Internal-combustion engines – Charge forming device – Heating of combustible mixture
Reexamination Certificate
1999-06-03
2001-01-23
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Charge forming device
Heating of combustible mixture
C123S514000
Reexamination Certificate
active
06176225
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an injection system for an internal combustion engine operating on self-igniting liquefied petroleum gas and including at least one injector per cylinder for direct fuel injection into the combustion chamber, with a fuel tank in which fuel is held at a freed pressure, and a high-pressure fuel pump delivering fuel to the injector, and a shutdown device enabling connection of pressurized parts of the injection system to the fuel tank by way of at least one pressure relief line.
DESCRIPTION OF THE PRIOR ART
Conventional injection systems are designed for injecting either self-igniting of extraneously ignited liquid fuels. Under conditions of ambient pressure and ambient temperature such fuels are supplied in liquid form; as a consequence the storage tank is unpressurized. Usually the liquid fuel is simultaneously employed as a lubricant for movable parts of the injection system. For this reason provisions are made for leakages and oil leakage pipes leading back to the tank.
In DE 35 23 855 A1 a method is described for operation of an internal combustion engine using a cracked gas obtained from methanol and air. Methanol is usually stored in depressurized condition in conventional storage tanks. The cracked gas, which is also known as synthesis gas and consists of hydrogen and carbon monoxide, is produced in a gas producer at the pressure required for injection, which is in the range at 80 to 100 bar. The cracked gas is ignited either by a spark or another ignitable fuel, such as diesel. Cracked gas is not a self-igniting, liquefied petroleum gas. It is not directly injected into the combustion chamber of the engine but blown in indirectly at high pressure. Such an injection system cannot be used for direct injection of a self-igniting, liquefied petroleum gas in an internal combustion engine operating on liquefied petroleum gas.
Another known type of fuel used in this context is a liquefied petroleum gas stored under pressure. Russian Abstract SU 1040-206-A (Soviet Inventions Illustrated, Q53, 1988) describes a gas-operated internal combustion engine with a fuel tank for liquefied petroleum gas, i.e., butane, which is pressurized by means of another compressed gas, i.e., methane. Conventional liquefied petroleum gases such as propane or butane are fuels whose ignition is effected by outside means and which are introduced into the combustion chamber as gases premixed with air (fuel for use with SI engines).
Newly developed liquefied gas fuels with high cetane number, such as dimethyl ether, have a vapor pressure or less than 30 bar at ambient temperature and can be used as self-igniting fuels. If such liquefied gases are used in conventional diesel injection systems, the danger of cavitation will rise on account of the high vapor pressure of such fuels, in particular in regions of local pressure drop, which will lead to fuel delivery problems and increased wear.
Since self-igniting, liquefied petroleum gas fuels evaporate under normal ambient conditions and since they can form an ignitable or explosive mixture together with air, the fuel must be prevented from leaking out into the environment under all circumstances. This is rendered difficult by the high permanent pressure that must be maintained in the system to keep the fuel in its liquid state. Especially after engine shutdown the internal pressure prevailing in the injection system represents a certain safety risk in the instances of leakages, no matter how small they are.
In DE 196 11 434 A1 an injection system of the above type is presented, in which at least one pressurized part of the injection system can be depressurized by means of a shutdown device. The shutdown device includes a collecting tank into which pressure relief lines are guided from the pressurized parts. The collecting tank is connected to the fuel tank by means of a valve and a pumping device. After the engine has been turned off the first valve positioned between the low-pressure storage tank and the fuel pump is shut and the second valve positioned between the pressurized parts and the collecting tank is opened. As a consequence the liquid fuel remaining in the system is drained into the collecting tank and gasified at low pressure. The pumping device compresses the gas and forces it back into the low-pressure storage tank, thus liquefying it again. Because of the additional collecting tank this known shutdown device requires some constructional efforts.
A similar injection system is also described in AT 001 924 U2, which includes a purge tank, i.e., an unpressurized reservoir into which the fuel from hugh-pressure parts of the injection system is drained after the engine has been turned off. By means of a low-pressure pump and a check valve the fuel is returned into the fuel tank once more. As regards construction volume and control this system again is fairly complex.
SUMMARY OF THE INVENTION
It is an object of the invention to avoid previous disadvantages and to further develop an injection system for self-igniting liquid furls as described above, which will ensure high safety in a simple manner.
According to the invention this object is achieved by providing at least one heating device, which will convert the liquefied petroleum gas, at least partially, into a gaseous phase, at least in section of pressurized parts of the injection system. It is provided in this context that a flow connection be established between at least one pressurized part of the injection system and the fuel tank after the fuel pump is turned off, and that in the pressurized part the liquefied petroleum gas be converted, at least partially, into a gaseous phase by heating it, at least in sections, such that a gas bubble will form, which will push the remaining liquefied gas from the pressurized part into the fuel tank, and that preferably the flow connection between the pressurized parts and the fuel tank be interrupted and, in particular, pressurized parts of the injection system be cooled.
Upon engine shutdown the liquid fuel is returned from the injection system into the fuel tank in which the fuel is kept in the boiling state. As the fuel in the tank is kept boiling the pressure equalization will not suffice to remove the entire amount of liquid fuel from the injection system. Due to the proposed heating of pressurized parts the fuel will partly evaporate such that at least one gas bubble will form, which is retained in the closed system. The injection system should be designed such that the gas bubble will form at a point which is furthest remote from the return line into the fuel tank. Since the gas cannot escape the pressure in the system is increased and the pressure rise is employed to force out the liquid fuel from the pressurized parts into the fuel tank.
It is provided in a preferred variant of the invention that the heating device be used to carry waste heat from the internal combustion engine to pressurized parts of the injection system. The heating of pressurized parts of the injection system may be effected by selectively improving the heat transfer between the engine casing, for example, the cylinder block of the engine and certain parts of the injection system. Such efforts may include the use of heat bridges between the engine block and pressurized parts.
In another preferred variant of the invention the proposal is put forward that the heating device be connected to the cooling system of the internal combustion engine. If the engine is at operating temperature it will produce sufficient waste heat for the fuel to form a gaseous phase in high-pressure parts of the system, thus forcing the fuel into the fuel tank.
In further development of the invention it is preferred that the heating device be configured as external heating, preferably an electrical heater. This will permit safety requirements to be fulfilled and pressurized parts of the injection system to be drained even if the engine is shut down in the cold state and at low ambient temperature.
It has proved an advantage if heat from the heating devic
Ofner Herwig
Sams Theodor
AVL List GmbH
Dykema Gossett PLLC
McMahon Marguerite
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