Diesel engines have high potential for better fuel economy due to a high thermal efficiency and fuel diversity. They are largely expected to contribute to a low carbon society in the future. This paper describes how the increase of the Biodiesel Fuel (BDF) mixing ratio reduces CO, HC, smoke and engine-out particle number (PN) concentration. Most notably, the PN concentration by using BDF100 can be reduced to approximately a half of diesel fuels. Additionally, this paper shows that the PN concentration from the tail pipe is reduced by over 99.95% with a DPF. Further, this paper also introduces the relationship between fuel consumption (FC), PN concentration and engine oil.