DE102017206021B3 - Combustion chamber arrangement for an internal combustion engine, injection method and use of a combustion chamber arrangement for injecting OME fuel - Google Patents

Abstract

The invention relates to a combustion chamber arrangement (12) for injecting an OME fuel (20b) into a combustion chamber (10) of an internal combustion engine, wherein an elevation angle β of an injection nozzle (16) is designed such that the injected OME fuel (20b) is in operation as close as possible to a piston longitudinal axis (26) of a hollow piston (14) impinges on the injector (16) the OME fuel (20b) injected. The invention further relates to an injection method for injecting an OME fuel (20b) into a combustion chamber (10) of an internal combustion engine, and to the use of the combustion chamber arrangement (12) for injecting OME fuel (20b) into the combustion chamber (10) of the internal combustion engine.

Description

The invention relates to a combustion chamber arrangement for forming a combustion chamber for an internal combustion engine for burning an injected into the combustion chamber OME fuel, an injection method for injecting an OME fuel into such a combustion chamber, and the use of such a combustion chamber arrangement for injecting OME fuel in the Combustion chamber of an internal combustion engine.

Up to now, it has been known to inject diesel or gasoline into a combustion chamber as fuel for an internal combustion engine by burning the respective fuel and thereby converting chemical energy stored in the fuel into kinetic energy, so that a piston arranged in the combustion chamber, sets in motion and thus drives the internal combustion engine. How the combustion chamber has to be designed to burn the diesel or gasoline in order to be optimally energy-efficient and to enable as low-emission combustion as possible is well studied and known.

Now, however, there is the problem that, especially with the use of diesel fuel legal requirements with respect to climate protection, that is, in particular with regard to unwanted emissions, are increasingly difficult to meet.

Efforts are therefore being made to replace diesel fuel with synthetic fuels, which release significantly less emissions when burned.

An example of such a synthetic fuel is oxymethylene ether, so-called OME, which has particular suitability as a fuel for diesel engines, since it, like diesel fuel, burns autoignition. Unlike diesel, however, OME burns significantly lower emissions. It would therefore be conceivable to replace diesel fuel with OME fuel in the long term.

Despite similar ignition properties of diesel fuel and OME fuel, there are differences in other physical parameters, in particular the calorific value H _U , which is significantly lower for OME fuel compared to diesel fuel. The calorific value H _U corresponds to the amount of heat that can be generated at an equal mass m of fuel. On average, the calorific value H _U in OME fuels is about half as large as for diesel fuels, ie, if only the calorific value H _{U is} considered, for an equal amount of heat or energy to be generated about twice the mass m burned to fuel.

If OME fuel is injected into a standard combustion chamber of a diesel internal combustion engine, the following problems arise with reference to 7 will be briefly explained.

7 shows a sectional view of a combustion chamber 10 for a diesel internal combustion engine. In the combustion chamber 10, a combustion chamber arrangement 12 is provided, which comprises a hollow piston 14 and an injection nozzle 16. The injection nozzle 16 is arranged so directed to a piston end face 18 that fuel 20, which is injected from the injection nozzle 16 into the combustion chamber 10, impinges on the piston end face 18.

The trough piston 14 has a trough 22, into which the injected fuel 20, for example diesel fuel 20a, is injected from the injection nozzle 16, and where the fuel 20 by a special geometric configuration of the trough 22 with a likewise present in the combustion chamber 10 air 24 mixed. By translational up and down movement of the well piston 14 along a piston longitudinal axis 26, the fuel 20, which has been injected into the combustion chamber 10 and has mixed with the air, compresses and ignites at a specific compression point itself. This ignition becomes chemical energy that is stored in the fuel 20, converted into kinetic energy and used for driving a diesel engine.

In 7 It can be seen that the trough 22 has a special geometric shape. It comprises a symmetrically about the piston longitudinal axis 26 centrally disposed dome 28, and also a symmetrically about the piston longitudinal axis 26 formed side wall 30 for limiting the trough 22. Between the dome 28 and the side wall 30, a U-shaped transition region 32 is provided. The side wall 30 forms, characterized in that a radially arranged to the piston longitudinal axis 26, extending away from the piston longitudinal axis 26 recess 34 is formed in the region of a piston end 36 of a trough lip 38 which projects in the direction of the dome 28 via the trough 22.

This special geometric configuration makes it possible to inject diesel fuel 20a from the injection nozzle 16 so that it impinges on the depression 22 in the recess 34, there by the shape of the recess 34 and the U-shaped transition region 32 and the dome 28 is deflected inwardly in a circle and thus forms a turbulence 40 through which the diesel fuel 20a can mix very well with the air 24 present.

Due to the particularly good mixing of air 24 and diesel fuel 20a arise in the Combustion significantly better emission levels and in particular a reduced soot formation.

If such a combustion chamber arrangement 12 designed for diesel fuel 20a is used to inject OME fuel 20b into combustion chamber 10, the problem initially arises that OME fuel 20b generates significantly less kinetic energy than hitherto due to the lower calorific value H _U used diesel fuel 20a at an equal injected fuel mass m. To compensate for this, the injector 16 would have to be adjusted so that, corresponding to the factor by which the OME fuel 20b generates less kinetic energy than a standard diesel fuel 20a, the injector 16 in its flow HD, that is, the mass m of fuel 20, which passes per predefined time unit .DELTA.t into the combustion chamber 10, is increased. This means, however, that significantly more mass m of fuel 20 burns in the trough 22 in the same time unit Δt.

In experiments, it has been found that thereby the trough lip 38 burns off at the same desired heat or energy generation and the trough piston 14 is thus destroyed.

EP 2 696 051 A1 . DE 10 2011 015 438 A1 . US 2010/0071653 A1 and US Pat. No. 7,431,012 B1 each disclose a combustion chamber with a trough piston with a central dome, wherein an injection nozzle injects fuel into the combustion chamber, which impinges just next to the dome.

M. Hartl et al., MTZ, 7, p. 68 (2014) describes oxymethylene ethers as CO2-neutral fuel.

The object of the invention is therefore to propose a combustion chamber arrangement for forming a combustion chamber for an internal combustion engine, with which OME fuel can be permanently burned to produce a correspondingly predefined heat or power to be generated in accordance with a diesel fuel.

This object is achieved with a combustion chamber arrangement with the feature combination of claim 1.

An injection method for injecting an OME fuel into a combustion chamber of an internal combustion engine, and the use of the combustion chamber arrangement for injecting OME fuel into the combustion chamber of an internal combustion engine are the subject of the independent claims.

Advantageous embodiments of the invention are the subject of the dependent claims.

A combustion chamber arrangement for forming a combustion chamber for an internal combustion engine for burning an injected into the combustion chamber OME fuel has a trough piston, which moves in operation in the combustion chamber along a piston longitudinal axis translationally, and an injection nozzle for injecting the OME fuel into the combustion chamber. The trough piston comprises on a piston end face a trough for receiving the OME fuel injected in the combustion chamber, wherein the trough is formed symmetrically about the piston longitudinal axis. The trough has a centrally disposed dome, which is arranged in the direction of a trough bottom extending circumferentially around the piston longitudinal axis, a circumferentially disposed about the piston longitudinal axis, extending substantially parallel to the piston longitudinal axis extending side wall for defining the trough, and a U-shaped transition region between the cathedral and the side wall. The injection nozzle is formed symmetrically about a longitudinal axis of the nozzle, wherein the injection nozzle is arranged so directed to the piston end side, that the piston longitudinal axis and the nozzle longitudinal axis coincide. The injection nozzle has a plurality of injection holes each having a hole axis for injecting the OME fuel. An elevation angle β between each of the hole axes and the nozzle longitudinal axis is formed such that the injected OME fuel, in use, impinges in the transition region closer to the dome than to the sidewall.

The hole axis corresponds to a jet axis of the injected fuel.

As already described, a diesel fuel normally injected with such a combustion chamber arrangement receives a momentum in the trough which results in a return flow in the direction of the dome, so that the diesel fuel mixes well with the air arranged around the dome. This is important to keep emissions, especially soot formation, small because this backflow and subsequent mixing optimizes the air / diesel fuel mixture. For this reason, the trough in the section of the piston longitudinal axis on the special shape with dome, transition region and side wall.

However, compared to diesel fuel, OME fuel now has a significantly lower calorific value H _U. In order to obtain the same performance as when injecting diesel fuel, whereby the term "power" should be understood to mean the same predefined heat to be generated per unit time Δt by the combustion, a mass M of OME fuel increased in the same time unit corresponding to the factor of the calorific value reduction must therefore be obtained Δt be injected and burned. In addition, OME fuel has a different ignition delay than Diesel fuel. The two factors - ignition delay and increased mass m of injected fuel - result in a changed beam pulse of OME fuel compared to diesel fuel and affect the location in the trough where the injected fuel ultimately burns off.

OME fuel therefore burns closer to a trough lip than diesel fuel, which results in the trough lip and thus the trough piston being destroyed. To form a good mixture of diesel fuel and air, diesel fuel is normally sprayed onto the side wall of the trough. Accordingly, the injection holes of the injection nozzle are arranged so that diesel fuel targeted impinges on the side wall and there receives a motion pulse for a return flow to then mix in the dome with the surrounding air can. However, since the combustion of OME fuel significantly less emissions, especially no soot, arise, the mixture formation of air-fuel less of concern. Therefore, it can be dispensed with a targeted impact of the injected OME fuel on the side wall, which would not be possible with diesel fuel. Therefore, in order to prevent burning of the trough lip, it is proposed to form the elevation angle β in such a way that the OME fuel now impinges on the side wall in the transition area close to the dome instead of the diesel fuel.

In a particularly advantageous embodiment of the elevation angle β is formed so that the injected OME fuel impinges in operation on the cathedral itself.

When injecting diesel fuel is specifically avoided that the diesel fuel impinges on the dome, as a mixture formation necessary for the combustion can not be guaranteed. However, since OME fuel does not cause mixture formation because there is no soot in the combustion process anyway, it is possible to cause the OME fuel to hit the sidewall so far that it can even hit the dome, and so on Burning the hollow lip can be prevented.

The elevation angle β is preferably in a range of 0 ° <β <75 °. Particularly advantageously, the elevation angle β is in a range of 30 ° <β <70 ° and in particular in a range of 45 ° <β <65 °. For diesel fuel, the elevation angle β must not be less than 75 ° because of the necessary mixture formation and is actually in a range of 75 ° to 82 °. If the elevation angle β is smaller than these values, undesirably much soot is produced as a combustion product. However, this is irrelevant in the case of OME fuel, so that the elevation angle β can be adjusted in a targeted manner so that the jet of the injected OME fuel no longer impinges into the depression in the region of the depression lip, but more centrally, which prevents burning off of the depression lip.

wobei 0,6 < K < 0,85. K liegt dabei besonders vorteilhaft in einem Bereich zwischen 0,7 und 0,8.The injection nozzle has a flow HD _OME , which corresponds to an increased by a magnification factor V flow HD _Diesel injector for diesel fuel,
the magnification factor V being dependent on a ratio of the heating value of diesel H _U , _DIESEL to a calorific value of OME fuel H _U , _{OME of} an OME fuel to be injected during operation, where: $$\text{V}=\left({\text{H}}_{\text{u}\text{,Diesel}}/{\text{H}}_{\text{u}\text{, OME}}\right)*\text{K}.$$

where 0.6 <K <0.85. K is particularly advantageous in a range between 0.7 and 0.8.

With regard to the different calorific value H _U of OME fuel and diesel fuel, which differ on average by a factor of about 2, the injection nozzle would normally have to be designed so that the flow HD for OME fuel is about twice as large as for diesel fuel. This twice the flow HD results in a large jet impulse which results in the burning location of the fuel moving away from the dome towards the trough lip as compared to diesel fuel. As a result, the trough lip is hotter and burns faster.

In experiments, however, it has surprisingly been found that OME fuel burns off faster than diesel fuel, d. H. the respective mass m to be combusted of the two fuels, which leads to the same heat development, requires less time unit Δt for OME fuel than for diesel fuel. This results in a lower temperature development in the exhaust gas. In particular, the burnout, i. the end of combustion, achieved much faster for OME fuel than for diesel fuel.

The exhaust gas temperature is important for the combustion chamber downstream elements of the internal combustion engine and must not exceed a predetermined value. Due to the faster burning of the OME fuel compared to diesel fuel but surprisingly results in a reduced temperature in the exhaust gas, which causes the respective mass m to be combusted fuel for the same heat over a prolonged period can be injected into the combustion chamber.

As a result, the injector need not be designed to increase its flow HD by a magnification factor V. which corresponds to the ratio of the heating values H _{U of} the two fuels, but that the injection nozzle must be increased by less than this magnification factor V. With regard to the temperature development, the magnification factor V decreases by a factor K which lies in a range between 0.6 and 0.85.

The reduced flow HD of the injector for the OME fuel, which is thus reduced compared to the expected flow HD, results in a reduced jet pulse and thus a migration of the injected OME fuel jet from the sidewall toward the dome.

Preferably, the injection nozzle has nine to twelve injection holes, which are arranged symmetrically about the nozzle longitudinal axis. Diesel fuel injection nozzles normally have about seven to ten injection holes to properly atomize the diesel fuel in the combustion chamber and to produce an optimum mixture with air. In order to reduce the jet pulse of the injected OME fuel, it is advantageous to provide more injection holes than diesel fuel. However, in order to continue to ensure a feasible production of the injector, a number of injection holes between nine and twelve has been found to be optimal.

Advantageously, the side wall of the trough has a radially extending from the piston longitudinal axis ersteckende, circumferentially arranged around the piston longitudinal recess whose depth in the extension direction is a maximum of 1/4 of the distance of the piston longitudinal axis to a parallel to the piston longitudinal axis extending portion of the side wall.

The trough lip is essentially formed by the region of the side wall running parallel to the piston longitudinal axis and protrudes in the direction of the piston longitudinal axis over the trough. The side wall has the recess which forms an undercut disposed under the trough lip, normally injecting the diesel fuel into this recess to be offset with the desired momentum for a return flow. The risk of burning the trough lip by injecting the OME fuel instead of the diesel fuel can be reduced by the trough lip is formed much less pronounced. The fact that a less pronounced trough lip also burns less strongly, the trough piston is also less damaged. Such a less pronounced expression than is normally provided in a diesel combustion chamber arrangement can be achieved by significantly reducing the recess and thus the undercut. Therefore, it is provided that the recess corresponds to a maximum of 1/4 of the distance between the parallel side wall, that is the end of the trough lip, to the piston longitudinal axis.

In an alternative embodiment, however, it can also be provided to provide the trough completely without trough lip, for example by the side wall is formed inclined away from the piston longitudinal axis. It is also additionally or alternatively conceivable that the side wall has a continuous curvature, which is rectified to the curvature of the U-shaped transition region, but smaller than this curvature of the U-shaped transition region. This also makes the trough lip is much less pronounced formed or completely omitted and can not burn during operation.

1. a) Vorsehen eines Muldenkolbens, der sich im Betrieb in dem Brennraum entlang einer Kolbenlängsachse translatorisch bewegt, und der an einer Kolbenstirnseite eine Mulde zur Aufnahme von in dem Brennraum einzuspritzendem OME-Kraftstoff aufweist, wobei die Mulde symmetrisch um die Kolbenlängsachse ausgebildet ist und einen zentral angeordneten Dom, der in Richtung von einem Muldenboden weg erstreckend umlaufend um die Kolbenlängsachse angeordnet ist, eine umlaufend um die Kolbenlängsachse angeordnete, sich weitgehend parallel zu der Kolbenlängsachse erstreckende Seitenwand zum Begrenzen der Mulde, und einen U-förmigen Übergangsbereich zwischen dem Dom und der Seitenwand aufweist;
2. b) Anordnen einer zu der Kolbenstirnseite gerichteten, symmetrisch um eine Düsenlängsachse ausgebildeten Einspritzdüse in dem Brennraum derart, dass die Kolbenlängsachse und die Düsenlängsachse zusammenfallen;
3. c) Einspritzen von OME-Kraftstoff aus der Einspritzdüse in die Mulde derart, dass der OME-Kraftstoff in dem Übergangsbereich näher an dem Dom als an der Seitenwand auftritt.

An advantageous injection method for injecting an OME fuel into a combustion chamber of an internal combustion engine comprises the following steps:

1. a) Providing a Muldenkolbens, which translates in operation in the combustion chamber along a piston longitudinal axis, and having on a piston end a trough for receiving injected into the combustion chamber OME fuel, wherein the trough is formed symmetrically about the piston longitudinal axis and a central arranged dome, which is arranged in the direction of a trough bottom extending circumferentially around the piston longitudinal axis, a circumferentially disposed about the piston longitudinal axis, extending substantially parallel to the piston longitudinal axis side wall for defining the trough, and a U-shaped transition region between the dome and the side wall having;
2. b) arranging an injection nozzle directed in the combustion chamber symmetrically about a longitudinal axis of the nozzle directed towards the piston end face such that the piston longitudinal axis and the nozzle longitudinal axis coincide;
3. c) injecting OME fuel from the injector into the trough such that the OME fuel occurs closer to the dome in the transition region than to the sidewall.

Advantageously, the OME fuel is injected so that it occurs on the cathedral itself.

Advantageously, a combustion chamber arrangement described above is used to inject OME fuel into a combustion chamber of an internal combustion engine.

The combustion chamber arrangement is optimized for injecting the OME fuel such that a hollow piston is no longer destroyed in an undesirable manner during operation.

• 1 eine Schnittdarstellung einer Brennraumanordnung zum Einspritzen von Kraftstoff in einen Brennraum einer Brennkraftmaschine aus dem Stand der Technik, wobei die Brennraumanordnung zum Einspritzen von Dieselkraftstoff ausgelegt ist;
• 2 eine Schnittdarstellung einer Brennraumanordnung zum Einspritzen eines OME-Kraftstoffes in einen Brennraum einer Brennkraftmaschine;
• 3 ein Diagramm, das ein Abbrennverhalten eines Dieselkraftstoffes im Vergleich zu einem Abbrennverhalten eines OME-Kraftstoffes schematisch darstellt;
• 4 eine Schnittdarstellung einer Brennraumanordnung mit einem Muldenkolben, der eine für die Einspritzung von Dieselkraftstoff optimierte Mulde gemäß dem Stand der Technik aufweist;
• 5 eine Schnittdarstellung einer Brennraumanordnung mit einem Muldenkolben, der eine Mulde mit einer für die Einspritzung von OME-Kraftstoff optimierten Geometrie gemäß einer ersten Ausführungsform aufweist;
• 6 eine Schnittdarstellung einer Brennraumanordnung mit einem Muldenkolben, der eine Mulde mit einer für die Einspritzung von OME-Kraftstoff optimierten Geometrie gemäß einer zweiten Ausführungsform aufweist; und
• 7 eine Schnittdarstellung eines Brennraumes für eine Diesel-Brennkraftmaschine aus dem Stand der Technik.

Advantageous embodiments of the invention will be explained in more detail with reference to the accompanying drawings. It shows:

• 1 a sectional view of a combustion chamber arrangement for injecting fuel into a combustion chamber of a combustion engine of the prior art, wherein the combustion chamber arrangement is designed for injecting diesel fuel;
• 2 a sectional view of a combustion chamber arrangement for injecting an OME fuel into a combustion chamber of an internal combustion engine;
• 3 a diagram schematically illustrating a burning behavior of a diesel fuel compared to a burning behavior of an OME fuel;
• 4 a sectional view of a combustion chamber arrangement with a dump piston, which has an optimized for the injection of diesel fuel well according to the prior art;
• 5 a sectional view of a combustion chamber arrangement with a well piston having a well with an optimized for the injection of OME fuel geometry according to a first embodiment;
• 6 a sectional view of a combustion chamber arrangement with a well piston having a well with an optimized for the injection of OME fuel geometry according to a second embodiment; and
• 7 a sectional view of a combustion chamber for a diesel internal combustion engine from the prior art.

1 shows a sectional view of a combustion chamber arrangement 12 in a combustion chamber 10 an internal combustion engine of the prior art, wherein the combustion chamber arrangement 12 is optimized for the injection of diesel fuel 20a. The optimized combustion chamber arrangement 12 for diesel fuel 20a has an injection nozzle 16, with the diesel fuel 20a is injected into the combustion chamber 10. In addition, a dump piston 14 provided a hollow 22 with one for the injection of diesel fuel 20a has optimized geometry. This is the diesel fuel 20a from the injector 16 targeted in the hollow 22 injected.

The hollow 22 has a geometry that causes the diesel fuel 20a in the trough 22 receives a motion impulse for a return flow, so that a turbulence 40 arises, so that the diesel fuel 20a Get along well with the one in the combustion chamber 10 arranged air 24 can mix. This is important to keep emissions, especially the formation of soot particles, small. Due to the special geometry of the trough 22 Accordingly, the mixture is optimized air 24 diesel fuel 20a. The hollow 22 is on average designed so that they are centrally symmetrical about a piston longitudinal axis 26a arranged cathedral 28 training, moving in the direction of a trough bottom 42 extends away and revolving around the piston longitudinal axis 26 is arranged. Next includes the trough 22 a side wall 30 that the hollow 22 limited. The side wall 30 extends substantially parallel to the piston longitudinal axis 26 but is designed to encompass two areas. Namely, on the one hand is actually parallel to the piston longitudinal axis 26 extending portion 44 is provided, which is directly adjacent to an end-side piston end 36 is arranged. Next, the side wall 30 has a recess 34 which extends radially away from the piston longitudinal axis 26. As a result, an undercut is formed in the trough in plan view 22 and thus a trough lip 38, which in the direction of the piston longitudinal axis 26 over the hollow 22 sticks out.

The injector 16 is symmetrical about a nozzle longitudinal axis 46 trained and so to a piston end face 18 directed arranged that the nozzle longitudinal axis 46 and the piston longitudinal axis 26 coincide. As a result, injection holes 48 that are in the injector 16 also symmetrical not just around the nozzle's longitudinal axis 46 , but also formed symmetrically about the piston longitudinal axis 26 and therefore inject symmetrically into the trough 22 Diesel fuel 20a one.

Between the cathedral 28 and the side wall 30 a U-shaped transition region 32 is arranged to make a bend 54 of the cathedral 28 in an oppositely directed curvature 54 the side wall 30 in the region of the recess 34 to convict.

The injection holes 48 each have a hole axis 50 substantially corresponding to the jet axis on which the diesel fuel 20a in the trough 22 incident. An angle between the respective hole axis 50 and the nozzle longitudinal axis 46 , which corresponds to the piston longitudinal axis 26, is referred to as elevation angle β.

In the in 1 known from the prior art combustion chamber assembly 12 for diesel fuel 20a is the elevation angle β designed so that the diesel fuel 20a in operation in the recess 34 and thus on the side wall 30 incident. Due to the special geometric shape of the trough 22 becomes the impinging diesel fuel 20a in the recess 34 down, over the U-shaped transition area 32 on the cathedral 28 steered and thrown upwards from there, so that the turbulence 40 arises and the diesel fuel 20a good with the air 24 in the area around the cathedral 28 is, can mix.

This mixture then ignites spontaneously during the movement of the dump piston 14, which in the diesel fuel 20a existing chemical energy is converted into mechanical energy.

During the injection of OME fuel 20b instead of the diesel fuel 20a with an arrangement according to FIG. 1, this would mean that, especially in full-load operation, the trough lip 38 burns off and thus the dump piston 14 gets destroyed. To provide an internal combustion engine with a conventional life, this is an undesirable effect.

The burning of the hollow lip 38 essentially results from the fact that the OME fuel 20b closer to the hollow lip 38 burns off as the diesel fuel 20a ,

This comes on the one hand, therefore, that the OME fuel 20b a different ignition delay than diesel fuel 20a has, and on the other hand with a larger beam pulse in the trough 22 incident. Due to the changed parameters ignition delay and beam pulse, the location in the trough also changes 22 where the fuel burns off. This place is near OME fuel 20b closer to the hollow lip 38 as with diesel fuel 20a ,

The modified jet pulse results, in particular, from the fact that, due to the significantly lower calorific value H _U , _{OME of} the OME fuel 20 b, a larger fuel mass m must be injected in the same time unit Δt than the calorific value H _U , _{Diesel of} the diesel fuel 20 a as with the diesel fuel 20a ie, a same predefined heat to be generated to release. Therefore, the injector becomes 16 formed with a larger flow HD. However, the larger flow HD results in a larger fuel mass m per unit time Δt, resulting in a larger jet pulse.

2 shows a sectional view of an optimized with respect to the jet pulse combustion chamber arrangement 12 , with the OME fuel 20b in the trough 22 is injected.

When compared with the combustion chamber arrangement 12 in 1 It can be seen that a height angle β in each case between the nozzle longitudinal axis 46 and the hole axes 50 significantly steeper is formed during the injection of OME fuel 20b as in the injection of diesel fuel 20a , This causes the OME fuel 20b to hit the trough 22 in the U-shaped transition area 32 closer to the cathedral 28 as on the sidewall 30 on. The injection holes 48 are therefore at the injection nozzle 16 arranged so that there is a height angle β, which is smaller than in the injection of diesel fuel 20a ,

At the injection of diesel fuel 20a because of the mixture formation of the elevation angle β must be in the order of 75 °, ie actually in a range of 75 ° - 82 °. The elevation angle β may be at the injection of diesel fuel 20a not be smaller, otherwise by the incomplete mixture formation of diesel fuel 20a and air 24 an undesirable soot formation during the combustion of the diesel fuel 20a occurs.

At OME fuel 20b However, the soot evolution in combustion poses no problem since soot is not a product of combustion. Therefore, the elevation angle β is selected so that the OME fuel 20b is closer to the piston longitudinal axis 26 for example on the cathedral 28 itself, hits, like this in 2 you can see. Thus, the combustion of the OME fuel 20b continues from the trough lip 38 away and the trough lip 38 does not burn down during operation.

The elevation angle β is in a range between 0 ° and 75 °, advantageously between 30 ° and 70 °, and in particular between 45 ° and 65 °. These are angular ranges necessary for the injection of a diesel fuel 20a would be unthinkable.

3 FIG. 12 is a graph illustrating the burn-off behavior of diesel fuel 20a as compared to the burn-off behavior of OME fuel 20b. In this case, the crankshaft angle cr crk, which essentially represents a time sequence, is shown on the x-axis. The y-axis represents the energy released by the combustion in J / ° crk. The burning of the diesel fuel 20a is shown with a black curve while the burning of the OME fuel 20b is shown with a gray curve. It can be seen that both fuels 20 initially have an abrupt combustion start at about -10 ° crk and the combustion with the largest amount of energy released takes place mainly in a plateau range between 0 ° crk and 30 ° crk. The respective end of the combustion is not abrupt as at the start of combustion, but runs slowly over time. It can be seen that the diesel fuel 20a still releases energy or heat over a longer period of time (crankshaft angle range 45 ° crk - 70 ° crk), while at OME fuel 20b no longer the case. Here, the end of the release of heat is already reached at a crankshaft angle of about 55 ° crk. OME fuel 20b burns in time seen faster than diesel fuel 20a at a mass m to be burned, which leads to an equal heat release. As the diesel fuel 20a burns over a longer period of time, the exhaust gases resulting from this combustion have a higher temperature than that of OME fuel 20b , By doing that, the OME fuel 20b a lower temperature development in the exhaust gas than the diesel fuel 20a it is possible, the mass m, which leads to an equal heat release, over a prolonged period .DELTA.t or .DELTA. ° crk in the combustion chamber 10 to inject and burn.

If only the ratio of the heating values H _{U of} the two fuels 20 were considered, the injection nozzle would have to 16 be increased according to this ratio in their flow HD to achieve an equal power / heat release.

The flow HD of the injector 16 for the OME fuel 20b would have to be increased by a magnification factor V in relation to the flow HD of an injection nozzle 16 for the diesel fuel 20a, so as to be able to achieve the same performance by the combustion of an increased mass m. It would apply the relationship: $$\text{V}=\left({\text{H}}_{\text{u}\text{,Diesel}}/{\text{H}}_{\text{u}\text{, OME}}\right)*\text{K}.$$

However, it has now surprisingly been found that OME fuel 20b has a lower temperature development in the exhaust gas during its combustion and therefore over a prolonged period in the combustion chamber 10 can be injected. Therefore, for injecting the mass m increased by the magnification factor V, a larger period of time is available in which this mass m enters the combustion chamber 10 can be introduced. Therefore, the injector needs 16 no longer have a flow HD, which is considered according to the magnification factor V only as a function of the two heating values H _U , but the magnification factor V can be reduced by a factor K, which corresponds to the lower temperature in the exhaust gas.

It therefore applies when increasing the flow HD of the injector 16 for the OME fuel 20b compared to the flow HD of the injector 16 for the diesel fuel 20a : $$\text{V}=\left({\text{H}}_{\text{u}\text{,Diesel}}/{\text{H}}_{\text{u}\text{, OME}}\right)*\text{K}.$$

From measurements it has been found that K is advantageously between 0, 6 and 0.85, and in particular between 0.7 and 0.8.

This has the advantage that the same mass m due to the extended time it is injected, with a smaller jet pulse in the trough 22 hits, and therefore closer to the cathedral 28 as on the sidewall 30 burns.

The calorific value H _U , _{OME of} the OME fuel is different 20b Therefore, for example, the heating value H _U , _{diesel of} the diesel fuel 20a by a magnification factor V = 2, the flow HD of the injector 16 not be doubled as expected, but can be multiplied by a magnification factor V of only 1.4 to 1.7.

The difference of the calorific value H _U by a magnification factor V = 2 is mentioned here only as an example, since this magnification factor V depends on the properties of the respective OME fuel 20b, which may be different for different OME fuels 20b.

To further reduce the jet pulse, the injector points 16 nine to twelve injection holes 48 on, about the fuel mass m of the OME fuel 20b injected in a distributed manner. injectors 16 for diesel fuel 20a In comparison, they typically have a number of injection holes in a range between seven and ten injection holes 48 , The injection holes 48 are symmetrical about the nozzle longitudinal axis 46 arranged.

To the burning of the hollow lip 38 to avoid the combustion chamber assembly 12 as described above by adjusting the geometry of the injector 16 be optimized.

However, there is also the option of using the geometry of the trough instead 22 adapt itself to prevent such burning of the trough lip 38.

A particularly advantageous embodiment would be an adaptation of both the geometry of the injection nozzle 16 as described above as well as an adaptation of the geometry of the trough 22 which is described below.

In particular, the geometry of the trough 22 Advantageously designed so that the geometry of the trough lip 38 to the properties of the new OME fuel 20b is adjusted. It is advantageous if the trough lip 38 is less pronounced or even omitted, since, as already explained above, an interpretation of the well geometry for mixture formation criteria for the use of OME fuel 20b unlike the use of diesel fuel 20a is not necessary.

Is the trough lip 38 no more or only very little pronounced, it can not burn anymore.

4 shows a sectional view of a diesel fuel 20a usual geometry of a trough 22 in the hollow piston 14 , It can be seen that the trough lip 38 is very strong and to the undercut or the recess 34 a large depth T in its direction of extent 52 , that is radially to the piston longitudinal axis 26, and thus is rather pronounced. Compared to a distance a between the parallel region 44 the side wall 30 and the piston longitudinal axis 26 has the recess 34 at the in 4 shown, known from the prior art well 22 a depth T, which is about 1/3 of this distance a.

5 shows a sectional view of a first embodiment of a matched in geometry to the injection of the OME fuel 20b well 22 , It can be seen that here the depth T of the recess 34 maximum 1/4 of the distance a between the parallel region 44 the side wall 30 and the piston longitudinal axis 26 is. The smaller this depth T is chosen, the less strong is the trough lip 38 pronounced and therefore can burn off less quickly during operation.

6 shows a sectional view of a second embodiment of an injection of OME fuel 20b optimized trough geometry of the trough 22 in the hollow piston 14 , Here you can see that the hollow lip 38 no longer exists at all. For this the sidewall runs 30 in a section parallel to the piston longitudinal axis 26 in a substantially rectilinear manner at least in a region of the side wall arranged adjacent to the end-side piston end 36 30 , The recess 34 and thus the undercut is completely missing in this second embodiment. Is not a hollow lip 38 more available, can also no trough lip 38 burn more.

6 shows an embodiment in which the side wall 30 essentially from the piston longitudinal axis 26 is inclined away. However, it is also alternatively conceivable that the side wall 30 adjacent to the end-side piston end 36 parallel to the piston longitudinal axis 26 runs.

To a substantially straight course of the side wall 30 in the region of the end-side piston end 36 to reach, indicates the side wall 30 advantageously a curvature 54 on, starting from the trough bottom 42 up to the end-side piston end 36 towards continuously reduced and in particular from the beginning is smaller than a curvature 54 of the U-shaped transition region 33.

Claims (7)

A combustion chamber arrangement (12) for forming a combustion chamber (10) for an internal combustion engine for burning an OME fuel (20b) injected into the combustion chamber (10), comprising: - a well piston (14) which, in operation, is located in the combustion chamber (10). along a piston longitudinal axis (26) moves translationally, and at a piston end face (18) has a trough (22) for receiving the in the combustion chamber (10) injected OME fuel (20b), wherein the trough (22) symmetrically about the piston longitudinal axis (26) is formed and a centrally disposed dome (28) extending in the direction of a trough bottom (42) extending circumferentially around the piston longitudinal axis (26), a circumferentially about the piston longitudinal axis (26) arranged, substantially parallel to the Piston longitudinal axis (26) extending side wall (30) for limiting the trough (22), and a U-shaped transition region (32) between the dome (28) and the side wall (30); and - an injection nozzle (16) for injecting the OME fuel (20b) into the combustion chamber (10), wherein the injection nozzle (16) is formed symmetrically about a nozzle longitudinal axis (46), the injection nozzle (16) in such a way to the piston end side (16). 18), that the piston longitudinal axis (26) and the nozzle longitudinal axis (46) coincide, the injection nozzle (16) having a plurality of injection holes (48) each having a hole axis (50) for injecting the OME fuel (20b) ; wherein an elevation angle β is formed between each of the hole axes (50) and the nozzle longitudinal axis (46) such that the injected OME fuel (20b) is in operation in the transition region (32) closer to the mandrel (28) than to the sidewall (32). 30), the injection nozzle (16) having a flow rate HD _OME corresponding to an enlarged by a magnification factor (V) flow HD _diesel injection nozzle (16) for a diesel fuel (20a), wherein the magnification factor (V) is dependent on a ratio of the calorific value H _{u, diesel} of diesel fuel (20a) to a calorific value H _{u, OME} of OME fuel (20b) of an OME fuel (20b) to be injected during operation, where: $$\text{V}=\left({\text{H}}_{\text{u}\text{,Diesel}}/{\text{H}}_{\text{u}\text{, OME}}\right)*\text{K}.$$

where 0.6 <K <0.85, in particular 0.7 <K <0.8. Combustion chamber arrangement (12) according to Claim 1 , characterized in that the elevation angle β is formed so that the injected OME fuel (20b) impinges on the dome (28) during operation. Combustion chamber arrangement (12) according to one of Claims 1 or 2 , characterized in that the elevation angle β is in a range of 0 ° <β <75 °, in particular 30 ° <β <70 °, more particularly 45 ° <β <65 °. Combustion chamber arrangement (12) according to one of Claims 1 to 3 , characterized in that the injection nozzle (16) has nine to twelve injection holes (48) which are arranged symmetrically about the nozzle longitudinal axis (46). Combustion chamber arrangement (12) according to one of Claims 1 to 4 , characterized in that the side wall (30) of the trough (22) has a radially extending from the piston longitudinal axis (26) away, circumferentially around the piston longitudinal axis (26) arranged recess (34) whose depth (T) in the extension direction (52 ) is at most 1/4 of the distance (a) of the piston longitudinal axis (26) to a parallel to the piston longitudinal axis (26) extending portion (44) of the side wall (30). Combustion chamber arrangement (12) according to one of Claims 1 to 4 , characterized in that the side wall (30) of the trough (22) is inclined away from the piston longitudinal axis (26) and / or has a continuous curvature (54) which is rectified but smaller than a curvature (54) of the U-shaped transition area (32). Use of a combustion chamber arrangement (12) according to one of Claims 1 to 6 for injecting OME fuel (20b) into a combustion chamber (10) of an internal combustion engine.

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