DE102008024561B4 - Method for operating an internal combustion engine - Google Patents

Abstract

Method for operating an internal combustion engine, which comprises, inter alia, a fuel tank (1), a low-pressure fuel circuit (1-13), an electrical system and a battery for supplying the same, characterized in that the following steps are carried out before starting the internal combustion engine: a) Detecting a signal induced by an electrical load by detecting a signal representative of a drop in the voltage across the battery due to the activation of the electrical load; b) starting a fuel circulation in the fuel low pressure circuit (1-13) in response to the detected signal , which is used as a start pulse for the start of the fuel circulation

Description

The invention relates to a method for operating an internal combustion engine according to the preamble of claim 1 and to an internal combustion engine according to the preamble of claim 12.

Otto engines are designed according to the state of the art for operation with the fuel gasoline. Accordingly, the control and regulation strategies of the engine management of the engine control unit and the maps used by him on the physical properties of the fuel gasoline are turned off, in particular on its evaporation characteristics.

The vaporization characteristic of the fuel gasoline, however, differs significantly from the vaporization characteristic of the fuel LPG. While gasoline has a boiling range of 25 ° C - 210 ° C and its vapor pressure in operation is approximately 0.5 bar, the boiling point of LPG at a pressure of 1013 mbar is -30 ° C (Applies to LPG fuel consisting of 60 % Propane and 40% butane) and the vapor pressure about 6 bar.

This difference in fuel vaporisation characteristics gives rise to specific problems in the operation of a gasoline engine with the liquid phase fuel LPG, especially when starting the engine both in cold (cold start) and warm (warm start) conditions.

Injection systems injecting LPG in the liquid phase have in principle the problem that the operating pressure must be at any point in the fuel supply of the fuel supply system from the fuel tank to the fuel injection valves above the evaporation pressure of the LPG used, so that the internal combustion engine can operate smoothly. This is ensured in known injection systems that inject LPG in liquid phase, an electrically driven fuel pump in the LPG tank in combination with a pressure regulator in the fuel return line. A fuel vapor pressure compensation of the pressure regulator ensures that the varying vaporization pressures due to different fuel temperatures of the LPG in the LPG tank need not be compensated by an overpressure to be generated by the fuel pump. However, the fuel vapor pressure compensation of the pressure regulator does not compensate for the local evaporation pressure increase caused by heating the LPG on its way from the LPG tank to the injectors by heat input from heat sources, such as fuel pump winding, LPG tank shut-off valve, heat conduction from the warm engine and adjusts the heated air in the engine compartment, fuel compression in the high-pressure pump, solenoid valves for locking the fuel against each other in bivalent operation. With the engine running, this problem is solved by a continuous, cooling fuel circulation in the fuel supply system and by the cooling fuel flow through the fuel injectors.

Known systems injecting liquid phase LPG into the intake passage of a gasoline engine have less heat input into the LPG than systems injecting liquid phase LPG directly into the combustion chamber. Therefore, in this mode of operation, they are normally satisfied with a 3-5 bar permanent overpressure to buffer the evaporative pressure-increasing heat inputs from the tank to the injectors in the liquid phase LPG path so that the LPG remains in liquid phase. However, even with this configuration, the residual risk remains that with prolonged, uninterrupted engine operation and a resulting low tank content in the LPG tank, the LPG in the LPG tank warmed up so much that its evaporation pressure is higher than the pressure that a pump a LPG fuel pump generates, so that a refueling of LPG is possible only after a cooling phase.

Direct injection systems, as used in the DE 101 46 051 are described, inject the LPG in the liquid phase in the combustion chamber of the gasoline engine, have an additional, higher heat input into the fuel through the high-pressure fuel pump and the solenoid valves that control the switching of the fuel.

In the DE 101 46 051 Therefore, a fuel supply system for LPG is described, which has in the fuel supply line connected to an air conditioning fuel cooling device. This configuration controls all heat input into the LPG while the engine is running.

Not dominated by the in the DE 101 46 051 the rapid warm start described after prolonged shutdown of a warm engine when components of the fuel supply system, here in particular the high-pressure fuel pump, have heated up strongly. The cause is the heat flowing from the engine block into the components, which is no longer dissipated by the fuel circulated in the low-pressure fuel circuit or injected into the combustion chamber of the gasoline engine. Then, when the engine is restarted, the engine's failure may fail because there is no liquid fuel available because it has temporarily vaporized and its vapor pressure is higher than the fuel pressure generated by the fuel feed pump in the LPG tank.

Otto engines, which are operated with gasoline, a short flow of the gasoline pump before engine start with a short-term increase in the fuel pressure is sufficient to eliminate fuel bubbles in the low-pressure fuel supply system, which may have been caused by heating. This gasoline pump flow is used in motor vehicles z. B. started by opening the driver's door.

Otto engines, which inject liquid LPG as fuel, have the problem that the LPG in the course of this heating process within the components of the injection system from the liquid phase into the vapor phase. If these fuel vapor bubbles are not removed in the injection system before starting the engine, the engine can not be started.

A start with LPG with a warm engine without fuel-cooling measures would be in gasoline engines, which now inject only with "top-fed" injectors liquid and intermittent injection into the intake (channel injection) and in the latest generation increasingly without fuel return from the fuel rail in the fuel tank manage to realize only with a very high fuel pump pressure.

These problems with starting the engine with LPG are circumvented in known systems by operating the gasoline engine with two complete fuel supply systems, typically the gasoline and liquid phase LPG fuels, the bottom-feeded LPG system "Injectors and a fuel return into the LPG fuel tank works and there is the possibility to switch between the fuels back and forth. These engines are typically started in LPG petrol mode. After a successful engine start, the control of the engine after a more or less long warm-up phase of the fuel gasoline switches to the fuel LPG.

In the EP 1 095 214 B1 a fuel system for port injection of LPG is described, which operates with variable pump pressures between 8 bar and 4 bar, with the temperature of the LPG in the fuel tank, the pump pressure of 8 bar to 4 bar, when the pressure in the LPG tank to 25 bar increases. For an injection system that injects LPG with "bottom-fed" injectors into the intake manifold, these pump pressures are sufficient to suppress gas bubble formation even during warm start, because only here, as in the DE 103 60 977 mentioned, temperature differences of about 12-16 ° C are to be suppressed, for which pressures above 4 bar certainly meet. The disadvantage here, however, the high pressure that must be permanently generated by the in-tank pump in the LPG tank, resulting in increased pump wear, increased heat input into the fuel and increased fuel consumption.

In the DE 103 60 977 A1 is proposed for a gasoline engine with port injection of LPG in liquid phase, to delay the engine start for predetermined periods of time, when a predetermined fuel temperature in the fuel line is not exceeded, while the fuel pump in the LPG tank pumped until shortly after engine start with maximum power. The period of interest is given as 15 to 30 seconds. This solution requires "bottom-fed" injectors and fuel return into the tank. Otherwise, it would have to operate with such high pressure of the in-tank pump in the LPG tank that would make the waiting time unnecessary.

In petrol engines that inject LPG directly, although the high-pressure fuel range is due to the prevailing high pressures vapor-critical, but are sufficient in the low pressure range of the high-pressure fuel-high-pressure pump also in the EP 1 095 214 B1 high pressures of 8 bar for prefeed pumps in the fuel tank, to the hot phase of the vapor bubbles, which can be due to the temperatures of about 70 ° C, which can heat up the high-pressure pump housing at a standstill after a long period of operation form, in the liquid phase due.

In the EP 06 023 298.0 is described by the author of the application that in gasoline engines with direct fuel injection operation with LPG in liquid phase with a warm engine, depending on the design of the high-pressure fuel pump, with reasonable technical effort is only possible if a low pressure fuel return line, preferably by an additional adapter or an additional Bore, is connected to the low pressure region of the high-pressure fuel pump that a low-pressure fuel circuit is formed, which flows well around the input to the high-pressure pumping chamber of the high-pressure fuel pump as a thermal critical point of the LPG fuel supply system, regardless of the amount of the fuel branched off for combustion.

However, a warm start without unacceptable time delay by the cooling process of the high-pressure fuel pump is not guaranteed only by this configuration in all types of high-pressure fuel pump. Unacceptable here is a period of time greater than 30 s. The period of 30 s was determined in tests as the period from the operation of the radio unlocking to the start of the engine is normally required, provided the seat belts are put on before the engine is started.

At the number DE 3231881 a patent has been filed for fuel cooling, in which it is proposed, especially in diesel internal combustion engines to integrate a fuel-carrying heat exchanger in the coolant circuit of a vehicle air conditioning system. Fuel cooling is normally not needed and used in the prior art Otto fuel injected engines, as well as in port injection of Otto engines in bivalent operation with the gasoline and LPG fuels.

The U.S. Patent 5,775,281 discloses a method of preventing the undesirable vaporization of LPG in a fuel plant due to heat build-up. If these are detected when the starter is actuated, the starting of the engine is delayed and the fuel system initially only filled with fuel and / or rinsed until it has cooled. Alternatively, the engine is initially supplied with an alternative fuel and started.

The DE 103 10 151 discloses a method of operating a fuel system for an LPG engine, in which the starting of the engine is delayed after the actuation of the starter by the driver and the LPG is first heated with a heater. This is to ensure that the LPG supplied to the engine is almost completely evaporated. In this case, the heating demand is determined at each start and the fuel supply to the engine at startup delayed by the determined heating time.

The invention is based on the problem to provide a method for operating an internal combustion engine and a correspondingly working internal combustion engine, with which the mentioned disadvantages are avoided when starting the engine.

This problem is solved by a method having the features of claim 1 and an internal combustion engine having the features of claim 12. Advantageous embodiments can be found in the subclaims.

According to the invention, a signal is first detected by an electronic control unit before starting the engine, which is due to a battery voltage drop, for example by pressing a remote arm. This signal is used as a start pulse for the start of a fuel circulation. As a result, cooling of the fuel to be ignited is achieved before starting the engine, in particular during warm start.

• – die Direkteinspritzung von LPG möglich wird, die sonst aus Platzgründen und auch aus Kostengründen scheitern würde,
• – die Vorhaltung eines zweiten Kraftstoffzuführungssystems für die Zuführung eines Normaldruck-Ottokraftstoffes, einschließlich des geschlossenen Kraftstoffsystems, das das Austreten von Kraftstoffdämpfen aus dem Kraftstofftank verhindert, aus technischen Gründen überflüssig wird,
• – ein Betrieb eines Otto-Motors ausschließlich mit LPG möglich ist,
• – kein teurer Normaldruck-Ottokraftstoff, vorzugsweise Benzin, zum Starten des Motors mehr benötigt wird, was besonders beim Einsatz von Start-Stopp-Systemen enorm an Bedeutung gewinnt,
• – durch das Vorgenannte CO2-Emission in einer Größenordnung von 15% und mehr vermieden wird,
• – der von der Kraftstoffpumpe im LPG-Tank im Betrieb vorzuhaltende Druck über dem LPG-Verdampfungsdruck gering sein kann,
• – die Kraftstoffpumpe im LPG-Tank keiner die Pumpenlebensdauer vermindernde Kavitation durch verdampfendes LPG ausgesetzt ist,
• – dass ein dem Betrieb mit dem Kraftstoff Benzin vergleichbar, sicherer Betrieb des Otto-Motors ausschließlich mit dem Kraftstoff LPG möglich wird (auch bei einem Betriebszustand mit hohen Außentemperaturen und geringem Kraftstoffinhalt im Tank, der sogar beim Betrieb mit Benzin einen kritischen Zustand darstellt).

In addition, it is achieved by the invention that

• - The direct injection of LPG is possible, which otherwise would fail for reasons of space and also for cost reasons,
• - the provision of a second fuel supply system for the supply of a normal pressure gasoline fuel, including the closed fuel system, which prevents the escape of fuel vapors from the fuel tank, is superfluous for technical reasons,
• - An operation of an Otto engine is possible only with LPG,
• - No expensive normal-pressure gasoline, preferably gasoline, more is needed to start the engine, which is particularly important in the use of start-stop systems enormously important,
• - avoided by the abovementioned CO2 emission of the order of 15% or more,
• The pressure to be maintained by the fuel pump in the LPG tank above the LPG evaporation pressure may be low,
• The fuel pump in the LPG tank is not exposed to pump life reducing cavitation by evaporating LPG,
• - That the operation of the gasoline fuel comparable, safe operation of the gasoline engine exclusively with the LPG fuel is possible (even in an operating condition with high outside temperatures and low fuel content in the tank, which is a critical condition even when operating with gasoline).

Embodiments of the invention will be illustrated and explained in a simplified manner below.

1 Shows the monovalent version of LPG direct injection in gasoline engines, which is operated with the method for operating an internal combustion engine according to claim 1.

2 - Shows a bivalent version of LPG direct injection in gasoline engines, in which in the operating mode LPG also the method for operating an internal combustion engine according to claim 1 is used.

The 3a , b - show a pressure regulator with internal evaporation pressure compensation, bypass and three variants of a device in the pressure regulator, which allow a short-term pressure increase.

In 1 press one, in a catch tank 3 housed fuel pump 2 from the pressure-resistant LPG tank provided with the prescribed safety fittings 1 , LPG in liquid phase 4 into the fuel supply line 5 to High-pressure fuel pump 6 out. In a preferred embodiment, the LPG flows through in liquid phase 4 on the way to the high-pressure fuel pump 6 a heat exchanger connected to an on-board air conditioning system 13 where it is additionally cooled. A hole 7 at a special location of the high pressure pump 6 attached, it allows the LPG in liquid phase 4 from the fuel supply line 5 at the entrance of the high pressure pump chamber in the high pressure pump over into the fuel return line 8th to the LPG tank 1 to flow. A valve controlled by the engine control in the high-pressure pump 6 allows the fuel needed for combustion to flow from the passing fuel flow into the high pressure pump chamber of the high pressure pump 6 drain where the fuel is 4 pressurized by the pump piston and via the high pressure fuel line 9 to the fuel rail 10 is pressed. The fuel rail 10 supplies the fuel injection valves 20 with the necessary fuel, which they inject with high pressure (40-200 bar) into the combustion chamber of the (not shown here) engine. On the way from the high pressure pump 6 back to the LPG tank 1 flows through the fuel 4 one with a bypass 12 provided pressure regulator 11 and a heat exchanger connected to the air conditioner 13 where the fuel 4 is cooled again so that he, despite the in the high-pressure fuel pump 6 heat input, in the liquid phase back into the catch tank of the tank module 3 in the LPG tank. This avoids cavitation by evaporating LPG in the catch tank 3 and the associated load on the fuel pump 2 ,

For safety reasons, the control unit detects 16 over the pressure sensor 14 during all phases of operation, including the pre-production phase and the trailing phase with the engine stopped, the pressure in the low-pressure fuel circuit. Is from the control unit 16 no pressure detected in the system, then stops the control unit 16 the operation of the LPG fuel pump 2 and closes the solenoid valve 18 in the fuel flow. A leak of LPG 4 from the LPG tank 1 It is thus both in leaking as well as torn off fuel line 5 / 8th prevented.

The control unit 16 detects at standstill of the motor induced by an electrical load voltage drop of the battery and uses it as a control pulse to the fuel pump 2 to get started. This ensures that a cooling fuel circulation in the low-pressure fuel circuit is already set in motion when z. B. the lock of a motor vehicle is unlocked, so even before opening a vehicle door. At the same time the control unit opens 16 the bypass 12 of the pressure regulator 11 , what the hydraulic resistance in the fuel line to the hydraulic resistance of the pressure regulator 11 reduced. This increases the fuel volume flow and thus the cooling effect.

After turning off the engine the control unit registers 16 over the temperature sensor 15 the temperature of the high pressure pump 6 , If this exceeds a fixed first value, the control unit continues 16 with the help of the fuel pump 2 in the LPG tank 1 a cooling fuel circulation in progress. To relieve the battery and to increase the cooling effect opens the control unit 16 the bypass 12 of the pressure regulator 11 so that its hydraulic resistance is bypassed. The cooling fuel circulation is maintained until a lower second defined temperature at the high pressure pump 6 is fallen short of. This control loop will run through until the controller 16 does not detect any temperature increase beyond the first defined temperature. In a control variant of the cooling fuel pump lag in the low-pressure fuel circuit, the temperature-dependent changing evaporation pressures in the LPG tank are taken into account. The control unit 16 registered after switching off the engine via the temperature sensor 15 the temperature of the high-pressure fuel pump 6 and compares them to the fuel temperature in the LPG tank 1 that has a temperature sensor 17 on or in the LPG tank 1 determined. If the temperature rises at the high-pressure fuel pump 6 a first defined, based on the vapor pressure curve of the LPG difference to the temperature of the fuel 4 in the LPG tank 1 , puts the control unit 16 with the help of the fuel pump 2 in the LPG tank 1 a cooling fuel circulation in progress. To relieve the battery and to increase the cooling effect opens the control unit 16 the bypass 12 of the pressure regulator 11 so that its hydraulic resistance is bypassed. The cooling fuel circulation is maintained until a second defined temperature difference between the temperature at the high pressure pump 6 and the temperature of the fuel 4 in the LPG tank 1 is fallen short of. This control loop will run through until the controller 16 does not detect a temperature increase beyond the first defined temperature difference.

In 2 is the equivalent bivalent version of direct injection of liquid phase LPG 4 pictured in petrol engines. There is a fuel supply line in the low pressure area 24 for fuel at normal pressure and normal temperature (normal pressure fuel) 21 , preferably gasoline, from an in-tank fuel pump 12 in normal pressure fuel tank 20 is charged and a corresponding fuel supply line in the low pressure range 5 for LPG. The fuel supply lines 5 / 24 for the two fuels 4 / 21 be upstream of the high-pressure fuel pump 6 coupled and through a check valve 31 and two solenoid valves 25 / 32 locked against each other. This ensures that only one of the two fuels 4 / 21 to the high-pressure fuel pump 6 is encouraged. In addition, in the low pressure region of the fuel supply of the normal pressure fuel, a second fuel pump 23 needed to switch from LPG to liquid phase 4 on the normal pressure fuel 21 the evaporation of LPG in liquid phase 4 to prevent.

This procedure is also controlled by the control unit 16 , In detail, the switching process in the DE 101 46 051 described.

An important difference in the fuel supply of the two fuels 4 / 21 also lies in the fact that the normal pressure fuel 21 without return, while the fuel LPG in liquid phase 4 with a fuel return 8th from the high-pressure fuel pump 6 in the LPG tank 1 operated as a fuel circuit, without which he would not be reliable.

This difference of fuels 4 / 21 in operation is also controlled by the controller 16 organized by fuel-specific the return valve 30 downstream of the output of the low pressure region of the high-pressure fuel pump keeps open or closed, namely opened in the liquid phase fuel LPG 4 , whereby a fuel circuit is generated here and closed at the normal pressure fuel 21 , The EP 06 023 298.0 specifies the requirements that the connection of the return line 8th to the high-pressure fuel pump 6 must fulfill in order for it to fulfill its function.

In the in the 3a , B illustrated embodiments of the fuel pressure regulator according to the invention 11 for a fuel injection system for the injection of liquid phase LPG 4 in a gasoline engine, set in a regulator housing 112 movable pressure regulating piston 111 the pressure-regulating component. The conical tip 117 of the pressure regulating piston 111 sits in a corresponding conical receptacle of the controller housing 112 and thereby seals. The sealing force is provided by a spring 113 determined on the back of the pressure regulating piston 111 suppressed. The pressure regulating piston 111 is axial with a flow bore 115 Mistake. It causes the evaporation pressure of the LPG 4 in the liquefied gas tank 1 also on the back of the pressure regulating piston 111 takes effect. The resulting pressure balance between the front and back of the pressure regulating piston 111 As a result, the force of the spring 113 not even the evaporation pressure of the LPG 4 must hold (internal evaporation pressure compensation). Through this internal pressure equalization is in the LPG tank 1 prevailing evaporating pressure compensates, so that the overpressure caused by the fuel pump 2 in the LPG tank 1 to prevent the LPG from evaporating from the evaporation pressure of the LPG 4 in the LPG tank 1 and thus independent of its current temperature.

The one from the fuel pump 2 generated overpressure has now only the function of overcompensating the increase in the evaporation pressure, which the LPG in liquid phase 4 on his way from the LPG tank 1 to the high-pressure fuel pump 11 by heat input from different sources, such as the fuel pump 2 itself, the electromagnetic shut-off valve 18 at the exit of the LPG tank 1 or the high-pressure fuel pump 6 experiences. This is necessary, as long as in the low-pressure fuel cycle 1 - 13 fuel 4 is circulated, with favorable design of the low-pressure fuel circuit 1 - 13 only a slight pressure increase compared to the fuel pressure in the LPG tank 1 ,

The situation is completely different with engine standstill after the engine has been operated. The lack of fuel circulation causes a large pressure difference between the evaporation pressure of the fuel 4 in the LPG tank 1 and, crucially for the operation of the engine, the evaporation pressure of the fuel 4 at the entrance to the high-pressure pump chamber in the high-pressure fuel pump 6 , Without the inventive method and the embodiment of the pressure regulator according to the invention, the spring force of the spring would have 113 Be sized to use the fuel pump 2 in the LPG tank 1 Forced to permanently create an overpressure that is higher than this evaporating pressure difference at engine standstill with warm engine, thus the fuel 4 also at the entrance to the high-pressure pump chamber in the high-pressure fuel pump 6 remains in the liquid phase. As a result, the fuel pump would have to 2 in the LPG tank 1 Even in the vast majority, uncritical operating conditions permanently create an unnecessarily high pressure with all the associated disadvantages.

The solution according to the invention of this problem 3a is that the compression spring 113 against a second, displaceable piston 114 (Booster piston) is stored. In the case of warm start this pressure booster piston 114 now shifted so that it is the pressure-generating spring 113 compressed by a predetermined amount and thereby generates a higher spring tension, which in turn via the pressure control piston 111 a higher fuel pressure in the low-pressure fuel circuit 120 causes.

3a shows two variants of the pressure increase by displacement of the pressure increasing piston 114 , In one variant, the displacement of the pressure increasing piston 114 by the energization of an external solenoid 119 and in the other by the at the entrance of the pressure control valve 11 branched off and on the back of the pressure booster piston 114 guided fuel pressure of the fuel low pressure circuit 120 causes. The positive feedback of the control loop increases the fuel pressure 120 in the low-pressure fuel circuit very fast. A pressure limitation prevents the pressure increase from reaching a preset value, and the delivery rate of the fuel pump 2 in the fuel tank 1 exceeds exceeding level. The duration of the pressure increase is determined by that of the control unit 16 controlled valve 19 determined by the pressurization of the pressure booster piston 114 with the fuel pressure of the low-pressure fuel circuit 120 completed. About the leakage at the pressure booster piston 114 then finds a gradual reduction of the pressure increase in the pressure regulator 11 instead, in parallel with the reduction in fuel temperature in the high-pressure fuel pump 6 runs.

The inventive solution of the problem in 3b This is the back of the pressure control piston 111 in addition to the pressure of the spring 113 to apply a defined pressure which is higher than the evaporation pressure of the LPG 4 in the LPG tank 1 ,

Claims (17)

Method for operating an internal combustion engine, which includes, among other things, a fuel tank ( 1 ), a low-pressure fuel circuit ( 1 - 13 ), an electric system and a battery for supplying the same, characterized in that prior to starting the internal combustion engine the following steps are carried out: a) detecting a signal induced by an electrical load by detecting a signal indicative of a drop in the battery applied voltage due to the activation of the electrical load is representative, b) start of a fuel circulation in the fuel low-pressure circuit ( 1 - 13 ) in response to the detected signal, which is used as a start pulse for the start of fuel circulation A method according to claim 1, characterized in that a gasoline engine is used as the fuel liquefied petroleum gas and as an internal combustion engine. A method according to claim 1 or 2, characterized in that after switching off the internal combustion engine upon reaching or exceeding a predetermined first temperature or a first, in particular between the temperature of a high-pressure fuel pump ( 6 ) and the fuel temperature in the fuel tank ( 1 ) measured temperature difference, a fuel circulation by the fuel low pressure circuit is started. A method according to claim 3, characterized in that the fuel circulation takes place until a second predetermined temperature or temperature difference is reached, which is below the first temperature. Method according to one of the preceding claims, characterized in that a in the low-pressure fuel circuit ( 1 - 13 ) on the return side provided pressure regulator ( 11 ) while the fuel circulation is bypassed when the internal combustion engine is switched off. Method according to one of the preceding claims, characterized in that at least one point in the fuel low-pressure circuit ( 1 - 13 ), preferably in a return line ( 8th ) thereof, a heat exchanger connected to a cooling device ( 13 ) of the circulated fuel ( 4 ) is flowed through. A method according to claim 6, characterized in that an on-board air conditioning system is used as a cooling device. Method according to one of claims 6 or 7, characterized in that a plurality of preferably combined in one component heat exchanger is used. Method according to one of the preceding claims, characterized in that when starting the internal combustion engine, the pressure in the low-pressure fuel circuit ( 1 - 13 ) is raised according to a system-specific predetermined fuel evaporation pressure. Method according to one of the preceding claims, characterized in that the delivery rate of the from the fuel tank ( 1 ) of subsidized fuel ( 4 ) is regulated. Method according to one of the preceding claims, characterized in that when falling below a predetermined pressure in the fuel low-pressure circuit, the fuel delivery is prevented. Internal combustion engine, which inter alia a fuel tank ( 1 ), a low-pressure fuel circuit ( 1 - 13 ), an electrical system and a battery for supplying the same, and a control unit ( 16 ) for controlling the internal combustion engine, characterized that the control unit ( 16 ) is adapted to carry out the following steps before starting the internal combustion engine: a signal induced by an electrical load by detecting a signal which is representative of a drop of the voltage applied to the battery due to the activation of the electrical load, as a start pulse for the beginning fuel circulation and fuel circulation in the low-pressure fuel circuit ( 1 - 13 ) as a lead before starting the internal combustion engine. Internal combustion engine according to claim 12, characterized in that in the fuel low-pressure circuit ( 1 - 13 ) a pressure regulator ( 11 ) is provided, which is designed, in the fuel circulation before the starting process, the fuel pressure in the fuel low-pressure circuit ( 1 - 13 ) and when starting the fuel pressure in the low-pressure fuel circuit ( 1 - 13 ). Internal combustion engine according to claim 13, characterized in that the fuel pressure regulator ( 11 ) a pressure regulating piston ( 111 ), which in addition to the pressure of a compression spring ( 113 ) can be acted upon starting with a predetermined hydraulic pressure which is greater than the evaporation pressure of the fuel ( 4 ) in the fuel tank ( 1 ). Internal combustion engine according to claim 13, characterized in that the fuel pressure regulator ( 11 ) a pressure regulating piston with internal evaporation pressure compensation ( 111 ), which is acted upon by a pressure at start, by the pressure regulating piston with internal evaporation pressure compensation ( 111 ) a spring pressure from a compression spring ( 113 ) is exercised. Internal combustion engine according to claim 15, characterized in that the fuel pressure regulator ( 11 ) a control piston ( 114 ) whose displacement the pressure of the compression spring ( 113 ) on the pressure regulating piston ( 111 ) changed. Internal combustion engine according to claim 16, characterized in that the control piston ( 114 ) at the rear of the fuel pressure regulator ( 11 ) applied fuel low pressure ( 120 ) can be applied.

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