Effects of intake fluctuation and chemical reaction on operating stability of a small displacement gasoline engine: An experimental and numerical study

In this work, the cycle to cycle variation (CCV) of a small displacement gasoline engine is investigated by experiment combined with CFD. Firstly, engine operating stability was tested: As increase of engine speed, the influence of load on CCV gradually declines. Below 4000 r/min, CCV gap is 4.47% between 40% and 100% load, when engine speed rises to 5500-7000 r/min, this gap declines to 1%. Then, the influences of intake fluctuation and chemical reaction on CCV was explored through specific simulation case matrix. The cyclic variation of in-cylinder global flow strength corresponds to intake fluctuation, but the ultimate working CCV is decided by flow field's macroscopical motion. The area of outer enveloping quadrilateral of flow locations in normal intake scenario is larger than average intake scenario by 53.42% at top dead center (TDC), which is close to CCV's increase amplification between these two scenarios. Further, this gap is enlarged to 278.06% from misfire to normal combustion scenario, chemical reaction has a more obvious effect on motion of flow field. Whatever intake fluctuation or chemical reaction, they contribute to engine CCV by affecting flow field's motion which plays a key role on flame propagation in such a limited space of combustion chamber.