What is Engine Lugging?

nicklockard said:

What does this mean

Clarify...you've got me confused: how does that last comment relate?

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In the original "word problem", he said "at 5000lbs"...presumably meaning 3000lbs of car + 2000lbs of trailer.

Mike

Fix_Until_Broke said:

I think your times actually should be 0.025 and 0.010 seconds respectively.
1200 rev/min = 2400 strokes/min divide by 60 sec/min = 40 strokes/sec = 0.025 seconds/stroke. Minor detail in regards to this topic.

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My error. I was thinking about 600 power strokes (20 strokes per second) so I had doubled the time available. Thanks for catching my mistake.

Mike_M said:

In the original "word problem", he said "at 5000lbs"...presumably meaning 3000lbs of car + 2000lbs of trailer.

Mike

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My mistake. I missed the "5000 lbs" part of the question (oops, sometimes a sloppy speed reader .)

So my answer to:

fix... said:

So when I'm at 3000 RPM in 4th (~65 mph) at 5000 lbs up a 8% grade and dropping rpm's because I only have 90 HP, Is that lugging?

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is that if he can apply more accelerator and maintain speed, then the engine is not lugging, but if no amount of accelerator input is sufficient to maintain speed and the car slows down, then yes, that is the very definition of lugging. And...not to be critical, but anyone who expects to go up an 8% grade towing an 8 foot tall barn wall weighing 2000 lbs with a small passenger sedan is asking for a very short engine life. The added load from aerodynamic drag alone is more than the sum of the parasitic load losses of the car at that speed (car's total load requirements: weight, RR, aero drag.) That's plain foolish.

Mike_M said:

In the original "word problem", he said "at 5000lbs"...presumably meaning 3000lbs of car + 2000lbs of trailer.

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nicklockard said:

My mistake. I missed the "5000 lbs" part of the question (oops, sometimes a sloppy speed reader .)

So my answer to:

Fix_Until_Broke said:

So when I'm at 3000 RPM in 4th (~65 mph) at 5000 lbs up a 8% grade and dropping rpm's because I only have 90 HP, Is that lugging?

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is that if he can apply more accelerator and maintain speed, then the engine is not lugging, but if no amount of accelerator input is sufficient to maintain speed and the car slows down, then yes, that is the very definition of lugging. And...not to be critical, but anyone who expects to go up an 8% grade towing an 8 foot tall barn wall weighing 2000 lbs with a small passenger sedan is asking for a very short engine life. The added load from aerodynamic drag alone is more than the sum of the parasitic load losses of the car at that speed (car's total load requirements: weight, RR, aero drag.) That's plain foolish.

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Foolish? I think I was foolish once, no...maybe twice...............this afternoon

Yes MikeM - 3K of car and 2K of trailer and stuff. It might have only been 6 feet tall, but yes the aerodynamic drag is way worse than the added weight.

Nicklockard: It's not so much that I expected to be able to make it up this hill in my 11% taller 5th gear with stock power pulling more than I should with a parachute at 10+ over the speed limit and maintain speed (duh), but that hill was between where I was and where I needed to be, and pulling the trailer on the flats and normal Wisconsin/Iowa slightly rolling hills was no problem so up the hill I go. I really don't think that 10 or so miles in 1-2 mile increments at 100% throttle will really shorten the life of my engine. FYI - boost stayed at ~13 psi and post turbo EGT's were ~ 800F

OK - So you're saying that lugging can occurr even at 3000 rpm?

I'm not sure that this follows the above theory that Lug Nut described (which makes sense to me the more I think about it, so please expand my tunnel vision if need be) where the speed of combustion becomes so short compared to the time of the power stroke that it is more like an impact on the top of the piston instead of a more constant push on the piston which creates the vibration/noise that we're familar with as "lugging" At 3000 RPM (assuming proper injection timing) can the combustion can happen fast enough to cause this to happen?

I think this is a continuous type of phenomena that happens over a range of conditions. It's not a digital thing.

Fix_Until_Broke said:

So when I'm at 3000 RPM in 4th (~65 mph) at 5000 lbs up a 8% grade and dropping rpm's because I only have 90 HP, Is that lugging? It's not making the same vibrations/sounds that it does at <1500 rpm in 5th (or any other higher gear) when you lean into it too much.

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I those conditions I'd calculate youd need 88HP, so the engine rpm's would have to be somehwere in the range 3600 to 3900 rpm to achieve that, choose the appropriate gear to get those rpm's
Running in 4th at 3000 rpm's would only give about 80HP, so you'd be short 8HP, and losing speed, notch into 3rd, and you'd likely be making too many rpm's and still not the right amount of HP.

Is that lugging? I wouldnt say so. Lugging is usually associated with low rpm's. That condition I would call overload, which is not the same thing at all.

hth

gdr703 said:

I those conditions I'd calculate youd need 88HP, so the engine rpm's would have to be somehwere in the range 3600 to 3900 rpm to achieve that, choose the appropriate gear to get those rpm's
Running in 4th at 3000 rpm's would only give about 80HP, so you'd be short 8HP, and losing speed, notch into 3rd, and you'd likely be making too many rpm's and still not the right amount of HP.

Is that lugging? I wouldnt say so. Lugging is usually associated with low rpm's. That condition I would call overload, which is not the same thing at all.

hth

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88 HP can be had at 3750 RPM, peak HP for the ALH90. I'd say downshift to 3rd and match speed with 3800 RPM.

gdr703 said:

I those conditions I'd calculate youd need 88HP, so the engine rpm's would have to be somehwere in the range 3600 to 3900 rpm to achieve that, choose the appropriate gear to get those rpm's
Running in 4th at 3000 rpm's would only give about 80HP, so you'd be short 8HP, and losing speed, notch into 3rd, and you'd likely be making too many rpm's and still not the right amount of HP.

Is that lugging? I wouldnt say so. Lugging is usually associated with low rpm's. That condition I would call overload, which is not the same thing at all.

hth

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Your 88 hp is short...you forgot he is towing a barn door! It (added aero drag) alone probably adds a 35++ hp load requirement.

Yes - I was trying to pull somethig too big, too fast up too steep of a hill with too little power - moving on...

Is lugging restricted to lower engine (therefore piston) speeds?

It has to have something to do with the quantity of fuel delivered and the timing of the delivery of that fuel.

Maybe it could be prevented with a change in the timing map - more retarted timing (or less fuel) in those conditions to knock down the peak cylinder pressure or move it later in the stroke. This is (one reason) why timing is retarted at higher loads to keep peak cylinder pressures down just after top dead center.

Interesting

Fix_Until_Broke said:

Is lugging restricted to lower engine (therefore piston) speeds?

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I agree its to do with low engine rpm, high load condition and timing.
The ecu does its best to compensate, and does it a lot better than any carburetted, distributor capped gasser engine which are a lot more susceptable to lugging effects.

A diesel engine can handle overload, its part of the fundamental. Example, my Yanmar YSM12, is rated 12HP max on overload, 10 HP continuous, at the same max 3000 rpm. I need that because its in a 5 ton sailboat. On a calm sea at full chat 10 HP is what it runs at spinning the screw merrily. Now start powering into a sea with a few breaking waves on it. The boat charges along and into the face of a wave, which despite its 5 tonnes, slows the boat, and meanwhile the surface of sea water is also travelling with the boat, (a fundamental of wave formation) so at this point in time that screw that was spinning merrily in 5 knots of water is now required to spin against 2 knots of water, thus loading up the propellor blades quite dramatically, the engine responds not by dropping revs, but by using the overload capability, to feed more power in, and maintain rpm. Diesel engines can do this, its a fundamental in their design, gassers dont have the same mechanisms at at all. A gasser engine in the same situation would drop engine rpm, and thus lose power, then attempt a recovery by overfuelling, by which time the wave has moved on, and the rpm and power have been dropped.

cheers.

found a reference on lugging

Found this google book on Mine environmental engineering about safe use of diesel equipment in underground mines describes lugging as "operating the engine at high load and low speed". It says a certain amount of power can be obtained at two different Fuel/Air ratios. "By operating at the lower F/A ratio of 0.032 at 2000rpm, CO, particulate, and exhaust gas temperatures will all be lower than at the corresponding F/A ratio of 0.05 at 1200rpm.

Practically, one could define lugging as a condition where the engine is unable to rev because of load/gearing. Standing on the gas will not make the engine go faster because of the load, consequently the F/A ratio increases and that causes the problems. Presumably it is the high exhaust temperature that is potentially dangerous for turbo bearings.

I presume that lugging at extremely low speed (idling in first gear) in a traffic jam is not as dangerous as the engine load is low and adding more fuel will increase engine speed easily.

More good information on lugging diesels and other interesting tidbits here: http://dodgeram.org/tech/dsl/FAQ/engine_op.htm

Bluey, rules that apply to diesel engines in general may not apply to TDIs in particular.
1) Our VNT turbos are a little more fragile than wastegate turbos at low engine RPM.
2) Our EGR systems tend to create clogging problems if engines are babied most of the time, i.e. through short-shifting.
3) From what I've read, lugging can cause increased wear to lower main bearings. I don't know that fuel/air ratios have anything to do with it.

My concept of lugging is this: If you are at such a low rpm that adding power causes a noticeable vibration, you are lugging. The firing impulses are too far apart for the flywheel to smooth out. On my TDI, it feels like that is about 1600. So no significant load under 1600 for me. Steady state cruising in lower gears, 1500 is no problem. Heavy accel only when above 1800. Works for me.

Heavy load like pulling a trailer requires load and rpm matching which is different. In general, if pulling a heavy load near full power, the diesel is happiest at higher rpm. More oil flow, air flow, coolant flow, and lower egt and fire deck (piston crown, valve and head surface) temps.

Choose a lower gear if pulling a big trailer. If you find additional push on go pedal does nothing, you are in too high a gear or simply trying to go too fast. You want to feel a little reserve power left in the go pedal.

EGT meter a must for pulling trailers near hp limit.

TornadoRed said:

Bluey, rules that apply to diesel engines in general may not apply to TDIs in particular.
1) Our VNT turbos are a little more fragile than wastegate turbos at low engine RPM.
2) Our EGR systems tend to create clogging problems if engines are babied most of the time, i.e. through short-shifting.
3) From what I've read, lugging can cause increased wear to lower main bearings. I don't know that fuel/air ratios have anything to do with it.

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I think VNT turbos should be less prone to low-speed stalling than fixed vane turbos.

I have not seen any evidence that the VNT sticking problems and EGR clogging problems aren't caused by high soot levels which appear more a function of low quality fuel (low cetane number) available in USA.

Demanding more engine power from lower RPM requires a higher fuel air ratio to generate the power from combustion which is what causes the bearing load.

bluey said:

I think VNT turbos should be less prone to low-speed stalling than fixed vane turbos.
I have not seen any evidence that the VNT sticking problems and EGR clogging problems aren't caused by high soot levels which appear more a function of low quality fuel (low cetane number) available in USA.
Demanding more engine power from lower RPM requires a higher fuel air ratio to generate the power from combustion which is what causes the bearing load.

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I am not sure whether VNT turbos are more or less prone to stalling, but they are fragile and if they are not damaged more often it is because of built-in safety features like limp mode.

TDI engines that are always babied tend to clog up earlier than those which are routinely given a heavy workout.

I don't know enough to address your last comment about fuel-air ratios.