A qualitative governing approach of a Spark Ignition (SI) engine incorporating Exhaust Gas Recirculation (EGR) was studied using AVL Boost. SI engines being quantitatively governed by controlling the quantity of charge inducted, leading to high throttling losses. To qualitatively govern the engine, charge purity was reduced by incorporating EGR, thereby reducing the amount of available oxygen in the charge inducted. The effect of charge dilution is to slow down the flame development and propagation, increasing the combustion durations. A simulation model which includes a curve fit equation to predict the combustion duration and start of combustion was created. The engine could be qualitatively governed by a maximum of 19% EGR, to reduce the brake mean effective pressure (bmep) by 20%. This led to 20% reduction in NOx and CO at full load, with 2.5% increase in brake specific fuel consumption (bsfc), also an increase in HC emissions by 50%.
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