Joel Oudart

Closed-Loop Control of SI-HCCI Mode Switch Using Fuel Injection Timing

Homogeneous charge compression ignition (HCCI) provides improved efficiency and emissions relative to current engine technologies. One of the barriers to implementing HCCI on production engines is the development of a robust control strategy to transition from traditional spark-ignition (SI) mode to HCCI mode and back. This paper presents such a strategy, based on the control of combustion phasing using fuel injection timing during the mode switch from SI to HCCI. The controller is based on a cycle-by-cycle combustion model developed in previous work. In order to obtain a state estimator for both modes, the model is linearized around operating points corresponding to the steady-states before (SI) and after (HCCI) the switch. The linearized HCCI model is used to synthesize a closed-loop controller to track a desired combustion phasing, with fuel injection timing as the controlled input. The control strategy is tested on a single-cylinder HCCI engine with direct injection. Experimental results at different operating points show that the controller is able to maintain a desirable phasing transient during the mode switch, prevent cycles with very early or late phasing and enable smooth transitions with minimal load fluctuations.Copyright

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.

Control-oriented modeling of spark assisted compression ignition using a double Wiebe function

Spark assisted compression ignition (SACI) is currently under exploration as a combustion strategy to extend the operating range of homogeneous charge compression ignition (HCCI), which provides efficiency benefits over standard spark ignition (SI) combustion. This paper presents a physics-based control-oriented approach to modeling combustion in SACI. A double-Wiebe function is developed to capture the two-stage energy release seen in SACI, where a portion of the fuel is burned through flame propagation initiated by a spark, which then initiates auto-ignition in the remaining fuel. This double-Wiebe function is incorporated into a previously developed continuous-time model of HCCI combustion, and correlations for the Wiebe function parameters are developed based on physical model states. A simpler cycle-by-cycle HCCI model is also extended with a two-step energy release description for SACI combustion. Both models accurately capture the behavior of SACI and its sensitivity to different actuators when compared to experimental data.