Wavelet Filtering of Cylinder Pressure Signal for Improved Polytropic Exponents, Reduced Variation in Heat Release Calculations and Improved Prediction of Motoring Pressure & Temperature

Recent advancements in the combustion control of new generation engines can benefit from real time, precise sensing of the cylinder pressure profile to facilitate successful combustion feedback. Currently, even laboratory-grade pressure sensors can deliver pressure traces with insufficient signal-to-noise quality due to electrical or combustion-induced signal interference. Consequently, for example, calculation of compression and expansion polytropic indices may require statistical averaging over several cycles to deliver required information. This lag in the resultant feedback may become a concern when the calculated combustion metric is used for feedback control, especially in the case of transients. The method described in this paper involves a special digital filter offering excellent performance which facilitates reduced-error calculation of individual polytropic indices. This enables precise calculation of individual combustion event heat release estimates, delivering information needed to effect the necessary correction in combustion-defining input parameters (e.g. intake pressure, injection timing, etc.), as calculated by the engine controller for use on subsequent combustion cycles. The pressure filter construction is based on pattern recognition techniques and guarantees equal performance regardless of engine rotational speed. The signal processing technique requires only invariant numbers of samples per combustion cycle to deliver excellent results in the angular span covering -180 thru +90 degrees with TDC firing being located at zero degrees. The performance of the technique is illustrated with experimental results involving calibration and testing of a Gasoline Direct Injection Compression Ignition (GDCI) engine.