Abstract: The establishment of cetane number(CN) with simple methodology is important in direct utilization of vegetable oils as diesel fuel.By using the method of measuring self-ignition temperature on the basis of linear relation between self-ignition point and CN,the improvement and measurement of the CN of the compound biodiesel was performed by adding the CN improvers such as n-butyl nitrate(NBN),di-n-butyl oxalate(DNBO),tert-butyl hydroperoxide(TBHP),and both of compounds.The results showed that the CN of the compound biodiesel could be effectively increased by 15-25 via adding CN with the amount of 0.1%-1.0%.n-Butyl nitrate was the most effective improver in three compounds.When the addition of NBN was 0.6%,the CN of compound biodiesel increased from 27 to 50.The synergistic effect was proved by compound experiment of DNBO and TBHP,the CN of the compound biodiesel increased to 52-54 by the adding amount of 0.6% with the ratio of the proportion changing from 1:9 to 9:1.DNBO and NBN didn't have synergistic effect.Under the guidance of self-ignition point measurements and the calculative CN,the effect of improving the CN and the prediction utility of the CN were verified by the combustion situation of single cylinder diesel.It was shown that this method is feasible.

Key words: self-ignition point, cetane number improver, seeds oil of Jatropha, compound biodiesel