Expected EGT and engine temp Kubota EB300?

[thomasonw]

I have a DC generator setup in out boat, it is a Kubota EB-300 (EA-300??) driving a mid-sized frame alternator.  A VERY common issue with these Kubota/DC generators is overloading of the engine, in some cases bring them to a very early demise (like 100's of hours).  A primary feature of the small engine controller and regulator I have been working on  http://www.microcogen.info/index.php?topic=2941.0 is the ability to closely control the amount of load placed on the engine (by monitoring both Volts and Amps produced by the alternator, and regulating on both values).

Another feature of the controller is an EGT sensor.  My intention is to monitor EGT to determine when the engine is running at an appropriate full load, vs. running overloaded. Could even have the controller 'regulate' to this value and self optimize for maximum production / min run time.   To date (the past several years have been using a simpler  commercial regulator) I looked for overloading by looking for Black Water out the exhaust. And  I would move the governor a small amount and see if the engine could respond to changes.  With an EGT probe I want to do better and here is my question:  What range of EGT should I expect for an appropriately fully loaded engine?  And at what point should I consider I am moving into overloaded?  There are lots of google hots on the web, but they are all from Diesel pickup guys - larger engines, loafing along except for short bursts, and these all have turbos as well.   Any idea what I want to see for a small non-turbo engine working near it continuous HP rating?

And where should I try to locate the EGT probe its self?  In my setup the exhaust makes a 90' bend soon after leaving the engine and then has a 12" raiser.  The 90' bent has lots of meat to drill and tap, but I wonder if I will be getting false reading being so close to the exhaust port.  Somewhere I picked up it an EGT probe should be located 10" or so from the exhaust port on non-turbed engines.  Any advice?  There is another set of bends 12" down the road, would that perhaps be too far away?


Finally, though I have not yet done a multi-hour generator run with this new controller in place, I did noticed during a 30 minute run the engine temp only raised to 137f   Was still climbing when I stopped, but very slowly and was so far away from 180-190f.  These small engines have no temp regulation in them, even when air-cooled, and I am sure they are engineered to work over a WIDE range of temps, but am wondering if 137f just indicates too much cooling (we have a sea-water heat exchanger in place now.  52f water these days.)   Do I need to be concerned about this 137f temp, maybe adding some type of sea-water bypass around the heat exchanger.  or am I likely OK.

[jcyoungs76]

well lets tackle the known 137 f is simply too low , i dont know the coolant scheme of this engine but some sort of regulation to bring it to 195 quickly is in order here . engine wear and oil life will be compromised at this low of a temperature as well as overall combustion efficiency will be reduced. i would target a warm up cycle of 3-5 min before 195-215 the temp you choose to run at has quite a bit to do with overall efficiency and it should be noted that modern auto engines electronically control coolant temp and do not make attempts at cooling until 219 degrees ( ex 2013 chev cruze ) the reason for pushing above 212 is to drive off moisture in the oil ,not an insignificant issue with your marine environment .

as to egt i can say with quite a bit of experience in the dodge cummins world 1300 f should be the max and 900 should be a reasonable " cruise temp". i would presume a non turbo engine could stomach higher egt without harm as there is not a large heat sink in the way. as to egt placement the dodge guys and all other installs i have seen were directly before the turbo charger as that is the apparatus you are trying to protect. i will presume your kubota is an iron head engine in which case i would think 1400 should be about the max but i doubt it would ever get that high being naturally aspirated . note all of the above is yet again based on large diesel experience so it is information only but i think it has some merit as a base line .   further on egt the higher it is throughout the exhaust system the better volumetric efficiency the  engine will see as hotter air has a lower coefficient of friction

i would probably try to tap the topm of the 12 in riser if it seems meaty enough as it will give you a stabilized section to read from ..

[thomasonw]

JC,

Thanks.  Yes, i was surprised to see the low coolant operating temperature - but do wonder what range the little Kubota is designed to run in.  In its 'native' configuration it uses a hopper radiator with a fixed speed fan, there is no way to control the cooling temperature.  So I have to think it was designed with extra margins to allow a wider range of operating coolant temperature, just have no idea what its design point is..

When I reconfigure it again later this fall I am going to tackle the cooling loop.  Putting in a bypass valve that I can control to bring the operating temperature up.  Given the controller is already measuring the engine temp (which is how I noted 137f in the 1st place), it is a simple matter of code  to add a control for the new bypass valve.

As to EGT, I found no help in picking a point.  As you noted most all the Diesel EGT talk comes from the pick-up guys - no help for me.  I ended up selecting 935f as a target and regulate engine load to match this temp.  I selected this by trial-n-error.  Loading the engine up until I noted black soot in the exhaust, indicting overloaded condition.   Then I backed off the load while I was making slight changes to the governor lever - looking for a point where the engine seemed to be able to respond 'without straining' to small changes in speed.  I would slow the engine down perhaps 200-300 RPMs, then advance the 'throttle' and judge how quickly it was able to come back up to speed.  With all this I got 950f.   Backed off some more to 935f...

It does have an iron head, but I was not able to get anywhere near 1400f.  Truth be told, the engine was a bit tired and I rebuilt it last winter (It was one of those army take-outs and had some blow-by when I 1st got it.  The machinist commented it looked like it sat for a long time with moisture in the cylinder as there was a pronounce depression/ring at one point in the cylinder)  Due to family commitments have not had a chance to retest it, but once broken in I will repeat the above and see if I come up with a new EGT max point.   I used 3/4" galvanized pipe for our hot exhaust, though only have a 10" riser , but also found sufficient meat in the pipe to dril-n-tap for the EGT sender.  Nice and simple.

Thanks for the reply, and if anyone else has some idea of a good EGT point for these small engines please pass it on!

[BruceM]

I like your idea of a computer controlled bypass, thomasonw;  a simple solution to improve engine life.  Your awesome state of the art controller/regulator is paying off nicely.  Bravo!

A side note on electronically controlled valves:
I saw a new twist in motorized ball valves, from China, recently-  one type has only two wires and automatic motorized close (or open) on removal of power (via a supercap and some logic).  Thus it provides the simplicity of a solenoid like action, but without the current drain and with much better CV (flow) of a ball valve.  Motorized ball valves from China are now on ebay at some amazingly cheap prices.  An automotive type coolant solenoid valve might be a better match for your application, though.

Best Wishes,
Bruce

[buickanddeere]

Low coolant temp will ruin an engine with accelerated bore, piston and ring wear.emissions will be increased. Engine will suffer more cylinder wall was down and lube oil dilution.
    Coolant must be 195F to 210F to run clean, economical and to reduce wear.
   Install a thermostat.
     EGT will vary due to various factors . 1200F is a nice round maximum.
    What temp at the 1st signs of black smoke? What temp at max power ?

[thomasonw]

Low coolant temp will ruin an engine with accelerated bore, piston and ring wear.emissions will be increased. Engine will suffer more cylinder wall was down and lube oil dilution.
    Coolant must be 195F to 210F to run clean, economical and to reduce wear.
   Install a thermostat.
     EGT will vary due to various factors . 1200F is a nice round maximum.
    What temp at the 1st signs of black smoke? What temp at max power ?

If  there was a way to install a thermostat, would have done it long ago.  But these little horizontal Kubota's use a hopper style thermosyphon radiator with no prevision for any thermal control.  In fact, from the factory there is a belt driven fan - cooling is fixed.  This always made me wonder what the design point was for these little engines, and if they took any special measures to allow for cold running.  The shop manual gives no hints, does anyone know what the designed-to operating temperature is for these little engines?

I have replaced the 'coolant to air' radiator with a 'coolant to water' heat exchanger (still hopper style), so my only control point is the external water flow through the heat exchanger.  Complicating things a bit is this uses sea water with its salt content. . .   I did locate a3/4" -  316 SS NC valve - its sourced from China, will see how long it stands up.  But it was under $50, and on the ++ side my system is set up to do a fresh water flush of the cooling system after operation - that helps a TON with corrosion issues.  Will use that for the bypass.

I like the idea of lower power usage of the move-n-hold, but can see one downside:  It does not have the fail to close that the NC value would.  So if a wire broke..  But then controller would fault from OverTemp in that case.  If this valve gives up the ghost, will look into one of the power to change ones you described.  And have just completed a group-buy of 10x of the controller boards, thinking in the next round I may add in a couple more FET driver ckts for things like cooling pumps, etc.  Each deployment is a little different (have folks covering: Marine, RV, and off-grid) and an extra port or two might come in handy.

Oh, I noted the engine starting to put soot into the exhaust around 950f EGT.  I am not sure of the load at that point, but backing down to a 1880w loading via the alternator gave me the 935f.  Assuming a 45% efficiency  (Alt + belts), this comes to  5.6Hp produced (Spec sheet is 5.9HP cont).    After I get the coolant temperature at a more reasonable range, and run in the new cylinder/rings, will use the same approach described above to re-sample a 'upper limit' EGT temp.  Will be interesting to see if it stays around the same, or moved much higher.

Does any one have some other thoughts on a procedure to ID the max load point for this engine other then what I described before???

[buickanddeere]

  Is it practical to go with water to air cooling and forget about salt water and it's problems ? Use a 12V automotive fan on an electric stat to kick on at 210F.
   Just how many horizontal single diesel hopper cooled diesels were there on the market ?

[thomasonw]

  Is it practical to go with water to air cooling and forget about salt water and it's problems ? Use a 12V automotive fan on an electric stat to kick on at 210F.
   Just how many horizontal single diesel hopper cooled diesels were there on the market ?

I ran our setup for about a year using the original air radiator, and it was OK.  This is a small engine, and even with the radiator its waste heat is small compared to radiated heat from our mains.   I switched over to sea-water becasue that was kind of traditional, it allowed me to use what is know as a 'wet' exhaust (dumping the cooling water into the exhaust, and then just using rubber hoses for the rest of the exhaust system).  FWIW, there was already a hole drilled in the boat for a generator wet-exhaust.  And also I need a salt-water source for our reverse osmosis watermaker... 

But doing it over again I think I would work to keep the radiator - install a small 12v fan like you say, and set things up for a 'dry stack' exhaust.  Then figure out something else for the watermaker..  If things get too Rube Goldberg, or I have too many more issues with the wet exhaust setup I may work to just convert it over again (though sadly I tossed the original radiator    )  Would likely need to also put in some forced air circulation into the generator room if I made it permanent.  (Hey, or into the main living space for that old VW heater atmosphere )

[veggie]

A side note on electronically controlled valves:
I saw a new twist in motorized ball valves, from China, recently-  one type has only two wires and automatic motorized close (or open) on removal of power (via a supercap and some logic).

BruceM,
I have had my eye on those motorized valves too.
They also make a 3 way version which can divert coolant from one loop to another.
Prices are reasonable in the $24 - $30 range.

veggie

[BruceM]

I've been using one of this type of valve (not with the supercap and logic for two wire)  for 3 years with about 6 cycles a day on/off.  Still working fine, a real bargain compared to the $370 I paid for a US made one I use in my engine room for compressed air shutoff. 

[quinnf]

"Coolant must be 195F to 210F to run clean, economical and to reduce wear."

I read through the entire threads looking for the following caveat but didn't see it.  Raw water cooled marine engines/generators have a 140F thermostat because salt will precipitate out of the cooling water in the cylinder head and exhaust manifold passages and plug them up in no time if the temperature is allowed to climb much above 140F.  If you're in fresh water, no problem.  Salt water:  problem.  Salt water in the tropics:  Even more so.

Either fresh water cooling through a heat exchanger or dry stack are the best ways to avoid salt precipitation, but a dry stack will always be noisier than a wet exhaust.  For generator duty, a small aqualift wet muffler will virtually eliminate the engine sound.  Fresh water cooling allows you to tap into the FW loop in order to heat water for showering, etc., and the hot water can also be run through a heater core to heat the interior of the boat, which in Puget Sound is always a good thing.

Quinn

[buickanddeere]

A closed loop system with anti-freeze will not have freezing, corrosion or plugging problems.  The generator will also operate if the ship is in dry dock or frozen in. Stand alone without relying on other systems. A loop of hot coolant with a fan forced heat exchanger certainly would warm a cabin, hallway or wheelhouse .