Click here to hear the start-up Initially you can hear the oil pump, then the starter blower and the high-energy spark discharges. Ignition is rather explosive, and the turbine spins up incredibly quickly (due to its small size) to about 60,000rpm. It runs up to 100,000 rpm, back to 60,000rpm and finally the fuel is switched off.
Starting procedure
The starting blower flexible hose is connected to the compressor inlet. There is a bayonet type fitting on the compressor inlet screen, so that the hose can be coupled securely. For test purposes, the venturi can be connected between the duct and the inlet. The venturi is then connected to a manometer, so that I can measure the inlet massflow. The venturi has a calibration graph, so that I can read off the manometer the pressure difference in mm, and then take the flow rate off the graph.
The fuel pump is connected to the fuel tank. My fuel of preference at the moment is paraffin, but I'm hoping to use cheaper kerosine or agricultural diesel. The fuel pressure control on the rig front panel is set to 3bar.
The oil pump is switched on. The pump speed is adjusted automatically by a closed loop PWM controller to a set pressure of 2 bar using an electronic pressure transducer. The wiring is arranged so that the oil pump switch must be on before any other function can be powered up to prevent attempting to start with no oil pressure.
The ignition module and fuel pump are switched on. These will not operate until the 'START' button is pressed.
The 'START' button is pressed. This causes a relay to latch which powers up the fuel pump and the ignition module. The starter blower is connected to 12V d.c. At 12V the blower provides just enough air to ensure easy ignition.
After a short delay, the combustion chamber lights up. A sensor in the exhaust detects that combustion has occurred, switches the blower to 48V and latches the fuel pump relay on. At 48V the blower assists in accelerating the turbine up to the speed where it self-sustains.
A comparator in the tacho circuit detects when the turbine has reached its self sustain speed, at around 35000 rpm, and switches off the blower and ignition.
The flexible duct from the blower is removed, and the silencer is fitted to the compressor intake in its place.