Effects of Prompt EGR on Warm-Up and Steady State Fuel Consumption and Emissions

The effects of prompt exhaust gas recirculation (EGR) on warm-up and steady state fuel consumption and emissions were evaluated in experiments using a single cylinder engine. Prompt EGR was achieved using a modified camshaft which re-opened the exhaust valve late in the inlet stroke. During steady state operation, the prompt EGR system lowered specific fuel consumption and specific NOx emissions. Unburnt hydrocarbon emissions were improved under some operating conditions, but became worse than those of the standard system at low loads. In warm-up tests from -10°C, prompt EGR provided a large reduction in hydrocarbon emissions and also improved CO emissions and specific fuel consumption. Combustion fluctuations were worse in some cases where a sudden reduction in warm-up enrichment took place. Charge dilution through the prompt recirculation of hot exhaust products was found to give combustion and emissions behaviour that differed markedly from the behaviour reported in the literature for external EGR.