Autoignition characteristics of diesel spray under different injection pressures and cold start strategy for compression ignition engines

Poor cold start performance is one of the main factors restricting the application range of compression ignition engines. Stable flame generation in the cylinder is the prerequisite for the successful start of the engine. In order to explore ways to improve the cold start ability of the compression ignition engine, the ignition characteristics of diesel sprays at different injection pressures were studied in a constant volume combustion chamber. A high-speed photography technique was used to obtain the color images of the initial flames of diesel free sprays. And the yellow flame is introduced as the criterion for a successful flame generation. It was found that under moderate injection pressures, the reactant concentration and energy dissipation rate reached equilibrium. Under this condition, the duration of the blue flame is relatively stable, and it is most conducive to the generation of the yellow flame in the cylinder. The negative temperature coefficient phenomenon is also observed, and the temperature range in which this phenomenon occurs is identical with the change of injection pressure. A cold start strategy for the compression ignition engine is proposed by controlling the compression-end temperature in the cylinder to be higher than the threshold ignition temperature of diesel spray.