Internal-combustion engines – Starting device – Auxiliary fuel supply device
Patent
1996-12-20
1998-07-07
Solis, Erick R.
Internal-combustion engines
Starting device
Auxiliary fuel supply device
123576, 123578, F02N 1700
Patent
active
057752818
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
This invention relates to fuel injection systems for internal combustion engines and methods of operation of such systems.
BACKGROUND OF THE INVENTION
Liquid fuels which can be injected using fuel injection are petrol, LNG and LPG. This present invention will be discussed mainly in relation to LPG but can be also applicable to petrol and low boiling point or high vapour pressure fuels. The invention is applicable to internal combustion engines operating with a single fuel or to such engines operating with dual fuels.
Fuel injection systems for internal combustion engines can be adapted to supply liquid fuels to the inlet manifold for each cylinder of an internal combustion engine. This system is known as multi-point liquid fuel injection. By suitable control of the operation of the injectors accurate amounts of liquid fuel can be supplied to each cylinder depending upon engine conditions and demand characteristics.
There is a problem, however, in that for liquid fuel injection to be accurate the fuel in the injectors adjacent the injection point must be liquid at all times.
The environment around each cylinder, however, can at times during engine operation be very hot and such a temperature in this region is not conducive to injection of a liquid fuel which has a low boiling point.
LPG (propane and butane) is in equilibrium pressure state with both gas and liquid being present inside a fuel tank of a vehicle because of its properties, that is its boiling point is usually lower than the ambient temperature (when the temperature is above zero). Considering these properties of LPG, the liquid will vaporise when the surrounding temperature is higher than the liquid temperature.
In a practical situation, such as liquid LPG flowing to a fuel rail and injectors of a fuel injection system, in under-bonnet typical temperatures, it will remain in a liquid state where there is a sufficient recirculation rate only. While the vehicle is running care is taken to ensure that there is sufficient circulation flow rate, minimum number of restrictions and some pressure elevation above that of the equilibrium pressure to maintain the liquid state. When the vehicle has been running and is stopped and the engine is not running, however, the LPG liquid in the fuel rails and injectors immediately starts to vaporise due to the high under-bonnet temperatures relative to the liquid temperature. This process will tend to raise the pressure in the fuel rail but the general design of fuel rails is to prevent build up of an overpressure by a relief valve. A mixture of liquid and vapour therefore flows into the LPG tank via a return line. It will be seen therefore that from the instant that recirculation stops the liquid in the fuel rail is replaced by dry gas and the temperature in the fuel rail injectors and valves start to rise steadily because of the heat transfer from the various components and the under-bonnet conditions. The rise in temperature and heating is a function of time and the surrounding temperature. The surrounding temperature is also a function of previous engine loads, engine speeds and running time.
These conditions may be referred to as heat soak conditions.
Starting the fuel pump after a heat soak condition will draw liquid LPG from the bottom of the fuel tank and the liquid is transferred into the fuel rail, injectors and valves. As the liquid fills the fuel rail it starts to vaporise until the surface temperature drops to that of the liquid temperature with a gradient distribution due to flow. The time taken for the fuel rail assembly to equalise in temperature to that of the liquid is dependant on the temperature of the LPG in the tank, fuel rail and injector design, surface to volume ratio of the metal parts and the absolute temperature of the fuel rail assembly.
It is an object of this invention, therefore, for efficient operation of a fuel injected engine operating with low boiling point fuels, to be able to determine by an easy method when such heat soak conditions occur so that suitab
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Solis Erick R.
The Energy Research and Development Corporation
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