Estimation of Air-Fuel Ratio and Cylinder Wall Temperature from Pressure Cycle in s.i. Automotive Engines

Two techniques for the estimation of both Air-Fuel (A/F) ratio and cylinder wall temperature (Tw), based on the measurement of in-cylinder pressure cycle, are presented. For the Air-Fuel ratio the results obtained by the approach originally proposed by Gassenfeit, Powell and Patrick for the evaluation of in-cylinder A/F ratio by using measured pressure cycle statistical moments are discussed. The detection of chamber wall temperature is based on the identification of the inversion point for the net heat flux between cylinder wall and gas mixture during compression stroke (i.e. local adiabaticity condition). In such conditions, the mean wall temperature can be assumed equal to the mean gas mixture temperature which in turn is computed from thermodynamic relationships. Both techniques have been applied on a wide range of experimental data during steady-state operating conditions and for some transient engine manoeuvres with satisfactory level of precision.