Experimental Study On Auto-Ignition Characteristics Of Low Carbon Fuel In Shock Tube

With the energy crisis and environmental degradation,in order to improve the thermal efficiency of engines and reduce harmful emissions,clean fuel,including low carbon fuels such as liquefied petroleum gas,natural gas and methanol,has attracted more and more attention.The auto-ignition characteristics of these hydrocarbon fuels are vital for the verification of the simplified chemical kinetics mechanism and the optimization for the combustion efficiency of engine.It was a basic combustion research.In this paper,on the own shock tube experimental platform,the ignition delay of three low carbon fuel,including liquefied petroleum gas,natural gas and methanol,were measured under different temperatures,pressures and equivalent ratios.This paper focuses on comparative research.The main completed works were as follows:The ignition delay of the liquefied petroleum gas mixture was measured.The experimental temperature was 1263~1795 K.The φ was 0.5,1 and 2.The pressure was 1.2 and 3 atm.Argon dilution ratio is 93%.It was found that when the equivalence ratio was constant,the ignition delay decreased with the increase of temperature and pressure.The experimental data of ignition delay for different pressure would across with the increase of ignition temperature,indicating that the ignition activation energy was affected by pressure,and the ignition activation energy rose with the increasing pressure.When the pressure and temperature were constant,it was affected by the reaction initiation and ignition activation energy.The ignition delay increased as the equivalence ratio increases.Meanwhile,the fitted straight lines for the ignition delay of liquefied petroleum gas under various equivalence ratio were parallel nearly,which indicated that the ignition activation energy was weakly affected by the equivalence ratio.The ignition delay was consistent with Arrhenius relation.The relationship among ignition delay,ignition temperature,pressure,equivalence ratio and fuel concentration was obtained through data fitting.The experimental temperature was 1300~1666 K,the equivalent ratio was 0.5,1,2,and the pressures were 1.2 and 3atm,respectively.The ignition delay of the Qatar natural gas mixture was measured under nitrogen dilution.The experiment showed the ignition delay was shortened with the increase of temperature and pressure,and increased with the increase of the equivalence ratio.And the ignition delay of Qatar natural gas was compared with the four commonly used natural gas mechanisms.It was found to be in agreement with the LLNLC1-C4 mechanism,and the natural gas produced in Australia and Chang Qing Oilfield was also simulated and compared.The simulation results showed that the higher the methane content,the longer the ignition delay.When the temperature was high,the gap was not big.However,the increased ranges of the ignition delay of Chang Qing oilfield natural gas was much greater than that the other two natural gases with the decrease of temperature.At the same time,it can be obtained from simulation calculation that the ignition delay of the three types of natural gas is shortened with the reduction of ignition activation energy and octane number.Under the higher temperature and pressure in the engine cylinder,the high-octane fuel with shorter ignition delay is more likely to have the abnormal auto-combustion phenomenon before spark ignition.The experimental temperature was 1063~1366 K,the equivalent ratio was 0.5,1,2,and the pressures were 3,4 and 5atm,respectively.The ignition delay of the methanol mixture was measured under nitrogen dilution.As the equivalence ratio increased,the collision of methanol molecules increased and the ignition delay was shortened.The experimental data of liquefied petroleum gas,Qatar natural gas and methanol were compared,and the three types of fuels were analyzed to have different changes with the increase of the equivalent ratio.At lower temperatures,the ignition delay of the two types of gaseous fuels were generally longer than that of methanol,but with the increase of temperature,the ignition delay of methanol was reversed.The ignition delay of natural gas was generally longer than that of liquefied petroleum gas due to the content of methane.