Experimental Investigation about the Effect of Double-Spark Plug Ignition on Combustion Characteristics for Motorcycle Gasoline Engines with a Mild Lean Mixture

[Image: see text] To investigate the effect of double-spark plug ignition (DSI) on the mild lean combustion characteristics of motorcycle gasoline engines, three combustion modes were set up on a gasoline engine for testing, namely, the single-spark plug ignition (SSI) stoichiometric combustion mode (λ = 1, λ represents the excess air coefficient), the DSI stoichiometric combustion mode (λ = 1), and the DSI mild lean combustion mode (λ = 1.1). The results show that the double-spark plug ignition as that in the DSI mild lean combustion mode and DSI stoichiometric combustion mode is more prominent in accelerating the combustion process, reducing the cyclic variation, and improving the lean burn stability. It is verified that the overall effect of double-spark plug ignition on accelerating mildly homogeneous lean combustion is mainly reflected during the early period of rapid burning, which improves the stability of mildly homogeneous lean combustion and extends the lean burn limit. Further, the bench test shows that at a moderate load, the DSI mild lean combustion mode can result in lower brake-specific fuel consumption (BSFC) compared to that of the DSI stoichiometric combustion mode. When using the DSI mild lean combustion mode, the fuel economy can be improved by about 3–6% compared to that when using the SSI stoichiometric combustion mode. And the emission reduction can also be clearly observed when using a three-way catalyst containing rare-earth materials. However, at a low load, limited by combustion stability, for the DSI mild lean combustion mode, λ should not exceed 1.05.