Load Control for an HCCI Engine

Homogeneous-Charge-Compression-Ignition (HCCI) engine operation in a vehicle drive cycle is a very dynamic process. In this paper, a controller is devised on the premise that the vehicle is operating under Drive-By-Wire so that the driver commands the engine torque output according to the perceived vehicle speed. Thus a load-following controller is appropriate. Such a controller was developed for a single cylinder engine with electromagnetic variable valve timing control (also known as Controlled-Auto-Ignition (CAI) operation). Under open-loop operation within the CAI regime, the results indicated that the engine response was bipolar in nature: (a) the engine either responded quasi-statically to the open-loop control, or (b) the CAI combustion failed. The latter happened in a load increase process in which the per-cycle increment was too high. Based on these results, a load following controller with a table-look-up feed-forward component and a feed-back component based on the cumulative difference between the targeted and measured output was developed. With the feed back feature, the engine was able to follow the commanded values of NIMEP and fuel equivalence ratio (Φ) dynamically under timing varying operating conditions.