Evaluation of Cylinder State Estimator using Fuel Evaporation Assessment in a PFI Methanol HD SI Engine

Modern spark-ignited (SI) engines offer excellent emission reduction when operated with a stoichiometric mixture and a three-way catalytic converter. A challenge with stoichiometric compared to diluted operation is the knock propensity due to the high reactivity of the mixture. This limits the compression ratio, thus reducing engine efficiency and increasing exhaust temperature. The current work evaluated a model of conditions at inlet valve closing (IVC) and top dead center (TDC) for steady state operation. The IVC temperature model is achieved by a cycle-to-cycle resolved residual gas fraction estimator. Due to the potential charge cooling effect from methanol, a method was proposed to determine the fraction of fuel sourced from a wall film. Determining the level of charge cooling is important as it heavily impacts the IVC and TDC temperatures. This method is based on air flow measurement and comparing information from the compression event during a transient from fired to motored conditions, while keeping the intake density constant. Experiments were conducted on a high compression ratio (14:1) heavy duty (HD) single cylinder research engine (SCRE). The fuel was methanol, injected via port fuel injection (PFI). The results indicate that the latent heat of vaporization of the fuel is far from being fully utilized, due to inherent design limitations of the intake system. It was also found that charge cooling could be altered by utilizing features of the swirl optimized cylinder head, while the same features also hinted that some stratification was possible. Accurate estimation of the IVC state and the later thermodynamic evolution is important for any closed cycle analysis. The result from the IVC and TDC condition estimators indicate that it is possible to capture expected trends.