Effects Of Iso-butanol On Direct Injection Spark Ignition Engine Combustion And Emission With Exhaust Gas Recirculation

Iso-butanol is a promising alternative fuel for gasoline due to its high octane number and high energy content.Meanwhile,through introducing Exhaust Gas Recirculation(EGR),the pumping losses of Gasoline Direct Injection(GDI)engines can be reduced at part loads,thereby the thermal efficiency can be improved.In the present study,experiments were conductedin a 1.8 L turbocharged GDI engine to investigate the effect of iso-butanol on the combustion and emission characteristicsunder different EGR rates.Major conclusions can be drawn as follows.As the volume fraction of iso-butanol in the iso-butanol/gasoline blend increases,the peak in-cylinder pressure,temperature,and heat release rate decrease.Thecarbon monoxide(CO),total hydrocarbon(THC),and nitrogen oxides(NOx)emissions in the engine fueled with the iso-butanol/gasoline are less than that of pure gasoline.Specifically,higher ratio of iso-butanol leads to lower CO and NOx emissions but higher formaldehyde,acetaldehyde,and methane emissions.The THC and 1,3-butadiene become much less at the medium ratio of iso-butanol.The combustion and emissions of iso-butanol was also compared with the isomers of butanol,i.e.,n-butanol,sec-butanol,and tert-butanol.It is found that the brake thermal efficiency of the engine can be improved as n-butanol,sec-butanol,and iso-butanol are used.However,the brake thermal efficiency of tert-butanol reduces lower emissions of CO and THC can be obtained for all the four butanol/gasoline blends than gasoline,among which TB50 and SB50 produce the highest CO and THC emissions,respectively.The highest combustion temperature of NB50 leads to the highest NOX emissions.As for the carbonyl emissions,NB50 and IB50 produce moreformaldehyde and acetaldehyde emissions but less 1,3-butadiene and methane emissions.A reverse trend is observed for SB50 and TB50.Both iso-butanol and ethanol show the extended duration of 0-10%MFB(mass fraction burned).Ethanol has a positive effect on the flame propagation speed when EGR is introduced.The higher latent heat of iso-butanol leads to lower combustion temperature and lower heat transfer losses,subsequently resulting in higher thermal efficiency.As EGR is employed,the engine fueled with iso-butanol can achieve lower fuel consumption at part loads.Moreover,the introduction of EGR is helpful for furtherreduction of NOX emissions for iso-butanol compared withethanol,in which the NOX emissions increase with the addition of ethanol.It is more effective to reduce the particle concentration by increasing the iso-butanol volume fraction than by increasing EGR rate.The proportion of the accumulation mode particles increase at higher load.All the four blends of butanol isomers produce less particle number emissions than pure gasoline,and IB50 is the most effective one in the reduction of the particle number,while TB50 is the least effective one.At the same blending ratio and EGR rate,iso-butanol has more significant impact on the reduction of particle number emissions.