Improvements to a CFR Engine Three Pressure Analysis GT-Power Model for HCCI and SI Conditions

While experimental data measured directly on the engine are very valuable, there is a limitation of what measurements can be made without modifying the engine or the process that is being investigated, such as cylinder temperature. In order to supplement the experimental results, a Three Pressure Analysis (TPA) GT-Power model of the Cooperative Fuel Research (CFR) engine was previously developed and validated for estimating cylinder temperature and residual fraction. However, this model had only been validated for normal and knocking spark ignition (SI) combustion with RON-like intake conditions (naturally aspirated, <52 °C). This work presents improvements made to the GT-Power model and the expansion of its use for HCCI combustion. The burn rate estimation sub-model was modified to allow for low temperature heat release estimation and compression ignition operation. After this, several updates were made in the GT-Power model parameters so that the air and fuel charge mass was correctly predicted under these different combustion (SI vs. HCCI) and intake conditions (boosted or heated). Thermodynamic verifications were made to compensate for uncertainty in some of the measured operating parameters, such as compression ratio, in the CFR engine. The updated CFR model was used to obtain the cylinder pressure-temperature trajectories of both HCCI and SI cases under different levels of intake pressure, intake temperature, and speed. Two additional common cylinder temperature estimation methods were compared to the results of the GT-Power model.