DESCRIPTION

Technical Description

Jet engines are gas turbines which generate thrust. Jet engines are used on aircraft for propulsion due to their low weight and high performance.

The ET 796 trainer investigates the behaviour during operation of a jet engine.

ET 796 includes the following components: jet engine (with compressor, annular combustion chamber, turbine, and propelling nozzle), fuel system, starter and ignition system, and measurement and control equipment. The gas turbine works as an open cyclic process, with the ambient air being drawn out and fed back in.

In the jet engine, the ambient air drawn in is first brought to a higher pressure in the single-stage radial compressor. In the downstream combustion chamber, fuel is added to the compressed air and the resulting mixture is ignited. The temperature and flow velocity of the gas increase. The gas flows out of the combustion chamber into the single-stage axial turbine and discharges a portion of its energy to the turbine. This turbine drives the compressor. In the propelling nozzle, the partially expanded and cooled gas expands to ambient atmospheric pressure and the gas accelerates to almost the speed of sound. The high-speed gas outflow generates the thrust. In order to reduce the outlet temperature, the exhaust gas stream is mixed with the ambient air in a mixing pipe. The gas turbine is started fully automatically with the aid of an electric starter. 

The annular combustion chamber is between the compressor and the turbine. With optimum fuel utilisation, low pressure loss, and good ignition properties, the ring shape of this combustion chamber is typical of the design used in jet engines. The movable turbine platform, with a force sensor, enables measurement of the thrust.

The speed, temperatures, and mass flow rates of the air and fuel are recorded using sensors. The measured values can be read on digital displays. At the same time, the measured values can also be transmitted directly to a PC via USB. The data acquisition software is included.

The well-structured instructional material sets out the fundamentals and provides a step-by-step guide through the experiments.

Learning Objectives / Experiments

- behaviour during operation of a jet engine including start-up procedure
- determination of the specific thrust
- determination of the specific fuel consumption
- determination of lambda (fuel-air ratio)