A Three-dimensional Numerical Study On Ignition And Combustion Of A Diesel Engine Fueled With Butanol-Diesel Blends

As the increase of energy crisis and environmental problems, development ofclean alternative fuel for internal combustion engines, and exploitation of highefficiency engines with low emissions have become one hot topic of internalcombustion engine research. Results of many experimental investigations on engineusing butanol indicated that butanol had great potential to be applied on engines.Relative to experimental investigation, numerical simulation of the combustion processin engine cylinder can provide a lot of information, and it is economical, highlyefficient and flexible to compare different design schemes. In this paper, threedimensional modeling work was carried out for a diesel engine using butanol-dieselblends based on the KIVA code to understand the in-cylinder ignition and combustionprocesses.Firstly, a numerical model of diesel engine was developed based on the KIVA-Ⅱcode. Good levels of agreement with the experiment data were obtained using the Shellignition model and characteristic-time combustion (CTC) model for ignition andcombustion. For simlicity, the butanol-diesel blend was converted into an unimolecularfuel, it properties were calculated using the property mixing law. Based on thisassumption, the ability of predicting butanol-diesel ignition and combustion processusing Shell/CTC model was discussed. The results showed that it was difficult topredict butanol-diesel ignition and combustion process accurately without changingthe kinetic parameters for reaction rates of the Shell and CTC models.The method using KIVA code coupling with chemical kinetics was then adoptedto simulated butanol-diesel ignition and combustion. An existing reduced n-heptaneoxidation mechanism was used to simulate diesel combustion. A discretemulti-componen（tDMC）model was used for the vaporization of butanol-diesel blends.So it simulates the vaporization and combustion of butanol and diesel separately. Inorder to reduce computational time for engineering application, a reduced n-butanoloxidation mechanism with94species and214reactions was developed starting froman existing detailed reaction mechanism through the main reaction path analysis in anadiabatic constant volume closed system using the Senkin program. The reducedn-butanol mechanism was validated using the detail mechanism over a range of initialconditions of pressure at70bar, temperature from750-1300K, equivalence ratio from 0.5-3.0. The results show that the reduced n-butanol mechanism gives reliableperformance of combustion prediction, and at the same time, the improvedcomputational efficiency which is important for feasible engineering simulationapplications.Finally, the reduced n-butanol mechanism was combined with the reducedn-heptane mechanism to form a butanol-diesel mechanism. The present butanol-dieselmechanism was applied in the modeling and the predicted ignition delays of thebutanol-diesel blends matched with the experimental data well. The results indicatethat the developed models are promising in simulating combustion of butanol-dieselengines.