Abstract:

Due to the change of air intake mode， the pumping loss of port injection （PI） unthrottled SI engine at medium and low loads is significantly reduced but its combustion performance is obviously deteriorated. In order to improve the combustion performance， a helical valve which can generate strong swirl in the intake process is designed， and the main structural parameters of the helical valve are optimized with the simulation software STAR-CCM+. The intake swirl ratio and the flow coefficient are measured on the steady flow test bench， which proves that the helical valve can generate strong intake swirl at small lift and improve the air intake flow state and fuel air mixing in the cylinder of the unthrottled SI engine. The helical valves are installed in an unthrottled SI engine with fully variable hydraulic valve system. The test results show that the intake swirl generated by the helical valve significantly improves the combustion rate of the unthrottled SI engine under low and medium load conditions and reduces cycle fluctuations， so that the fuel economy performance has been significantly improved.

Key words: unthrottled SI engine, helical valve, swirl ratio, simulation calculation, combustion performance