Control-oriented physics-based modeling of engine speed effects in HCCI

This paper presents an approach to model the effects of a varying engine speed in HCCI within a control-oriented framework. Using experimental data from a single-cylinder HCCI engine and a continuous-time simulation model, three primary physical characteristics are identified as being influenced by engine speed - chemical kinetics (time available for reactions), intake and exhaust flow dynamics, and heat transfer. Based on this, three speed-dependent parameters are introduced in a discrete-time control-oriented model developed in previous work - volumetric efficiencies for the intake and exhaust and a heat transfer factor during combustion. Model predictions in steady-state as well as during speed transients are seen to match closely with experimental data, indicating the promise of this approach in designing a cycle-by-cycle HCCI controller over a broad load-speed range.