Using detailed chemical kinetics 3D-CFD model to investigate combustion phase of a CNG-HCCI engine according to control strategy requirements

Homogeneous Charge Compression Ignition (HCCI) method decline soot and NOx emission by offering high thermal efficiency in order of diesel engine. However, controlling HCCI combustion phenomena is known as the significant setback for its development. Control-oriented models use CA5, CA10, CA50 and CA90 as the most important dependent variables. Start of combustion (SOC), for instance, has already been traced via pressure rise versus crank angle. In fact, these simplifications have been progressed to reach real-time response as the main nature of controlling target. In this study, a 3D CFD model coupled with detailed chemical kinetics has been modified to devise a brief relation between these controlling parameters and what really happens in combustion chamber. The model has been validated with experimental results in four distinct conditions. To detect combustion phase, hydroxyl radical (OH) has been suggested as an indicator among all other chemical species due to its significant role in CNG combustion. Various sets of simulations have come up with noticeable findings that CA50 in CNG fueled HCCI engine equals crank angles when OH concentration and pressure rise rate reach their peaks. This result represents OH as a potential robust parameter in HCCI engine control even though this relation is not established well in weak combustion region rather than high heat release rate (HHR) cases. Finally, IMEP and BSFC, as the most important performance parameters of an engine have studied versus CA50 and OH concentration variation. The comparison proved good agreement between these two terms except in near-TDC combustion cases.