Performance Analysis Of A Spark Ignition Engine Fueled With N-butanol/Gasoline Blends

Developing and disseminating high efficiency,clean and renewable biofuels as alternative fuels for automobile is an important energy security and environmental protection measure.As an alternative transportation fuel,biobutanol,known as n-butanol,has positive effect on the future availability of fossil oil reserves and reduction in emissions due to its advantages of higher lower heating value,better mutual solubility with other fuel,using safely,storing and transporting easily etc.In this study,a performance analysis of spark ignition engine fueled with n-butanol/gasoline blends was conducted with experiment and numerical simulation.The main research tasks and results are described as follows.Firstly,the physicochemical properties of the gasoline/n-butanol blend-fuel with0%,10%,20%and 30%n-butanol by volume,such as density,low heating value,and the stoichiometric air-fuel ratio,were measured and calculated.The engine's power,fuel consumption and emission characteristics were tested on an inline four-cylinder SI engine fueled with gasoline/n-butanol blend-fuel.The results showed that,without any modifications of the engine,the engine's power decreased,and the brake specific fuel consumption increased when the butanol fraction in the blends increased.However,increasing the butanol fraction in the blends would not decrease the effective efficiency.In terms of the emission characteristics,the HC and NO_x emissions decreased with increasing the butanol fraction in the blends,which had little influence on the CO emission.Then,this study presented a detailed energy and exergy analysis of a gasoline/n-butanol blend-fueled spark-ignition(SI)engine by means of numerical simulation.A quasi-dimensional two-zone model,including Wiebe function to model the actual combustion process based on fuel types and operating conditions was developed.The solution of the governing equations of compression,combustion and expansion process was done with C program.On the basis,the effects of volume fraction of n-butanol in the blends,spark timing,load and EGR rate on an SI engine's energy and exergy distribution were analyzed.The results showed that,under the conditions conducted in this paper,the first-law efficiency increases as well as the brake specific fuel consumption(BSFC)with the increase of n-butanol in the blends.Increasing butanol fraction in the blends increases the percentage of total irreversibility in total availability,while decreases the second-law efficiency slightly.However,with increasing EGR rate appropriately,the percentages of availability transferred by heat transfer and net exhaust availability both decrease,which can increase the first and second-law efficiencies simultaneously.As the percentage of total irreversibility in total availability increases with increasing butanol fraction in the blends,using iso-octane as the gasoline surrogate,the entropy production and exergy balance of n-butanol and iso-octane constant volume combustion process were analyzed with the CHEMKIN software by considering detailed n-butanol-iso-octane chemical reaction mechanisms.The results showed that,the exergy destruction of n-butanol adiabatic constant-volume combustion is obviously higher than iso-octane.During combustion process,the internal thermal energy exchange between hightemperature product and the unburned reactant via a series of chemical reactions is the major reason for the exergy destruction,especially the reactions of small molecule intermediate products.For a more detailed comprehension of n-butanol combustion kinetic process,a reduced n-butanol chemical kinetic mechanism was developed based on direct relation graph with error propagation(DRGEP),sensitivity analysis,reaction-path analysis and entropy analysis method with the CHEMKIN software.The experimental data from shock-tube ignition delay time,premixed flame species concentrations and laminar flame velocity was taken to validate the proposed refuced mechanism.