Fuel Nozzle Maintenance: What to Watch Out For
Did you know the opening at the tip of each fuel nozzle in a PT6A engine is as small as a pin hole in diameter? It doesn’t take much to obstruct one. Make sure the fuel continues flowing freely and correctly in your engine.
WHY FUEL NOZZLE BLOCKAGES HAPPEN
Fuel nozzle maintenance is needed when there are blockages, usually caused by carbon build-up at the tip. This can happen due to low-quality fuel or in some cases, inappropriate operating practices. For example, to avoid raw fuel hitting the nozzle just before shutdown, it’s important to stabilize the engine for two minutes before shutting down after a flight to avoid a fuel nozzle blockage.
WHAT TO WATCH OUT FOR
Look out for streaking, spitting and drooling around a fuel nozzle’s spray tip. If you see any of these symptoms, it’s possible that large drops of unatomized fuel (which has stayed in a liquid state, whereas it needs to convert to a misted spray to properly burn in the combustor) are being dispersed outside the spray cone or hitting the nozzle face. Fuel needs to be evenly distributed throughout the combustion chamber liner for optimal burn and engine performance.
WHAT FUEL NOZZLE MAINTENANCE WILL DO FOR YOUR ENGINE
Poor fuel nozzle flows are a major cause of reduced hot section life. They can wreak havoc on components, especially the vane ring and even the turbine blades. If fuel nozzles are not maintained in good condition, it could also lead to local overheating or burning, improper flame propagation and small exit duct or compressor turbine vane burning, to name just a few fuel nozzle maintenance issues.
RUN REGULAR FUEL NOZZLE MAINTENANCE TESTS
It’s a good idea to conduct borescope inspections as well as periodic fuel nozzle leak and function tests. Leak tests will reveal any problems between the nozzle tip, lock tab and adapter assembly at the sealing areas. Flow checking will reveal any irregularities in the spray patterns, such as streaking or dripping. If you have any doubts about a fuel nozzle’s flow pattern, it’s best to play it safe and reject the tip.
KEEP YOUR FUEL NOZZLE CLEAN
It’s recommended that you remove fuel nozzles and clean them ultrasonically every 200 to 600 hours of flight. Some PT6A engines are equipped with trend monitoring systems that remove the guesswork when it comes to cleaning frequency by alerting operators if their fuel nozzles are performing poorly. When cleaning nozzles, it’s well worth taking the extra time to clean them thoroughly: improper cleaning often results in unnecessary replacements.