Charge Stratification in a Spark Ignition Engine

Abstract

The effect of charge stratification on lean mixture combustion in a Ricardo E6 single-cylinder four-stroke reciprocating engine has been investigated. To do this, a commercially available spark plug was modified so that small amounts of pure methane gas could be injected, via the spark electrode, into a lean mixture within the combustion chamber prior to ignition. The effect on engine performance of variations in the methane injection process were analysed. The research has led to the following conclusions: 1. The lean limit of a homogeneous air-fuel mixture is extended by this relatively simple charge stratification process. 2. The effectiveness of charge stratification is most noticeable at lean air-fuel ratios in terms of improved brake specific fuel consumption. 3. Unburnt hydrocarbon emission levels are higher with the stratified charge process when compared to normal homogeneous mixture operation. 4. Carbon monoxide levels with stratified charge combustion are almost the same or a little lower than normal operation at the leanest air-fuel ratios.

Combustion characteristics of natural-gas direct-injection combustion under various fuel injection timings

“…Recently, a direct-injection gasoline engine has entered into production for both automobile engines and two-stroke marine use. The charge strati cation in the combustion chamber permits extremely lean combustion that increases the thermal e ciency but gives the penalty of high NO x and even particulate emissions [5][6][7][8][9]. Therefore much work still needs to be carried out to address this emission problem.…”