Examination of Charge Dilution with EGR to Reduce NOx Emissions from a Natural Gas-Fuelled 16 Valve DOHC Four-Cylinder Engine

Charge dilution is commonly used to reduce emissions of nitrogen oxides (NO_x) from internal combustion engine exhaust gas. The question of whether to use air or exhaust gas recirculation (EGR) as a charge diluent for the natural gas-fuelled test engine is addressed first. The decision to use EGR is based on the potentially lower NO_x and unburned hydrocarbon emissions that could be achieved if a three-way catalyst were applied to the engine. The effect of EGR on the spark advance for maximum brake torque (MBT), NO_x, and unburned hydrocarbon emissions is then examined in detail. The effect on fuel efficiency is discussed briefly.