Experimental Research On The Effects Of N-butanol And Its Isomers On Low Temperature Diesel Combustion

Low Temperature Combustion (LTC) has been considered as a potentialhigh-efficient and clean combustion method which can fulfill the even strict emissionregulations in the future. Butanol, as a second generation biofuel, has broadapplication prospect and its fuel properties, such as low cetane number, oxygencontent and high volatility, are in favor of improving LTC characteristics and smokeemissions. In this article, effects of blending fuels of diesel and four butanol isomers(n-butanol, sec-butanol, iso-butanol and tert-butanol) on LTC characteristics andemissions are investigated by experimental research.Firstly, diesel blended with n-butanol was studied. As the increasing of blendingratio and Exhaust Gas Recirculation (EGR) rate, it showed prolonged ignition delayand stronger premixed combustion, especially for high EGR rate area. For the betterfuel-air mixing process and combustion quality, thermal efficiency of blending fuel atmid-EGR was improved compared to pure diesel and would be even better withhigher blending ratio. Mainly because of low cetane number and oxygen content,n-butanol was able to significantly suppress the soot emissions of LTC. As blendingratio increasing from20%to40%, total soot reduction was more than doubled. Allfuel properties had better performance on reduction of soot emission and the effects ofother properties (including volatility, ingredients, boiling point etc.) grown into a keyfactor while the cetane number contributed a larger scale increasement on sootreduction. Furthermore, higher injection pressure had more obvious effects on sootreduction in large EGR rate area. By blending with n-butanol and application ofhigher injection pressure, one could achieve high-efficiency combustion in widerEGR area.Then the isomers of n-butanol, sec-butanol, iso-butanol and tert-butanol werestudied. The ignition delays of four diesel-butanol blending fuels were sequenced asT20-N20-S20-I20from short to long while the rank of combustion durations wasopposite. As the blending ratio being higher, combustion characteristics amongdifferent blending fuels differed.40%blending fuels performed better on thermalefficiency compared with diesel in larger area of EGR rate than fuels with20%blending ratio, but were easier to misfire in high EGR rate. All butanol isomers could significantly reduce soot emissions and better with higher blending ratio. What’s more,soot emission differences among four diesel-butanol blends were much moreobviously in high blending ratio condition. And the total soot emissions weresequenced opposite to the ignition delays, which meant I40ignited latest and sootleast while T40reversed.NOxemissions declined to ultra-low level at high EGR rate conditions for allblending fuels. HC and CO emissions remained a problem facing with diesel/butanolLTC. Formaldehyde emission after butanol added was worth paying attention.