A problem of major importance to aircraft gas turbine is that of re-establishing combustion after a flame-out at high altitudes. The problem is aggravated by the fact that almost all of the accepted means of improving relight performance usually incur penalties in other important aspects of combustion performance. A question that often arises is why the ignition energy requirements of gas turbine combustors are so much higher than the corresponding values obtained from more basis studies of minimum ignition energy in gaseous and heterogeneous fuel/air mixtures, as reported in the literature. In order to shed more light on this question, a series of experiments have been conducted on the influence on minimum energy of various relevant parameters such as air pressure, temperature, velocity, turbulence, fuel/air ratio and, in the case of liquid fuels, mean drop size. The results show that, in addition to the adverse effects on ignition of low air pressure and temperature, the main reasons for the large ignition energies associated with turbojet combustors is the high level of turbulence in the primary combustion zone. Another important consideration is the mean drop size of the fuel spray. It is found that quite modest improvements to atomization quality can reduce appreciably the amount of spark energy needed to effect ignition. (Wassmann)
Basic ignition research related to altitude relight problems
Grundlagenuntersuchung zur Zuendung bezueglich der Probleme beim Wiederzuenden in grosser Hoehe
1980
13 Seiten, 5 Bilder, 8 Quellen
Conference paper
English
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