Antiknock,ignition And Engine Combustion Of Butanol-Gasoline Blends

With energy shortage and environmental pollution turning into a global concern,clean and renewable alternative fuels have become research focus.Thanks to the recent technology breakthrough in butanol production process,butanol is far more competitive.Besides,butanol has the advantages of high energy density,weak hydrophilicity and small corrosivity,and no need for large-scale modification of engines.Therefore,it is vital to study the ignition and combustion research of butanol fuel.In this thesis,research octane number（RON）of butanol/PRF blends and butanol/TPRF blends was measured on a CFR engine.The antiknock tendency difference of butanol gasoline was explained by chemical kinetics analysis.Based on a constant volume combustion device,the spray auto-ignition of butanol/gasoline was obtained.Furthermore,the flame development and heat release process of butanol/gasoline were analyzed combined high-speed photography with in-cylinder pressure test on direct-injection optical gasoline engine.Main conclusions are as follows:Butanol addition to gasoline surrogate increases RONs,and the RON boosting effects of butanol isomers change with the fuel compositions,i.e.i-butanol>s-butanol>n-butanol>t-butanol for PRF fuels and i-butanol>s-butanol>t-butanol>n-butanol for TPRF fuels.The RONs of fuel blends show higher linearity with the molar percentage than with the volumetric percentage of butanol addition.Additionally,butanol/PRF blends exhibit higher RONs than butanol/TPRF blends.The addition of butanol isomers reduces the low temperature activity of fuel and increase the ignition delay time.The reaction sensitivity analysis in auto-ignition reveal that the H-abstraction reactions of butanol isomers by OH radical suppress fuel reactivity,thus elevating the fuel RONs when butanol was added to the gasoline surrogates.Compared with the butanol/PRF blends,the positive sensitive reactions related to n-heptane were of higher importance,while the inhibitive effects of sensitive reactions related to butanol and iso-octane decrease for the TPRF/butanol blends,thus leading to lower RONs of the TPRF/butanol blends than those of the butanol/PRF blends.Butanol addition inhibits the spray auto-ignition propensity of PRF80or TPRF80 surrogate fuels,and extends both the ignition delay（ID）and combustion delay（CD）times.The four butanol isomers extend the ID times of gasoline surrogates in an order of i-butanol>s-butanol≈n-butanol>t-butanol,and the shortest ID times of the t-butanol/gasoline surrogate blends are attributed to their earliest first-stage heat release.Generally,the CD extension effects of the four butanol isomers are ranked as i-butanol>t-butanol≈s-butanol>n-butanol,but the effects of s-butanol and t-butanol are slightly sensitive to the gasoline surrogate type and ambient temperature.The increase of ambient temperature leads to the significant reduction of ignition delay and combustion delay.Butanol addition reduces the pressure peak and the reducing effect are ranked as n-butanol<i-butanol<s-butanol<t-butanol,which is due to higher latent heat vaporization,higher viscosity and lower heat value of butanol.The ignition delay and combustion duration of t-butanol/gasoline surrogates are the longest while that of n-butanol are the shortest.Butanol addition reduce particle number,and the order of reducing effect is s-butanol>i-butanol>n-butanol>t-butanol.The spread velocity of butanol/gasoline surrogates blends slows down and yellow flame area is less than gasoline surrogates,due to the intermediate product C₄H₈ of butanol.