For reasons of economy, gas turbine atomizers are often tested at lower pressures and temperatures than exist in the engine. The spray behaviour differs in the rig from that in the engine. For good measurement practice it is necessary to find rig operating conditions at which the aspect of the two phase flow being measured (e.g. patternation, droplet size) is similar in the rig to that in the engine. We describe a number of strategies for finding operating conditions which allow good measurement. These conditions reduce the air and fuel flow rates below engine values but conserve certain flow quantities. We define an error function to quantify how well the rig conditions match key non-dimensional groups.We consider an example of a typical aero gas turbine airblast atomizer operated in a rig at 323 K. To preserve patternation it is desirable to conserve the Reynolds (Re), Mach (Ma) and Stokes (Stk) numbers. A perfect match is not possible but we find a number of acceptable compromise strategies. The match improves as the rig pressure increases up to ∼600 kPa where Re and Ma are matched and Stk is correct to an order of magnitude. Further pressure increase give little improvement. It may be possible to match Stk by using a different fuel.

Combustion instabilities have impeded the development of lean burn low NOx gas turbine combustors. Acoustic waves in the combustor interact with the fuel/air mixing process to modulate the air-fuel ratio (AFR). The fluctuating AFR causes the heat release rate to fluctuate. If the Rayleigh criterion is obeyed the acoustic wave is amplified. The acoustic intensity may reduce the lifetime of the mechanical parts, due to vibration and increased heat transfer, or cause the operating noise levels to exceed regulatory limits. The fuel injector has an important role in the interaction of the acoustic field and the AFR. In rig tests, injectors of slightly different design can yield different noise levels in the same combustor. We have applied planer LIF and Mie imaging and Laser Sheet Dropsizing (LSD) to study the interaction of the fuel injector spray with an imposed acoustic disturbance in low cost non-combusting tests. The injector is run at pressures up to 7 bar in the Cranfield optical sprays rig. By careful scaling of the injector operating conditions the spray structure found in the rig can be made representative of that in the engine. An acoustic perturbation is imposed on the airflow. The spray field is probed with a dual LIF/Mie laser sheet imaging system. Laser Induced Fluorescence (LIF) images are calibrated to yield maps of AFR. The LIF and Mie images are ratioed and calibrated to produce maps of the Sauter Mean Diameter. Images are taken at several phases in the acoustic perturbation cycle. From these the oscillatory response of the spray to the acoustic perturbation is extracted. A transfer function describing the strength and phase of the response of AFR and SMD to the acoustic perturbation is extracted. Both AFR and SMD exhibit fluctuations which are coherent with the imposed acoustic oscillation. Comparison of the transfer functions to the results of combustion tests suggest that the spray measurements can predict which injectors are likely to encourage strong instability in the combustor.

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The need of the hour is to look forward to alternative fuels to swipe out the dependence on fossil fuels, as biofuels from various feedstocks are being experimented worldwide. However, it is difficult to implement biodiesel from a single feedstock to replace the existing fossil fuels. It is reliable to obtain biodiesel from local feedstock and to make multiple biodiesel mixtures blended with diesel. The present work relies more on biofuels and acts as a step towards fossil fuel-free engine or at least to snatch the lion's share of the fossil fuels. In this contest, the experiment was carried out by using treble biofuels i.e., WCOBD + PSBD + Bio-hydrogen at different injection pressures (i.e., 200bar, 225bar and 250bar) and compared them with a similar engine that utilised fossil fuel as the stand-alone fuel. The mixture ratios were B10, B20 and B30 and the enrichment of hydrogen was done at 4lpm, 6lpm and 8lpm. The results showed that the brake thermal efficiency of dual biofuel blended diesel decreased as compared to that of the base fuel and increased with hydrogen enriched biodiesel. Hence, the brake specific energy consumption decreased for the hydrogen enriched fuel and the exhaust emissions of CO and CO2 were reduced, however, NOx showed an increasing trend as usual.