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Improving Fuel Consumption of Stoichiometric Spark Ignition Engines By the Use of High Egr Rates and High Compression Ratio
Published June 24, 1996 by Institution of Mechanical Engineers in United Kingdom
Event: International Seminar on Application of Powertrain and Fuel Technologies to Meet Emissions Standards
This paper describes an experimental study aiming to assess the potential for fuel economy of stoichiometric high compression ratio engines in presence of Exhaust Gas Recirculation (EGR).
Previous experiences have shown that EGR can limit the knock tendency of stoichiometric mixtures even with high compression ratio engines running at full load. The experiments, carried out on a commercial four-cylinder stoichiometric spark-ignition engine have confirmed the trends obtained on single cylinder engines.
At medium and high loads, efficiency improvements higher than 10% have been obtained with a compression ratio equal to 11.5. Similar improvements have been obtained for CO emissions while (HC + NOx) reductions are ranged between 20% and 30%.
At low loads, cycle-by-cycle variation limits the effectiveness of EGR. Probably, for these conditions, high swirl or high tumble are required to take full advantage by the present strategy of combustion control of stoichiometric spark ignition engines.