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Diesel Exhaust Gas Temperature

7267 Views 15 Replies 5 Participants Last post by Zanshin, Sep 14, 2009

Zanshin

Discussion Starter · Sep 9, 2009

I am thinking of putting an EGT gauge on my Yanmar and using the temperature to ensure that I don't overwork my engine. I have a Gori prop with a cruising mode which, if run at too high RPM, could end up overheating the engine (I've done that before) and think I could use the EGT to adjust the RPMs to an optimal value.

Has onzone here actually used EGT on a marine diesel?

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sailak

· #2 · Sep 9, 2009

My only experience with EGT has been on aircraft engines...and used only to adjust fuel/air mixture.

I would think manifold pressure or BMEP would be a better way to measure power/workload on the engine.

negrini

· #3 · Sep 10, 2009

Once you measure the backpressure at SWOT, it will never change (unless you clog the exhaust somewhere), so BMEP at manifold (??? not sure how to use it there !!) will not tell you what you want. This is a fixed theoretical measure, not counting on propeler load. I never used a market EGT, but used the VOLVO accessory installed right after your manifold, for that on my previous boat (MD2040). Used to quickly imdentify high temp on engine, by measuring exhaust temp, you clearly will get alarms for temp increase waaay earlier than water temp gauge. A good achieve if something has clogged the water colling system. But to adjust rpm<>load ..... best is to keep engine at peace revs

Zanshin

Discussion Starter · #4 · Sep 10, 2009

The "cruising mode" propellor setting at 2500rpm in calm waters is fine, but the same rpm in medium swell at sea (can) cause overheating. I can't overheat the diesel with normal setting, but get significantly less mileage and speed in that mode. Thus I am looking for a way to dynamically adjust my RPMs and not to overheat or overload the engine and can only think of the EGT between the exhaust manifold and the turbocharger. I know this is used a lot in trucks to get optimal performance, but since I can't adjust the AFR in the Yanmar I was thinking (again) of using the exhaust temperature. I did have a diesel mechanic in St. Martin tell me it wasn't necessary, but he wasn't the one whose engine alarm went off while trying to get through Antigua's English Harbour before darkness set in

negrini

· #5 · Sep 11, 2009

hummmm, an Autoprop would adjust itself ? Providing a variable pitch to self-adjust to the load ? When you say "dynamically adjust" you mean an automated adjustment ? I think the EGT at your manifold would provide a rasonable source of heating measure, reliable, and fast enough to not overheat engine, but your engine will reduce rpm for other reasons other than just overload, and response might be somehow slow. Another source could be your engine's governor so you can have a sense of load posing resistance to your drivetrain. I think you should measure the governor and balance with rpm (compared at no load). A simple (mechanical) solution would be more elegant .... I think.

Zanshin

Discussion Starter · #6 · Sep 11, 2009

negrini - I meant that I would adjust the RPM so that the system didn't overload/overheat, nothing mechanical or automatic. And I don't mean changing the settings continually, but finding the highest setting for a given wind/wave/sail combination. Right now I really can't tell unless I wait the 10-15 minutes after making a change and if the water temp alarm doesn't go off then I'm still OK...

dieselboy

· #7 · Sep 11, 2009

Zanshin said:
negrini - I meant that I would adjust the RPM so that the system didn't overload/overheat, nothing mechanical or automatic. And I don't mean changing the settings continually, but finding the highest setting for a given wind/wave/sail combination. Right now I really can't tell unless I wait the 10-15 minutes after making a change and if the water temp alarm doesn't go off then I'm still OK...

With respect i must say that you may not be looking at the big picture.

While a EGT will give you advance warning of an pending over heat. You should not be running that fine line to begin with. That is a very dangerous and costly game to be played.

I would recommend taking a step back and examining the whole situation.
If your load is causing an over heat then look in to the cond of the cooling system. sea pump, air relief line on the head to remove any steam or air,location of the air up take," is it breathing in hot air from the exhaust", does it also have a water pump? t-stat? how smooth does the engine run? do you have weak fuel inj's causing fuel to be injected in in a stream not at a high pressure " fog" this causes hot spots..
Factors like these are what you really need to be looking in to.
just remember that the two biggest and most common death's of Diesel engines are over heating and water contamination.. Your doing one right now..

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Zanshin

Discussion Starter · #8 · Sep 11, 2009

I am trying to do this in order to ensure that I don't overheat the engine. The engine is more than sufficient to plug away at 2500rpm all day when the propellor is in normal mode, which gives me 6ish knots. If I motorsail in the so-called "overdrive" mode the same RPM gives me 8 knots or more with the same fuel consumption. What I am trying to find is as high an RPM setting that I can cruise with when necessary without undue stress to the engine. My Yanmar panel only has an enginer overheat light but nothing to give me advance warning that I am approaching that point.
I wonder if a cooling water temperature gauge would be simpler to install and could give me the same information, albeit somewhat slower.

dieselboy

· #9 · Sep 11, 2009

Install a direct feed " non electric" it will give a real time temp feed just mount ti where you can see it.

jrd22

· #10 · Sep 11, 2009

I'm not familiar with the Gori, but from what you said it seems that in "overdrive" mode you must be lugging the engine which will lead to an early death. Can you reach the recommended WOT rpm's when in overdrive? If not, then it is the same as having the incorrect prop installed. If I am missing something regarding the situation please let me know, but you can't have increased speed through the water at the same rpm without a change of pitch or diameter of the wheel. The exception would be the Autoprop, which automtically adjusts pitch based on rpm and boat speed, and load.

negrini

· #11 · Sep 11, 2009

Zanshin, if you're looking for a temp gauge on a permanent mount, I think EGT on manifold will be the fastest way to warn you against overheat. VOLVO sells an exhaust mounted sensor to measure the temp of raw water mixed to gas discharge, and claims this way, you can get warnings earlier than the fresh coolant temperature. Otherwise, you can simply use a precise poin-and-shoot temp sensor and create your own table rpm/speed/temp, then add a 10-15% safety factor.

Zanshin

Discussion Starter · #12 · Sep 12, 2009

jrd22 said:
...I'm not familiar with the Gori... but you can't have increased speed through the water at the same rpm without a change of pitch or diameter of the wheelQUOTE]
Correct, the Gori prop in overdrive mode has a different pitch.

jrd22

· #13 · Sep 13, 2009

Zan- thanks, I'll have to read up on the Gori prop, but on the surface it would seem that in overdrive you are no longer using the correct pitch and therefore putting a dangerous load on the engine. When does Gori advise using the overdrive mode, and is there a warning against prolonged use or % of maximum rpm to run? Seems like a very strange concept to incorporate into a prop, it's hard enough to dial in the correct pitch in order to achieve WOT, why would you want to change it?

Zanshin

Discussion Starter · #14 · Sep 13, 2009

jrd - Yes, Gori does warn against overdriving the engine with the overdrive mode. It is designed for and particularly useful when motorsailing, using the added pitch to let the engine work at lower RPMs for a higher resultant speed. I am looking into a way at trying to get the most out of that mode without overworking the engine or other systems, the only time I used was on one passage to Antigua when I was delayed a couple of hours because of a lobster pot that got caught on the boat. Even with radar, I didn't want to go into English harbour at night and used the overdrive mode so that I would make it in time. The engine alarm caught me just as I was heading in, so I ended up heaving to and researching the cause and by the time I had it figured out it was dark (so I went into Falmouth harbour instead, where I had already anchored several times). Thus I decided to see about ensuring that I could not overheat my engine inadvertantly again and the EGT seemed the most direct solution.
The Gori propellor has 2 pitches, the "overdrive" being engaged by putting the boat into reverse until the boat makes no headway or slight aft headway, then shifting through neutral to forward. This ensures that the blades remain in their "reverse" mode, which has a stronger pitch than forward mode. By switching while the boat is moving the blades don't go into neutral, feathering mode as they are held in place by the boat motion and centripetal force keeps them extended. A very nifty and elegant solution and the overdrive mode really does make a difference to fuel consumption when motorsailing (and when not overheating the system).

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jrd22

· #15 · Sep 13, 2009

Hmmm, interesting. So in fact you are turning a properly pitched prop into an over pitched prop in order to get more speed at a lower rpm. Over pitched is over pitched, doesn't matter what rpm you are turning, it's hard on your engine (that's why it overheated). The EGT will definitely give you advanced warning of overloading, and eventual overheating, of the engine. In trucks that I have run with EGT (generally referred to as pyrometers, or "pyros") the EGT will start to climb, rapidly, when you start to climb a hill if you don't downshift. I would think that by monitoring the EGT on the boat you might be able to gradually raise the rpm and see when the temp starts to spike (the actual temp will depend on the location of the sensor). If you can locate the probe in a spot that does not have cooling water mixed with the exhaust I think you will get a much better indication of actual EGT. Good luck, be careful, seems like you're walking a fine line between fuel savings and engine damage.

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Zanshin

Discussion Starter · #16 · Sep 14, 2009

Thanks for all the advice - I've ordered an EGT gauge and meter and will install it (once the hurricane season is over and I can move aboard again).

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