Quantitative Study Of Structure And Concentration Of Diesel Spray In Heavy Duty Diesel Engine Like Conditions By PLIEF Technique

For diesel engine, fuel injection, atomization and mixing with the air is a key step to the whole combustion process. However, the study of diesel spray were mainly carried out in the low ambient density (below 35 kg/m3) by predecessor by far, which is far from the modern heavy-duty diesel engine high-load operating conditions (ambient density of 60 kg/m3 and above). It is necessary to quantitatively study the diesel spray under the modern heavy-duty diesel engine similar conditions.A constant-volume bomb was developed to obtain high ambient density and high temperature environment. The highest 1100K temperature and density of 60kg/m3 environmental simulation was achieved. The concentration and temperature both of vapor phase and liquid phase were quantitatively calibrated. On this basis, the effects of ambient density, ambient temperature, injection pressure, injector diameter and oxygen concentration on diesel spray structure and concentration were quantitatively studied under heavy-duty diesel engine similar conditions in the constant-volume bomb by using planar laser induced fluorescence technique. The experimental range of temperature was 800-1100K and 20-100 kg/m3 for density, and 100-220MPa for injection pressure, and 0-10-0.18mm for injector diameter.It was found that the diesel spray structure could be described by parameters such as penetrations and cone angles both of vapor phase and liquid phase, liquid core, the sheath of vapor phase spray, dense mixed zone (Φ> 2), lean mixed zone (Φ≤2), vapor phase spray head and so on under heavy-duty diesel engine similar conditions. Accordingly, structure model of diesel spray was established under heavy-duty diesel engine similar conditions, in which there was vapor phase spray with relatively high equivalence ratio in the liquid core zone, which is different from the spray model established by John E. Dec. The concentration both of vapor phase and liquid phase gradually increase from 0 to a maximum from outside to the inner, the temperature of vapor phase spray decreases gradually from the mean environmental value to the lowest from outside to the inner under heavy-duty diesel engine similar conditions. Spray development process can be divided into three stages of early, mid, full development period. In the early stage of spray development, liquid core length increases linearly with time, the penetrations and cone angles both of vapor phase and liquid phase are almost the same with each other, the equivalence ratio of vapor phase spray is low. In the middle stage of spray development, liquid core length increases exponentially with time until to its maximum value, the penetrations and cone angles both of vapor phase and liquid phase are almost the same with each other too, the transient maximum equivalence ratio of vapor phase spray gradually increases. In the full development stage of spray, liquid core length remains basically unchanged, vapor phase spray keeps on developing forward, there is obviously vapor phase spray head, the transient maximum equivalence ratio of vapor phase spray rises to its maximum value and then decreases, liquid core,vapor phase dense mixed zone and vapor phase low temperature core overlap each other in principle.It was also found that the ambient density, ambient temperature, injection pressure, injector diameter and oxygen concentration had important influence on the diesel spray temporal structure and concentration, the diesel spray structure and concentration near ignition timing (namely the starting point of combustion path in theΦ-T diagram) were significantly impacted by the factors too under heavy-duty diesel engine similar conditions. For the increase of vapor phase fuel mass fraction in the lean mixed zone and improvement of spray homogeneity in the vapor phase spray head, and incrassation of the sheath of vapor phase spray, the reduction of injector diameter and decrease of ambient temperature and increase of ambient density were highly substitutable. Moreover, the maximum equivalence ratio of vapor phase spray significantly decreased by the reduction of injector diameter and decrease of ambient temperature. There was no dense mixed zone in the vapor phase spray when ambient temperature was reduced to 800K near ignition timing.