Feedforward/Feedback control of HCCI combustion timing

Homogeneous Charge Compression Ignition (HCCI) engines have the advantage of low Nitrogen Oxides (NO_x) and soot emissions. In HCCI engines, a lean premixed air-fuel mixture is compressed until the temperature is high enough for combustion to occur. HCCI engines have a limited operating range and are limited by knock at high loads and misfire at low loads. They are without a direct source to initiate ignition so HCCI requires combustion timing control. Some of the factors that affect HCCI combustion timing are mixture composition, pressure and temperature at the time of inlet valve closing. One effective way to control HCCI combustion timing is Variable Valve Timing (VVT). VVT changes the amount of trapped residual gas and the effective compression ratio. These factors have a strong effect on HCCI combustion timing. One main advantage of VVT is that it is fast enough to handle rapid transients. Based on a simplified control oriented model that models the effect of trapped residual gas on combustion timing, a Feedforward/Feedback controller is designed for HCCI combustion timing control. The controller requires feedforward information of the valve timing and feedback information of the combustion timing. This controller tracks the desired combustion timing trajectory both in simulation and experiment by modulating the trapped residual gas using VVT actuation.