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By Colin Kilmaster
Compressor washes should be a routine procedure for those who maintain and operate gas turbine engines.
Albeit some engineers/A&P mechanics might consider compressor washes to be just another mundane task we must do other than - “because it is written into our operations procedures” - let’s consider how compressor washes affect turbine engine performance and life cycles.
The T53 engine variant is a free power turbine engine that employs a five-stage axial and single-stage centrifugal compressor driven by a two-stage gas producer turbine. Dramatic engine performance degradation occurs with the ongoing accumulation of airborne contaminants within the compressor module thereby reducing the aerodynamic efficiency of the compressor blades that can result in deteriorating engine performance, unsatisfactory acceleration and higher than normal Exhaust Gas Temperature (EGT).
Contamination, especially in high salt operating environments, can also lead to abnormal corrosion of the engine components. In order to maintain engine performance and reduce the corrosive effects on the engine, the debris that builds up in the compressor needs to be removed.
We do this through routine compressor washes.
Tips for effective compressor washes
A typical compressor wash involves:
- chemical wash (pre-mix product solutions that are biodegradable and non toxic or spray solvents into an engine with low core temperature),
- pre-determined soaking period (as required) a thorough water rinse followed by;
- an engine ground/drying run activating bleed air functions to ensure relevant accessories are also dried
Operators may choose to establish a wash schedule, the frequency of wash events relating to the amount of contaminants being ingested into the engine subject to the operating environment, while abiding by recommended OEM procedures.
First and foremost, always refer to the OEM procedures to ensure compliance with the specific engine type. The OEM specifies which chemicals can be used to wash the compressor, often referencing between a military specification or readily available solutions with a set specific chemical parameter. It is recommended operators develop a compressor wash schedule that best meets the operating situation IAW Honeywell MM references;
330.2 Maint. Manual, section 72-00-00, page 702
"290.2 Maint. Manual, section 72-00-00, page 702
350.2 Maint. Manual, section 72-00-00, page 702
Note: use injection hardware and equipment that is also approved by the applicable OEM or engineering group to ensure correct/ proper wash and not introducing FOD hazards. Removing the contaminants restores engine efficiency, resulting in better fuel economy. It may result in lower EGT, lower corrosion, and restored performance.
Compressor washing is the single most cost-effective maintenance procedure for turbine engines. Performance is affected by both gas turbine thermal efficiency and the mechanical health of the components. Since the compressor typically consumes approximately 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. Reduced engine power margins can induce safety of flight considerations especially as the working environments that contribute the most contaminants to these performance degradations are those environments we least want performance issues.
Not only is engine performance affected, but damage to the compressor blades caused by contamination can lead to engine failure. Performed correctly, compressor washes can dramatically improve engine performance, increase engine life cycles and lower operating costs through:
• First line of maintenance action in any engine performance recovery related issues;
• Reduce potential engine compressor stalling
Lowering fuel consumption;
Improving engine compressor efficiency;
• Reducing Exhaust Gas Temperatures (EGT);
• Increasing hot section rotating group longevity;
• Reduce corrosion effects on the engine; and
• Extend Time Between Overhauls (TBOs)