Combined effects of high energy ignition and tumble enhancement on performance of lean combustion for GDI engine

•The influence of ignition energy and tumble level on lean combustion is studied.•Particle image velocimetry is used to evaluate intake port tumble modification.•The arc development images and the exact arc area are considered.•High energy ignition extends the lean-burn limit, high tumble improves the stability.•The advantages of high energy ignition is analyzed from the flame development images. Lean combustion can greatly improve the thermal efficiency of gasoline engine. Increasing ignition energy and tumble level can effectively expand its application range. Optical glass liner was used to clearly observe the in-cylinder state. Particle image velocimetry(PIV) was used for quantitative evaluation of tumble modification. The integral tumble ratio of the high tumble intake port is 1.67 times that of the basic intake port. Ignition energy was increased from 65 mJ to 300 mJ. Under the condition of no fuel injection, the duration of 300 mJ ignition arc is longer, and the peak arc area is about 4 times that of 65 mJ. The effects of ignition energy and tumble level on combustion stability, lean-burn limit, fuel economy and flame development were studied. The results show that high energy ignition can enlarge the lean-burn limit, but has no significant effect on combustion stability. High tumble has the opposite effect and can effectively improve fuel economy. The micro flame development images under the ultra-lean condition are different. The flame area of 300 mJ is larger and the combustion is more intense. High energy ignition contributes to the formation of initial flame kernel and flame propagation, so it can improve the lean-burn limit.