Compressor Discharge Temperature (CDT) Probe – How it works in Aircraft?

For the uninitiated, the gas turbine you see in the single and twin-engine aircraft is an internal combustion engine that uses air to drive the engine and propeller, which in turn, propels the airplane. It achieves this with the help of heat energy from fuel that it converts to mechanical energy via the pistons.

Here’s how the gas turbine combines with the compressor:

1. Intake of air
2. Compression of the air
3. Air is mixed with right quantity of fuel and ignited.
4. Energy release in above process is used to drive the plane forward.

Now just as a car engine gets hot and needs to be kept cool, ditto the aircraft engine. In fact, keeping the aircraft engine cool is even more critical because result of a fire in the aircraft engine (caused due to ignition of fuel due to excessive heat), would be a crash and probable death of all occupants. A car on the other hand, can just be brought to a stop by the road side.

Compression always leads to heat. So, when air is compressed in an aircraft engine, heat is generated. Also, the mass flow rate of air through the engine will have an effect on engine temperature and engine performance. Other factors that affect aircraft engine performance include the engine operating temperatures, the pressure ratio of the compressor, turbine inlet temperature, and also the individual component efficiencies.

An optimum turbine inlet temperature, pressure ratio, and air mass flow rate are selected to obtain the required performance in the most efficient manner. For this reason, it is imperative that the compressor temperature be closely monitored and corrective action be initiated in the event of excessive compressor temperature.

The compressor supplies air at high static pressures typically 33 pounds of air per second. This causes a raise in the temperature of the air by about 550F as the air is compressed and moved rearward. Excess heat will lead to a drop in the aircraft engine performance. This is where the Compressor Discharge Temperature (CDT) probe comes into play.

JPI instruments manufacturers the World’s best quick responding CDT Probes which is installed just after the inter-cooler. The probe is installed with a #40 stainless steel clamp. A large clamp is supplied to fit around the airport leaving the inter-cooler.

Every CDT probe is provided with a stainless steel clamp Thimble, a Stainless Steel Exhaust Seal Washer, a Stainless Steel Screw Type Clamp and a 10 Ft. Option Wire. The CDT probe is either connected to an Electronic Data Management Systems in the cockpit or to a standalone temperature gauge.

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