NACA-RM-E51A25

Abstract

<strong>INTRODUCTION</strong> <br>Experience has shown that the performance of a turbojet combustor is dependent on flight conditions and that poor performance is generally encountered at high altitudes and at low engine speeds. Consequently, a general program to determine the performance characteristics of turbojet combustors under various flight conditions is being conducted at the NACA lewis laboratory with a view to establishing optimum design criterions. Steady-state characteristics, such as altitude operational limits, combustion efficiently, and pressure drop, of single combustors both of the annular and of the can type have been investigated for different designs and for a number of deferent fuels (for example, references 1 to 4). Altitude ignition and acceleration are, of course, of temporarily inoperative or for single-engine fighters incurring blow-out at high altitudes. A study of the ignition characteristics of several fuels in a single can-type combustor is presented in reference 5 and a wind-tunnel investigation of altitude starting and acceleration characteristics of the J47 engine is reported in reference 6. <br>In addition to such factors as inertia of the rotating parts and decreased air mass flow at altitude, an important factor affecting acceleration of a turbojet plane is the temperature rise produced by the combustor in excess of that required t maintain the engine at steady-state operation for a given flight condition. This excess temperature rise available for acceleration is normally limited for two reasons: (1) Flame blow-out may occur as the result of over-rich fuel-air ratios; or (2) allowable turbine-inlet temperatures may be exceeded. <br>The investigation reported herein was conducted to determine the altitude ignition and acceleration characteristics of a single J47 combustor. Additional data were obtained to evaluate the altitude operational limits, combustion efficiency, and total-pressure losses of the combustor. Ignition limits were determined at an altitude of 30,000 feet and at engine rotational speeds below and above equilibrium wind-milling speeds for simulated flight speeds of 400 and 354 miles per hour, respectively. Additional ignition-limit tests were made over a range of altitudes for a simulated flight speed of 400 miles per hour and an engine speed equivalent to equilibrium windmilling speed. Acceleration characteristics were determined at a 30,000-foot simulated altitude over a wide range of engine rotational speeds (12.7-to 88.6-percent rated engine speed) at a simulated flight speed of 400 miles per hour at and below equilibrium windmilling speed and 354 miles per hour above equilibrium windmilling speed. All tests, including those for altitude operational limit and combustion efficiency, were made with weathered aviation gasoline that corresponded to MIL-F-5572, grade 115/145 fuel, form which 15 percent of the more volatile constituents had been removed to simulate altitude vaporization losses. Limited tests for comparisons were made with MIL-F-5616, a kerosene-type fuel that is the design fuel for the J47 combustor.