Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Patent
1993-11-29
1994-10-25
Argenbright, Tony M.
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
123527, F02D 1108, F02D 4114
Patent
active
053579380
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to the control of the fuel supply to internal combustion engines fuelled by gaseous fuels such as liquefied petroleum gas (LPG) or compressed natural gas (CNG) or methane or hydrogen. Liquefied petroleum gas, (LPG) is a mixture of butane and propane and is a well accepted high octane, lead free fuel for internal combustion engines. Several million engines worldwide are powered by a variety of gaseous fuels for use in cars, vans, and fork lift trucks.
The equipment used to supply the fuel/air mixture to such engines is substantially the same for all engines. Compressed or liquefied gas from the fuel storage tank is fed to a device known as a pressure regulator or a vaporizer. This device reduces the pressure of the gaseous fuel in one or more initial stages from tank pressure to, generally, slightly less than atmospheric. In all cases, this results in a severe temperature drop. In the case of LPG, the fuel is stored in the tank in its liquid phase and the pressure reduction in the vaporizer causes it to boil to its gaseous phase. The latent heat of evaporation is supplied by heat from the cooling system of the engine via a heat exchanger integral with the vaporizer. In the case of compressed gaseous fuels, a similar cooling of the compressed gas on expansion is countered by an entirely analogous heat exchanger integral with the pressure regulator. The gaseous fuel, still at fuel tank pressure, is further reduced in pressure using a final stage pressure reducing valve. This final stage valve includes a diaphragm-responsive valve element the diaphragm of which is responsive to atmospheric pressure. In this way it can be ensured that the fuel exit pressure is always slightly less than atmospheric.
Gas from the pressure regulator or vaporiser is then fed to a device which mixes it with the charge air to the engine. There are two devices available for mixing the gas with the charge air. One, widely used on cars, is a venturi device placed either in the air filter or in a flexible pipe connecting the air filter to the carburettor. Alternatively, the venturi device can be attached to the top of the carburettor on the intake side. In each case, engine charge air passing through the venturi creates a depression which is a function of the air flow. The venturi is so constructed that there is an annular passage round it which on the one side is connected to the throat of the venturi via a multitude of small holes and on the other side is connected to the gas supply from the pressure regulator or vaporiser using a flexible rubber or braided metallic pipe. The amount of gaseous fuel induced into the engine is a function of the depression and thus of the charge air flow rate. By careful design and subsequent testing, a gas fuel/air ratio which approximates to stoichiometric is achieved. This method is widely used where a gas powered engine is designed to revert to being powered by petrol when needed.
The other device, widely used for dedicated systems in which the engine is fuelled only by gas and cannot revert to petrol operation, is a gas carburettor. Conventional gas carburettors incorporate diaphragm valve elements the diaphragms of which are responsive to atmospheric pressure.
In both cases, it will be appreciated that the gas flow to the mixing device, and thus the actual gas/air ratio to the engine, is a function of the supply gas pressure from the regulator. The reason for maintaining the supply gas pressure slightly less than atmospheric is that in the event of the connecting pipe falling off, there is not a full bore gas leak into the engine compartment.
Operating desiderata for internal combustion engines include the control of exhaust emissions and the ability to operate vehicles with low fuel consumption. To achieve compliance with current and future exhaust emission legislation, engine manufacturers have been forced to use exhaust gas catalytic purifiers. These contain rare earth components which cause undesirable components of the exhaust gas such as carbon monoxide, unbu
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Bedford Timothy J.
Kirkland John W.
Argenbright Tony M.
Blenko, Jr. Walter J.
Green Power International Limited
Stacey George K.
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