Experimental Validation of a Global Reaction Model for a Range of Gasolines and Kerosenes under HCCI Conditions 2011-24-0024

Compact and computationally efficient reaction models capable of accurately predicting ignition delay and heat release rates are a prerequisite for the development of strategies to control and optimize HCCI engines. In particular for full boiling range fuels exhibiting two-stage ignition a tremendous demand exists in the engine development community. To this end, in a previous investigation, a global reaction mechanism was developed and fitted to data from shock tube experiments for n-heptane and five full boiling range fuels. By means of a genetic algorithm, for each of these fuels, a set of reaction rate parameters (consisting of pre-exponential factors, activation energies and concentration exponents) has been defined, without any change to the model form. In the present paper, an extensive validation of the model using these existing and unaltered parameters from the shock tube optimization is presented, by comparing calculated pressures, heat release rates and ignition delays with data from HCCI engine experiments. The validation is performed for all fuels at a wide range of HCCI operating conditions: load was varied from 2 to 6 bar IMEP, intake temperatures from 40 to 80°C and exhaust gas recirculation rates (EGR) from 0 to 65%. The results of the 3D-CFD simulations show a good overall agreement with the HCCI experiments for each of the fuels considered for the majority of the operating conditions investigated. The efficiency and good predictive capability of the model, even for the complex gasolines and kerosenes considered here, make the model particularly suited to study the impact of changing operating conditions on the ignition behavior and heat release in real HCCI applications. The promising results obtained furthermore indicate that the model could, in principle, be applied to any hydrocarbon fuel, providing suitable adjustments to the model parameters are carried out.