Diesel EGT

[Burnit]

What is the best position to mount a thermocouple for EGT readings in NON Turbo Diesel applications.
Some variables apply i know like Extractors, in this case is the collector the best position. I suppose this is self explanitory without individual thermocouples for each cylinder.
Also STD manifolds where the exhaust runners merg into one oultet would seem to be best.

The issue i see is the varying lengths of the primary tubes of extractors compared to the short style std manifolds--how much variation in EGT can be expected due to the varying lengths.

Or should the EGT be taken further along the exhaust at a set distance regardless of the type of manifold, extractors used?

Also a word on the correct tune EGT for diesels would be helpful for full load maximum power WOT etc.

Thank you

 

[Lou Scannon]

The location to measure EGTs should be specified by the OEM. Otherwise it's just guesswork. Only the OEM knows what the safe limits are for EGT measured at a specific location using a specific sensor under specific operating conditions. This is a bit of a greased pig to get your arms around, and unless you have the resources of an OEM to take engines to the limit and beyond and/or perform analysis to predict operating limits via modelling, you need to find out the OEM's criteria for field evaluation and use them.

 

[Burnit]

Thanks hemi,

Yes, i understand where your coming from & your correct with your answer but just wondering if we could generalise the questions to gain a broader approach rather than an exact science so to speak. Say it was guesswork what approach should we take?

Thanks

 

[IceStationZebra]

I come up with two different ideas.
1. Put the thermocouple near the manifold outlet so you are averaging all of the cylinders together.
2. If you know that one cylinder runs hotter than the others put it just past the manifold inlet flange. I would assume on most engines that the rear cylinders run the hottest, but that would depend on the intake design, airflow around the engine, etc.

In general you want to keep the thermocouple close to the engine so that you see the hottest temps. The farther away the less responsive it will be.

If you are taking the manifold off to drill and tap the hole it wouldn't be hard to add a second hole. You could try both locations under the same conditions and see which one is hotter.

As for temp range:
-Bank recommends keeping turbine inlet temps below 1300°F, >1400°F is playing with fire.
- GM 6.2L NA, 1100max/900 sustained
- Ford 6.9/7.3 NA, 1250max/950 sustained degrees

ISZ

 

[Burnit]

IceStationZebra,

Thanks for that, the sustained degree numbers are helpful.

The bigger problem i have is the fitting of extractors & reading the EGT without mulitple probes & or drilling & tapping holes in each primary pipe.

I have thought of tuning with the std type manifolds first & then changing to extractors but one can then only assune the same tune will be the result.
With the increased flow of the extractors surely the tune will change.

Is reading the actual Surface temp of the extractors near the head flange out of the question, this would seem a lot easier & less expensive to do with surface mount sensors instead of drilling & tapping & the expense of all the probes & multi channel thermocouple readout etc.

What do you think?

Thanks

 

[samplesecond]

Ideally you have one thermocouple at the BASE of each exhaust port. If only installing a single thermocouple, then (as mentioned above) place at the base of the hottest running cylinder.

Placing the thermocouple at the base of the exhaust port discharge will help ensure the measured temperature is closely representative of what is actually happening in the combustion chamber.

 

[patprimmer]

Thermocouples are really quite cheap.

You can get by with two. One stays in place as a reference point, the other is moved from cylinder to cylinder and is referred each time to the one that stays put.

With two, you can easily read manually real time and compare. With more than two this quickly gets more complicated.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[IceStationZebra]

As to your question regarding surface temp - it would be close if you are running a steady state condition, but wouldn't be very good for transitory use.

I was going to mention the relatively cheap cost of thermocouples, but didn't want the discussion to diverge. If you want to use industrial equipment instead of automotive type gauges - I checked Omega and 6" K-types with inconel sheath are ~$30. K-type is good to approx 2280°F/1250°C. Stainless steel is only good to approx 1600°F which is fairly close to the 1400° you could see so go with inconel (2100°F). Handheld meters can be had for $65 on up. Many multimeters are now equipped with K-type inputs as well.

ISZ