A single-velocity-component phase Doppler particle analyzer is used to survey and measure local variations in drop-size distributions and drop velocities in the nearnozzle region of a practical, contraswirling, prefilming airblast atomizer. The technique of laser sheet imaging is used to obtain global patterns of the spray. All measurements are taken with a constant pressure drop across the atomizer of 5 percent, at ambient air pressures of 1, 6, and 12 bar. The liquid employed is aviation kerosine at flow rates up to 75 g/s. The results show that increasing the air pressure from 1 to 12 bar at a constant air/fuel ratio causes the initial spray cone angle to widen from 70 to 105 deg. Farther downstream the spray volume remains largely unaffected by variations in atomizer operating conditions. However, the radial distribution of fuel within the spray volume is such that increases in fuel flow rate cause a larger proportion of fuel to be contained in the outer regions of the spray. The effect of ambient pressure on the overall Sauter mean diameter is small. This is attributed to the fact that the rapid disintegration of the fuel sheet produced by the contraswirling air streams ensures that the atomization process is dominated by the “prompt” mechanism. For this mode of liquid breakup, theory predicts that mean drop sizes are independent of air pressure.

A single-velocity-component Phase Doppler Particle Analyzer is used to survey and measure local variations in drop-size distributions and drop velocities in the near-nozzle region of a practical, contra-swirling, prefilming airblast atomizer. The technique of Laser Sheet Imaging is used to obtain global patterns of the spray. All measurements are taken with a constant pressure drop across the atomizer of 5 percent, at ambient air pressures of 1, 6 and 12 bar. The liquid employed is aviation kerosine at flow rates up to 75 g/s. The results show that increasing the air pressure from 1 to 12 bar at a constant air/fuel ratio causes the initial spray cone angle to widen from 85° to 105°. Further downstream the spray volume remains largely unaffected by variations in atomizer operating conditions. However, the radial distribution of fuel within the spray volume is such that increases in fuel flow rate cause a larger proportion of fuel to be contained in the outer regions of the spray. The effect of ambient pressure on the overall Sauter mean diameter is small. This is attributed to the fact that the rapid disintegration of the fuel sheet produced by the contra-swirling air streams ensures that the atomization process is dominated by the ‘prompt’ mechanism. For this mode of liquid breakup, theory predicts that mean drop sizes are independent of air pressure.

Airblast atomisation drop size is a function of the liquid and gas flow conditions. It is also subject to the atomisation geometry, or more specifically the jet breakup mechanism. Plain jet atomisation featuring coaxial air and fuel flows has been investigated to assess the injector geometry effect on the spray characteristics. Results from various flow conditions and atomiser configurations suggest that a prompt atomisation correlation that was evaluated for prefilming injectors can be applied to plain jet airblast atomisation, in a slightly modified form. Changes in the velocity term are necessary to fit the measured data. A scaling factor has been established to compensate for the velocity term change. This factor may also imply the underlying difference between flat sheet and round jet atomisation. The liquid atomisation mode is dependent not only on the manner of geometrical air-liquid contact but also on flow conditions. In this study, the combined air-fuel velocity ratio VR and Weber number (WeVR) is found to be a criteria that determines the air flow pattern influence on atomisation. Data from this experiment show that a small change in the axial distance between the liquid jet and air orifice entrance results in marked difference in spray drop mean size under low air momentum flow conditions.

The difficulties in making spatially-resolved measurements of soot concentration inside practical combustors, which do not rely on sample extraction techniques, are highlighted. Restricted optical access presents the principal constraint to the adoption of established tomographic techniques. A novel hybrid approach, which combines a traversable laser shielding tube and conventional integrated absorption measurement, is demonstrated in two tubular combustors operating at a range of AFRs, inlet air temperatures and pressures. Measurements are reported which have been taken through existing primary and dilution ports and through additional line-of-sight holes drilled in the liner specifically for that purpose. Distinctive radial profiles of soot volume fraction emerge, reflecting the annular development of richer mixtures, which favour soot formation, downstream of the fuel injector.

Jet fuel thermal stability at high temperature is receiving increased attention recently as advanced aero engines are being pushed to high power, high pressure and temperature regimes for improved engine cycle performance and low emissions. This paper describes the rig experimental tests to assess the high fuel temperature effect on combustor emissions. A special test rig facility has been designed and set up for emission measurements with preheated fuel. The purpose of the tests is to evaluate the combustor emission characteristics under nominal and elevated fuel temperatures. The scope of the project is two fold: (1) to design, procure and establish a dedicated hot fuel deoxygenation, fuel preheat facility that can reach temperature up to 600 °F (589 K); (2) to measure combustion emissions, mainly NOx, CO and UHC, at normal and elevated fuel temperature under representative engine operating conditions. The test rig has run for extended duration and proved reliable over the whole test campaign. Measured emission results show that fuel temperature effect on NOx, CO, UHC emissions are marginal, possibly due to the low emission capability of the sector combustor that is less sensitive to fuel inlet condition changes than other combustor designs. These results indicate a manageable risk for engine development with elevated fuel temperature from the emission viewpoint.