This paper describes the development of a prechamber-type torch ignition system on a modified 4-cyl, 140 in3 engine. The prechamber consists of a blind cavity coupled to the main chamber with an orifice. Fuel is supplied to the prechamber with an electronic fuel injector and this mixture is ignited by a spark plug. The prechamber produces an ignition torch which ignites a main chamber that is supplied with a lean mixture carbureted in the conventional manner. The performance of this combustion concept was evaluated on the basis of vehicle drivability, exhaust emissions, and fuel economy in a 3000 lb weight class vehicle.
In addition to adjustable engine variables, such as air fuel ratio and spark advance, electronic fuel injection and mechanical parameters were varied to improve combustion of lean mixtures. As examples, the carbureted main chamber air fuel ratio was explored from 18-26:1, the prechamber fuel injection rate was varied by modulating injector pulse width and fuel injection timing was evaluated during the exhaust, intake and compression strokes.
The electronic fuel injection torch ignition concept produces an ignition source which penetrates and inflames the lean mixture in the main chamber and increases the rates of combustion substantially. Typical road load spark advances are about 12 deg (MBT) before top center, compared to 40 deg for a stock engine. This combustion process reduces carbon monoxide and oxides of nitrogen emissions, in comparison to a conventional combustion chamber. The reduction in carbon monoxide is attributed to improved cold starting with less carburetor choking, and the burning of lean mixtures in the main chamber. The reduction in oxides of nitrogen is attributed to the lower combustion temperatures of the lean mixtures.