Impacts of low-pressure (LP) compressor’s deterioration of a turbofan engine upon fuel-usage of a military aircraft

Abstract

Some in-service deterioration in any mechanical device, such as an aircraft's gas-turbine engine, is inevitable. However, its extent and rate depend upon the qualities of design and manufacture, as well as on the maintenance/repair practices followed by the users. Deterioration of an engine normally results in the engine seeking a different steady operating-point relative to that for an engine without any deterioration. The variation in engine's steady operating point leads to changes in the specific fuel consumption (SFC) and/or fuel flow (FF). Any rise in SFC and/or FF and thereby the increased quantity of fuel required is of prime importance in military aviation.For a military aircraft's mission-profiles (consisting of several flight-segments), using a bespoke computer simulations, the consequences of low-pressure compressor's deterioration of an aeroengine upon the weight of the fuel that has to be carried and consumed are predicted. This will help in making wiser management decisions (such as whether to remove an aero-engine from the aircraft for maintenance or to continue using it with some changes in aircraft's mission profile). Hence improved engine utilization can be achieved, so resulting in lower overall life-cycle costs.Many criteria have to be satisfied to ensure the overall effectiveness of an aircraft. Among these, the fuel-usage is the most important. Besides higher fuel costs, the weight of the fuel carried has a direct effect on the cargo pay-load or/and number of passengers that can be conveyed in the case of civil aviation and on the weapon-carrying capability, range, combat time and the time to reach the target for military operations (2) .

Impacts of low-pressure (LP) compressors’ fouling of a turbofan upon operational-effectiveness of a military aircraft

“…SFC for engines with 10% LPC's FI is significantly higher as compared with that for engines without any LPC's fouling. Whereas FF for engines with 10% LPC's FI is initially less but later it becomes higher as compared with that for engines without any LPC's deterioration because the rate of increase of FF with increasing TET for engines with fouled LPC's is higher than that of engines without any LPC's fouling [24].…”

“…Whereas at the same altitude and Mach number, the SFC increases almost linearly with increasing LPC's fouling for all four conditions (i.e. constant net-thrust, constant LP spool-speed, constant TET and constant HPT's rotational-speed) considered separately [24].…”

“…Both are significantly less for engines with reheat ON as compared with that without reheat. The difference of FF and SFC values for engines with reheat ON and without reheat increases almost linearly with increasing Mach number [24].…”

“…However, the variation of FF and SFC for engines with 10% LPC's FI as compared with that without any LPC's fouling decreases almost linearly with increasing altitude. Also both are significantly less for engines with reheat ON as compared with that without reheat [24].…”

“…The trend of variations at different altitudes as well as Mach numbers remains almost same. However, both are significantly less with reheat ON as compared with that of without reheat [24]. As a result of reheat ON, the flight Mach-number would start increasing until the thrust available from engines is balanced by the aircraft's drag.…”