ENGINE COMPRESSOR WASHES
For most of us as kids growing up, Saturday night was bath night. I don’t know how that particular night was chosen over the other nights of the week. Perhaps it has to do with the expression that cleanliness is next to godliness — and the next morning being Sunday, quite a few of us were off to church. I guess God does not like it if you come to pray and you are dirty. Now that most of us are grown up, some of us take a shower more often than others, but we all recognize the need to get clean. As aircraft maintenance professionals, we work in environments and aircraft that get dirty. There is also the matter of working with grease, solvents, oils ... you understand. Getting clean is not only good for us, but it also helps to keep us healthy. A regular washing of your aircraft’s engine(s) help to keep them healthy also and that means that they run better.
Why do we need to perform a compressor wash?
Compressor washing is the single most cost-effective maintenance procedure for any jet engine. Jet engine performance is affected by both gas turbine thermal efficiency and the mechanical health of the components. Since the compressor typically consumes 60-70 percent of power generated, compressor health is critical to engine health management. Contamination in the compressor section leads to deteriorating thermal efficiency which causes reduced engine performance. Not only is performance affected, but damage to the compressor blades caused by contamination can lead to engine failure. Compressor washes can dramatically improve engine performance, increase engine life cycles and lower operating costs by:
• Improving compressor efficiency
• Lowering fuel consumption
• Reducing exhaust gas temperatures (EGT)
• Increasing hot section parts lives
• Reducing corrosion
• Extending time between overhauls (TBOs)
How does the aircraft’s flight environment come into play?
The aircraft flight environment defines the types of contamination the engine is exposed to during operation. This is a function of the local atmospheric environment, run procedures and flight patterns. Contaminants are suspended throughout the air. These airborne contaminants are a mix of organic and inorganic fine particles including dirt, oil, soot and salt. Because of the large volume of air consumed by engine compressors, large volumes of contamination are also ingested. The contamination builds up to form a coating on the internal compressor components commonly referred to as fouling.
The accumulation of these contaminants reduces air flow and erodes the engine performance. The fouling reduces the aerodynamic efficiency of the compressor blades, resulting in further deteriorating engine performance. This performance loss is commonly referred to as the degradation curve (see example in Fig.1). The contamination, particularly in saline operating environments, also leads to corrosion of the engine components.
The loss of performance and efficiency leads to increased fuel consumption, reduced engine power, higher exhaust gas temperature (EGT) and potential stalling. Corrosion can shorten component life, increase overhaul costs and even lead to premature component failure. Although the operator cannot eliminate performance loss due to mechanical wear, degradation as a result of fouling can be reversed. The best way to maintain peak engine performance and reduce the corrosion effects on the engine is to clean the compressor on a regular schedule (see Figure 2).
What type of wash chemicals should be used and how often?
Most compressor wash chemicals are formulated to break down the organic bonds of the contaminants and dissolve the inorganic matter. This allows the contamination to be flushed out of the engine.
The engine OEM normally specifies which chemicals can be used to wash their compressors. The approved list varies from manufacturer to manufacturer. Most OEMs have tested products that are compatible with their engine materials and have a specific list of approved chemicals in their maintenance manuals. Some OEMs reference a military specification like MIL-85704 or set specific chemical parameters that the chemical must meet and confirmed with independent lab testing.
It is extremely important to use approved chemicals, such as R-MC compressor wash, that have been properly evaluated by the OEM or validated by a third party. Formulating effective compressor wash detergents requires the selection of the proper surfactants, detergents and corrosion inhibitors to achieve cleaning and still be safe for the engine and airframe. Similarly, using unapproved engine washes could cause damage to the engine or airframe such as corrosion, acrylic crazing, hydrogen embrittlement, stress corrosion cracking and other defects. Ask your supplier or overhauler to supply certifications that the products they are providing meet the engine and airframe OEM specifications.
What are the advantages and disadvantages of each type of wash?
There are two broad categories of cleaners: solvent based and detergents. Although solvents work well to dissolve organic contamination, they do not tend to work as efficiently on inorganic contamination sources like salt. This is particularly important to helicopter operators that are exposed to heavy industrial or saline environments.
There are multiple types of detergent material than can be used to design gas path cleaners. However, some are significantly more effective and have additional attributes such as higher temperature stability and corrosion inhibiting properties. These products are usually biodegradable, nontoxic and non-flammable. They are safer to use by maintenance personnel, easier to store and can be disposed of at a lower cost.
Once a product is selected, the specific wash procedure varies for each engine OEM, but the core procedure involves a few major elements. The typical compressor wash will include compressor preparation, an injection of chemical wash, a water rinse, returning the engine to its original setup and finally an engine run.
How does water quality affect the wash?
Water quality is an extremely important part of effective compressor washes. During compressor washing, water is used for mixing with concentrate and consumed during the rinse cycle of the wash. The OEMs and chemical manufacturers always recommend de-ionized or de-mineralized water. Using high-quality water minimizes the potential for introducing contaminants that would cause erosion or corrosion. Specifically, tap water contains elements like fluorine, chlorine, sodium, potassium and a host of other dissolved contaminants. At even low levels, these elements increase corrosion in jet engines. Using a poor water source or even tap water may introduce the contamination back into the engine.
How often should a compressor be washed?
Compressor wash schedules should be established by each operator based on their specific fleet and operating conditions. The frequency of wash is set by how fast the engine performance decays versus the cost of the engine wash. The local ambient environment plus flight patterns impact contaminant levels. Shorter runs at lower elevations or near the coast will accelerate the fouling curve.
By reviewing their engine trend data, every helicopter operator can construct a compressor wash schedule that best meets their economic goals. The engine data will show the effects of fouling through higher EGT and increased fuel consumption. The operator can then perform an economic analysis of what the break-even point is for the optimum wash frequency. The engine wash task can then be fit within the appropriate check point in their maintenance schedule. As an example, in a saline environment it could be a wash every day. If the helicopter is used infrequently, it could also be up to six months before a wash is needed. Consult a firm like ECT for engineering support of your wash program, equipment and optimizing your cleaning program.
Dos and don’ts of compressor washes.
Customers should always refer to their OEM maintenance manual procedures since they are engine specific. Products that are biodegradable and non toxic like R-MC yield high cleaning efficiency while improving personnel safety and lowering disposal costs. If solvents are used, make sure the proper collection, disposal and government reporting are maintained. A high-quality water source is recommended for both mixing and for rinsing. The mechanics should inspect all hardware to ensure that foreign objects are not ingested into the engine. Finally, they should be using injection hardware and equipment that is approved by the OEMs or their engineering group to ensure they are getting a proper wash and not introducing FOD hazards. Using the right equipment ensures proper pressure and flow during the compressor wash.
Engine compressor washes may not be a Saturday night ritual, but they are a means to keeping your aircraft’s engines running at peak performance and keeping healthy.
Tassone is president of Engine Cleaning Technology (ECT), located in Bridgeport, PA. He has more than 30 years’ experience with turbo machinery and holds patents in the areas of power augmentation, specialty nozzles and jet engine cleaning, all focusing on turbine performance enhancements. His private industry work experience included roles at Sermatech International and General Electric’s Industrial Turbine divisions. He holds a bachelor’s of science degree in mechanical engineering from the University of Pennsylvania and a master’s degree in business from the Wharton School of Business.