Numerical Calculation Of Diesel/Biodiesel Fuel Atomization And CFD Simulation Of Internal Flow And Cavitation Phenomenon

Environmental pollution and petroleum resources are restricted the development ofdiesel engine, but road transportation cannot leave the truck, however most of the truckengine is diesel engine. In order to solve these problems, people begin to research the newcombustion mode, and looking for diesel replacement products, the new combustion modedevelopment based on control atomization formation of combustible mixture. This papermainly studied the nozzle internal cavitation phenomenon of fuel atomization process, anddroplet size distribution of diesel and bio-diesel atomization.First of all, build and mesh the two-dimensional calculation model of nozzle by using thegambit software then simulated the nozzle internal cavitation phenomenon by using fluentsoftware. The results show that cavitation takes place more easily by improving spraypressure and reducing outlet pressure. Then change the nozzle structure and further studiedthe structure change influence on cavitation phenomenon of nozzle internal flow. The resultsshow that increase lengthdiameter ratio restrains the cavitation phenomenon. And increase thenozzle inlet edge radius avail of the fuel flow, but restrains the cavitation phenomenon. Theshape of the spray hole has a great influence on the cavitation phenomenon, when the outletdiameter is smaller than the inlet diameter its called compression spray nozzle, when theoutlet diameter is larger than the inlet diameter its called expansion spray nozzle, compressionspray nozzle easily generated cavitation phenomenon, but the cavitation phenomenon of theexpansion spray nozzle was inhibited.Secondly, simulation results of cavitation phenomenon show that the diesel andbio-diesel spray holes cavitation phenomenon is the same, just different in nozzle exit velocity,diesel nozzle exit velocity is greater than the biodiesel nozzle exit velocity. Droplet sizedistribution function is derived by prof. Cao Jianming based on the maximum entropyprinciple. According to this function to write a FORTRAN calculation program, thencalculated the diesel and bio-diesel droplet size distribution, and compared with theexperimental results, the results show that the droplet size of the biodiesel is greater than thediesel. In order to improve the atomization quality of the biodiesel, we have formulated abiodiesel and LPG mixed fuel L10(biodiesel has a mass fraction of90%and the LPG has a mass fraction of10%), and L20(biodiesel has a mass fraction of80%and the LPG has a massfraction of20%), then calculated the the droplet size distribution of these two kinds of mixedfuel, the result show that atomization quality of L20is better than the L10, and L20atomization quality closer to the diesel atomization quality. Furthermore, the most importantfactor of theoretical calculation is the initial guess of the Lagrange factor variation coefficient,for this paper selected operating conditions, when the Lagrange factor variation coefficientinitial guess value is about1.9, the theoretical calculations and experimental results have beenwell fitted.