Controlled auto-ignition (CAI): A new highly efficient and near-zero NOx emissions combustion process for gasoline engine application

New engine combustion processes such as diesel Homogeneous Charge Compression Ignition (HCCI) and gasoline Controlled Auto-Ignition (CAI) are seen among the most promising ways to meet the environment challenges of the future powertrains used in transportation, which will have to target lower and lower CO2 emissions and fuel consumption (ACEA commitments) with associated robust ultra low pollutant emissions. In this paper, it will be shown how by using appropriate control strategies of the internal EGR charge, it is possible to obtain the auto-ignition of a lean mixture and to control it (in terms of ignition timing, heat release rate, cylinder pressure increase, ...) in an existing automotive gasoline 4-stroke engine with conventional compression ratio and without requiring heating of the intake air charge. In such controlled conditions, and compared to the conventional Spark Ignition (SI) combustion process, the newly-developed lean burn CAI combustion process allows to achieve part load fuel consumption improvements in the range of 15% to 20% combined with near zero NOx emissions ("one digit" ppm of NOx emissions is usual in some conditions). By allowing to run a gasoline engine in lean burn mode without requiring any fuel-sensitive DeNOx aftertreatment technology, the CAI combustion process further increases the already known Variable Valve Actuation (VVA) technologies benefits in terms of fuel efficiency and low CO2 without needing any other engine modification or redesign. It is therefore expected that the coming new generation of VVA technologies and associated engine management system, will make possible the introduction of the CAI combustion process (in at least some operating range) in the automotive gasoline engines of the short to medium term future.