Combustion variation control strategy with thermal efficiency optimization for lean combustion in spark-ignition engines

A widespread consensus among internal combustion engine researchers is that higher thermal efficiency can be achieved with lean combustion. However, compared with a normal combustion mode (i.e., under a stoichiometric air-fuel ratio), combustion variation under lean operation is much more distinct, creating a bottleneck of thermal efficiency maximization. In this paper, a combustion variation control strategy that considers thermal efficiency optimization is proposed. This proposed strategy consists of two main components. One component focuses on diminishing combustion variation from cylinder to cylinder using a hypothesis test-based method. The other component provides the optimal value by searching for spark timing to maximize thermal efficiency. The effectiveness and performance of the proposed method are experimentally validated on a production spark-ignited gasoline engine test bench. From the experimental results, a notable combustion variation restrain performance with an average of 27% variation reduction is achieved using the proposed method. In addition, the self-optimization performance of spark timing under environmental changes is proven to be effective.