Measuring Absolute-Cylinder Pressure and Pressure Drop Across Intake Valves of Firing Engines

This paper describes a technique which can accurately measure firing-cylinder full-load absolute pressure during critical intake events, thereby providing useful cylinder-pressure data for valve-timing optimization. To achieve this, an absolute-pressure transducer is connected to a port drilled through the cylinder wall at an axial location uncovered approximately midway through the piston stroke. This placement spares the transducer from thermal shock caused by flame-front impingement upon the diaphragm, since the combustion is normally completed by the crank angle of passage exposure.

The described technique was used to study valve-timing and manifold-runner design effects on the intake process of a V-8 engine and to determine thermal-shock magnitudes and their effect on conventionally-measured pumping-loop data. The results indicate the technique could be a valuable intake-system development tool and also revealed large thermal-shock errors which destroyed conventionally-measured pumping-loop accuracy.