Impact of Harsh environment on Commercial engines

Aviation, like any other form of transport is dependent on the atmosphere conditions (weather). Hence the need to analyze the impact of the environment on the lift force, drag, and a thrust of the aircraft engines. The values of these parameters are proportional to the density of the air. While in practice, the effect of an altitude on the engine thrust is considered, influence of the temperature and humidity is often overlooked. Higher values of these two parameters are decreasing the lift force and engine thrust. Such conditions are limiting safe takeoff of heavy loaded aircraft (including aerostats).

For now, I would like to discuss on the impact of the operating environment on Turbine engines .

In general a harsh operating environment, for a jet/turbofan engine will result in an accelerated deterioration rate in performance or part failure. Thermal transits that are experienced from engine start to stabilized cruise and can have a major impact on overall engine performance.

Higher humidity increases the likelihood of inlets icing and can cause engine shutdown during flight. The phenomenon, which is hard to observe is a gradual loss of thrust due to the erosive effects of dust on the aerodynamic profiles of the blades and vanes, and its deposition in cavities of engine ducts where locally speed is reduced or direction of airflow is changed. The source of dust are mainly contaminated runways, industry, and occasionally volcanic eruptions or dust storms. The more dirt/sand there is in the air the faster the deterioration rate of the engine. The main issue here is erosion of the low and high pressure compressor airfoils. HPC blade erosion has a major impact on performance deterioration as the sand/dirt is centrifuged outward and erodes the blade tip chord length. This degrades the compressors ability to pump air, which means a loss of performance. Another issue is loss of surface finish of the compressor blades which further reduces the compressor efficiency. One other impact of particulate in the airflow of the engine is that some of it will make its way into the internal cooling cavities of the turbine blades and vanes. This will cling to the internal surfaces of the blades and vanes, reducing the efficiency of the cooling air passing through the airfoils.

The main impact of these temperature conditions are felt in the hot section of the engine, and can result in cracking of the nozzle guide vanes and oxidation of the turbine blades.

The engine itself can grow several inches in length and various rotating components and cases grow at different rates which impacts blade tip clearances and thus efficiency . Operating from airports where the outside air temperature is consistently at or near corner point (the max. OAT where the engine can make full rated thrust) the harder it is on the engine and will result in an increased performance deterioration rate.

The engine on wing time for those operating in Harsh environment are affected greatly and inturn induces high operating cost as the MTBO / MTBR are impacted due to low ON WING performance .

Even though the engines maybe of same configuration , but depending on the operating environment they are valued considerable at lower price if it has a history of harsh environment operation. Many ADs and SBs have been released to compensate the operating condition but in the end the asset value is depreciated nonetheless. Maintenance Reserves and lease fees are adjusted accordingly but in the end it is the asset owners and the operators who bears the burnt of it. Interestingly, the harsh environment region is growing every day and newer countries are now bein added into the list. The high depreciation and cost of shop visits have a direct impact on the enconomic status of each fleet which inturn starts a chain reaction of transferring the cost, from Asset owners to operators to pax. Maybe there will be some further modification from OEM side or reduced new engine price for harsh environment operators to compensate rhe impact. Well, time will tell.

#harshenvironment #civilaviation #mro #maintenance #aviation