CRYOGENIC PROBLEMS OF FLYING LONGHAUL AT 40,000 FT IN STRATOSPHERE AT -57C

摘要

To achieve higher fuel economy, the latest long-haul passenger jets, such as the Boeing 777 plus Rolls Royce Trent 800 engines, are flying higher in the stratosphere at 40,000 ft, rather than at 30,000 to 34,000 ft at the top of the troposphere, where the previous generation of passenger jets, such as the Boeing 747, are flying today. There is a sharp drop in temperature with increasing height above the troposphere, so that the latest jets are flying in much colder air at average temperatures of -57C. Moreover, the unpredictable weather patterns in the stratosphere can yield static air temperatures down to -77C, significantly colder than the air temperatures at 34,000 ft in the predictable weather of the troposphere. This paper will examine the recommendations made, and engineering solutions adopted, by the UK and US Air Safety Boards, following uncontrolled jet-engine "rollbacks", and discuss the problems more fully, including: 1. the formation of ice and hydrocarbon hydrates in the jet fuel, due to water coming out of solution, on long-haul flights in the stratosphere. 2. the possible sudden release of frozen precipitate from tank walls and/or fuel-lines, during descent to warmer temperatures and higher pressures, leading to unexpected fuel-lines blockages and uncontrolled jet-engine power failures. These problems urgently require answers, before any further uncontrolled jet-engine rollbacks take place.