DE102009026574A1 - Internal-combustion engine i.e. gas engine, has laser ignition device comprising ignition laser with ignition point, where ignition point lies in region of combustion chamber, in which flow rate at time of ignition is low - Google Patents

Abstract

The engine (10) has a cylinder (12) and a piston (16) that are provided to limit a combustion chamber (14). A laser ignition device (27) comprises an ignition laser (26) with an ignition point (ZP), where the ignition point lies in a region of the combustion chamber, in which flow rate at the time of the ignition is low. The ignition point is shifted orthogonal to a longitudinal axis of the cylinder bore that lies up to the ignition point in a region of low flow rate in ignition time point. The piston includes a hollow portion in the piston head.

Description

State of the art

The The invention relates to a laser ignition device equipped internal combustion engine, in particular a gas engine, according to the preamble of claim 1.

From the DE 10 2004 001 554 A1 a laser ignition device for igniting an air-fuel mixture in an internal combustion engine is known, wherein an ignition laser of the laser ignition device protrudes into a combustion chamber of the internal combustion engine. The ignition laser is optically coupled via a light guide with a pump light source.

Large gas engines are usually operated close to the lean limit of an air-fuel mixture, to achieve a good efficiency. It must when ignition a stable flame core are formed, so that afterwards in the combustion chamber air-fuel mixture burned as quickly as possible becomes. Especially with extremely lean-burned gas engines, it is of of utmost importance to reduce the burning time and thereby to increase the efficiency of the engine. As burning time the period is defined within that between 10% and 90% the energy conversion takes place.

at conventional high-voltage ignition with spark plugs if the ignition location is forcibly close to the combustion chamber roof, so that the flame in a first approximation hemispherical spreads into the combustion chamber in the direction of the piston crown. Thereby the burning time is comparatively long. To this long burning time Nowadays, internal combustion engines are often used as short-hoppers, that is with a bore diameter larger as the stroke of the piston is formed. This will make the flame paths shortened in the direction of the piston. Nevertheless, a fast burn through the mixture is achieved, must have a high flow rate and resulting high turbulence in the combustion chamber prevail. This is in conventional internal combustion engines by swirl flows, Tumbleströmungen and / or squish flows achieved.

Around these currents and the resulting turbulence generate considerable flow losses before Especially on the suction side of the engine and / or it will be unfavorable Required combustion chamber geometries in which the ratio between surface and volume is large, so that high wall heat losses occur. Both the charge exchange losses as well as the wall heat losses reduce the efficiency the internal combustion engine.

at the charge movement in the cylinder, that is the flow of the in-cylinder fuel-air mixture differs into a swirling flow and a tumble flow. As a swirling flow is a rotational movement of the charge to the cylinder axis indicates while as Tumbleströmung denotes a rotational movement of the charge perpendicular to the cylinder axis becomes. Of course, there are also mixed forms of both Currents. The advantage of the increased burning speed is in the possible Gemischabmagerung and the associated Reduction of specific fuel consumption.

Disclosure of the invention

task the invention is an internal combustion engine with laser ignition device, to develop so that a safe and low-emission combustion in different operating points, especially in a lean Fuel-air mixture, at the same time very good efficiency is guaranteed.

The Task is by an internal combustion engine with ignition laser solved with the features of claim 1. For the Invention important features are further found in the following Description and in the drawing, the features in both Unique position as well as in different combinations for the invention may be important without wishing to do so is explicitly noted. Advantageous developments can be found in the subclaims.

These The object is achieved according to the invention that the ignition point is placed in a region of the combustion chamber in which the flow velocity at the time the ignition is low. As low flow speed In the context of the invention, a flow rate <10 m / s, preferably <5 m / s is considered. This makes it possible to reduce the flow losses in the Air system of the engine to reduce significantly and consequently the Significantly increase the efficiency of the internal combustion engine, without any loss in terms of pollutant emission and operating behavior the internal combustion engine. In addition, the production costs remain the internal combustion engine unchanged, so that in total a very advantageous and economical improvement of the internal combustion engine results.

In connection with the claimed invention is to be noted that the temporally and spatially highly resolved determination of the local flow velocities in the combustion chamber of an internal combustion engine today belong to the established investigation methods that are regularly used in the development of internal combustion engine the. In this case, it is possible, for example, to obtain the desired information about the flow velocity in different regions of the combustion chamber at different times by means of a computer-aided simulation of the flow velocity (CFD). Alternatively, it is also possible to detect the local distribution of the measurements by a series of measurements with impellers arranged in the combustion chamber or flow velocity sensors. Overall, therefore, the determination of the velocity distribution with high spatial and temporal resolution in the combustion chamber is a currently established method, which therefore does not need to be explained separately in connection with the claimed invention. The inventive arrangement of the ignition point in the combustion chamber, various optimization strategies can be followed, with which the efficiency of the internal combustion engine is improved.

in the so-called lean gas operation, that is, when the fuel-air mixture is substoichiometric (λ> 1), the swirl flow and / or the squish flow in the combustion chamber to a thermodynamic Brought optimum, so that in the combustion chamber at the time of ignition Existing turbulence for rapid burn-through after safe ignition leads. At the same time they are caused by the turbulence Flow losses in the intake manifold of the internal combustion engine minimized. Now the ignition laser is arranged so that its ignition point is located in a region of the combustion chamber in which a flow velocity of 10 m / s at the ignition point at the ignition point not exceeded becomes. It is particularly advantageous if the flow velocity at the ignition point at the ignition time is less than 5 m / s. In this case, a secure ignition can be realized and at the same time is due to the still existing flow and Turbulence at the ignition of the ignition caused by the ignition Flame core for fast burn through of the remaining cylinder charge carried in the combustion chamber. In conventional gas engines can the flow velocity at the ignition point for Zündzeitpunkt be about 30 m / s-40 m / s. Out the comparison of the flow velocities becomes the potential the internal combustion engine according to the invention in terms reduced flow losses and improved efficiency significantly.

If desired, the formation of the flame kernel and the burn-through can be realized by the use of several ignition pulses / laser pulses in the flame kernel. This is possible, for example, in that several laser pulses in the combustion chamber at intervals of up to 100 .mu.s 14 be emitted.

In a stoichometric operation (λ = 1) when the Internal combustion engine, for example, with a three-way catalyst is operated, the optimization of the internal combustion engine is slight different. As for the ignition of a fuel-air mixture under combustion chamber conditions only a minimal ignition energy is necessary, arise in this mode of operation two optimization options.

Either the ignition point, as in lean operation also, in one Range of flow positioned at up to 10 m / s. By a Nachzündung after a period of up to 100 microseconds can be ignited here in the same flame kernel and thus the ignition safety can be increased. This is included Motors with poorly homogenized mixture advantageous.

alternative it is also possible in a multiple ignition, wherein the different laser pulses a time interval larger than 100 μs or by choosing a firing point with higher flow rates as 10 m / s, a series of consecutively in a stream of thread Fuel-air mixture arranged flame cores to produce which lead to a faster burn through of the cylinder volume. As a result of this firing strategy several flame cores form independently and thus several flame fronts in the Combustion chamber are present, a faster burnout of the combustion chamber volume reached.

Both Optimization paths, especially in lean operation as well as in Stoichometric operation is common to that of the ignition Once structurally determined for each combustion chamber and then unchanged remains. There are only differences in the number and the time interval of the laser pulses, so that when changing the Operating mode, for example, from lean operation in the stoichiometric Operation and vice versa, only the control of the laser ignition device must be switched accordingly. As a result, both in lean operation as well as in λ = 1 operation the invention Advantages fully realizable.

A further advantageous embodiment of the invention Internal combustion engine provides to set the ignition point so that he is near the ignition at the time of ignition Piston crown or near the bottom of a piston recess located. Because in the immediate vicinity of the piston wall respectively the bottom of the piston recess due to Newton's adhesive condition inevitably a low flow rate prevails in a simple way a Zündort low flow velocity. Once the flame core has formed spatially, achieved he inevitably also areas with larger ones Flow velocity that entrains the flame kernel and thus for a quick burnout and short burning time provides.

Further Advantages and advantageous embodiments of the invention are the subsequent drawing, the description and the claims removable. All in the drawing, the description in the claims disclosed features can be both individually, and in Any combination with each other essential to the invention.

Brief description of the figures

following Be with reference to the figures embodiments of the invention exemplified. Show it:

1a a schematic diagram of an internal combustion engine with a laser-based ignition device;

1b a schematic representation of the ignition of 1a ;

2 to 4 detailed representations of internal combustion engines according to the invention.

An internal combustion engine carries in 1a Overall, the reference number 10 , It can serve to drive a motor vehicle, not shown. The internal combustion engine 10 usually includes several cylinders, of which in 1a only one with the reference numeral 12 is designated. A combustion chamber 14 of the cylinder 12 is from a piston 16 limited. Fuel enters the combustion chamber 14 directly through an injector 18 , the to a designated as rail fuel pressure accumulator 20 connected. Alternatively, the fuel-air mixture outside the combustion chamber 14 , for example, in a suction tube, are formed.

That in the combustion chamber 14 existing fuel-air mixture 22 is by means of a laser pulse 24 ignited by an ignition laser 26 comprehensive laser ignition device 27 in the combustion chamber 14 is emitted. The ignition in the combustion chamber 14 can also in a combustion chamber upstream antechamber (in 1a not shown). The ignition laser 26 is via a light guide device 28 powered by a pump light, which is from a pump light source 30 provided. The pump light source 30 is from a control unit 32 controlled, that too the injector 18 can drive.

How out 1b shows, the pump light source feeds 30 several optical fiber devices 28 for different ignition lasers 26 , each one cylinder 12 the internal combustion engine 10 assigned. For this purpose, the pump light source 30 several individual pump laser light sources 34 on that with a pulse power supply 36 are connected. Due to the presence of several individual pump laser light sources 34 the pumping light becomes as it were "dormant" to the various laser devices 26 distributed so that no optical splitter or the like between the pumping light source 30 and the ignition lasers 26 required are.

The ignition laser 26 has, for example, a laser-active solid 44 with a passive quality circuit 46 on that together with a coupling mirror 42 and a Auskoppelspiegel 48 forms an optical resonator. Under pressure from the pump light source 30 generated pump light generated by the ignition laser 26 in a conventional manner, a laser pulse 24 by a focusing optics 52 on one in the combustion chamber 14 (or in a pre-chamber, not shown) located ignition ZP is focused. The in the case 38 of the ignition laser 26 Existing components are through an exit window 58 for the laser beams 24 from the combustion chamber 14 separated.

In 2 eats a cylinder head 17 with indicated gas exchange valves 19 and a screwed ignition laser 27 visible, noticeable. In the embodiment according to 2 is the combustion chamber roof 69 just.

The piston crown of the piston 16 has a piston recess 15 with substantially a cylindrical wall and a flat trough bottom (no reference numeral) on. Here is a center MP (see the top view in the right part of 2 ) offset to a longitudinal axis 54 the cylinder bore 12 arranged. In the illustrated embodiment, the ignition point ZP is not in the center of the piston recess 15 but shifted radially outwards. At the same time the ignition point is still in the illustrated position of the piston 16 in the immediate vicinity of the bottom of the piston recess 15 arranged so that prevail there due to the velocity distribution near the wall and the Newtonian adhesive condition relatively low flow velocities. Of course, it is possible by a corresponding design of the focusing optics of the laser ignition device 27 the ignition point ZP in the direction of the longitudinal axis 54 to move according to the requirements of the internal combustion engine. Thus, the ignition point ZP can be placed closer to the bottom of the piston recess or closer in the direction of the combustion chamber roof as needed 69 be moved if this should be necessary in the course of optimization of the internal combustion engine according to the invention. This is only the optics of the laser ignition device 27 to be provided with a correspondingly changed focal length.

Between combustion chamber roof 69 and the piston crown is formed in the illustrated position of the piston 16 a squish flow, radially from flows outside inwards and, as known from the prior art, forms a partially required turbulence. In the right part of the 2 is a plan view of the piston 16 and the piston recess 15 , it being assumed that in this embodiment a so-called swirl flow is formed, which is formed by concentric curved circular arrows in the piston recess 15 is indicated. The center of these concentric circles is equal to the center MP of the piston recess 15 , It is, and this is for the optimization of the internal combustion engine of importance, the flow rate of the various indicated by the circular arrows streamlines, depending on the distance of the flow lines from the center MP, different. Basically: With increasing distance of the streamlines to the center MP of the piston recess 15 increases the flow velocity. In the immediate vicinity of the cylindrical wall of the piston recess, the flow velocity decreases again. The real velocity distribution in the piston recess at the ignition point can be determined with the methods available today, be it computer simulations or measurements in the combustion chamber, with sufficient local and temporal resolution, so that the knowledge of the local flow velocity at the time of ignition can be assumed as given.

According to the invention, a fluidically optimized internal combustion engine can be further optimized in that the ignition point ZP not only in the direction of the longitudinal axis 54 the piston crown, but also radially to the center MP of the piston recess 15 can be moved. This is in the right part of the 2 by different ignition points ZP, which are once in the center MP and then at different distances from the center MP, indicated.

This shift of the ignition locations or ignition points relative to the center MP of the piston recess 15 can be changed by a positioning of the laser ignition device 27 in the cylinder head 17 realize.

In 3 another embodiment of an internal combustion engine according to the invention is shown. In this embodiment, the combustion chamber roof 69 not even, but, similar to a pitched roof trained. Of course it is also possible, the combustion chamber roof 69 and the piston bottom 15 in the form of a hemisphere or a dome. Also the piston recess 15 has over the embodiment according to 2 Differences. So it is in the illustrated cross section through the piston 16 essentially semi-elliptic and symmetrical to the longitudinal axis 54 arranged the piston. In this embodiment, flow at ignition timing is a so-called tumble flow, which is also represented by concentric but elliptical streamlines. In contrast to the swirl flow according to 2 In the case of the tumble flow, the flow is essentially transverse to the longitudinal axis 54 of the piston 16 instead of. Again, it is again the case that the flow velocity of the different streamlines indicated by elliptical arrows is different. As a result, it is possible to shift the ignition location of the ignition point ZP in the direction of the longitudinal axis 54 set the ignition point ZP in a range whose flow velocity is less than 10 m / s.

In 4 a third embodiment of an internal combustion engine according to the invention is shown. Here, the ignition point ZP is consciously in the immediate vicinity of the piston recess 15 been set at the time of ignition, due to the velocity distribution near the wall of the piston head or the piston recess 15 Again, a low flow rate can be achieved. Since the ignition timing of an internal combustion engine depends inter alia on speed and load, the ignition point ZP can be more or less placed in the vicinity of the piston crown or the piston recess by the change of the ignition timing load and speed dependent, so that thus a further parameter for optimizing Combustion and in particular the burn-through of the combustion chamber 14 located charge while minimizing the flow losses in the intake of the engine can be achieved.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102004001554 A1 [0002]

Claims (10)

Internal combustion engine with at least one cylinder ( 12 ), a piston ( 16 ) and a cylinder head (10), wherein the cylinder ( 12 ) and the piston ( 16 ) a combustion chamber ( 14 ), with a laser ignition device ( 27 ) comprising an ignition laser ( 26 ) with an ignition point (ZP), characterized in that the ignition point (ZP) in a region of the combustion chamber (ZP) ( 14 ) in which the flow velocity at the time of ignition (ignition timing) is low. Internal combustion engine according to claim 1, characterized that in the ignition point (ZP) at the ignition time a Flow rate less than 10 m / s, preferably smaller 5 m / s, prevails. Internal combustion engine according to claim 1 or 2, characterized in that in the combustion chamber ( 14 ) prevails at the ignition time a swirl flow. Internal combustion engine according to claim 1 or 2, characterized in that in the combustion chamber ( 14 ) at the time of ignition prevails a tumble flow. Internal combustion engine according to one of claims 2 to 4, characterized in that the ignition point (ZP) orthogonal to a longitudinal axis ( 54 ) of the cylinder bore ( 12 ) is shifted until the ignition point (ZP) is in a range of low flow velocity in the ignition timing. Internal combustion engine according to one of claims 2 to 5, characterized in that the ignition point (ZP) in the direction of the longitudinal axis ( 54 ) of the cylinder bore ( 12 ) is shifted until the ignition point (ZP) is in a range of low flow velocity in the ignition timing. Internal combustion engine according to one of the preceding claims, characterized in that the piston ( 16 ) a trough ( 15 ) in the piston head. Internal combustion engine according to one of the preceding claims, characterized in that the ignition point (ZP) at the ignition time in the trough ( 15 ) is located in the piston crown. Internal combustion engine according to one of the preceding claims, characterized in that the ignition point (ZP) at the ignition point in the immediate vicinity of the piston crown, in particular in the trough ( 15 ) is located. Internal combustion engine according to one of the preceding Claims, characterized in that the ignition in a range between 30 ° CA before TDC and 5 ° CW before TDC lies.