| In recent years,Low Temperature Combustion(LTC)has attracted an extensive attention.It can simultaneously reduce engine NOx and PM emissions,and has the potential to further improve the engine’s effective efficiency.Building appropriate fuel stratification is essential to control the combustion process of LTC,which is beneficial to achieving high loads.Experiments and simiulations were based on an ethanol/diesel dual-fuel single-cylinder engine to study the effects of reactctivity stratification on Ethanol/Diesel dual-fuel engine combustion.Fuel physicochemical properties,injector nozzle-holes number and multiple injection strategies were researched.Based on these,the concept of HPCCI(High Premixed Controlability Compression Ignition)was condensed,which might be conducive to broaden the load of LTC.Compared ethanol/diesel and butanol/diesel engine combustion process found that ethanol/diesel had a hysteretic combustion phase.The main reason was that ethanol had high ethanol octane value which led to decrease air/fuel mixture reactivity,and the high latent heat of ethanol evaporation resulted in in-cylinder temperature decrease.The effect of ethanol on the in-cylinder temperature was eliminated by the intake air heating,and the difference in the combustion process of ethanol and butanol was compared.Results showed that ethanol/diesel engine still has a restard combustion phase than butanol/diesel engine,these was caused by ethanol’s high octane.But,the influences of reactivity were weaker than temperature.Based on the different direct injection timing and premixing ratio,the influence of injector nozzle-holes number on the combustion and emission characteristics was studied.Results showed that reduce nozzle-holes number lowered the distribution area of high reactivity fuel,which reduced the initial ignition positions.Fewer nozzle-holes number injector realized a moderate combustion with lower peak pressure release rate and peak pressure.NOx was reduced with a decrease nozzle-holes number,while SOOT was still at low level.With the increase of ethanol proportion,the effect on combustion and emissions of different nozzle-holes number was increased first and then decrease.And the effect was gradually reduced with advanced direct injection timing.High premixd controllability compress ignition(HPCCI)combustion strategy was defined.In HPCCI combustion strategy,most of the fuels were port injected(port-injection)and in-cylinder pre-injected(pre-injection)to contruct an appropriate air-fuel mixture,and micro-fuel was injected(main injection)in cylinder near top dead point.Port injected fuel was high reactivity fuel(ethanol),and in-cylinder injected fuel was high reactivity fuel(diesel).The strategy showed two-stage combustion.The first stage was diffusion combustion of micro-main injected fuel,and the second stage was premixed combustion of air-fuel mixture. |
