Lugging a diesel engine?

[PHILIP8N]

I might be way off base here, but the OP's quote... that was referring to over-the-road trucks, yes? Aren't they just about all turbo-charged? Other than the oil issue, could that be the difference?

I know on my Jetta TDI, it's recommended the you "drive it like you stole it" --that is, much higher shift points/higher rpms than what I've been accustomed to-- to keep the turbo from carboning up.

For someone who prefers high-torque/low-rev engines, that took a bit of getting used to!

I am going out on a strong limb here but I will say 100% of all OTR truck enignes in North America today are turbo charged, which will give you a much stonger torque curve in the lower rpm range. Tractor engines which are turbocharged will also give you a much stronger torque curve in the lower rpm range. My engine is naturally aspirated, so its peak torque is at 1700 rpm and peak horsepower at 2800 rpm. Philip

 

[Chilly807]

The reference was to CUT and utility sized ag tractors. While I never purposely "lug" an engine as described here, I often just use the foot throttle since the work is light and there is no chance of lugging in the obvious sense. But should I be doing this?
Should I instead set the hand throttle at a higher RPM even though I have no need for the power created? Are there degrees of unintentional lugging even though it does not appear that I am "lugging" in the textbook sence?

Using the foot throttle is fine, as long as you're aware of the load on the engine and the rpm. Seat-of-the-pants feel is the best way I can describe it.

The type of transmission plays a role as well, with an HST trans you may be better off using the hand throttle, in fact I don't think too many HST tractors even have a foot throttle??

I occasionally use the hand throttle while brush hogging, but only if I'm doing long unbroken loops. My tractor is traditional gear trans, with clutch. I don't like engaging or disengaging the clutch with the engine above idle if I can help it, to avoid any extra wear and tear on the clutches. If I'm in a stretch of heavy cutting, I try to keep the PTO rpm close to 540 to get better results from the mower, and I try not to cut much below 2000 rpm on the tach at any time. With mine, 540 PTO speed equates to about 2350 engine rpm. I engage the PTO at idle, let the clutch out to start the PTO turning, then the drive clutch. As I start into a cut, I'm close to the 540 PTO rpm.

Diesels are a pretty tough engine, using the majority of the available rpm range won't cause you any grief. Most PTO driven implements work best at their designed speed of 540 rpm, post hole diggers being the first exception that comes to mind. Trying to dig a post hole at 540 rpm can get exciting in a hurry. I'm usually at idle or just above it when using the PHD, if the engine seems to be labouring I increase the speed until it smooths out. Again, seat-of-the-pants feel.

Diesels are happiest working at about 80 % of the rated power output in the middle of their torque curve, this will keep carbon buildup to a minimum, prevent ring and cylinder glazing, etc.

For most of us that isn't possible, the highest load I see is usually brush hogging or snow removal.

Still, with proper engine design they are almost "idiot proof" as far as operation is concerned. There will always be a few people who will have problems, usually those who think that letting it idle overnight is a good idea, or that they have to run at max rpm no matter what they're doing.

Like most things in life, moderation is the key to success over the long term.

My personal opinion, obviously !!

Sean

 

[CharlieS]

Even with no load, I idle the engine at 1500 RPM...never below 1000.

context.

I dont see any justification for this. Mainly it would be a waste of fuel. If it wasnt safe to idle the engine at a lower rpm, manufacturers wouldnt set the idle as low as they do.
Most manufacturers i've talked to, and its numerous through the years, cat, cummins, detroit, FNH, international, case IH, all pretty much agree, on a cold start, leave throttle at idle speed until oil pressure builds, then raise the idle slightly say 1000 to 1100 rpm's until the engine warms, then higher throttle usage is safe.
With diesels, starting to work them hard before they are warmed up, can result in pistons heating faster than the sleeves, thus expanding more, and it can pull a sleeve.

While todays OTR trucks mainly are turbo'd and have a wider operating rpm range there are still some older trucks around both with turbos, and naturally asperated, that the driver maintained a limited rev range. Cat and Cummins notibly you maintained engine speed between 1800 and 2100 rpms. Detroits never below 1800, but try to keep the revs up. bumping the governer was where a detroit was happy.
with the cummins and cat if you needed/wanted more HP, you dropped a bigger button in the pump and turned up the rail pressure.
Then if you wanted even more you drilled a dime, and/or dropped a stinger in the fuel return line.

Mainly if any engine sounds happy, the operator isnt lugging or overspeeding it.

 

[JoeL4330]

So, we typically have a mechanical flyweight type governor. For anything a tractor was intended to do they are perfectly suitable, and far more cost-effective.

They do have one inherent characteristic that impacts on this discussion, in that they will reduce the speed setting as load on the engine increases. This isn't a design goal, it's a limitation of that particular governor type.

So for example, imagine you are running a brush hog at a steady 2300 rpm engine speed, over a sparsely grown field. Near the edge of the field is a heavily weeded, densely grown area. As the tractor and brush hog moves into this area, the rpm drops slightly as the load on the engine increases.

Sean

I believe that the RPM setting to achieve 540rpm at the PTO is just past (past) the torque peak [on the back side of the torque curve]...so, as described, when the load increases beyond a point and the governor operates as described then (Tada)...the torque increases, which means you typically can power through a slight tough patch of whatever.

 

[SPYDERLK]

If you look at this Dyno chart , it shows an engine's horsepower and torque curves . As you can see this particular engine can be run at 1700 rpm before the horsepower starts to drop off which is only about 10hp down from full throttle , but looking at the torque curve the engine will lug all the way back too 1200 rpm and is still making 800 ft/lb of torque which will carry it through a tough patch of grass etc.

Better check that torue curve, something is way off, numbers dont add up. What engine is that for? Philip.

Yeah ... multiply hp or divide torque by 2. :confused2:
larry

 

[flusher]

I cut and pasted this info below from another thread regarding lugging a diesel engine and would like to get more feedback about it. We are very careful about "lugging" an engine and we all know what serious lugging is and sounds like. However, could some of us be lugging an engine and not know it? Are there degrees of lugging? Any more thoughts on this?


"......There is one firm rule that every equipment operator and truck driver memorizes on their first day: NEVER LUG A DIESEL ENGINE! With the throttle wide open under load, keep the RPMs above 80% of the maximum RPMs. For example, if your maximum engine RPM is 2600, never let it lug below 2000. When you get below that you will drop off the power curve anyway, and lugging a diesel will hammer the rod bearings right out of the engine....."

This old TBN thread discusses another potential effect of lugging a tractor diesel

http://www.tractorbynet.com/forums/john-deere-owning-operating/4698-diesel-running-backwards.html

 

[TripleR]

This is a very interesting thread; lots of good information.

 

[RoyJackson]

I dont see any justification for this. Mainly it would be a waste of fuel. If it wasnt safe to idle the engine at a lower rpm, manufacturers wouldnt set the idle as low as they do.

Maybe you ought to read the Deere manuals about extended idling... Anyway, I've seen the result of mains being pounded. Better a bit higher RPMs then buggering the engine.
As far as fuel...well, the tractors I've owned sip fuel frugally (the jury is stll out on the 4400, however) so that is a minimal concern.
Bottomline, you idle your diesels at whatever RPM you think is best...that's what I do.
Of course, if you've read some of the earlier threads, idling doesn't mean all night...rarely any more then 15 minutes, if that.

 

[Chilly807]

I agree that the 540 PTO speed should coincide with the maximum torque created by the engine. It's not hard to engineer, once you know where the engine creates the most power/torque, you can adjust the gearing to place the PTO speed where you want it.

I suspect that it is also toward the back side of the torque curve as Joel suggested, it makes sense.

I don't have a dyno chart for a given tractor, but considering the displacement and horsepower created by mine, it is definitely tuned for torque, not horsepower. Undersquare cylinders and longer stroke is a recipe for torque.

Roy makes a good point about idle speed. My 3400 without the loader attached shakes considerably more at low idle than it does with it. Bumping the rpm a bit with the throttle lever smooths things out quite a bit.

My normal cold-weather starting procedure involves letting the engine warm up for at least 5 minutes, maybe more depending on how cold it is. The Kubota temp gauge has a small tic mark just above the cold end, I don't do any serious work until the needle rises above that mark. Once the engine is running for a minute or so, I'll bump the throttle up to between 1200-1500 rpm and finish my pre-work routine while it warms up.

Once I'm ready to go, so is the tractor. I drop the rpm back to the normal low idle before I start work.

Turbocharging makes an appreciable difference as well, which many don't realize. The turbine end is driven by exhaust gas, the compressor wheel on the other end compresses air for combustion. The turbo is dependent on exhaust flow to work. The higher the rpm and fuel delivery volume, the more pressure and exhaust volume there is to drive the turbo. So, more load and rpm means more boost, which means more power.

Turbo engines are typically smaller displacement to create the same horsepower as a naturally aspirated engine. So if you follow that line of thinking, they are not always able to create as much power unless the turbo is working in it's design power range.

One of the reasons I chose Kubota was that the 3400 isn't turbocharged. I don't worry much about fuel economy for the amount of work I do, and I do appreciate the lack of complexity. Almost all the engines I work on are turbocharged, both for efficiency and to get more power out of a smaller package. They typically produce between 20 and 45 psi of boost at full power. All have a cool-down cycle unless it's an emergency stop situation, normally from 5-10 minutes at idle until the oil temperature has stabilized enough that the hot turbo won't cook the oil left in the turbo. I've seen turbo exhaust-end castings so hot they're almost white at full load, and dull to cherry red isn't uncommon at all.

My operating style might be different with a turbo-charged engine. I like to see at least a bit of boost while the engine is working, and a cool-down cycle would be a must after any serious work. Lugging a turbocharged engine may be more harmful than a naturally aspirated one, if I had to guess.

Having said all that, I've not seen the water temp gauge on the Kubota move much from winter to summer use, it pretty much stays in the same spot no matter what you do. An oil temperature gauge would be interesting, I may add one after warranty is up. That tells you a bit more about what is going on in the engine. Water temp controls oil temp to a large degree, as the oil is actually cooled by the engine block as it drains back to the sump.

Sorry about the wander from the original topic.

Sean