What Causes Performance Degradation in a Gas Turbine Engine?

A gas turbine engine is simultaneously a straightforward concept and an incredibly sophisticated piece of machinery. Performance degradation can result from numerous factors that impact the environment, the fuel, and the components within the system itself. There are more than we list here, but the following four represent some of the most significant causes of performance degradation in a gas turbine engine.

Fouling

Fouling results from particular contaminants that build up on the airfoil (blade) and annulus surfaces. As the buildup increases, it will severely impact flow capacity within the gas turbine engine. Fouling can reduce performance by altering the shape of the airfoil, changing the inlet angle, creating unwanted blade surface roughness, or even decreasing the opening of the airfoil throat. Increased roughness results in friction losses and corresponding reductions in efficiency. Regular cleaning of the blades or flushing of the system while in operation (with a properly selected solvent) effectively eliminates blade fouling.

However, the more common type of gas turbine engine fouling is to the compressor. In fact, it’s been shown that 70 to 85% of all performance loss to in-operation gas turbine engines can be attributed to compressor fouling. That makes fouling the single greatest cause of performance degradation. It’s critical to avoid the introduction of contaminants to the compressor through fuel, water, steam, inlet air, or cooling air.

Erosion

Erosion involves the striking of objects in the flow path with solid particles that enter through the inlet or gas stream. It’s even possible for bits of carbon build-up to free from the nozzles or ice shards to break away from the inlet and cause gradual erosion damage. Impacts from hard particles can create abrasive removal of material and introduce other damaging particles into the path (minuscule pieces of the engine material itself). As with fouling, erosion can gradually damage or roughen the components in the flow path, altering friction and geometry and causing performance degradation.

Air filtration generally protects industrial gas turbine engines from particles that can cause erosion, but engines used in aviation are at particularly high risk. Pumps or compressors that process fluid that may carry solid materials can also be impacted by erosion.

Corrosion

Corrosion is the result of chemical reactions between internal components and various contaminants—salts, acids, or reactive gasses—introduced into the system. Hot corrosion results in both lost material from components in the flow path and the adhesion of these materials to aero components further down the path. Another corrosion risk is high-temperature oxidation or the chemical reaction that results from metal atoms (in the components) and oxygen in the extreme temperatures of the hot gaseous environment that surrounds them. Any mechanical damage or erosion to components can impact the effectiveness of anti-oxidation coatings or treatments. 

Heat

It’s important to measure temperatures at points throughout the engine and maintain a robust thermodynamic history, not only in factory tests but also in the field. As described above, high-temperature oxidation (one of many risks of excessive gas turbine engine heat) creates performance degradation via damage to internal components. However, it is not the only heat risk. 

The combustion exit temperature profile can also be impacted by deterioration, leading to variation in local temperature peaks that can damage the gas turbine engine. Altered temperature profiles have consequences (such as increases to secondary flow) that reduce turbine efficiency and performance. 

Particle fusion is another cause of performance degradation. In older engines, dry particles could pass through without fusing to hot surfaces without injuring the engine. However, newer generation gas turbine engines run hotter. They can experience problems when engine heat exceeds the fusion temperature of the particles, which will melt and stick to the heated metal of the components. Molten masses cause performance degradation by clocking cooling passages, changing airfoil shape/creating roughness, interfering with heat transfer, and causing thermal fatigue.

There are other heat complications relative to inlet temperatures, exhaust temperatures, and more. However, it suffices to say that unexpected spikes in temperature—even in a small, localized area of the engine—can dramatically reduce efficiency and cause irreversible performance degradation (or even catastrophic failures) in gas turbine engines.

Real-time temperature tracking technology with on-blade sensors effectively combats the threat of engine hot spots and intermittent heat spikes in the thermal cycle. The groundbreaking wireless sensor technology pioneered by Sensatek is positioned to revolutionize temperature sensing capabilities in gas turbine engines. Contact us for more information on how this technology can reduce maintenance costs and optimize fleet performance.