Low temperature combustion within a small bore high speed direct injection (HSDI) diesel engine

Homogeneous Charge Compression Ignition (HCCI) combustion employing single main injection strategies in an optically accessible single cylinder small-bore High-Speed Direct Injection (HSDI) diesel engine equipped with a Bosch common-rail electronic fuel injection system was investigated in this work. In-cylinder pressure was taken to analyze the heat release process for different operating parameters. The whole cycle combustion process was visualized with a high-speed digital camera by imaging natural flame luminosity. The flame images taken from both the bottom of the optical piston and the side window were taken simultaneously using one camera to show three dimensional combustion events within the combustion chamber. The engine was operated under similar Top Dead Center (TDC) conditions to metal engines. Because the optical piston has a realistic geometry, the results presented are close to real metal engine operations. In this paper, six operating conditions were investigated to address the influences of injection pressure, EGR rate and injection timing on the evolution of HCCI combustion. The observation that no liquid fuel injecting into luminous flame is found shows premixed combustion for all of the six cases. Low temperature reaction was observed for certain operating parameters. New parameters were defined to evaluate the combustion process and flame structure. Results show that low temperature combustion is feasible in an HSDI diesel engine with a higher injection pressure, a higher EGR rate, or later injection timing with little penalty on power output. It was also found that injection timing has more influences on HCCI combustion using single main injection than the other two factors.