Internal-combustion engines – Combustion chamber means combined with air-fuel mixture... – Having a single combustible mixture inlet combined with...
Patent
1987-04-15
1989-04-04
Argenbright, Tony M.
Internal-combustion engines
Combustion chamber means combined with air-fuel mixture...
Having a single combustible mixture inlet combined with...
123 27GE, 123525, F02D 1910
Patent
active
048175684
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION OF INVENTION
This invention relates to a dual fuel compression ignition engine. In this specification the term "compression ignition engine" is intended to refer, not only to an engine operating on a constant pressure, i.e. diesel cycle, but also an engine operating on a compression ignition cycle. In such an engine, during dual fuel operation, a gaseous fuel is mixed with air and the mixture is inducted into the engine. The temperature and pressure prevailing at the end of the compression stroke, whilst they would be sufficient to ignite diesel oil, are insufficient to ignite the gas/air mixture. Accordingly, to achieve ignition, a small amount of diesel oil is injected into the engine using a conventional injection pump and injector system. This small amount of diesel oil, hereinafter referred to as pilot fuel, ignites and consequently ignites the gas/air mixture so that combustion thereof takes place.
It is desirable to inject the minimum amount of pilot fuel in order to minimise the proportion of diesel fuel used since diesel fuel is more expensive than gas.
Practical experience shows that a suitable ratio at full throttle operation for a typical automotive diesel which it is desired to convert to operate on gas is around 10% diesel oil and 90% gas in terms of the energy provided by the respective fuels.
The injection of the required amount of pilot fuel is achieved by positioning a control member, conventionally referred to as the rack, in an injection pump of the type which pumps discrete volumes or "slugs" of fuel to the injector system, to the position appropriate for the amount of fuel. It has been found that if the control member is maintained in a fixed position to give the desired amount of pilot fuel at full throttle operation, the amount of pilot fuel injected per stroke of the engine increases significantly, and sometimes very substantially, with engine speed.
An object of the invention is, therefore, to provide a dual fuel compression ignition engine wherein the above mentioned problem is overcome or is reduced and, more generally, more accurately to control the amount of pilot diesel fuel injected.
According to one aspect of the present invention we provide a dual fuel compression ignition engine comprising a gas fuel supply system for the engine, a diesel fuel supply system for the engine, including an injection pump having a governor and a control means to control the amount of diesel fuel injected into the engine by the pump, and means to arrest movement of a control member, in the direction to increase the supply of diesel fuel to the engine, at a position to supply pilot fuel at a constant, or substantially constant rate, said position being determined in accordance with at least one operating condition of the engine.
The position of the injection pump control member can thus be determined, for example from rig testing, to be in its optimum position to give good ignition with the minimum amount of pilot fuel.
Said at least one operating condition of the engine may comprise the engine speed.
The position at which movement of the control member of the pump is arrested can be determined, not only on the basis of engine speed, but also by other operating conditions such as the position of the speed control (i.e. throttle) of the engine, alone or in combination with the engine speed.
If desired a feed-back signal may be used in determining the position at which movement of the control member is arrested.
The feed-back signal may be indicative of the amount of pilot fuel injected into the engine.
The feed-back signal may be dependent upon the temperature of the pilot fuel, or the actual power developed by the engine.
If desired other means may be provided to generate a feed-back signal, which signal may be used to check that the amount of pilot diesel fuel actually being injected into the engine corresponds with that required for the position of the control member in accordance with the operating condition.
According to another aspect of the present invention we provide a dual
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Argenbright Tony M.
Gaspower International Limited
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