Study of High Speed Gasoline Direct Injection Compression Ignition (GDICI) Engine Operation in the LTC Regime

An investigation of high speed direct injection (DI) compression ignition (CI) engine combustion fueled with gasoline (termed GDICI for Gasoline Direct-Injection Compression Ignition) in the low temperature combustion (LTC) regime is presented. As an aid to plan engine experiments at full load (16 bar IMEP, 2500 rev/min), exploration of operating conditions was first performed numerically employing a multi-dimensional CFD code, KIVA-ERC-Chemkin, that features improved sub-models and the Chemkin library. The oxidation chemistry of the fuel was calculated using a reduced mechanism for primary reference fuel combustion. Operation ranges of a light-duty diesel engine operating with GDICI combustion with constraints of combustion efficiency, noise level (pressure rise rate) and emissions were identified as functions of injection timings, exhaust gas recirculation rate and the fuel split ratio of double-pulse injections. Parametric variation of the operation ranges was also investigated with respect to initial gas temperature, boost pressure and injection pressure. Following the modeling, experiments were performed under the conditions suggested by the numerical results in order to confirm the feasibility of GDICI operation at full load, as well as to validate the numerical simulations. The results showed good agreement between the experiments and the model predictions. Due to the high volatility and low cetane index of gasoline combined with reduction of combustion temperature through utilization of EGR, both PM and NOx emissions could be reduced to levels of about 0.1 g/kg-f while maintaining experimental gross ISFC at about 180 g/kw-hr. The numerical simulations helped to explain the incylinder spray combustion behavior and to identify characteristics of GDICI that differ from those of diesel-fueled operation. Maps of operable conditions were generated that allow extension of low-emission engine concepts to full load operation in high speed GDICI engine operation with fuel efficiencies comparable to those of corresponding diesel fuel operation while meeting emissions mandates in-cylinder.