Method and apparatus for measuring engine compression ratio

摘要

A method and apparatus for measuring compression ratio and/or clearance volume in an internal combustion engine cylinder wherein the crankshaft angle associated with piston top dead center position is obtained and cylinder pressure is measured at a number of incrementally spaced piston positions, including the TDC position. Changes in cylinder volume between the incrementally spaced piston positions are determined from nominal engine design parameters. These multiple pressure and volume figures are then employed in a programmed microprocessor to determine the constants gamma and k in the polytropic equation for relating cylinder pressure to volume PV gamma =k. Clearance volume VTDC is then determined using the constants gamma and k and the measured pressure at TDC. Compression ratio is then determined by the fraction (VDP+VTDC)/VTDC, where VDP is total piston displacement volume obtained from nominal engine design parameters.