In recent years, small diesel engines for industrial use are required to achieve still higher power output per engine size (high power density) and to have the performance to comply with stringent exhaust emissions standards as well. To meet these social demands and market requirements, there are various engineering tasks yet to accomplish. In this paper, two important technical issues have been focused, those are, combustion system improvement to enable lower exhaust emissions and higher power output than conventional models and new cooling system as a solution for increased heat load issue accompanying the progress of high power density.
Firstly, for combustion system improvement, the swirl adjustment technique has been developed that will optimize the swirl ratio for each engine application with different load and speed condition. Intake airflow has been analyzed using Computational Fluid Dynamics (CFD) approach to enable adjustment of swirl ratio that plays an important role in creating air fuel mixture. The swirl was successfully controlled by providing the originally designed configuration on the wall, from cylinder block side, which introduces the intake air from valve throat area into cylinder. As a result, it is now possible to set optimum swirl ratio for each engine application while securing high volumetric efficiency.
Next, a new cooling system has been introduced to cool down the neighborhood of top deck between cylinders where temperature becomes highest in cylinder block. The new coolant channels with built-in multiple water passages was incorporated by casting between cylinders. As a result, the temperatures between cylinders and in piston ring groove could be lowered remarkably.
After overcoming these engineering challenges, the advanced high power density has successfully been materialized in small direct injection (DI) diesel engine for industrial use.