Effect of Thermal Strain on Measurement of Cylinder Pressure

Cyclical exposure of a piezoelectric transducer to high temperature gas results in an error in the measured pressure due to thermal strain of the transducer diaphragm. Thermal strain results in a decrease in the measured values of IMEP and PMEP, while burn times calculated using the method of Rassweiler and Withrow are relatively unaffected. The severity of the effect can be minimized by coating the transducer diaphragm with RTV. When the effects of thermal strain persist into the intake stroke, a method of detection at low speed is to overlay and compare the firing and motoring intake stroke pressure traces.