Analysis of Failed Startup Sequence of a Single Spool Turbojet Engine

During the static testing of a single spool turbojet engine (400 N Titan Engine) running on Jet A-1 as fuel, the startup sequence failed, however, the engine started successfully upon changing the fuel to diesel. Till that point, the engine was running successfully and a series of tests were conducted for about 5 hours. The ambient temperature varied from 15 ⁰C (winter) to 37 ⁰C (summer) and relative humidity varied from 40% to 90%. The start sequence failed at the maximum temperature (35 ⁰C) and moderate humidity conditions (50%). In this manuscript, the starting sequence is investigated using the measured parameters which include pressure, temperature, rotor speed and mass flow rate. The data was recorded using the computer-based data acquisition system from National Instruments^®_­.

During the starting sequence, the rotor speed is required to follow a path reaching the calibration speed for the successful start sequence. However, during the actual testing, after the engine reaches ~80% of the calibration value, a sudden drop in the rotor speed is observed. This sudden drop in rotor speed is followed by the surge of the compressor and flameout in the combustion chamber.

The data suggests that, as the rotor speed reaches ~80% of the calibration value, there is significant drop in the combustion efficiency which results in reduction of the net shaft power available (negative). This decrease in net shaft power reduces the shaft speed to which the engine control system responds by increasing the fuel flow rate. After this, the compressor operation moves towards the surge region (as suggested by dynamic pressure measurement) followed by flameout. However, the engine started successfully upon changing the fuel to diesel (from Jet A-1) which has different properties from Jet A-1.

Based on this, it is asserted that the ambient conditions in addition to the fuel properties affect the combustion behavior (in terms of efficiency), especially during the engine transients.