Fuel viscosity effects

Droplet size, particularly at high velocities, is controlled primarily by the relative velocity between liquid and air and in part by fuel viscosity and density (7). Surface tension has a minor effect. Minimum droplet size is achieved when the nozzle is designed to provide maximum physical contact between air and fuel. Hence primary air is introduced within the nozzle to provide both swid and shearing forces. Vaporization time is characteristically related to the square of droplet diameter and is inversely proportional to pressure drop across the atomizer (7). 

Increasing fuel viscosity by the addition of more viscous fuel components will probably not be an effective solution to this problem. The addition of viscous, high-boiling-point components to fuel may lead to combustion smoke and soot formation. 

Fuel may be highly paraffinic/waxy Fuel viscosity may be too high to effectively filter and pump at low temperatures Product is near or at its pour point... 

Effects of Fuel Viscosity and Pressure on Spray Formation. Atomizer is Delavan 90A, 2 gph and Fuel is No. 6 Oil. 

The specific values of exponents a, b, and c determined for the two distillate fuels are presented in Table II. The correlation of SMD with mass flow rate, pressure, and viscosity are in generally good agreement with typical values for petroleum fuels (11). Due to the limited properties variation available with these three fuels, the effects of surface tension and density could not be determined independently. 

While fuel viscosity variations were large and had a dominant effect on spray formation, differences between SRC-II and No. 2 fuel oil are also consistent with surface tension and liquid density differences. 

Smoke emissions increased with hydrogen deficient fuels. Results indicated that the smoke level was primarily sensitive to fuel hydrogen content and fuel preparation technique. Smoke levels also showed sensitivity to fuel viscosity and initial boiling point. A better understanding of these interrelated effects is necessary to more confidently translate these subscale results into definitive design data. 

Because of viscosity effects, the velocity of the fluid is zero at the fuel surface. The velocity vectors of the fluid layers increase as one moves further away from the surface, as indicated in Fig. 6.7. Since the fluid layer in contact with the fuel is at rest, heat actually flows by conduction from the element to this layer, and the rate of heat flow will depend on the temperature gradient of the fluid at the surface. This in turn, however, depends on the rate at which heat is being carried away by the moving layers of the coolant, and so is a function of the coolant flow rate. The equation which gives the heat flux from the fuel plate to the coolant is... 

Refractive Index. The effect of mol wt (1400-4000) on the refractive index (RI) increment of PPG in ben2ene has been measured (167). The RI increments of polyglycols containing aUphatic ether moieties are negative drj/dc (mL/g) = —0.055. A plot of RI vs 1/Af is linear and approaches the value for PO itself (109). The RI, density, and viscosity of PPG—salt complexes, which maybe useful as polymer electrolytes in batteries and fuel cells have been measured (168). The variation of RI with temperature and salt concentration was measured for complexes formed with PPG and some sodium and lithium salts. Generally, the RI decreases with temperature, with the rate of change increasing as the concentration increases. 

Paraffin crystalline waxes Apart from asphaltenes, a number of differing molecular weight paraffinic waxes are also present. These progressively crystallize at lowering temperatures (their respective pour points). These waxes increase friction and resistance to flow, so that the viscosity of the fuel is raised. This type of problem is controlled by the use of pour-point depressants (viscosity improvers), which limit the growth of the crystals at their nucleation sites within the fuel. They also have a dispersing effect. 

---