brooksjg
10th May 2010, 08:51
Quite a lot of thought has gone into other threads around here about what happens BEFORE volcanic ash gets into a turbine hot section - but not so much about what happens afterwards. For example, how to forecast? how to avoid? how to recover when the engines stall?
I've tried to start some discussion about post-flight data collection, on the principle that there will be some data to collect. However, not a lot of interest. Or maybe interest but few comments on grounds of commercial secrecy - which would be quite understandable!
Anyway - it occurs to me (as an 'outsider') that there are some interesting (??) questions not yet come up.
- OK: probably your engines DID ingest some ash during a flight on route(s) defined as 'safe' but with ash present at density x. Or a post-flight inspection shows some ash (somewhere! - depends a lot on the inspection regime in force. Present immediate post-flight checks seem MOST unlikely to find anything). What now? Log 'potential cumulative damage' and carry on flying? Do a borescope check of the hot sections of each engine (3 hours + per engine??),...?
And what about other maintenance ops? Certain operators use 'engine washing' (as in the P&W Eco-Power system, and probably other techniques too) to improve fuel performance. Presumably this works by getting the dust off compressor blades and vanes, so that airflow efficiency improves. Southwestern reckon it's cost-justified, anyway. HOWEVER, it means flushing quite a lot of water through a cold engine cranked by the starter motor. As far as the compressor goes - no problem. But what about the hot section, especially the cooling plenums and blade galleries / holes? Historically, the Romans used volcanic ash as an ingredient of cement!
So assume you've already got ash in fine powder form in the turbine cooling system. Does it make sense to allow cold, liquid water to go anywhere near it? If left alone and exposed to cold-ish air at high flow rates, it might tend to disperse through the cooling holes by itself - the particle sizes involved are definitely smaller than the holes, so it seems that the principle risks are ash particles clumping together and / or forming mud / cement due to exposure to water or moist air. Once it's formed into 'mud' I reckon it ain't ever coming out!
I already enquired at Pratt &Witney / United Technologies about the relevance / risks of Eco-Power use with ash in the engine. However, they have not done me the honour of any reply!
Another angle: What process(es) on the ground post-flight are likely to flush ash safely out of an engine? Are there any? Or do we have to assume that any ash that gets into an engine cooling system will stay there and accumulate over time? If the latter, the accountants must be sweating over their calculators, even as we speak!
I've tried to start some discussion about post-flight data collection, on the principle that there will be some data to collect. However, not a lot of interest. Or maybe interest but few comments on grounds of commercial secrecy - which would be quite understandable!
Anyway - it occurs to me (as an 'outsider') that there are some interesting (??) questions not yet come up.
- OK: probably your engines DID ingest some ash during a flight on route(s) defined as 'safe' but with ash present at density x. Or a post-flight inspection shows some ash (somewhere! - depends a lot on the inspection regime in force. Present immediate post-flight checks seem MOST unlikely to find anything). What now? Log 'potential cumulative damage' and carry on flying? Do a borescope check of the hot sections of each engine (3 hours + per engine??),...?
And what about other maintenance ops? Certain operators use 'engine washing' (as in the P&W Eco-Power system, and probably other techniques too) to improve fuel performance. Presumably this works by getting the dust off compressor blades and vanes, so that airflow efficiency improves. Southwestern reckon it's cost-justified, anyway. HOWEVER, it means flushing quite a lot of water through a cold engine cranked by the starter motor. As far as the compressor goes - no problem. But what about the hot section, especially the cooling plenums and blade galleries / holes? Historically, the Romans used volcanic ash as an ingredient of cement!
So assume you've already got ash in fine powder form in the turbine cooling system. Does it make sense to allow cold, liquid water to go anywhere near it? If left alone and exposed to cold-ish air at high flow rates, it might tend to disperse through the cooling holes by itself - the particle sizes involved are definitely smaller than the holes, so it seems that the principle risks are ash particles clumping together and / or forming mud / cement due to exposure to water or moist air. Once it's formed into 'mud' I reckon it ain't ever coming out!
I already enquired at Pratt &Witney / United Technologies about the relevance / risks of Eco-Power use with ash in the engine. However, they have not done me the honour of any reply!
Another angle: What process(es) on the ground post-flight are likely to flush ash safely out of an engine? Are there any? Or do we have to assume that any ash that gets into an engine cooling system will stay there and accumulate over time? If the latter, the accountants must be sweating over their calculators, even as we speak!