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Experimental research on the evolution characteristics of diesel particles under the cooling conditions has been carried out. The results showed that the cooling of the exhaust had important effect on the mass concentration of the diesel particles in the exhaust. The main cause that resulted in the change of the particle mass concentration was the condensation of gaseous hydrocarbon on the particle surface or existing in the form of liquid drop. The cooling of the exhaust promoted the increasing of the particle dimension and the decreasing of the particle numbers, especially for the smaller particles below 0.1 microm. The cooling temperature of the exhaust had important effect on the evolution of diesel particles. After exhaust cooling, the volume concentration of diesel particles between 0.1 microm and 1.0 microm exhibited a tendency of decreasing. Moreover, exhaust velocity also had effect on the evolution of the diesel particles. The number concentration and volume concentration of the diesel particles between 0.01 microm and 1.0 microm decreased along with the decreasing of the exhaust velocity.

The evolution characteristics of particle distribution in the vehicle exhaust plume have been investigated based on the models of nucleation, coagulation and condensation of particles. The simulated results showed that nucleation created a large number of new nanoparticles, and coagulation and condensation changed the distribution of particles in the vehicle exhaust plume. The effect of nucleation on the distribution of exhaust particles was weaker, and the distribution of exhaust particles was affected mainly by the effect of coagulation and condensation. The process of nucleation, coagulation and condensation was intense near the exit of the tailpipe and the variation of the particle distribution with time was strong. With the increase of the distance from the exit of the tailpipe, the evolution of exhaust particles got weaker. This work can provide much more information necessary for the establishment of vehicle emission control strategies and the study of the effect of vehicle particles on the human health.