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The object of this study is to investigate a principle of obtaining stratified charge in spark ignition engine. The stratification is obtaining in a large prechamber which comprises 50% of the compression volume and which is connected to the main combustion chamber through a relatively large flow transfer passage. The fuel is injected (at any load) into the transfer flow passage, during the compression stroke and the air-fuel mixture is carried toward the spark plug. The control of mixture stratification and emissions can be achieved by the injection timing variation. The values of the specific fuel consumption and specific NOX emission are of the same level comparing to the values obtained for a Diesel engine with divided combustion chamber. While combustion stability at very lean operation is guaranteed intake air throttling in the part load range is necessary to keep combustion temperature high enough for effective oxidation of CO and HC.

This paper describes a method to obtain a triple stratification - uncooled EGR / air / air-fuel mixture - in a large prechamber spark ignition engine and the influence on the emission level at unthrottled light load. At this load, the critical problem is the HC emissions. The goal of the obtaining uncooled stratified EGR is the reduction of HC emissions at unthrottled light load. In the first part of the intake stroke, the exhaust gases are drawn into the cylinder and, in the second part of this stroke, the air. The prechamber comprises 50% of the compression volume and is the place where the stratification air / air-fuel mixture is obtained. The fuel is injected on a hot pin situated in the transfer flow passage (between prechamber and main combustion chamber) during the compression stroke and the air-fuel mixture is carried toward the spark plug. At high EGR levels, a certain quantity of recycled exhaust gas can get into the pre-chamber.