Experimental Investigation Of Ignition Delay Time Of N-heptane In Shock Tube

Shock tube is one of the tools for the research of ignition characteristics of fuels. It can provide conditions with specific pressure and temperature and let us measure the ignition delay time under various conditions. Compared with rapid compression machine and engine test bench, experiments with larger temperature and pressure range can be done in shock tube.N-heptane is an alkane fuel with macromolecules. Its cetane number is 56, which is very close to diesel fuel. So n-heptane is always used to simulate the diesel engine combustion process. Therefore, the ignition delay characteristics of n-heptane in shock tube were studied in this thesis, for the improvement of our understanding on the combustion characteristics of n-heptane and to provide a reference for the combustion characteristics of engine. The main contents of this thesis are as follows:(1) The definition of ignition delay time in this thesis is pointed out. The ignition delay time of n-heptane in synthetic air is measured with temperature range from 1100K to 1400K, equivalence ratio from 0.5 to 1, pressure 5.7bar. The results show: ignition delay time increases with increasing equivalence ratio; ignition delay time and the temperature approximately meet the Arrhenius equation.(2) The influences of CO₂ ratio and pressure on ignition delay time with various equivalence ratios are studied. In the experiments, the CO₂ and O₂ ratios are changed, with temperature range from 1100K-1400K, pressure 5.7bar and 2.4bar. The results show: the ignition delay time increases with increasing CO₂ ratio and decreases with increasing pressure.(3) The influences of CO₂ ratio with specific equivalence ratios are studied. In the experiments, equivalence ratio is maintained, with temperature range from 1100K-1400K, and pressure 5.7bar. The results show: with the same equivalence ratio and P4/P1, ignition delay time increases when CO₂ ratio increases.(4) Temperature- ignition delay time curves show: with the same CO₂ ratio, ignition delay time increases with increasing equivalence ratio; the influences of the equivalence ratio on ignition delay time became smaller when the ratio of CO₂ became lager.