Quantification and Reduction of IMEP Errors Resulting from Pressure Transducer Thermal Shock in an S.I. Engine 1999-01-1329

A major problem with making accurate cylinder pressure measurements using piezoelectric pressure transducers in IC engines is thermal shock. This affects most derived parameters although the greatest error is in the indicated mean effective pressure (IMEP), which can be affected by over 10%. In this paper, thermal shock has been quantified for a wide range of engine conditions. Thermal shock was found to be most significant at low engine speeds, high loads and advanced ignition timings. A good correlation between thermal shock and peak pressure has been established for Kistler 6123 and 6125 transducers when dealing with cycle averaged data. This resulted in the development of a numerical thermal shock correction routine which was used for all subsequent data processing. Use of this improved analysis software demonstrated that the error in the calculated IMEP was significantly improved for the Ford Zetec engine tested. The range of Kistler 6123 IMEP errors were reduced from between -7% and -20% to between -1.5% and +1.4% after correction. Equivalent values for a Kistler 6125A transducer were -4.9% to -2.1% uncorrected down to between -0.4% and +0.8%.