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The effects of Variable Valve Timing (VVT) on Homogeneous Charge Compression Ignition (HCCI) engine energy distribution and waste heat recovery are investigated using a fully flexible Electromagnetic Variable Valve Timing (EVVT) system. The experiment is carried out in a single cylinder, 657 cc, port fuel injection engine fueled with n-heptane. Exergy analysis is performed to understand the relative contribution of different loss mechanisms in HCCI engines and how VVT changes these contributions. It is found that HCCI engine brake thermal efficiency, the Combined Heat and Power (CHP) power to heat ratio, the first and the second law efficiencies are improved with proper valve timing. Further analysis is performed by applying the first and second law of thermodynamics to compare HCCI energy and exergy distribution to Spark Ignition (SI) combustion using Primary Reference Fuel (PRF). HCCI demonstrates higher fuel efficiency and power to heat and energy loss ratios compared to SI.

A Model Predictive Control (MPC) strategy for Homogeneous Charge Compression Ignition (HCCI) combustion timing and output work control that takes into account actuator constraints is designed. The MPC is based on the linearized version of a nonlinear Control Oriented Model (COM). The COM for the HCCI engine has combustion timing and engine load as outputs and valve timing and fueling rate as the inputs. The COM model is developed and validated and found to be accurate enough for control purposes and can be implemented in real-time. A Detailed Physical Model (DPM) is used to test the controller using the valve timing and fueling rate as constrained actuators. Constraints on combustion timing and output work are also considered to prevent ringing or misfire. The simulation results show that the developed controller works over a range of load conditions and can maintain HCCI combustion timing and load to their desired values.

Homogeneous Charge Compression Ignition (HCCI) is a promising concept for combustion engines to reduce both emissions and fuel consumption. HCCI combustion control is a challenging issue because there is no direct initiator of combustion. Variable Valve Timing (VVT) is being used in SI engines to improve engine efficiency. When VVT is used in conjunction with HCCI combustion it is an effective way to control the start of combustion. VVT changes the amount of trapped residual gas and the effective compression ratio for each cycle both of which have a strong effect on combustion timing in HCCI engines. To control HCCI combustion, a physics based control oriented model is developed that includes the effect of trapped residual gas on combustion timing. The control oriented model is obtained by taking a physics based model of the reaction kinetics and transient dynamics and systematically reducing the model using simplification of reaction mechanisms.