Selecting Compression Ratio for Optimum Fuel Economy with Emission Constraints

An experimental program is described for selecting engine compression ratio to optimize vehicle fuel economy, with imposed emission constraints. A method was developed to relate quantitatively the results of single cylinder engine experiments to vehicle emission test results. Engine and vehicle experiments were conducted to validate the method. This study concludes that compression ratio optimization is determined primarily by hydrocarbon emission restrictions. Projections for a 1975 400 CID engine in a 5000 lb vehicle demonstrate that the traditional relationship between fuel economy and compression ratio is reversed below CVS-CH HC levels in the range of 1.0 - 1.5 gm/mile.