| Abstract | A brief series of tests was performed to examine the effects of changes in the Pilot and Main Specific Gravity adjustments of the Afterburner Fuel Control on the steady-state and transient performance of a J85-CAN-15 turbojet engine. In particular, it was believed that, by resetting these adjustments to the "JP5 & 6" positions while operating the engine on JP4 fuel, slightly lower afterburner Pilot and Main fuel flowrates would be scheduled by the control unit, resulting in less severe rotor speed fluctuations during the initiation and development of the afterburning process. This in turn would reduce the transient stress levels in the turbine/compressor shaft and alleviate a cracking problem experienced by this component in operational service.
Throttle bursts to MAX Λ/B were performed from initial power settings of 40% THRUST and 95% SPEED. The test results showed no distinct difference in compressor rotor acceleration rate as a function of Afterburner Fuel Control Specific Gravity settings. Moreover, it was noted that the maximum acceleration rates occurred prior to afterburner light-up and hence the maximum transient torque values were unaffected by the Afterburner Fuel Control Specific Gravity adjustments. It was also noted that the maximum rotor acceleration rates recorded during the bursts from 40% THRUST to MAX A/B (8000 rpm/sec) were approximately twice those recorded during the bursts from 95% SPEED to MAX A/B. However, even these maximum accelerations were estimated to raise compressor shaft torque by only about 15% above steady state conditions at MILITARY or AFTERBURNER power settings.
Inconsistent and erratic nozzle behaviour during development of the afterburning process in both series of transients caused fluctuations in all recorded dependent variables. Although these fluctuations were not severe, they may be significant in Low Cycle Fatigue life consumption. |
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