naca-rm-e50h31
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National Advisory Committee for Aeronautics, Research Memorandum - NACA Research on Combustors for Aircraft Gas Turbine - I - Effect of Operating Variables on Steady-State Performance
Systematic research on current aircraft gas-turbine combustors was
conducted to determine and to generalize for this type of combustion
system the effect on performance of operating variables, of geometric
or design variables, and of fuel variables. The effect of operating
variables on steady-state performance of turbojet combustors is pre-
sented; the results described pertain to liquid-fuel turbojet com-
bustors of the type in general use at present and operating on
the fuels for which they were designed - gasoline or kerosene. Trends
depicting the effect of inlet-air pressure, temperature, and velocity
and fuel-air ratio on performance characteristics, such as combustion
efficiency, maximum temperature rise attainable, pressure loss, and
combustor-outlet temperature distribution are described for a number of
combustors. These trends are further discussed as they effect signif-
icant changes in the turbojet engine, such as altitude operational lim-
its, specific fuel consumption, thrust, acceleration, and turbine life.
The combustion efficiency decreases if combustor-inlet pressure
p or temperature T is decreased, or if-combustor velocity V is
increased. The parameter pT/V plotted against combustion efficiency
generalizes a large-amount of combustor data adequately. Because of
the effects of the combustor-inlet pressure and temperature, combustion
efficiency decreases with increased altitude or decreased engine speed.
The maximum temperature rise attainable from a given combustor
also decreases if combustor-inlet pressure or temperature is decreased,
or if combustor reference velocity is increased. As a result, for any
aircraft gas turbine, at each engine speed an altitude exists above
which the engine will not operate because of a limit in temperature
rise available from the combustor. These same factors similarly
impose a limit on the temperature rise available for acceleration at
altitudes below the operational limit Just described.
According to examination of data on various combustors, more than
one—half of the usual 4- to 6-percent loss in the combustor of the
inlet total pressure is usually due to aerodynamic drag in the com-
bustor.
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