The startability of diesel engines with sunflower oil was much poorer than with No.2 diesel oil. The author has designed a new fuel injection system (double injection system) which improves the startability. In this system, a specified fuel was first injected into the pre-combustion chamber (pre-chamber) during the compression stroke at about −200°CA while the flow velocity at the connecting passage way (canal) is still low. This injected spray easily penetrates to the main combustion chamber (main chamber) and causes a pre-reaction here. The subsequently injected fuel spray at −5°CA causes the main combustion with a short ignition lag, and the engine is easily started. With sunflower oil and an ordinary injection system, the minimum temperature where the engine could start at the first compression stroke, was 25°C and the lowest temperature, where the engine never started, was 10° C. With the double injection system, the minimum temperature at which the engine could start at the first compression stroke, was 12°C and the minimum temperature at which the engine never started, was −1°C. This system improved the cold startability of not only the sunflower oil but also of other fuel such as No.2 diesel oil.