METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE HAVING SPARK IGNITION

1 . A method for operating an internal combustion engine having a spark ignition unit, comprising:

mixing a liquid fuel with air using injection in a combustion cylinder and combusting the liquid fuel that is mixed with the air while discharging mechanical power after an ignition by the spark ignition unit;

combusting a liquefied gas as the liquid fuel;

at least partially injecting the liquefied gas using a direct injection nozzle into the combustion cylinder before the ignition by the spark ignition unit; and

cooling the liquefied gas in a line with a cooling unit.

2 . The method according to claim 1 , wherein the line is a return line.

3 . The method according to claim 1 , wherein the line is a supply line.

4 . The method according to claim 3 ,

wherein the supply line for the liquefied gas to the direct injection nozzle that protrudes into a combustion chamber of a cylinder head, and

wherein the method further comprises:

direct injecting of a liquefied gas quantity under high pressure into the combustion cylinder during an intake phase in the combustion chamber of the cylinder head;

compressing a cylinder volume that is charged with a liquid gas-air mixture in the combustion cylinder using a reciprocating piston in a direction toward the combustion chamber of the cylinder head;

igniting the liquid gas-air mixture that is under high pressure using an ignition spark in the combustion chamber close to an apex of the reciprocating piston; and

combusting an at least partially injected liquefied gas quantity while discharging mechanical power to a crankshaft via a connecting rod; and

cooling the liquefied gas in the supply line that is under high pressure.

5 . The method according to claim 3 , further comprising supplying the liquefied gas from a pressurized liquid gas container using a high-pressure pump via the supply line to the direct injection nozzle.

6 . The method according to claim 1 , further comprising combusting a fuel mass proportion of greater than approximately 50% in a scale of approximately 0% to approximately 100% during the combusting and converting into mechanical power using a direct injection of the liquefied gas.

7 . The method according to claim 1 , further comprising cooling the liquefied gas by atomizing and vaporizing.

8 . The method according to claim 4 , further comprising reducing a flashpoint of the liquefied gas by a direct injection of the liquefied gas into the combustion chamber of the cylinder head after a compression phase.

9 . The method according to claim 8 , further comprising increasing an oxygen uptake in the combustion cylinder caused by a cooling effect during the direct injection of the liquefied gas into the combustion cylinder during the compression phase of a second stroke of a four-stroke internal combustion engine.

10 . The method according to claim 8 , further comprising performing multiple direct injections of the liquefied gas successively in a power phase during a third stroke of a four-stroke internal combustion engine after the ignition of a lean liquid gas-air mixture having charge stratification in the combustion chamber.

11 . The method according to claim 3 , further comprising cooling the supply line with the cooling unit after heating by a compression process in a high-pressure pump so the liquefied gas is supplied in a noncritical liquefied aggregate state to the direct injection nozzle.

12 . The method according to claim 2 , further comprising:

cooling excess fuel in the return line with the cooling unit; and

cooling in a supply line with the cooling unit.

13 . An internal combustion engine, comprising:

a direct injection unit of a liquefied gas having a direct injection nozzle in a cylinder head,

an injection valve configured to connect the direct injection unit to a fuel supply line; and

a cooling unit connected to a return line that is connected to the injection valve to cool the liquefied gas in a noncritical liquid state.

14 . The internal combustion engine according to claim 13 , further comprising a liquid gas container that is configured for pressurization and configured to contain the liquefied gas that is connected via a supply line to the direct injection nozzle.

15 . The internal combustion engine according to claim 14 , further comprising a high-pressure pump configured to compress the liquefied gas before the supplying in the supply line.

16 . A computer readable medium embodying a computer program product, said computer program product comprising:

a program for operating an internal combustion engine having a spark ignition unit the program configured to:

mix a liquid fuel with air using injection in a combustion cylinder;

combust the liquid fuel that is mixed with the air while discharging mechanical power after an ignition by the spark ignition unit;

combust a liquefied gas as the liquid fuel; and

at least partially inject the liquefied gas using a direct injection nozzle into the combustion cylinder before the ignition by the spark ignition unit; and

cool the liquefied gas in a line with a cooling unit.

17 . The computer readable medium embodying the computer program product according to claim 16 , wherein the line is a return line.

18 . The computer readable medium embodying the computer program product according to claim 16 , wherein the line is a supply line.

19 . The computer readable medium embodying the computer program product according to claim 18 ,

wherein the supply line for the liquefied gas to the direct injection nozzle that protrudes into a combustion chamber of a cylinder head, and

wherein the program is further configured to:

direct inject a liquefied gas quantity under high pressure into the combustion cylinder during an intake phase of a reciprocating piston or a compression phase in the combustion chamber of the cylinder head;

compress a cylinder volume that is charged with a liquid gas-air mixture in the combustion cylinder using the reciprocating piston in a direction toward the combustion chamber of the cylinder head;

ignite the liquid gas-air mixture that is under high pressure using an ignition spark in the combustion chamber close to an apex of the reciprocating piston; and

combust an at least partially injected liquefied gas quantity while discharging mechanical power to a crankshaft via a connecting rod; and

cool the liquefied gas in the supply line that is under high pressure.

20 . The computer readable medium embodying the computer program product according to claim 18 , the program further configured to supply the liquefied gas from a pressurized liquid gas container using a high-pressure pump via the supply line to the direct injection nozzle.