ntries of the world, this study researches the reason for dioxin in diesel car exhaust. We analyzed dioxin by the qualitative method with important marked products instead of the quantitative method by the researcher in foreign. This paper is progressing in three parts. First of all, we measure the unsaturated organic chlorine content in diesel oil from the two oil company of Taiwan, and compare the difference of the two oils. That can provide the forward analysis of the formation for dioxin. For the second, we use the method of experiment to discuss the pyrolysis stage (from injection to combustion) characteristic and the pyrolysis gas component trend variety with temperature. We get the mole formation, mean molecular weight and the variety trend of chlorine content in three phase. Finally, from the carbon-hydrogen and the carbon-hydrogen-chlorine compounds in pyrolysis, we use conservation of mass and chemical equilibrium, concentrating on the variety of operating condition of diesel engine, to simulate variety trend of product with pyrolysis temperature. We identify these data as the actual measure value, and set the concentration of the marked products for Dioxin, especially inorganic or organic chloride, V.O.C. carbon particles etc. On the other hand, from the formation model of dioxin, we investigate the variety trend between the precursors and Dioxin from different operating condition of engine , and　set the accurate mechanism in diesel dioxin exhaust. We hope that this study can show the contribution of dioxin in diesel car to the air. In this way, our government can easily establish the emission inventory and emission restraints for dioxin of automobile pollution sources.

vehicle,Dioxion