Investigation of realizing SDI with high swirl charge in a motorcycle engine

The targeted developments for future vehicles are how to reduce fuel consumption, pollutant emission while maintaining high level of engine performance. To deal with those issues, fuel system has been taken great concerns by scientists for a long period of time. As we know, Port Fuel Injection system (PFI) and Gasoline Direct Injection system (GDI) are popular techniques which are being used on commercial vehicles. This paper presents the possible improvement of engine performance by applying effect of swirl motion on lean-limit of semi-direct injection SI engine. The fuel goes into cylinder directly through intake valve near the middle intake stroke to make richer mixture around the spark plug, which is called semi-direct injection (SDI). Thus, this system includes high swirl charge, injection during intake valve opening, and air-assisted fuel injection. The modifications of intake port by using baffle plate and the other by closing one intake valve for the 125 cc, 4-valve, port-fuel-injection (PFI) engine to increase swirl ratio of in-cylinder air motions which helped to form rich mixture around spark plug, and lean mixture at other location which is so-called stratified charge. The CFD software was use to investigate the in-cylinder air motion. After that, the combustion characteristics of swirl charge were investigated. The SDI engine then was tested under lean conditions at 4500 rpm and 5300 rpm. Experimental results indicated that lean-limit was extended to maximum air-fuel ratio 25.26 (excess air ratio = 1.73) at swirl ratio 3.5 while brake specific fuel consumption and coefficient of cycle variation were very low. Finally, the ECE-40 driving cycle simulation was employed for lean burn SDI engine as well as the original PFI engine. Results show that by using SDI mode at low engine load operation of ECE-40 driving cycle, the fuel consumption, CO emission, and NOx emission were improved by 4%, 31.1%, and 5.9%, respectively. However, the HC emission was increased by 25%. Keywords— CFD, Lean burn, Semi-direct Injection System, Swirl ratio