Benefits of application of biofuels produced on the basis of plant oils in diesel engines are shown. Specific features of fuel spraying process in diesel engine operating on rape oil biofuels are considered. Necessity of coordination between the length of spraying fuel jets and the combustion chamber dimensions is shown. Calculation research is conducted for the Д-245.12С diesel engine with various shapes and sizes of combustion chamber, as well as for the parameters of diesel engine with asymmetrical fuel injectors positioning. A method for optimization of fuel injector positioning in combustion chamber is suggested, taking into consideration the indices of fuel efficiency and exhaust gases toxicity.