Lefebvre, A. H.
Abstract:
A correlating parameter for gas turbine combustion performance, based
on a 'burning velocity' theory for primary zone combustion is derived using
a more direct approach than that originally employed by Greenhough and
Levebvre.1 The various applications of this parameter are discussed and it is
shown that the shape of correlated performance curves is directly related
to the combustion processes taking place in the various zones of the chamber.
An alternative, more basic, theory is presented in which it is assumed
that the low-pressure performance of a spray-type combustor is controlled by
a balance between the separate effects of chemical reaction, fuel evaporation
and mixing. It is argued that combustion efficiency is a function of p2 /M
where x = 2.0, 1.7 or 1.0 depending upon whether the rate of heat release is
governed by chemical reaction, fuel evaporation or mixing respectively. It
is postulated that the amount by which values of x determined experimentally
fall below 1.7 provides a useful practical indication of the extent to which
mixing is intervening in the overall combustion process. At high pressures
the mixing process predominates, x = 1, and it is shown that, for any given
fuel-air ratio, the rate of heat release depends only on flame-tube geometry
and mode of fuel injection, and is independent of chamber size, pressure loss
factor and the operating conditions of pressure, temperature and velocity.
The basic principles involved in the design of primary combustion zones
for maximum volumetric heat release rate and maximum stability in terms of
wide burning range are discussed.