http://www.dsti.net/News/54534.htm
波音和加拿大研究人員在發動機結冰研究上取得突破
[據英國《飛行國際》2009年6月14日報導] 波音和加拿大國家研究委員會(NRCC)相信,他們可能已經弄清楚為什麼冰塊會在發動機內部溫度遠高於結冰溫度時仍然可以在壓氣機中形成並導致發動機失效。
過去人們對這一現象無法完全理解,發動機結冰曾導致2006年一架快達航空公司的空客A330飛機雙發空中停車。現在,波音和NRCC的研究人員計畫在一個發動機試車臺上重現這一過程。
NRCC總裁Pierre Coulombe表示:“這些結果對於理解發動機怎樣在冰晶條件下結冰是重要的第一步。現在,我們可以開始模擬這一現象,並加以預測和阻止。”
Coulombe指的是發動機內部結冰形成後,導致發動機失速或熄火的現象。在高空時,如果附近有雷暴,會形成比平時尺寸要小的冰晶,這使得它們不易被機載設備(例如氣象雷達)發現,這些小冰晶一旦被發動機吞入,它們的習性就會改變。
在NRCC位於渥太華的高空研究中心,研究人員發現他們能夠重新創造真實的高空條件,包括發動機內結冰環境溫度、低壓和更溫暖的環境。
研究人員隨後製造出一些“濃度低於15 g/m3、大小為70~200微米”的冰晶,並將它們吹入模擬的發動機試車台中。
NRCC和波音公司表示結果比預期的更好。他們認為:“這個專案的目標是在溫度高於0°C (32°F)時,在一個模擬發動機的S型進氣道內造成冰塊以不同的數量增長,以便研究人員能夠建立影響發動機性能的冰塊大小的模型。此外,由於測試過程已經採用正規和高速錄影做了記錄,他們能夠判斷哪些條件下冰塊會增加,哪些條件下不會增加。”
波音公司航空安全部門主管Corky Townsend表示:“這是波音公司為解決這個重要的業內安全問題所進行的多步驟計畫的一個關鍵部分。”由於發動機在飛行中失去推力或失效而引起的公務機和民航機事故已達14起。在所有的事例中——包括快達航空公司的A330,發動機都成功的重新啟動了。
這個問題非常嚴重,因為許多高空、遠端飛行都要經過熱帶地區穿越海洋,這時高空常出現暴雨,因此增加了發動機結冰的風險,使得航空公司基於雙發延程規則而提供的安全承諾受到了挑戰。(中國航空工業發展研究中心 胡海)
http://www.flightglobal.com/articles/2009/06/14/327934/paris-air-show-engine-icing-research-breakthrough.html
PARIS AIR SHOW: Engine icing research breakthrough
By David Learmount
DATE:14/06/09
SOURCE:Flight Daily News
Boeing and the National Research Council of Canada (NRCC, Hall 3, E41) have chosen Le Bourget to announce that they may have cracked the mystery of how ice can form in jet engine compressors despite internal temperatures being well above freezing, causing engine failure.
This phenomenon, which caused both engines in a Qatar Airlines Airbus A330 to shut down in flight near Shanghai in 2006, has been imperfectly understood, but now the Boeing-NRCC partnership has managed to reproduce the process in a test rig.
NRC president Pierre Coulombe says: "These results are an important first step in understanding what's happening at the particle level with engine icing in ice crystal conditions. Now we can begin the process of modelling the phenomenon to predict and prevent it."
Coulombe is referring to the conditions under which internal engine icing has occurred, causing engine stall or flameout. At high level, in the vicinity of thunderstorms, ice crystals are believed to form in smaller sizes than they normally do, making them less detectable to aircraft equipment like weather radar, and changing their behaviour when they are ingested into an engine.
At the NRCC's Ottawa altitude research centre, the organisation reveals, it has been able to recreate realistic high-altitude conditions, including the freezing ambient temperatures, low pressure, and the warmer conditions inside the engine.
Researchers then produced ice crystals "in the range of 70 to 200 microns in concentrations up to 15 grammes per cubic metre" and blew them into the simulated engine rig.
The result, says NRC-Boeing, was more promising than they expected: "Although the goal of the project was to create ice accretion in any quantity in a simulated engine S-duct in temperatures above 0°C, the researchers...were able to build ice formations of the size which could offset engine performance. In addition, because the tests were recorded using regular and high-speed video, they were able to determine some conditions in which accretion will and will not occur."
Boeing's aviation safety director Corky Townsend says: "This is a critical part of Boeing's multi-step plan to tackle this important industry safety issue." There have been some 14 incidents involving business jets and airliners in which the engines lost power or failed in flight. In almost all cases - including the Qatar A330 - they were successfully restarted.
This issue is critical because more high-level, long-range flights than ever are crossing oceanic areas via the tropics where high-altitude storm activity is normal, so the engine icing risk is increased, and this challenges the premises on which extended range twin engine operations rules are based.