Numerical Study On Clean Combustion Of Butanol-diesel Dual-fuel

It is found that to seek appropriate alternative fuels for internal combustionengines is an effective method to reduce petroleum dependence and emissionpollution. Butanol is a new promising biofuel for engines, the effects of butanol onthe combustion and emissions of a diesel engine were investigated by numericalsimulation.First of all, the reduced chemical kinetics model of butanol-diesel dual-fuel wasdeveloped. A reduced n-butanol chemical mechanism consisting of69species and149reactions was established using a directed relation graph with error propagationmethod. The predicted results of the reduced mechanism were validated with detailedmechanism and exeperiment data in a wide operating range. The results show thatexcellent agreements between reduced and detailed mechanism and experiment datawere achieved. Then, a n-butanol-n-heptane reduced mechanism consisting of75species and167reactions was developed by coupling the n-butanol reducedmechanism with a validated reduced n-heptane mechanism. The final mechanism cangive reliable performance for combustion prediction of butanol-diesel dual-fuel, andallow computational efficiency improvement without a veracity penalty.The multidimensional simulation work was conducted to study the combustionprocess of butanol-diesel dual-fuel after the calibration of spray model constants. Adiesel engine, operating in butanol-diesel blend fuel direct-injection mode anddual-injection mode were investigated by experimental and numerical simulation. Theresults reveal that compared with pure diesel and dual-injection mode, blend fueldirect-injection mode has the longest ignition delay primarily due to high heat ofevaporation of butanol. The combustion duration of these two injection modes areboth shorter than that of pure diesel mode because of the oxygenated fuel feature andfaster burning speed of butanol. Compared with pure diesel, NOx emissions of blendfuel direct-injection mode and dual-injection mode increase by28%and9%,respectively, while blend fuel direct-injection mode has higher NOx due to its widerhigh-temperature combustion region. As for soot emissions, blend fueldirect-injection mode reduces by40%than pure diesel due to the addition of butanolleading to overall equivalence ratio reduction and local equivalence ratio distributionuniformity improvement. However, the local over-rich mixture of dual-injection mode results in higher peak value of soot in combustion process, so that this mode hasn’tachieved obvious soot reduction as the blend fuel direct-injection mode does.Finally, the effects of twin injection of diesel on butanol-diesel dual-injectionmode were investigated based on the platform of calibrated numerical model. Theresults indicate that two stage of heat release appears if the twin injection strategy ofdiesel is used. And the first peak of heat release rate increases with the increase ofinjection mass, but it decreases with the advance of injection timing. The effects oftwin injection on fuel consumption and emissions are complex, the good compromisebetween fuel consumption and emissions can be achieved when the injection timing isfixed at approximately-33°CA ATDC with an injection mass of8mg.The study in this paper has a useful reference on the understanding ofbutanol-diesel dual-fuel combustion fundamental and clean combustion theory ofbutanol in diesel engines.