Smokeless combustion within a small-bore HSDI diesel engine using a narrow angle injector

Combustion processes employing different injection strategies in a High-Speed Direct Inject (HSDI) diesel engine were investigated using a narrow angle injector (70 degree). Whole-cycle combustion was visualized using a high-speed digital video camera. The liquid spray evolution process was imaged by the Mie-scattering technique. Different injection strategies were employed in this study including early pre-Top Dead Center (TDC) injection, post-TDC injection, multiple injection strategies with an early pre-TDC injection and a late post-TDC injection. Smokeless combustion was obtained under some operating conditions. Compared with the original injection angle (150 degree), some new combustion phenomena were observed for certain injection strategies. For early pre-TDC injection strategies, liquid fuel impingement is observed that results in some newly observed fuel film combustion flame (pool fires) following an HCCI-like weak flame. For late post-TDC injection strategies, strong fuel impingement is seen for injection timing close to TDC with very strong soot luminosity in the combustion chamber. However, by further retarding the injection timing smokeless combustion is possible for the post-TDC injection strategy. Typical diffusion burning occurs in the combustion chamber for certain conditions with the fuel film combustion from the first early injection. In order to obtain a smokeless combustion process for the second main injection, the pool fires for the first early pre-TDC injection must be eliminated or reduced to a great extent. Multiple injection strategy provides a promising approach to achieve low soot and low NOx combustion while keeping high fuel efficiency. Compared to the original injection angle, the narrow angle injector provides the opportunity for injection strategy optimization without liner wall wetting.