Technoeconomic study of engine deterioration and compressor washing for military gas turbine engines

Abstract

Despite spending much of their operating life in clear air, aircraft gas turbine engines are naturally prone to deterioration as they are generally not fitted with air filters. Engines are particularly at risk during takeoff and landing, and whilst operating in areas of pollution, sand, dust storms, etc. The build-up of contaminants, especially on the compressor surfaces, leads to a dramatic reduction in compressor efficiency, which gives rise to a loss of available power, increased fuel consumption and increased exhaust gas temperature. These conditions can lead to flight delays, inspection failures, withdrawal from service, increased operating costs and safety compromises.With the growing interest in life cycle costs for gas turbine engines, both engine manufacturers and operators are investigating the tradeoffs between performance improvements and associated maintenance costs. This report introduces the problem of output and efficiency degradation in two aero gas turbine engines (the T56–A–15 and the F110–GE–129) caused by various deterioration factors. Their causes are broadly discussed and the effects on powerplant performance are simulated and analyzed. One of the key factors leading to performance losses during operation of these engines is compressor fouling. The fouling can come from a wide variety of sources; hydrocarbons from fuel and lubricating oils; volcanic ash; pollen; marine aerosols; dust; smoke; pollution, etc. The presence of these fouling sources acts as a bonding agent for the solid contaminants, ‘gluing’ them to the compressor surfaces. Thus, the aggravation in terms of power output, fuel consumption and additional time to carry out a typical mission will be assessed and an economic analysis will be attempted in order to quantify the effects of compressor fouling on the additional costs which arise, because of this specific deterioration. The effect of compressor fouling can be maintained by frequent cleaning to improve efficiency, resulting, hence, in improved power output, fuel savings and prolonged engine life. Compressor cleaning is thoroughly presented, and the implementation of on-wing off-line cleaning on the performance of the F110 engine was investigated from a technical and economical standpoint. Finally, according to the results obtained, the optimal frequency of compressor washing for the F110 engine is estimated, in order to eliminate safety compromises, improve performance and reduce the engine’s life cycle cost.