Exam question

Hi,

They are all related.

I am assuming a medium or hi speed four stroke engine here

(a)exhaust temp - If they are individual cylinder temps this will tell you about what is happening in the cylinder itself, the collective types don't allow you to identify individual cylinders with problems but can readily be an indication of excess back pressure or if in the wet section a lack of cooling water. when you have individual indicators and have the readings all over the place a good first thing to check is you LP FO Press.

(b)temp before and aft turbocharger. - The inlet to the turbine side will be a lot higher than the outlet, the temps of both are a good indication as to how the engine is running.

If the question refers to the Charge Air Cooler, the temp before the cooler where the air from the TC Compressor is delivered should be somewhat hotter than the air after the cooler, you should also be aware of what the dew point is if it is a CA Cooler where the operator can adjust the water flows and vary the cooling capacity of the cooler. ( You will only find this system on old engines)

Some modern engines will have a wax type Thermostatically controlled Valve to control the water flow if on Raw Water as was the case on the early Electronic ignition CAT 3500 Series engines or be Jacket Water Cooled as in the case of a current CAT 3500 Series 2 Engine

(c)inlet air temp - This will have a direct bearing on the other Air and Exhaust side temps. The higher the inlet air the higher the exhaust temp and all temps in between as a rule.

What exams are you going for?

And note that exhaust temperature is first and foremost an indicator of the load on a diesel engine. High loads will produce higher exhaust temperatures and may become the limiting factor when inlet air temperature is high due to environmental conditions.

Temperature differential across the turbine of a turbocharger is an indication of the efficiency of the unit. A properly functioning turbocharger will extract heat from the exhaust relative to the work it performs to convert inlet air to charge air. If the engine is loaded up and has high exhaust temps but there is little drop across the turbine, something is wrong with the compressor, which in turn will lead to higher exhaust temps for the same load.

You record those figures so that you can track performance and anticipate maintenance issues, and to get you thinking about what that hot stinky thing is doing out there in the world beyond air conditioning.

Good information above.

As a rule of thumb I have found about a 300F drop across the turbo. Before and after temps excessively lower than that is an indication of a turbo problem .
For every 1 F increase of inlet temp there should be a 5 F increase of exhaust temp. Therefor monitoring inlet temp can be used to adjust expected exhaust temps. There will be specs for exhaust temps at specific engine RPM or load that can be obtained from the engine manufacturer these temps can be compared to actual readings. There will also be a maximum allowed inlet air temp that when exceeded will cause a shortened time between rebuilds or a loss of power.

Exhaust temps are an indicator that the delivered fuel is being burned efficiently. causes for low exhaust temps are faulty injectors, incorrect valve settings either timing or lash, a loss of compression in one or more cylinders ( many causes for a loss of compression are possible).