A comparative injector test was performed with a direct injection turbocharged, intercooled tractor diesel engine, fueled with a vegetable oil pressed from mustard seeds.The un-esterized mustard seed oil (MSO) was cleaned by simply letting it stand and clear. Engine operation, performance and exhaust emissions were investigated using two-spring injectors as the injection valves. Two injector tips with different orifice diameters were tested.Injection timing was first optimized. Thereafter, performance and exhaust emissions were measured in the large load-speed envelope.The results showed that some benefits were obtained with two-stage injection, particularly at idle, but also at low loads at intermediate speed. The wet exhaust content of oxides of nitrogen decreased at idle, while the CO content and some species of HCs remained almost constant. The NOx emissions also decreased at low loads at intermediate speed. At this speed, lower smoke and CO emissions were measured than with standard injectors.At higher loads, the NOx emissions increased, however, as they did at rated speed. As a whole, the NOx emissions were rather high and exceeded the future EU Stage II emissions limits. In contrast, the CO emissions were well below the proposed limit.More efficient charge air cooling and further optimization of the injectors and the injection system were thought to be the main subjects for the next phases of the research program.