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A multi-zone Controlled Auto Ignition (CAI) model for simulating the combustion and emissions has been developed and reported in this paper. The model takes into account the effects of the boundary layer, crevice volume, and blowby. In order to investigate the influences of in-cylinder inhomogeneity, the main cylinder chamber has been divided into multiple core zones with varying temperature and composition. Mass and energy transfer between neighbouring zones were modeled. A reduced chemical kinetic mechanism was implemented in each zone to simulate the CAI combustion chemistry and emission formation. An in-house code, the LUCKS (Loughborough University Chemical Kinetics Simulation), was employed to solve the coupled differential equations of the system. The model was validated against experimental results at various Internal Exhaust Gas Recirculation (IEGR) levels and was then used to analyze the thermal and chemical effect of the IEGR on the CAI combustion.

Controlled auto ignition (CAI) is a form of combustion which uses an auto-ignited homogeneous air/fuel mixture but is controlled (or moderated) by regulating the quantity of internal exhaust gas residuals. In this paper, using a fully variable valve train and a newly developed exhaust valve control strategy, we substituted EGR with hot nitrogen or hot air. We found that the internal exhaust gas residuals have both thermal and chemical effects on CAI combustion. To investigate the thermal effect, nitrogen was used as it is a chemically inert gas. Although its temperature was raised to that of the internal exhaust gas residuals during testing, CAI combustion could not be promoted without assistance from a spark in a form of hybrid CAI, thus indicating that exhaust gas residuals have a chemical effect as well.

Controlled Auto Ignition (CAI) uses compression heat to auto ignite a homogeneous air/fuel mixture. Using internal exhaust gas recirculation (IEGR) as an indirect control method, CAI offers superior fuel economy and pollutant emission reductions. Practically, this can readily be achieved by a method of early exhaust valve closure and late inlet valve opening to trap exhaust gas residuals within the cylinder from one cycle to the next. In order to understand the combustion mechanism, we did a comprehensive investigation on CAI fuelled with iso-octane. Test data was gathered from a single cylinder research engine equipped with Lotus' Research Active Valve Train (AVT) System, and the modelling study was based on detailed chemical kinetics. It was found that CAI can only occur when the thermal energy of the engine charge, which is a mixture of air / fuel and IEGR, reaches a certain level.