Experimental Study Of The Effects Of Fuel Properties And Oxygenated Fuels On Low Temperature Diesel Combustion

With a great potential of reducing emissions, the diesel low temperaturecombustion (LTC) has gained wide attention home and abroad. Fuel properties arebelieved to be critical parameters that influence both LTC combustion and emissioncharacteristics. By the means of separation of variables, a series of experiments wereconducted in a single cylinder diesel engine to test the effects that fuel properties haveon low temperature combustion, including boiling point, fuel composition, cetanenumber (CN), oxygen content and oxygenated fuel structures.Diesel fuel was blended with several hydrocarbons to test the fuel influence ofphysical and chemical properties on LTC. The results show that CN is a importantparameter that influences both LTC combustion and smoke emission characteristics.Low CN fuels can effectively increase the combustion ignition delay, improve fuel-airpre-mixing, and thus reduce smoke emissions; both combustion and smoke emissionsshow more sensitivity to lower CN at the condition of higher EGR rates. The changein the blending fuel’s boiling points and fuel compositions plays no obvious role inLTC combustion，however, do have an impact on smoke emissions. This thesis hasseen smoke reduction from a fuel with low boiling point in the case of higherblending ratio, indicating that boiling point effect works; however, such effects arenot clearly seen in the case of low blending ratios.Based on the above research of fuel property effects on LTC, the thesis thengoes further to explore the oxygenated fuel effects on LTC. Based on the research onthe diesel-n-butanol blending fuel LTC, conclusion is made that CN plays the criticalrole in LTC combustion characteristics. Diesel-n-butanol blending can effectivelyreduce LTC smoke emissions, due to the lower boiling point, lower cetane numberand oxygen content effects. Of all of the three factors, low CN effect is seen to bevery effective, however, behind the effect of oxygen content effect. Oxygenated fuelstructure is believed to play a role in the reduction of smoke emissions. In this thesis,butanol isomers of n-butanol and2-butanol, in which positions of hydroxyl (-OH) aredifferent, have almost the same performance in smoke reduction; However, the factthat methyl octanoate shows a higher smoking tendency than n-butanol, indicating that fuel oxygenated function group of hydroxyl (-OH) is more effective in smokereduction than that of ester group (-COO-).In the experimental condition of this thesis, fuel properties show no obviousinfluences on the emissions of gaseous NOx, CO and THC.