An Investigation On Surrogate Mixture And Its Chemical Kinetic Models Of Bio-diesel Fuel

In recent years, biodiesel has got high popularity in the world as a substitute fuelfor a new environmental diesel, it has similar physical and chemical properties to diesel,it does not only be the fuel of existed diesel, but have better emission performance thantraditional engine fuel. So biodiesel has great significance in reducing the oilconsumption and protecting the environment.Firstly, based on Methyl Decanoat (C₁₁H₂₂O₂) and n-Heptane （nC7H16） as analternative biodiesel fuels, it builds a691components, the3226elementary reactionsbiodiesel alternative fuels detailed chemical kinetic mechanism. It constructs a detailedchemical kinetic mechanism of biodiesel alternative fuels which including691components and3226elementary reactions. Followed it verifies the ignition delay timeof the detailed mechanism in the different working conditions of the shock tubeconditions is reasonable. Then through the cylinder combustion under the conditions ofHCCI engine calculate its cylinder pressure, the main emissions in different workingcondition to prove the building mechanism is reasonable, the results show that themechanism is able to simulate the combustion process of a combustion engine.Through the analysis of the bio-diesel alternative fuel combustion in HCCI enginecondition process, we can know that alternative fuels bio-diesel show two stage: lowtemperature combustion process and high temperature combustion process, and the twoheat transfer processes of the two stage is separated by the negative temperaturecoefficient region. In the low temperature stage, n-Heptane mainly throughdehydrogenation of dehydrogenated radical OH, HO2and oxygen process consumed;Methyl Decanoate not only through those two ways to deplete, it can be decomposedinto methyl ester, it has much less carbon atom number, the main reason is that that theenergy among chemical bonds in the internal structure of the dehydrogenation product（Methyl Decanoate） is unbalance.Through the analysis of the evolution of the N elements, we can know that in theprocess of change from N2to NO_Xwhich into the cylinder, the radical CH₃, OH, H, Oand O2are key intermediate substances, and by controlling the generation of theseimportant intermediate substances we can effectively reduce the NO_Xemissions in theexhaust gas.With the combined method of the sensitivity analysis and path analysis, the mechanism of biodiesel alternative fuel combustion is simplified, a simplified dynamicmodel is obtained with113components and306elementary reactions. With thecomparison of various shock tube and fire delay time of the detailed mechanism, it isfound that the simplified mechanism is able to coincide with the fire delay time of themethyl decanoate and n-heptane. Meanwhile, With the comparison of the simplifiedmechanism and the experimental mechanism of the biodiesel, the simplified mechanismis also able to coincide with the cylinder pressure and temperature and reproduce thevariation tendency of the main components, so the simplified mechanism is proper.The detailed and simplified mechanism of the biodiesel substitute fuels burned inHCCI engine are compared and analyzed, the results show:（1） fire can be ahead of timeand cylinder temperature rises and pressure changes seldom while inital temperature ofengine is increasing;（2） fire can be ahead of time and cylinder pressure rises andtemperature changes seldom while inital pressure is increasing;（3） cylinder pressureand temperature both increases while the equivalent ratio is increasing.