catalyst ( 11 ) for the exhaust gas ( 13 ). 13. The method according to any one of claims 1 to 12, characterized in that the homogenization spraying (H) is turned off, if necessary.