An Assessment of the Economic Viability of Engine Wash Procedures on the Lifecycle Cost of an Aircraft Fleet

Abstract

Aircraft operators find themselves in an environment in which the economic and ecological pressure on companies is constantly increasing. To address this, significant improvements of aircraft efficiency are necessary. One way to reduce both operating cost and the environmental impact is to regularly perform on-wing engine washes which reduce the exhaust gas temperature as well as improve aircraft fuel consumption. To estimate the lifecycle impact of engine cleaning procedures, a variety of factors must be taken into account, ranging from environmental to operational. The lifecycle costing method developed by DLR, known as LYFE (Lifecycle Cash Flow Environment), enables the consideration of various factors to investigate the impact of engine washes over the lifetime of an aircraft or fleet. LYFE uses discrete event simulation to model the product lifecycle from order to operation until disposal of an aircraft fleet. For this analysis the tool is extended to separate the lifecycles of the engines and those of the aircraft, which enables the modeling of switching engines among aircraft. To more realistically represent engine fouling and engine performance degradation, representative weather data at airports is also included in the simulation. Using this information, we have developed a prognostics model to monitor the health of the engine, predict the timing of engine shop visits and automatically and dynamically schedule engine wash events. For the latter, three different algorithms varying in the prognostic horizon were developed and compared to one another. The results show that engine washing can improve the time on wing of the engine by up to 2240 flight cycles. Due to lifetime limitations by life limited parts and assumptions within this study, no extension of the service life of the engine can be achieved within the scope of this investigation. On the other hand, the fuel cost could be reduced at an average of 1.2% while the total cost remained the same. With this holistic view of how engine washes within a fleet influence the time on wing of the engine and affect its lifecycle cost a much more realistic statement about this on-wing maintenance action is possible.