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Old 14-04-2006, 10:59   #16
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I am not playing... can you simply cite an article that explains this whole deal.
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Old 14-04-2006, 11:19   #17
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It is not so much the load or rpm that is important, as the engine temperature. If it is loaded enough to run at what ever temperature it is designed for, then it will do just fine. High-speed idle will not bring it to operating temperature.
Remember, a diesel doesn't have a conventional throttle, like your gas engine - it has a governer, which is advanced.

Some on-line references:

“Diesel Engines @ Slow Idle” ~ By James Clausen (Power Cruising 2005)
http://www.maxumowners.org/MVSSDieselEnginesSlow.html

“Engine Operating Guidelines “ ~ from Yanmar Pleasure Boat Marine Engine Help
http://www.yanmarhelp.com/operate.htm

Diesel Engine Troubleshooting “ ~ from Bowers Power Systems
http://www.bowrspower.com/Diesel_Troubleshooting.htm
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Old 14-04-2006, 11:32   #18
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I read the first two articles ... Thanks... the third link did not work.

My reading is that this is almost entirely a matter of cold operating temperatures... and the inference is that idling an engine it is not warm enough. The load thing... still I still don't quite get except that at a given RPM the engine would burn more fuel and a bit hotter under load than no load.

This means that idling low revs run too cool. no? I would think that higher revs, more explosions, run a bit warmer too... no?

The first article also notes that the load thing is rarely explained.
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Old 14-04-2006, 11:36   #19
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Typo

Gord,

There's a typo in your last url. The correct address is: http://www.bowerspower.com/Diesel_Troubleshooting.htm
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Old 14-04-2006, 11:57   #20
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And speaking of temperature... I have a Volvo with a VDO temp gauge which is a graphic display. I have no idea what the temp is.. only if it is in the green (good) or red (too hot) zone.

I have seen it creep toward red when saw the raw water system was clogged.

What I haven't noticed is any change within the green for normal operating... idle... after it warms up... or running under load or low or high revs... it pretty much stays put in the same postion on that green scale.

If this load thing equates to a temperatire thing shouldn't a load show some change in the graphic display?

I do notice that loads can slow engine rpms... for example when an engine drive compressor for the frig kicks in. My interpertation of what happens in this example.... is that the compressor normally free wheels... no load... but when it is working there is resistance because the compressors pulley is no longer free wheeling.

This seems to place a "strain" or load on the flywheel... which translates into a lower rpm. If I want to lift the RPM I advance the throttle. I don't know if I burn more fuel at the same RPM with the compressor on or not. But logic would indicate that I do.

So this means that there is more fuel in the cylinder for each compression. And so???? That is where I am lost. Does this mean hotter? the "right" hotness?
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Old 14-04-2006, 12:37   #21
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Energy

A by product of energy is heat. More horsepower used or produced, more heat. That is basic hot rodding. These engines are not running very hot. The piston ring is basically going up and down. Most engines require heat to fire, that comes from the compression, not enough compression no fire. So I would say that if the thing is running it has created enough heat. Under load more heat will be created but more water is provided to contorl it. In my bit about the tractor I mentioned that oil frothing happens when a motor is not run warm enough. The moisture is not being cooked off. I can see this as being a cause of problems. That's why we put thermostats in the old Fords. They were for plowing fields in the warmer months, we use them to plow snow and they do not get hot enough. Hot enough is 160 F. Some motors are designed to run at higher revs and have valve openings ( controlled by the cam ) that are not satisfactory for slow speeds. They will load up ( be too rich ) at slow idles. But that is usually not the case with a diesel. I am still thinking that it should be okay to run a good diesel at 200 or so revs above idle.
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Old 14-04-2006, 12:48   #22
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More fuel doesn't raise the temperature of combustion (by itself), but it does increase the amount of heat released by that combustion. This released heat raises the temperature of the gases in the cylinder (DeltaT=Q/mc) and helps do some of the work of the engine (the conversion of a few molecules of fuel to a larger number of molecules of byproducts also contributes, PV=nRT). However, the heat needs to be removed before the next cycle, and we don't want the tempearture to rise too much (such that the metal parts expand too much and bind). The heat flows away from the cylinder by conduction through the metal, by advection through the coolant, and by advection with the exhaust of the byproducts of combustion. To operate effectively, we need to achieve a balance between energy input (fuel burned) and energy output (work done and heat removed).

I guess this still doesn't answer the question of why a load is better than no load, but I can see how it might be possible for an engine operating at low RPM's (low fuel consumption) to never warm up (heat removal mechanisms of advection being too effective).

EDIT -- but reading Mike's reply above, if the engine is running, it's basically warm enough, isn't it?!

Sorry, Jef -- don't know if this helps or not.

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Old 14-04-2006, 13:07   #23
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Charging batteries

If unloaded operation of the diesel engine is to be avoided, is the suggestion that the boat should be taken out for a cruise whenever the house batteries need charging on boats lacking wind/solar/shore chargers?
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Old 14-04-2006, 13:18   #24
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I am going to propose that the notion that a diesel MUST have a load or it suffers degradation is a myth.

I can accept that operating below and above the design temperature range will cause degradation of the engine. But if the engine is operating within it's tempature guidelines it should be OK.

Do I know what I am talking about? No. But until someone steps forward with an explanation of how placing a load on a deisel engine PREVENTS degradation... I wil consider this a myth.

Anyone please????
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Old 14-04-2006, 18:25   #25
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the test

My solution is for you to put this myth to the test.Run your engine for a week and get back to us with the results.We don`t just talk about the myths we try them out.Busted or plausible,i`ll be waiting.
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Old 14-04-2006, 22:45   #26
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Quote:
Originally Posted by defjef
Do I know what I am talking about? No. But until someone steps forward with an explanation of how placing a load on a deisel engine PREVENTS degradation... I wil consider this a myth.
I believe the answers you seek have already been presented.

From http://www.maxumowners.org/MVSSDieselEnginesSlow.html

Quote:
So far so good, the engine has started and is now idling at the dock, as it idles, the temperature of the engine block is rising to its pre determined operating temperature. BUT, in many diesels to achieve this temperature we must be at a speed above idle!
At idle, the engine is not burning much fuel. If you don't burn as much fuel, you don't get as much heat. Remember that heat is not the same as temperature. A match flame is several thousand degrees, but it can't heat your whole house.

Keep in mind that your temperature gauge does NOT measure the temperature of the engine block! It measures the temperature of the coolant. The thermostat opens and closes to regulate the flow of coolant. It was designed specifically to keep the coolant temperature in a narrow temperature range. When the coolant temperature rises, the thermostat acts to lower it. When the coolant temperature drops, the thermostat acts to RAISE it.

Why would you ever want to RAISE the coolant temperature? If the coolant is too cold, it will suck too much heat out of the engine, and the fuel will not burn well.

Quote:
AND to achieve the complete fuel burn we must have a load put on the engine, (propeller turning, pushing the boat).
RPM is not all that closely related to power output. Think of pedaling a bicycle on a flat road. Now pedal uphill at the same speed. The RPM of the bicycle wheel will be the same, but you will work much harder.

Quote:
But many of the engines out there today idle in the 550 to 600 RPM range. Great for docking, but too low of an RPM to achieve the internal temperature needed for complete combustion. “So what,” you may say.
Incomplete diesel combustion causes that “white smoke” upon startup. The white smoke is actually a combination of unburned, and partly burned fuel droplets, this condition is typical, until the walls of the combustion chamber gradually heat up, and should last no more than a minute. Continued operation in this idle range will continue the incomplete combustion of diesel fuel and will cause:


Quote:
1.- Carbon build up.
I'll assume you can believe that dirt in the engine will be bad for it.

Quote:
2.- Low compression due to sticky piston rings.
Quote:
3.- Piston rings not sealing properly.
These two are really the same effect. If contamination prevents the piston rings from making a good seal, pressure that should be moving the pistion is just blowing past the pistion and escaping through the crankcase ventilation. If the compression is poor enough, the engine will not even run.

Quote:
4.- Choked valves.
I'm not sure specifically which valve problem he is referring to here, but any interference with the valves will be a problem. If it doesn't open, doesn't open far enough, doesn't close far enough...

Quote:
5.- Increased heat on the piston surface leading to a “holed piston”.
The engine is designed for the fuel to burn more or less uniformly throughout the combustion cylinder. The burning begins when the injector sprays the fuel into the cylinder. Anything that causes uneven fuel distribution (e.g. unburned fuel laying there from the last cycle) will cause uneven heating. If the heat builds up enough in one area, the metal can even melt and/or burn. (Yes, iron burns.)

Quote:
6.- Unburned diesel fuel dripping past the pistons wiper ring, into the lubrication oil, thus contaminating it and increasing the wear to all of the interior bearing surfaces of the engine.
seems clear enough.

Quote:
7.- Build up on the injector spray nozzle, causing an incomplete spray pattern.
This is basically dirt buildup blocking the spray nozzle. A bad spray pattern can lead to incomplete combustion and/or hot spots.


So, how does the load prevent degradation? By running the engine under load, you burn more fuel, and you burn it more completely.

Does that help clarify it?

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Old 15-04-2006, 00:16   #27
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Yes it does. And what happens when you run the engine in neutral but at higher revs?.. Say 1200 rpm or 1500?

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Old 15-04-2006, 04:40   #28
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k

With all due respect sir.I will drill it through your head with a diamond tipped bit,because that is apparently what it will take.Quote:
AND to achieve the complete fuel burn we must have a load put on the engine, (propeller turning, pushing the boat).
RPM is not all that closely related to power output. Think of pedaling a bicycle on a flat road. Now pedal uphill at the same speed. The RPM of the bicycle wheel will be the same, but you will work much harder.end quote There are many knowledgeable people on this board giving up their time to help people with their problems,it seems to me that you are pushing the limits of what would be called reasonable.The last post put the whole mess together in what i would call a well written explanation.Maybe i wouldn`t make a great teacher,but i can`t see you making a great student either.Signing off
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Old 15-04-2006, 05:11   #29
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jeez man..

All you do is say the same thing but don't explain why or how more fuel is burned when there is load. Screaming it over and over again is not explaining the mechanism. Sorry prof... I am a dumb stoodent. How is more load translated into higher temps or whatever you describe as "complete fuel burn"? I can understand that carbon build up would be bad and could be caused my several things... is absence of load the cause of carbon built up? Is it unburnt fuel?.. Only some of the fuel burns? Sorry for being dense...

If you don't want to explain... fine... thanks for trying.

jef
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Old 15-04-2006, 06:32   #30
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Heat is a product of “work”. Very little work (torque or rotational power) is required to keep an un-loaded engine turning at any speed (rpm), hence an idling engine performs very little work, producing little heat.

More load requires more fuel to maintain set speed (rpm), generating more heat in combustion.

The primary function of a diesel fuel injection system is to measure accurately, vaporize, and inject the fuel at the proper time according to the power requirements of the engine. The quantity of fuel injected determines the amount of energy available to the engine through combustion.

Diesel engine speed is controlled solely by the amount of fuel injected into the engine by the injectors. Because a diesel engine is not self-speed-limiting, it requires not only a means of changing engine speed (throttle control), but also a means of maintaining the desired speed (governor). The Governor provides the engine with the feedback mechanism to change speed as needed and to maintain a speed once reached. Governors used on diesel engines control engine speed through the regulation of the quantity of fuel delivered to the cylinders. Its job is to maintain the set RPM as dictated by throttle position. If the load on the engine changes, the governor will automatically call for more fuel (or less) to meet the load requirements.
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