Development And Application Of Quantitative Calibration Method On The Diesel Sprays Characteristics Using Planar Laser Induced Exciplex Fluorescence Technique

Low Temperature Combustion (LTC) engines are being paid much attention and widely investigated due to their potential of high thermal efficiency and very low emissions of NOx and particulate matter (PM). However, for the diesel-fuel LTC engines, there are still some critical problems that need to be solved. Improvement of the mixing rate between spray and air over the whole injection and ignition period is one of the most important technique to realize LTC and control the combustion rate and ignition time. In this study, both the essential characteristics and control approaches of diesel-spray were investigated by Planar Laser Induced Exciplex Fluorescence technique by measuring the images of liquid and vapor phase of spray. A constant vessel which designed to simulate the high temperature and pressure environment in diesel engine was developed and Planar Laser Induced Exciplex Fluorescence system was established for the investigation of evaporated diesel spray. Liquid and vapor phase of spray can be measured simultaneously and the highest ignition pressure of constant vessel can reach up to 14Mpa and simulated temperature up to 1200K. Also, the pulse fuel injection system was developed with the 7.5:1 and 10.5:1 pressure amplifier equipment. And the signal control system for ignition, laser, injection, imaging, gas filling is established to arrange the signal timing according to the need of experiments.The quantitative calibration method for PLIEF was developed and established to acquire the relation betweent the fluorescence and concentration of spray, i.e. to get the coefficient Kvapor. Quantitative concentration distribution of vapor and liquid-phase spray were acquired by the method. Also, the factors which had effect on the calibration were investigated during the experiments. It was found that with the increasing of ambient pressure the Kvapor decreased and at higher ambient temperature the faster rate of the decreasing. And ambient gas component had no influence on the Kvapor. The enhancement of ambient temperature promoted the K before 600K and lower the Kvapor after 600K which is the inflexion. According the results the 3-D Map about ambient temperature and pressure for Kvapor was established and the quantitative information of spray concentration can be acquired from the 3-D Map.In the research of evaporated spray characteristics some injection parameters such as injection pressure and nozzle diameters, and ambient parameters such as ambient pressure, density and temperature were investigated by using the quantitative calibration results. It was found that the improvement of injection pressure promoted the kinetic energy of the spray and the penetration rate of vapor-phase was enhanced. It also affected the breakup of liquid-phase so as to accerelate the form of vapor-phase and increased the homogeneity of the spray as a result. Smaller injector nozzle diameter shorten the penetration and narrow the angle of the spray. The mixing condition between fuel and air was deteriorated. But on the other hand the breakup and evaporation of liquid-phase was enhanced clearly because of smaller nozzle. The vapor-phase of spray distributed more homogeneously. The shorter penetration was got with the higher density of ambient gas so as to the diffusion rate decreased. But the mixing rate of fuel and air increased because of higher density environment bring more gas in constant space volume. Ambient temperature had a key effect on the evaporating rate of the spray. The liquid penetration was shorten and max equivalence appeared earlier with the increasing of ambient temperature. It proved that the temperature enhancement promoted the heat exchange between fuel and air. Therefore the evaporating rate was increased and the form of vapor-phase became easier and faster.In the experiment in optical engine it was found that the bump ring in the BUMP combustion chamber can strip off the wall jet to form secondary jet and after the impingement more homogeneous and broader distribution of vapor was formed. And this effect was significantly enhanced with the rising of injection pressure. But there was a minimal height of bump and appropriate secondary distance existing for the bump ring to work effectively. CT technique can acquire the 3-D distribution of spray with different sheet position betweent laser and spray. It provided the new way for analysis the spray characteristics and in favor of acquirement of precise information of the spray.