Experimental Studies On Autoignition Phnomena Of Kerosene And Cracked Kerosene In A Shock Tube

In this thesis,auto-ignition phenomena of kerosene aerosol and cracked kerosene were experimentally studied to obtain ignition delay and high resolution images of radical emission and fluorescence behind a reflected shock wave.Pressure and temperature can be changed in a wide range by changing Mach number of an incident shock wave.The works are summarized as follows:(1) In chapter one,related background and progress,as well as some topics in this thesis are briefly introduced for ignition studies.(2) In chapter two,an aerosol shock tube was developed for ignition studies, including its design and assembly,fuel atomization,aerosol inlet,SMD(Sauter mean diameter) measurement by Mie scattering.Finally,long test time was confirmed in conditions of tailored contact surface at low temperature.(3) In chapter three,ignition delay timeÏ„_ig was obtained at different equivalence ratioφ,pressure p and temperature T based on detected the time histories of pressure and OH-emission.Ï„_ig is ranged from 0.10ms to 6.36ms for stoichoiometric kerosene aerosol when pressure ranged from 0.1MPa to 0.6MPa and temperature from 1163K to 1653K.AndÏ„_ig decreases as p increases under the same temperature,Ï„_ig is fitted asÏ„_ig=4.75×10^-7p^-1.16exp(17360/T).WhereÏ„_ig, p and T are in units of ms,MPa and K.Ï„_ig is ranged from 0.07ms to 5.04ms for atmospheric cracked kerosene,when temperature is ranged from 1348K to 1940K andφfrom 0.5 to 2.AndÏ„_ig increases asφincreases under the same temperature.Asφincreases,Ï„_ig deceases but ignition temperature increases,Ï„_ig is fitted asÏ„_ig=1.45×10^-7φ^1.85exp(24950/T).Regression on logarithm In(Ï„_ig) shows good linearity to T at different pressure and equivalence ratio.This provides a way to analyze the ignition delay at different pressure and equivalence ratio.According to the pressure time history,the critical temperature of deflagration increases as p decreases orφincreases.AndÏ„_ig is less than 1ms for the cases in which deflagration occurs.(4) In chapter four,images of emission and OH-PLIF were got at different pressure and equivalence ratio for kerosene aerosol and its cracked products. Instantaneous emission spectrum of CH and OH were also presented.These results show detailed flame structure and its propagation with time marching. When p is 0.1MPa,0.3MPa and 0.6MPa respectively,emission images were obtained for stochiometric kerosene aerosol at different temperature.At initial stage of ignition,the images illustrate distinguished mechanism at high and low temperature.In the case of low temperature,several flame kernels locate randomly in induction zone.Then,kernels recombine and merge into a large zone and propagate outwards,especially to reflected end of shock tube.This means that auto-ignition doesn't take place in vicinity of the reflected end.In the case of high temperature,kernels move to the end as temperature increases. Finally,kernels locate at the end whenever temperature is greater than 1600K. Furthermore,approximate images and similar mechanism were observed for cracked kerosene at different temperature whileφis kept unchanged.Weak ignition mechanism is still kept when temperature is ranged from 1536K to 1568K.If temperature is higher than 1700K,flame can overtake shock front and deflagration appears in test section.When temperature up to 1850K,detonation occurs accompanying with incoming flows and flame completely combines with shock front at the end.In this chapter,the energy of first laser pulse was qualitatively measured to check whether laser can reach its steady state after re-firing.Usually,re-firing is necessary for laser external triggering in a shock tube.The maximum time interval was determined to keep laser steady state.After solving difficulties of synchronization,OH-PLIF can be successfully obtained and detailed flame structure can be seen in cracked kerosene air mixture.Instantaneous emission spectrum of CH(CH₄/air mixture,wavelength 431nm) and OH(H₂/O₂ mixture,wavelength 308nm) were detected and compared to those calculated by LIFBASE software.The radiation temperature was also fitted by LIFBASE.(5) In chapter five,some conclusion and proposals for future studies were presented in this thesis.Some fresh ideas and methodology are listed as follows:(1) To suggest kerosene atomized outside shock tube and aerosol filled into shock tube by a special inlet device.By this way,homogeneous aerosol can be obtained in a shock tube.This provides a new way to study ignition phenomena of hydrocarbon fuels with low vapour pressure.In this thesis,almost the same pressure,temperature and fuel aerosol are provided which correspond to those in a scramjet combustor.(2) Ignition delay time of kerosene and its cracked fuels at different conditions is measured and collected which is key important for design of engine combustor.(3) Emission imaging of combustion field shows that ignition mechanism at low temperature is quite distinguished from that at high temperature for both kerosene and its cracked products.(4) OH-PLIF images were obtained for combustion field of cracked kerosene while synchronization is solved among shock tube,laser and ICCD camera.The images of emission and fluorescence demonstrate flame structure at high time and space resolution.This provides more information to understand turbulence flame.PLIF is successfully extended to diagnose ignition phenomena in a shock tube.(5) The ignition delay and spectroscopy images are key important to verify fuel chemistry kinetics.Also,these are beneficial to design the combuster of scramjet and pulsed detonation engines.