ESTIMATING IN-CYLINDER PRECOMBUSTION MIXTURE TEMPERATURES USING ACOUSTIC RESONANCES

The air-fuel ratio of automotive engines during the warm-up period is difficult to control and contributes a substantial portion of the emis sions on the EPA test cycle. High bandwidth estimation of the in-cylin der charge temperature provides opportunities for improvement in spark ignition (SI) engine control algorithms. Pressure sensor based algori thms for estimating air-fuel ratio (AFR) have been shown to be improve d by bulk temperature information. This paper explores the suitability of using acoustic resonances to estimate charge temperature in the pr esence of an unknown AFR and without the 'sharp' excitation of diesel or knocking SI combustion. A technique that allows for the estimation of the precombustion average bulk charge temperature during a 1-2 ms i nterval based on acoustic resonance data gathered from a pressure tran sducer is described. A parameter estimation algorithm suitable for ext racting the required frequency information from short data sets is ide ntified. The variation in temperature estimates as a function of AFR h as been explored using a computer simulation that accounts for the cha nge in the ratio of specific heats with changing mixture strength. The performance of the acoustic resonance based temperature estimates has been evaluated by comparing them to predictions based on a polytropic compression.