Clifford A. Moses

Effects of Flame Temperature and Fuel Composition on Soot Formation in Gas Turbine Combustors

Abstract The dependence of relative soot concentration on flame temperature and fuel composition was measured in a small-scale research combustor. The purpose was to gain a better understanding of the correlation of soot formation with H/C ratio. First, the effect of flame temperature on soot concentration was determined by varying the burner inlet temperature. Then, 10 fuels with H/C ratios in the range of 1.98 to 1.55 were used in an experiment 10 determine the effects of both flame temperature and fuel composition on relative soot concentration. Flame temperatures were calculated and measured optically by the Kurlbaum technique. Flame opacity measurements were used to determine relative soot concentration. The results showed that while soot concentration increased significantly as flame temperature increased, the ncrease in soot with fuels of lower H/C ratio was much stronger than could be attributed to associated increases in the tlame temperature.

Fuel-Specification Considerations for Biomass Pyrolysis Liquids to be Used in Stationary Gas Turbines

A review of the physical and chemical properties of various biomass pyrolysis liquids suggests that they will require special consideration for use in current gas turbines for power generation. A new balance between fuel quality and engine design characteristics will have to found for the effective use of these liquids. Unfortunately, the values of many critical properties are beyond the range of experience with any distillate fuel, residual fuel, or alternate fuel such as coal liquids or shale oil. Furthermore, there appear to be some characteristics which are new and may require additional considerations in the fuel specification. Some system testing with biomass fuels covering the range of properties will be necessary to develop relevant relationships before design modifications can be made to accommodate biomass fuels and for fuel specifications to be established.Copyright

Effect of Reynolds Number on Deposition in Fuels Flowing Over Heated Surfaces

An increasing demand is being put on the fuel as a heat sink in modern aircraft. In the end, the fuel flows through the atomizer which on the one hand is the hottest part of its thermal history, but on the other hand the most critical for resisting deposition. Most studies have concentrated on the chemistry of deposition, and in recent years there have been modeling efforts. Deposition is really the end product of a coupling between heat transfer to the fuel, chemical reactions to form insoluble gums, followed by the transport of these gums to the surface to form deposits. There is conflicting evidence and theory in the literature concerning the effect of turbulence on deposition, i.e., whether deposition increases or decreases with increasing Reynolds number. This paper demonstrates through a heat transfer analysis that the effect of Reynolds number depends upon the boundary/initial conditions. If the flow is heated from the surface, deposition decreases with increasing Reynolds number; however, for isothermal flows, i.e., preheated, deposition will increase with Reynolds number.Copyright

Diagnostics for fuel sprays as applied to emulsified fuels

Measurements of drop-size distributions and vaporized fuel concentrations have been combined with a spray model in the comparative study of the evaporation of sprays of mulsified and non-emulsified (neat) fuels at elevated temperatures and pressures. The fuel spray was generated by a pressure jet atomizer and was polydisperse; the air stream was approximately fully-developed turbulent flow in a constant area duct. Diagnostic techniques have been adapted or developed which allow rapid measurements of overall drop-size distributions in the presence of evaporation in high-temperature high-pressure air, and also the fuel vapor concentration distribution within sprays. It was concluded that even in conditions of turbulence and high Reynolds number for drop motion relative to the air, some emulsified fuel drops apparently undergo microexplosions. Further, it was determined that the initial atomization quality depends on the air conditions, with better atomization at higher air densities. This implies that spray drop-size measurements performed at atmospheric conditions need to be corrected for air density and temperature effects to predict atomization quality for altitude relight or high-pressure combustion. A spray model has been developed which represents the spray being studied and provides data in a form comparable to the experimental diagnostics. Comparisons are provided between the predicted and measured drop-size distribution and fuel-vapor concentrations during the evaporation process. Trends for changes in drop-size distribution (both average size and width of the distribution) with distance from the nozzle are predicted fairly well by the model except close (

Drop Size Measurements in Evaporating Realistic Sprays of Emulsified and Neat Fuels

A comparative study has been performed of the drop-size distribution of sprays of emulsified and neat distillate-type aviation fuels at elevated temperatures (308K to 700K) and pressures (101 kPa to 586 kPa). All drop-size data were obtained with a Malvern Model 2200 Particle Sizer based on the forward angle diffraction pattern produced by the drops when illuminated by a collimated HeNe laser beam. Fuels included a standard multicomponent jet fuel, Jet-A, and a single component fuel, hexadecane, in both neat form and emulsified with 20 percent (by vol.) water and 2 percent (by vol.) surfactant. The initial breakup and atomization of a neat and emulsified fuel were quite similar at all conditions, and the evaporation rates appeared similar at various temperatures for pressures at or below about 300 kPa. At higher pressures with elevated temperatures the emulsified fuels of both types produce drops of significantly smaller Sauter mean diameter than the neat fuels as distance from the nozzle increases. These results are consistent with the microexplosion hypothesis, but there could also be alternative explanations. A detailed computer model which predicts heat up rates, steady state drop temperatures, evaporation rates, and drop trajectories has been used to help interpret the results. An additional point which has been observed is that the initial Sauter mean diameter produced with constant differential nozzle pressure is dependent on the air pressure with an exponent of about −0.4, i.e., SMD ∼ Pair−0.4. Some recent correlations often quoted omit the pressure (density) of air term.Copyright

INJECTION, ATOMIZATION AND COMBUSTION OF CARBON SLURRY FUELS

Three different carbon blacks were used to formulate nine different slurries in DF-2. The rheological properties of each formulation were examined to determine deviations from Newtonian behavior. The spray characteristics of selected formulations were then examined in a highpressure, high-temperature injection bomb. The cone angle decreased and the penetration rates increased for all of the slurries tested as compared to straight DF-2. These changes were more pronounced as the concentration of carbon black increased. Six formulations of three types of carbon black were tested in a single-cylinder, direct injection CLR engine. Apparent heat release rates were computed as a function of crankangle from the cylinder pressure data. Based on the engine performance tests and some limited durability testing it appears that wellformulated carbon black slurries have only minor effects on engine performance and durability.

Crude sources and refining trends and their impact on future jet fuel properties

Forecasts of heavier, higher sulfur crudes show the need for more hydrotreating for sulfur removal. Increasing demands for middle distillate products will require more conversion of heavy fractions and more hydrogen processing. JP-5 jet fuel, normally a straight run product, is likely to be made by hydrogenation and hydrocracking with resulting changes in properties. Synthetic crudes from oil shale and coal have special processing needs and will introduce other changes in chemical and physical properties. The study identified properties of future JP-5 production for use in an alternate test procedure to qualify new Navy jet fuels. 21 refs.