An Experimental Study On Diesel Engine Combustion And Emissions With Butanol-Diesel Blend Fuels

Due to the global energy crisis and the increasingly stringent emission regulations,development of new clean alternative fuel has become one hot topic of internalcombustion engine research. In this paper, the effect of diesel blended with largeproportion of butanol (40%by volume fraction of butanol, B40) on combustion andemissions performance of a diesel engine was investigated experimentally. The resultswere compared with those when the neat diesel was used.The results showed that, compared with those of the neat diesel, the peakcombustion pressure and the maximum pressure rise rate of the B40blend increased,the ignition delay prolonged, the combustion duration shortened, and the indicatedthermal efficiency decreased slightly. With the B40blend fuel, the engine sootemissions reduced significantly. The NOx emissions were lower and the CO and HCemissions were higher than those with the neat diesel at low engine loads, while theNOx emissions were higher, the CO and HC emissions were about the same atmiddle-high engine loads.It is known that Exhaust Gas Recirculation (EGR) has great influence on thecombustion process and emissions of diesel engines. The present results indicated thatat the low-medium EGR rate, the peak combustion pressure and maximum pressurerise rate decreased with the increase of the EGR rate, the combustion ignition delayprolonged slightly, the indicated thermal efficiency rose smoothly, the indicatedspecific fuel consumption decreased slightly, and the CO and HC emissions keptalmost invariable. When the EGR rate was increased to a certain "inflection point", thepeak combustion pressure, the maximum pressure rise rate and the indicated thermalefficiency decreased sharply, correspondingly the indicated specific fuel consumption,the CO and HC emissions increased rapidly. The EGR rate at which the "inflectionpoint" appears for the B40blend fuel was smaller than that for the neat diesel. As theengine operating conditions changed, the EGR rate’s "inflection point" changedaccordingly. With the increase of the EGR rate, the NOx emissions reducedsignificantly, while the soot emissions of the B40blend remained almost the samesince their qualities were so small.The engine fueled with the B40blend has an optimal injection timing varyingwith the engine operating conditions, at which the EGR rate before the “inflection point" occurs reach the widest range. When advancing the injection timing, the ignitiondelay advanced, the combustion duration lengthened, the crank angle at which themain heat release occurred advanced, the indicated thermal efficiency increased, theindicated specific fuel consumption decreased, while the maximum pressure rise rateincreased. Correspondingly, the CO emissions reduced, the soot and HC emissionsalmost unchanged, and the NOx emissions increased.When a pilot fuel injection was added, the maximum pressure rise rate for the B40blend fuel decreased, the ignition delay advanced, the combustion duration lengthened,the crank angle at which the main heat release occurred advanced, the indicatedthermal efficiency and the indicate fuel consumption improved, and the CO emissionsincreased slightly while the NOx and HC emissions decreased.In summary, this work demonstrated that under the conditions of using a middleEGR rate level, an appropriate injection timing and a pilot-injection, the engine couldachieve smooth operations with good fuel economy, lower NOx emissions, and thelowest soot emissions for the blend with a large amount of butanol. The obtainedresults in this study can add values for the application of engines using clean butanolalternatives.