Steady-state multiplicity and stability of thermal equilibria in homogeneous charge compression ignition (HCCI) engines

The stability of the autothermic process governing the autoignition of HCCI engines is analyzed in this paper. We find conditions under which steady-state multiplicity exists with stable, unstable, and limit-cycle equilibria. This analysis is conducted taking into account the internal feedback structure of the thermal autoignition dynamics. Specifically, HCCI autoignition timing determines the combustion heat produced and is determined by the heat provided through high internal exhaust gas recirculation from previous combustion cycle. It is shown that the thermal equilibria are characterized by a simple returning map consisting of two curves, namely the breathing temperature curve and the combustion temperature curve. The returning map and the stability analysis of the multiple steady state equilibria is confirmed with a high order dynamic nonlinear model that includes manifold filling and composition dynamics.