The Effects of Combustion Chamber Design and Compression Ratio on Emissions, Fuel Economy and Octain Number Requirement

Four combustion chamber designs and three compression ratios (8:1, 9:1, and 10:1) were investigated for their emission, fuel economy, and octane number requirement characteristics using a 1.6 L (96.9 CID) 4-cyl engine. Time resolved measurement of hydrocarbon emissions was carried out to clarify the reason for differences in tail pipe emission between these combustion chambers. The “High Turbulence Type” combustion chambers, which included swirl (piston swirl) and/or squish, indicated better fuel economy under emission and octane number requirement constraints. The HC emission of the combustion chamber with squish and swirl was lower than that of the combustion chambers with squish alone. The time resolved measurement of HC emissions explained the difference in the exhaust process of these unburned hydrocarbons. A compression ratio of 9:1 was the best compromise for optimum fuel economy with this high turbulence combustion chamber, under the target constraints for HC and NO_x emissions assumed for these tests.