General Discussion

Abstract

As far as aircraft engines are concerned, quite apart from the emissions aspect, the combustion situation has been getting more difficult all the time. The so-called “advanced technology” engines pose formidable problems due to the very high pressures and temperatures at which they operate. Since high pressures and temperatures are both conducive to combustion it might be argued that life should be getting easier. However, high pressures increase the liner buckling load and also enhance flame radiation leading to higher wall temperatures. The problem of wall cooling is further aggravated by the corresponding increase in inlet air temperature, so that more air is required for film-cooling. This in turn has an adverse effect on temperature traverse quality and gives rise to combustion inefficiency at altitude cruise. At the same time the problems associated with low pressures, such as altitude relighting capability are still as important as they have always been. Another significant factor is that compressor developments have led to higher and less uniform combustor inlet velocities, which have created difficult problems of air flow distribution and control, expecially in annular chambers. All things considered it is clear that emissions is a problem that we do not really need.