Environment-adaptive method to control intake preheating for diesel engines at cold-start conditions

Preheating the fresh charge is an effective way to improve the diesel cold-start performance. In the present study, the minimum intake preheating powers at different ambient temperatures and densities were investigated by using the optical experiments, engine bench tests and thermodynamic theory, to explore an environment-adaptive method of intake preheating power at cold-start conditions. The optical experiment results show that the critical ignition temperature of diesel spray decreases rapidly and then slowly with the decrease of in-cylinder density, and a relation between them is established. The results of engine bench tests show that the actual in-cylinder pressure is smaller than the theoretical compression pressure, and the relation between them is established in a wide speed range. Based on the experimental results and the thermodynamic theory, we establish a map chart of the intake preheating power with the ambient temperature and altitude. The results show that the minimum intake preheating power increases linearly as the ambient temperature decreases at the speed of first injection, and it first decreases and then increases as the speed increases during speed-up period. The requirement of the minimum intake preheating powers at the speed of first injection and speed-up period have different turning points with the change of altitude. •An environment-adaptive control method of intake preheating power was put forward.•The critical ignition temperature was investigated in a wide density range.•The thermodynamic theory of the minimum intake air temperature was established.•The minimum intake preheating powers have turning points as the altitude increases.