DE102017211226A1 - Method for operating an internal combustion engine and internal combustion engine - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine (1), wherein in a multi-fuel mode of the internal combustion engine (1) in a first combustion cycle a first mixture of combustion air and a first, gaseous fuel in a combustion chamber (3) of the internal combustion engine (1) to combustion gas is implemented, wherein the combustion gas is at least partially maintained in the combustion chamber (3), wherein in a second combustion cycle, a second mixture of the combustion gas and a second, different from the first fuel to fuel is converted to exhaust gas. Furthermore, the invention relates to an internal combustion engine.

Description

The invention relates to a method for operating an internal combustion engine and an internal combustion engine.

In internal combustion engines, which are operated with a fuel gas, there is the problem that at the end of a combustion event unburned fuel gas remains, for example in Feuerstegbereichen, columns or the like in combustion chambers of the internal combustion engine. This is due in particular to flame-extinguishing effects that can occur on combustion chamber walls. During expansion with decreasing pressure in the course of combustion, this unburned fuel gas exits the gaps and when pushed out into an exhaust path of the internal combustion engine. This undesirably increases the hydrocarbon emissions thereof. This is particularly problematic when using methane-containing fuel gases, because methane has a high climate relevance. Furthermore, in this case, formaldehyde emissions are problematic.

The invention has for its object to provide a method for operating an internal combustion engine and an internal combustion engine, said disadvantages do not occur.

The object is achieved by providing the subject matters of the independent claims. Advantageous embodiments emerge from the subclaims.

The object is achieved in particular by providing a method for operating an internal combustion engine in which a first mixture of combustion air and a first, gaseous fuel in a combustion chamber of the internal combustion engine is converted into a combustion gas in a multi-fuel mode of the internal combustion engine in a first combustion cycle, wherein the combustion gas is at least partially or completely held in the combustion chamber, and wherein in a second combustion cycle, a second mixture of the combustion gas and a second, different from the first fuel fuel - is converted into exhaust gas in the same combustion chamber. Thus, it is possible to combust portions of the first gaseous fuel which were not burned in the first combustion stroke in the second combustion stroke together with the second fuel. In this way, an emission of portions of the first fuel can be reduced, preferably avoided, whereby the hydrocarbon emissions of the internal combustion engine can be reduced.

The internal combustion engine is preferably designed as a reciprocating engine. The first combustion cycle and the second combustion cycle are preferably associated with a same, common operating cycle of the internal combustion engine and separated only by a compression stroke - which is preferably carried out with closed valves of the combustion chamber. In this way, the still unburned, the first fuel combustion gas is prevented from getting out of the combustion chamber and in the sequence in the environment.

The internal combustion engine preferably has a plurality of combustion chambers, in particular four, six, eight, ten, twelve, sixteen, eighteen or twenty combustion chambers. Other or larger or smaller numbers of combustion chambers are possible.

The term "combustion gas" here refers to a product gas of the first combustion cycle, which is in particular a gas mixture which is composed of the combustion products of the combustion air and the first, gaseous fuel, as well as unburned first, gaseous fuel and unreacted combustion air. The term "exhaust gas" refers to a product gas of the second combustion cycle, which is in particular a gas mixture of the combustion products of the combustion of the combustion gas and the second fuel. The combustion gas may comprise portions of combustion air not converted during combustion, in particular oxygen and / or nitrogen. Also, portions of unconsumed combustion air may be contained in the exhaust gas.

As the first, gaseous fuel in particular a fuel gas, particularly preferably a methane-containing fuel gas is used. The first fuel may preferably be natural gas, liquefied natural gas (LNG), compressed natural gas (CNG), or other fuel gas, or mixtures thereof.

The advantages of the method proposed here are realized in a special way when using a methane-containing fuel gas as the first fuel.

The second fuel other than the first fuel is preferably a liquid fuel under normal conditions, that is, especially at 1013 mbar and 25 ° C. This has the particular advantage that such a fuel undergoes no increase in volume comparable to the increase in volume of a fuel gas during expansion, so that alone Problem of increased hydrocarbon emissions with respect to the second fuel to a much lesser extent - if any - exists, as with the first, gaseous fuel. The hydrocarbon emissions of the internal combustion engine are therefore effectively reduced in the context of the method proposed here, even if optionally remain shares of unburned second fuel after the second combustion cycle.

The exhaust gas is in particular discharged from the combustion chamber. In particular, the exhaust gas is preferably passed through an exhaust path provided for this purpose in an environment of the internal combustion engine, wherein in the exhaust path in per se known manner means for exhaust aftertreatment and in particular exhaust gas purification can be provided, for example, particle filters, catalysts and / or the like.

According to one embodiment of the invention, it is provided that an ignition oil is used as the second fuel. The second fuel may then be used at the same time to ignite the combustion in the second combustion stroke. It is particularly preferable to use diesel, dimethyl ether or polyoxymethylene dimethyl ether (OME) as the second fuel.

According to a development of the invention, it is provided that the first mixture in the first combustion cycle is ignited by an addition of an ignition quantity of the second fuel into the combustion chamber. In this case, an ignition quantity is understood as meaning an amount of the second fuel which is dimensioned such that it causes an ignition of the first mixture in the combustion chamber, but contributes at most to a negligible extent to the overall energy conversion in the combustion chamber. The proportion of energy introduced into the combustion chamber via the ignition quantity of the second fuel is thus negligible in the first combustion cycle in comparison with the proportion of energy introduced into the combustion chamber in the form of the first, gaseous fuel. Such ignition by means of an ignition amount of the second fuel is also referred to as ignition spark ignition. If the first mixture is ignited by adding the ignition quantity of the second fuel, no additional ignition device is required in the combustion chamber. In particular, a spark plug or the like can thus be dispensed with in an advantageous manner, so that the internal combustion engine has fewer components, being less expensive and less maintenance.

According to one embodiment of the invention, it is provided that the internal combustion engine is operated with a duty cycle comprising six cycles, wherein a first cycle comprises a compression of the first mixture, wherein a second cycle, which adjoins the first cycle, is the first combustion cycle wherein a third clock following the second clock comprises compression of the combustion gas resulting from the first combustion clock, a fourth clock following the third clock being the second combustion clock, a fifth clock being adjoining the fourth stroke, comprising discharging the exhaust gas formed in the fourth stroke from the combustion chamber, and wherein a sixth stroke following the fifth stroke comprises introducing the first mixture into the combustion chamber. The first cycle then in turn joins the sixth cycle, so that the internal combustion engine is operated cyclically with a succession of successive working cycles, each comprising the six cycles described here. In addition to the conversion of the unburned portions of the first fuel in the second combustion stroke, which in turn increases the efficiency of the combustion of the engine in addition to reducing the hydrocarbon emissions, since the first fuel is fully or at least almost fully utilized, then as described herein The advantage of the six-stroke cycle is that it has a total of six strokes, which corresponds to a 1: 3 work cycle share on the duty cycle. This is advantageous in comparison to a conventional four-stroke cycle in which the ratio of the single cycle to the entire cycle is only 1: 4. The six-stroke duty cycle described here thus lies between the conventional four-stroke operation of an internal combustion engine and operation with a two-stroke cycle in which the fraction of the work cycle over the entire cycle is 1: 2. However, compared to a two stroke cycle, the six stroke cycle proposed herein has significantly more efficient operation in terms of improved utilization of the fuel employed and significantly reduced hydrocarbon emissions.

For the sake of completeness it is pointed out that the counting or assignment of the individual clocks can also be carried out in a manner other than that described. It does not necessarily have the clock in which the first mixture is compressed, counted as the first clock. Rather, the count can be started at any clock of the duty cycle. A particularly intuitive counting method can be carried out, for example, by designating the cycle in which the first mixture is introduced into the combustion chamber as the first cycle.

The first mixture is preferably aspirated in the sixth cycle. It is also possible that the internal combustion engine has at least one Compressor with which combustion air or a premixed combustion air-fuel mixture of the combustion air and the first fuel, thus the first mixture is compressed. In particular, it is thus possible that the first mixture is premixed introduced into the combustion chamber. In particular, the first fuel can be introduced into a charging path of the internal combustion engine by means of multipoint injection or single-point injection. It is also an admixture of the first fuel upstream of the compressor possible, so that the internal combustion engine is operated as a mixture supercharged internal combustion engine. But it is also a direct injection of the first fuel into the combustion chamber possible, wherein the first mixture is then generated in the combustion chamber, so that only at least one of the combustion chamber associated intake valve combustion air is introduced into the combustion chamber.

The second fuel is preferably introduced by direct injection into the combustion chamber. Thus, in particular by the injection timing selected for the second fuel at the same time an ignition timing can be set. This is especially true for the second combustion cycle, but - in Zündstrahlzündung - also for the first combustion cycle.

According to one embodiment of the invention, it is provided that in the first combustion cycle, a homogeneous or partially homogeneous combustion of the first mixture is performed. In particular, as already described, this can be introduced premixed into the combustion chamber or generated homogeneously or at least partially homogeneous in it. In particular, the combustion in the first combustion cycle is configured as a pre-mixed flame front Otto engine combustion.

Alternatively or additionally, it is provided that an inhomogeneous or stratified combustion, in particular a combustion with a diffusion flame, is carried out in the second combustion cycle. The second combustion in the second combustion cycle is particularly performed as a diffusion engine diesel engine combustion.

While in the first combustion cycle unburned, first fuel remains in particular in columns of the combustion chamber, this is distributed during the expansion by the falling pressure in the combustion chamber. In the second combustion cycle then advantageously takes place a contribution of the second fuel in the existing combustion chamber filling, which consists of combustion air, combustion products from the first combustion, which are also referred to as residual gas, and unburned first fuel. The unburned first fuel is then burned during the second combustion stroke so that it contributes to energy expenditure, and its energy content can be used as work. At the same time, the residual amount of unburned first fuel is burned, wherein the combustion chamber acts quasi as a thermal reactor for the residual amount of the first fuel.

According to one embodiment of the invention, it is provided that the valves associated with the combustion chamber are kept closed between the second clock and the third clock and during the third clock. Between the first combustion cycle and the second combustion cycle therefore no gas exchange takes place between the combustion chamber and its surroundings, but the combustion gas is completely held in the combustion chamber and used for the second combustion cycle, thus the fourth cycle. In particular, at least one exhaust valve associated with the combustion chamber is kept closed. Preferably, all the exhaust valves associated with the combustion chamber are kept closed. In addition, at least one inlet valve assigned to the combustion chamber is preferably kept closed. Preferably, all intake valves associated with the combustion chamber are kept closed. Particularly preferably, all valves associated with the combustion chamber are kept closed between the second clock and the third clock as well as during the third clock. Especially in this case, the combustion gas is completely held in the combustion chamber.

However, it is also possible for at least one valve assigned to the combustion chamber, preferably at least one outlet valve, to be opened temporarily in the third cycle, in particular at the beginning of the third cycle. In this way, pressure peaks in the combustion chamber can be reduced, with hardly any relevant hydrocarbon emission from the combustion chamber occurs, since at the time of opening of the valve in its area at least almost hydrocarbon and especially methane-free exhaust gas is arranged. Namely, the expansion of the unburned hydrocarbons occurs mainly from an annular gap around a piston which is located at the beginning of the third stroke near its bottom dead center and thus away from the valve. The valve is preferably between a crankshaft angle associated with bottom dead center at the beginning of the third stroke, referred to below as the dead center crank angle, and crankshaft angle 120 ° (° CA) after the dead center crank angle, preferably between the dead center crank angle and 90 ° KW after the dead center crank angle, preferably between the dead center crank angle and 60 ° CA after the dead center crank angle, preferably between the dead center crank angle and 30 ° CA after the dead center crank angle, preferably between the dead center crank angle and 15 ° CA after the dead center crank angle, opened, preferably in each case for the entire crankshaft angle range given here, or only temporarily within this range. In these cases, the combustion gas is at least partially held in the combustion chamber.

According to one embodiment of the invention, it is provided that a lean mixture is reacted as the first mixture in the first combustion cycle. The internal combustion engine then works in particular as a lean-burn gas engine, whereby its efficiency can be particularly high. Particularly preferably, the first mixture with a combustion air-fuel ratio, which is also referred to as lambda value, of at least two, preferably generated by two. The fact that a lean mixture is burned in the first combustion cycle, it is also ensured that even for the combustion in the second combustion cycle is still sufficient combustion air in the combustion chamber, although preferably no gas exchange between the combustion chamber and the environment between the first combustion cycle and the second combustion cycle takes place.

The combustion in the second combustion cycle preferably takes place above a soot boundary. As a result, the combustion chamber performance - in particular also depending on the combustion air-fuel ratio of the first mixture - may be reduced. However, this specific power reduction is not pronounced, especially since a mean pressure reduction is compensated even for 50% in the second combustion cycle by the lean gas operation in the first combustion cycle.

The fact that the combustion takes place in the second combustion cycle above the soot boundary means, in particular, that the amount of second fuel introduced into the combustion chamber in the second combustion cycle is such that soot formation in the second combustion is negligible, preferably prevented.

According to one embodiment of the invention it is provided that the internal combustion engine is operated in a single-component mode with a four-stroke cycle, wherein in the single combustion cycle of the four strokes a third mixture of combustion air and only the second fuel, or combustion air and only the first fuel , is implemented. In this way, the internal combustion engine can continue to be operated with the other of the two fuels even if the supply of one of the two fuels fails. In particular, if the fuel gas supply, thus the supply of the first fuel fails, the internal combustion engine with the four-stroke cycle can be operated solely on the basis of the second fuel, in particular in diesel mode. Also, a supply only with the first fuel is possible, which then possibly requires an additional ignition device in the combustion chamber to ignite the combustion air-fuel mixture, which comprises only the first fuel. However, especially in large internal combustion engines with high mean pressures and compression ignition of the first, gaseous fuel is quite possible.

The four bars of the four-stroke cycle are known per se in a conventional compression stroke, a subsequent combustion cycle or power stroke, an adjoining Ausschiebe- or Ausbringtakt to expel exhaust gas, and this in turn subsequent intake stroke or Einbringtakt for generating the combustible mixture in the combustion chamber.

In particular, the fact that the third mixture has only the second fuel or only the first fuel means that the third mixture is free of the first fuel if it has only the second fuel, and it is free of the second fuel if it only having first fuel.

Alternatively, it is also possible for the engine to be operated in a single-fuel mode with a six-stroke duty cycle, but in the first combustion stroke and the second combustion stroke of the six strokes only the second fuel - not the first fuel - or only the first Fuel - and not the second fuel - is burned. In particular, if lean combustion occurs in the first combustion cycle, the remaining combustion air may be used for a second combustion in the second combustion cycle, even if only one fuel is used.

With the aid of the single-substance operating modes of the internal combustion engine described here, in particular further operation can be ensured, even if the supply of one of the fuels fails. Thus, in particular, a "limp home" function can be provided. Thus, for example, a ship operated with a corresponding internal combustion engine can still be safely brought to a port even if a supply of one of the fuels used fails.

According to one embodiment of the invention, it is finally provided that between the multi-fuel mode and the single-substance operating mode by controlling a combustion chamber associated, variable valve train is switched. This relates in particular to the control of the gas exchange valves of the combustion chamber, in particular of the exhaust valves and intake valves. In particular, such a variable valve train can be used to switch between a six-stroke cycle and a four-cycle cycle.

For switching between the Mehrstoffbetriebsart and the Einstoffbetriebsart preferably also a fuel supply for the combustion chamber of the internal combustion engine is switched so that on the one hand the combustion chamber in the Mehrstoffbetriebsart the first fuel and the second fuel are supplied, on the other hand supplied in the single-fuel mode of the combustion chamber only one of the two fuels becomes.

The object is also achieved by providing an internal combustion engine which is set up for carrying out an embodiment of the method described above. In connection with the internal combustion engine, in particular the advantages that have already been described in connection with the method are realized.

The internal combustion engine is preferably associated with a first fuel supply for the first fuel and a second fuel supply for the second fuel. Furthermore, the internal combustion engine preferably has a variable valve drive.

The internal combustion engine preferably has a control device, which is set up to operate the internal combustion engine in the multi-fuel mode and preferably also in the single fuel mode, in particular to control it.

The internal combustion engine is preferably designed as a reciprocating engine. It is possible that the internal combustion engine is arranged to drive a passenger car, a truck or a commercial vehicle. In a preferred embodiment, the internal combustion engine is used to drive in particular heavy land or water vehicles, such as mine vehicles, trains, the internal combustion engine is used in a locomotive or a railcar, or ships. It is also possible to use the internal combustion engine to drive a defense vehicle, for example a tank. An exemplary embodiment of the internal combustion engine is preferably also stationary, for example, used for stationary power supply in emergency operation, continuous load operation or peak load operation, the internal combustion engine in this case preferably drives a generator. A stationary application of the internal combustion engine for driving auxiliary equipment, such as fire pumps on oil rigs, is possible. Furthermore, an application of the internal combustion engine in the field of promoting fossil raw materials and in particular fuels, for example oil and / or gas, possible. It is also possible to use the internal combustion engine in the industrial sector or in the field of construction, for example in a construction or construction machine, for example in a crane or an excavator.

In the method and the internal combustion engine described here, it is particularly advantageous that in the second combustion cycle high temperatures can be provided for the direct oxidation, in particular of methane, without requiring the use of methane oxidation catalysts or additional thermoreactors. Furthermore, the hydrocarbons not combusted in the first combustion cycle are used in the second working cycle, their chemical energy being converted into work, the fraction of unburned hydrocarbons, in particular in the case of lean gas engines, being 1% to 2% of the introduced fuel energy. In the context of the method, small amounts of nitrogen oxide in the exhaust gas are produced by the very lean combustion in the first combustion cycle and the low nitrogen oxide formation in the second combustion cycle due to the inherently very high exhaust gas recirculation rates - the combustion gas of the first combustion remaining in the combustion chamber for the second combustion cycle contains a high proportion of exhaust gas. wherein at the same time there is a high proportion of water in the combustion chamber during the second combustion of the first combustion. The intrinsically realized, high exhaust gas recirculation rates for the second combustion also have the consequence that there is no need for external exhaust gas recirculation.

The invention will be explained in more detail below with reference to the drawing. The single figure shows a schematic representation of an embodiment of an internal combustion engine and an embodiment of a method for operating the internal combustion engine.

The only Fig. Shows a schematic representation of an embodiment of an internal combustion engine 1 , which is designed as a reciprocating engine, wherein the internal combustion engine 1 a combustion chamber 3 on the one hand by a cylinder wall 5 and on the other hand from a piston 7 is limited, the volume of the combustion chamber 3 in a conventional manner by periodic movement of the piston 7 in one the cylinder wall 5 having cylinder 9 is variable.

The internal combustion engine 1 is operated in a Mehrstoffbetriebsart so that in a first combustion cycle, a first mixture of combustion air and a first, gaseous Fuel, in particular a preferably methane-containing fuel gas, in the combustion chamber 3 is converted to combustion gas, wherein the combustion gas at least partially, preferably completely, in the combustion chamber 3 is held, wherein in a second combustion cycle, a second mixture of the combustion gas and a second, different from the first fuel, preferably liquid fuel, is converted to exhaust gas. The exhaust gas is then removed from the combustion chamber 3 applied. In this way, unburned portions of the first fuel from the first combustion cycle in the second combustion cycle can be converted, wherein the proportion of energy can be converted into work, and wherein the hydrocarbon emissions of the internal combustion engine 1 be reduced in an advantageous manner and at the same time in a simple and cost-effective manner.

The second fuel used is preferably an ignition oil, in particular diesel, dimethyl ether or polyoxymethylene dimethyl ether (OME).

The first mixture is preferred in the first combustion cycle by adding an ignition amount of the second fuel into the combustion chamber 3 ignited.

Preferably, in the first combustion cycle as a first mixture, a lean mixture, preferably with a combustion air-fuel ratio of more than 2 or the same 2 , burned.

In the figure it is shown that the internal combustion engine 1 in the multi-fuel mode is operated in a duty cycle comprising six strokes, which are shown here from a) to f).

In this case, in a first cycle - shown at a) - the preferably lean, first mixture is compressed. In a second cycle shown at b), the first mixture is - preferably by adding an ignition amount of the second fuel in the combustion chamber 3 - ignited and converted to the combustion gas. Due to the falling pressure in the combustion chamber 3 The unburned first fuel expands and distributes itself in the combustion chamber 3 ,

In a third cycle, shown at c), compression of the combustion gas formed in the second cycle takes place, the unburned, first fuel no longer being present in gaps of the combustion chamber 3 collected, but rather in the combustion chamber 3 distributed.

Finally, in a fourth cycle represented at d), the conversion of the second mixture of the combustion gas and the second fuel to exhaust gas takes place, wherein preferably a diesel combustion is carried out. The second fuel is in particular by direct injection into the combustion chamber 3 brought in. In the second combustion cycle, the energy content of the unburned, first fuel is used at the same time and converted into work. The diesel combustion in the fourth cycle preferably takes place above a soot limit, so that the internal combustion engine 1 can be operated soot poor.

In a fifth cycle shown at e), the exhaust gas formed in the fourth cycle is removed from the combustion chamber 3 ejected.

In a sixth cycle shown at f), finally, the first mixture in the combustion chamber 3 introduced, in particular sucked in premixed or directly in the combustion chamber 3 generated.

In the first combustion cycle, in particular a homogeneous or partially homogeneous combustion takes place, particularly preferably an Otto engine combustion with premixed flame front. In the second combustion cycle, preference is given to inhomogeneous or stratified combustion, in particular a diesel engine combustion with a diffusion flame.

The combustion chamber 3 associated valves, in particular gas exchange valves, in particular exhaust valves and intake valves are kept closed between the second clock and the third clock and during the third clock. Thus, in particular no gas exchange between the combustion chamber 3 and its environment between the second clock, thus the first combustion, and the fourth clock, thus the second combustion, instead. Only the second fuel is introduced into the combustion chamber for combustion in the second combustion cycle, thus the fourth cycle, preferably by direct injection.

But it is also possible that at least one of the combustion chamber 3 associated valve, preferably at least one outlet valve, in the third clock temporarily, in particular at the beginning of the third clock, is opened.

The internal combustion engine 1 For example, in a single-component mode, it may be preferred to operate with a four-stroke duty cycle wherein in the single combustion stroke of the four strokes, a third mixture of combustion air and only the second fuel, or combustion air and only the first fuel, is reacted. Alternatively, it is possible that the internal combustion engine is operated in the single-fuel mode with a six-stroke duty cycle, wherein both the first combustion stroke and the second combustion stroke only the second fuel, or only the first fuel is burned. In this way, the internal combustion engine 1 continue to be operated if a supply of one of the two fuels fails. In particular, so can a "limp home" function for the internal combustion engine 1 to be provided.

Between the multi-fuel mode and the single-fuel mode is preferably by controlling a combustion chamber 3 switched associated variable valve train.

With the method proposed here and the internal combustion engine 1 It is possible, in a low-cost, cost-effective manner, not only the hydrocarbon emissions, in particular of the designed as a gas engine internal combustion engine 1 but also exploit the energy content of a gaseous fuel better than in known gas engines and put into work.

Claims (10)

Method for operating an internal combustion engine (1), wherein in a multi-fuel mode of the internal combustion engine (1) - In a first combustion cycle, a first mixture of combustion air and a first, gaseous fuel in a combustion chamber (3) of the internal combustion engine (1) is converted into combustion gas, wherein - The combustion gas is at least partially held in the combustion chamber (3), wherein - In a second combustion cycle, a second mixture of the combustion gas and a second, different from the first fuel fuel is converted to exhaust gas. Method according to Claim 1 , characterized in that an ignition oil, in particular diesel, dimethyl ether or polyoxymethylene dimethyl ether, is used as the second fuel. Method according to one of the preceding claims, characterized in that the first mixture is ignited in the first combustion cycle by an addition of an ignition amount of the second fuel into the combustion chamber (3). Method according to one of the preceding claims, characterized in that the internal combustion engine (1) is operated with a six-stroke duty cycle, wherein: - a first clock comprises a compression of the first mixture; a second cycle is the first combustion cycle; a third clock comprises a compression of the combustion gas from the second clock; a fourth stroke is the second combustion stroke; - A fifth cycle comprises the discharge of the exhaust gas formed in the fourth cycle from the combustion chamber (3), and wherein - a sixth cycle comprises the introduction of the first mixture in the combustion chamber (3). Method according to one of the preceding claims, characterized in that in the first combustion cycle, a homogeneous or partially homogeneous combustion is performed, and / or that in the second combustion cycle, an inhomogeneous or stratified combustion, in particular a combustion with a diffusion flame is performed. Method according to one of the preceding claims, characterized in that the combustion chamber (3) associated with valves between the second clock and the third cycle of the six-stroke cycle and during the third cycle are kept closed, or that at least one of the combustion chamber (3) associated Valve in the third clock temporarily, especially at the beginning of the third clock, is opened. Method according to one of the preceding claims, characterized in that a lean mixture is reacted as the first mixture in the first combustion cycle. Method according to one of the preceding claims, characterized in that the internal combustion engine (1) in a single-fuel mode a) is operated with a four-stroke duty cycle, wherein in the single combustion cycle of the four cycles, a third mixture of combustion air and only the second fuel, or b) is operated with a six-stroke cycle, both in the first combustion cycle and in the second combustion cycle, only the second fuel or only the first fuel is burned. Method according to one of the preceding claims, characterized in that switching between the multi-fuel mode and the single-fuel mode of the internal combustion engine (1) by driving a variable valve train associated with the combustion chamber (3). Internal combustion engine (1) adapted to carry out a method according to one of Claims 1 to 9 ,

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