Combustion fuel droplet

Moreover, the same surfactant structures that favor dispersion of fuel droplets in the combustion chamber most iikely play a role in reducing particulate emissions. (... 

A minimum volatihty is frequently specified to assure adequate vaporization under low temperature conditions. It can be defined either by a vapor pressure measurement or by initial distillation temperature limits. Vaporization promotes engine start-up. Fuel vapor pressure assumes an important role particularly at low temperature. For example, if fuel has cooled to —40°C, as at arctic bases, the amount of vapor produced is well below the lean flammabihty limit. In this case a spark igniter must vaporize enough fuel droplets to initiate combustion. Start-up under the extreme temperature conditions of the arctic is a major constraint in converting the Air Force from volatile JP-4 to kerosene-type JP-8, the military counterpart of commercial Jet Al. 

A non-invasive infrared (IK) method has been developed for the measurement of temperatures of small moving fuel droplets in combustion chambers. 7111 The IR system is composed of two coupled off-axis parabolic mirrors and a MCT LWIR detector. The system was used to measure the temperature variations in a chain of monosized droplets generated with equal spacing and diameter (200 pm), moving at a velocity of >5 m/s and evaporating in ambient air. The system was also evaluated for droplet temperature measurements in flames under combustion conditions. 

First, the evaporation rate of a single fuel droplet is calculated before considering the combustion of this fuel droplet or, to say it more exactly, one calculates the evaporation of a fuel droplet in the absence of combustion. Since the concern is with diffusional processes, it is best to start by reconsidering the laws that hold for diffusional processes. 

Transient Heating of Droplets When a cold liquid fuel droplet is injected into a hot stream or ignited by some other source, it must be heated to its steady-state temperature Ts derived in the last section. Since the heat-up time can influence the V/2 law, particularly for high-boiling-point fuels, it is of interest to examine the effect of the droplet heating mode on the main bulk combustion characteristic—the burning time. 

Suppose fuel droplets of various sizes are formed at one end of a combustor and move with the gas through the combustor at a velocity of 30m/s. It is known that the 50-pm droplets completely vaporize in 5 ms. It is desired to vaporize completely each droplet of 100 pm and less before they exit the combustion chamber. What is the minimum length of the combustion chamber allowable in design to achieve this goal ... 

Sirignano, W. A. 1983. Fuel droplet vaporization and spray combustion theory. Progress Energy Combustion Science 9 291-322. 

Williams, F. A. 1973. Combustion of droplets of liquid fuels A review. Combustion Flame 21 1-31. 

One effect of valve sleeve, piston ring, and cylinder wall wear is leakage of lubricating oil into the combustion chamber. When lubricating oil accumulates in the combustion chamber and bums with fuel, the exhaust smoke appears blue in color. Wear due to abrasion or corrosion has the same effect. At times, unbumed fuel can also appear as blue smoke if fuel droplets are finely dispersed in the exhaust. Blue smoke is a symptom of a mechanical problem rather than a fuel performance problem. 

In order for fuel to combust and bum efficiently, it must be atomized into extremely small droplets. Fuel injectors aid tremendously in performing this role. However, if fuel viscosity is high, atomization into small droplets becomes difficult. Highly viscous fuel will not disperse freely after being sprayed from the fuel injector. The fuel instead sprays as a stream or large drops rather than as a fine mist. The result is a decrease in fuel efficiency and power due to incomplete burning of larger fuel droplets. 

The assumption of steady-state combustion as used in the preceding theoretical development is a good approximation for those fuel droplets which exhibit a short life time so that the average temperature in the interior of the liquid lags sufficiently. For slow burning droplets, on the other hand, the temperature pattern within the droplet may show large variations with time. Therefore, the heat required to vaporize a unit weight of fuel will also be a function of time. But even more important are the chemical phe-... 

Kobayasi, K., Experimental Study on the Combustion of a Fuel Droplet, Fifth Sym-... 

Kumagai, S., Isoda, H., Combustion of Fuel Droplets in a Vibrating Air Field, Fifth... 

Miesse, C. C., Stability of the Flame Front in the Combustion of Liquid Fuel Droplets, ... 

Lag of Fuel Droplets, Fifth Symposium on Combustion, p. 148, Reinhold, New York, 1955. 

Gas-continuous impinging streams with a liquid as the dispersed phase has wide application, such as in the combustion of liquid fuel droplets, absorption, water-spray cooling of air, etc. [9]. In such systems the dispersity of liquids plays a very important role affecting heat and mass transfer rates, because it influences both the interface area and the mean transfer coefficient. Wu et al. [68] investigated the influence of impinging streams on the dispersity of liquid. 

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