Research On The Evaporation Characteristics Of Diesel-azides Blend Droplets And Influence Machanism

In order to meet the demands of high mobility in the future, great improvementofpower density of diesel engine is very important to the vehicle. High power density dieselengine needs efficient and rapid combustion, which is the key factor and also one of thetechnical bottlenecksto improve the power density.For improving the combustion, goodliquid fuel atomization and evaporation characteristicsare necessities. This paper tries toexplore the droplet evaporation mechanism of diesel-azdies blend based on the liquid phasedecomposition reaction of azide, which provides a possible way to realize rapid combustionfor high power density diesel engine.First of all, all the possible effects of liquid phase decomposition reaction of azide onthe droplet evaporation characteristics of diesel-azides blendwere analyzed theoretically.All the possible effect ways were concluded from the views of onset, position, quantity andrate of liquid phase decomposition reaction.And all the possible changes of evaporationcharacteristics brought by the released heat and nitrogen were analyzed qualitatively.Eventually the theoretical hypothesis of diesel-azides blend droplet evaporation with liquidphase decomposition reaction was proposed. By using theoretical calculation andexperimental analysis, the reaction paths, themal behaviours and exothermic decompositionkinetic were obtained, which supported the following experimental data analysis and modelconstruction.Secondly, the evaporation characteristics of azides and diesel-azide blend wereanalyzedusing a suspended droplet device. The rapid evaporation characteristics ofdiesel-azide blend droplet with3phases were obtained from the curves of squared dropletdiameter and droplet temperature and the phenomenon of different phases and typical times,which supported the conclusion that the diesel-azides blend has a rapid combustioncharacteristic in the experiment of single cylinder diesel engine.Then, for the optimizationof diesel-azides blend and application of diesel engine, the effect rules of benzyl azide massfraction, initial droplet diameter and ambient temperature on the droplet evaporationcharacteristics were also obtained.Thirdly, amulticomponent droplet evaporation model based on effective diffusivitywhich includesfiber heat transfer, radiative heat transfer,exothermic decomposition of azideand vapor-liquid phase equilibrium based on UNIFAC was built,ignoring the nitrogen generation and possible droplet breakup. This model can partially reflect the dropletevaporation characteristics of diesel-azides blend and has been validated with theexperimental results.Fourthly, the effects of the multicomponent characteristics of diesel, the differences ofphysical properties between benzyl azide and diesel, the released heat and nitrogen ofbenzyl azide’s decomposition on evaporation characteristics of diesel-azides blend weredecoupled. The internal mechanism of droplet evaporation characteristics of diesel-azidesblend was obtained. The results shows that the rapid evaporation characteristics ofdiesel-azides blend result from the above all factors, in which the released nitrogen is themain reason of droplet fluctuation and breakup. In addition, the effect rule of exothermicdecomposition on droplet evaporation was also obtained, which could be used foroptimization of diesel-azides blend.Finally, the droplet evaporation process of diesel-azides blend was predicted. Theeffect rules of initial droplet temperature, relative droplet velocity, initial droplet radius andambient temperature were summarized.