Real time calculation of residual gas fraction utilising the polytropic coefficient of compression

Abstract

An algorithm is developed to serve as a stand-alone residual gas fraction diagnostic tool which utilises the polytropic coefficient of compression and an inverse thermodynamic algorithm to determine trapped residual gas fraction. The model requires: 1) cylinder pressure resolved with at least crank angle resolution; 2) high accuracy manifold pressure (preferably crank angle resolved and measured very near the intake port; 3) equivalence ratio of the fuel-air mixture; 4) mass estimations of cylinder contents other than residual, namely air mass, and fuel mass; 5) cylinder geometry (bore, stroke, clearance volume); 6) timing of the intake valve closing event. This work outlines the algorithm methodology and assesses its performance on both an ensemble averaged and individual cycle basis. However, the current RGF calculation methodology is shown to produce unacceptable levels of error on an individual cycle basis. Suggestions are provided for algorithm enhancement.