Exhaust gas Temperatures 2

[Wilbo99]

* Can anyone tell me why the exh. gas temp. after a cylinder is less than the exh. gas temp at the Turbo inlet?? Engine is a 8000 kW Wartsila 12V38.

* How to check the condition of the turbo on the temp. parameters?

Thanks in advance

 

[MikeHalloran]

The exhaust gas will lose some heat to the manifold that carries it to the turbo, and there will be some pressure drop, too.

The turbo _outlet_ temperature will be _much_ lower than the turbo inlet temp, because the gas loses energy to the turbo.



Mike Halloran
Pembroke Pines, FL, USA

 

[rmw]

The gas leaving the cylinder through the valves is usually at a high velocity. As it enters the manifold the velocity slows down and there is a pressure recovery. If this is what is going on, you should read a slightly lower pressure at the cylinder outlet than the turbo inlet as well. Since pressure and temperature are related, the pressure recovery causes a temperature rise.

rmw

 

[Wilbo99]

Thanks for the replies. Just came back from sea so no time to reply...

Fact is that the Temp. after cilinders are about 490 degr C. Inlet of the Turbo's (V-engine) is about 530 degr.C. So where is the 40 degr C temp incr. is coming from???

 

[aviat]

Your turbine is a restriction in your exhaust system (approx. 8” Hg). When the gases come down the pipe and encounter this restriction they slow down, and the pressure and temperature go up as per Bernoulli’s principle. How much pressure you get depends on the speed of the compressor, which depends on how much flow there is through the turbine. If you keep increasing exhaust, the compressor keeps increasing. This circle would continue until the turbo would destroy itself. To prevent this the engineers put a control in the exhaust. Often a waste gate is used, which is plumbed in parallel with the turbine, and references and is controlled by the inlet air, to provide feedback.

When you first start the engine (idle) most of the exhaust is bypassing the turbine though waste gate and TIT will be lower than EGT. When you give engine more fuel the controller senses the change and closes the waste gate somewhat, which sends more exhaust through the turbine. The closing of the waste gate will cause the TIT to reach a point where it is hotter than the EGT, and they both go up together with nearly the same spread until you reach your max TIT.

This is a simplified explanation because there are several more things occurring. The location of the probes has an effect on readings, as well as the EGT can change from day to day. But after you get used to the system you can use to temps to troubleshoot the engine.

 

[mohpower]

how about the fact that each cylinder release gases after each combustion cycle (4-cycles engines) and the all gases coming from all cylinders go to outlet exhaust pipe and then to the turbo and in this case the turbo receives continuously hot gases.

just a thought.

thanks

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