Atomization and Combustion Characteristics of Antimisting Fuels Using JT8D and Air-Boost Injectors

An experimental evaluation of a bill-of-material JT8D injector, a low emission airblast JT8D injector, and an air-boost injector has been conducted at United Technologies Research Center to determine the atomization levels of antimisting fuels at operating conditions simulating engine conditions. In addition, Pratt & Whitney has evaluated the effects of using antimisting kerosene (AMK) on the performance of the components from the fuel system and the combustor of the current in-service JT8D aircraft engine. Spray characterization tests were conducted at ambient conditions using six different fuels, i.e. Jet A, one and three-pass JT8D fuel pump degraded, one and two-pass Gaulin degraded, and undegraded AMK fuels. The results of the tests indicated that the use of AMK fuel causes a noticeable decline in the quality of the spray and specifically a large increase in the Sauter Mean Diameter (SMD) for all three injectors. The undegraded AMK fuel resulted in a grossly incomplete atomization of the fuel with the spray being characterized by ligaments of fluid rather than droplets. In addition, the idle patternation data indicated that the low emission injector fuel distribution changed from a hollow cone Jet A spray with no fuel in the center to a semi-hollow spray cone using the 1- and 3-pass AMK, and this change could disrupt the primary zone recirculation pattern. Processing the AMK using the JT8D fuel pump as the degrader enhanced the atomization and spray quality, but combustion tests at P&WA using the JT8D degraded fuel indicated that the emissions levels produced were excessive and the lean blowout, relight and starting characteristics were somewhat deficient. The results from the spray quality and combustor performance tests coupled with the P&WA fuel component laboratory evaluations pointed out the need for extensive AMK degradation. Based on the levels of degradation required for successful cold filter tests and the transition velocities measured with Jet A fuel, AMK was processed with a Gaulin homogenizer to transition velocities of 5 and 9 cm/sec. Subsequent spray quality evaluations with these two levels of degraded fuels and Jet A using the JT8D airblast low emission fuel injector indicated that the gross characteristics of the Jet A and the degraded AMK fuels were similar. Perhaps even more important was the distribution data at idle, where the highly degraded fuels were almost indistinguishable from Jet A. Based on the early combustion results, it is implied that low power emissions might be very close to Jet A using the Gaulin degraded fuels.