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Discussion Starter · #1 ·
I am new to running a diesel engine. I got my 990 about 2.5 months ago. I have learned some about them and found this thread interesting about the idling etc http://www.greentractortalk.com/forums/showthread.php?3040-Idling-vs-Re-Starting-Engine. What are the benefits or why is it better to have a diesel engine for a tractor than a gasoline engine. What further benefits are there to the diesel engine.

Matt's point in the idling thread were helpful and I did not want to hijack the thread so I thought that I would start a new one hear and just sit and learn from all of you who are knowledgeable in this area where I am very ignorant.
 

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Diesel engines normally produce more torque than gas engines and the torque is produced at a low rpm. That makes diesels perfect for tractors as you do not have to rev the engine to WOT to get full torque. Also, diesels are more efficient than gas engines, so your fuel will last longer. Diesel engines will, under normal conditions, outlast a gas engine before needing a rebuild.

So there is power, efficiency and longevity.

There are other benefits, but those are the main ones.

Unfortunately, the maintenance of the engines can cost more than a gas engine. The initial cost is higher and repair is also normally higher in cost. IMHO, well worth it and most things can be avoided with proper maintenance of fuel and oil.
 

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A diesel engine will output much more torque than a gas engine. With cars you may find a diesel and gas that are the gas has 50 more HP, but the torque is nearly the same or more on the diesel. Even though the gas has more HP, because the diesel has more torque, it will feel like it has more hp and will be peppier. And, the diesel will burn less fuel than a gas engine.

Dawgannit, Brian beat me to it!
 

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Brian hit all the high points

HP is a mathematical figure based off of torque and RPM. So if you compared a gas burner to an oil burner at the same RPM, the typical torque figures will be significantly higher on the diesel. The BSFC is also much lower. (Brake Specific Fuel Consumption.) Diesels will only burn enough fuel to get the work done, no more. A gas engine has to have the same air/fuel ration over the entire load/rpm spectrum. The air/fuel ratio on a gas engine is around 14.7-1 while a typical diesel can be as low as 100-1 at idle and as high as 30-1 at full load.:hi:
 

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Discussion Starter · #5 ·
Brian, Jason and Al,

Thanks for the input on this. OK they have more torque, especially at low RPM's and are more efficient and they last longer. Those are clearly advantages. My next question is why do they have more torque and are more efficient and last longer? I am assuming it has something to do with the fuel that they use but are there specifics regarding the engine design that makes them this way where a gasoline engine is not? Maybe I am trying to be too technical but I always like to know the why and how and get into the details so that I can understand it better.

In the thread on the idling of the engine Matt had raised several things about what happens with the idle etc. It was also interesting to me that it is best to let the diesel engine idle for 5 minutes before one shuts it down after working it hard. This in my mind is all important information as one seeks to know the whys and hows of running a diesel engine. Maybe I am being too analytical but I still like to know. Maybe someone else will benefit from the shared knowledge as well.

Thanks
 

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The reason why people idle their engines for a while after they work them hard is to cool the turbo. When you work a diesel engine, your turbo is pushing high PSI's to the intake and all the hot exhaust is running through the turbo. By idling it, you are cooling the entire turbo and its oiling system. If you turned off a hot engine, your oil could "coke" or create sludge in your turbo lines. Those lines are needed to feed fresh oil to the turbo.

Think of it just like your cooling system on your tractor. If you shut off a very hot engine, you can boil coolant because it can no longer circulate and go through the cooling process. Your oil is the same way, but it will create a film or burn on items rather than boil in most cases.

I forgot your other question....:morning2:
 

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Rob its not really the fuel that gives you more torque but the operating principals. The diesel operates totally different than a gasoline engine just like a 2 cycle gas operates different than a 4 cycle gas engine.

Stroke and compression are typically very different. If you are wondering why everything isnt just diesel to start with its because a diesel is very heavy duty and was cost prohibitive in most applications. But now things are changing and they are becoming cheaper to build so you are seeing them in smaller applications.

I often wonder if we are going to start seeing cheaper built diesels that will have similar longevity to a gas.
 

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If you get into thermodynamics say at a first college level course and study the carnot cycle engine and do your calculus or at least can follow the instructors calculus it turns out that effeciency goes up as the compression ratio goes up. That has got to figure into the why more effecient. Typically longer stroke might as well. As best as I know there is no butterfly type valve in a diesel intake so think of the gas engine as sucking against a vacuum most all of the time.

Whether a diesel is really more long lasting than a gasoline engine with a governor so it stays in the same rpm range for the same displacement might well be up for a fair discussion. The gasoline burning by products are more corrosive at least I have read that. Because of the higher compression of the diesel it has to be designed for it and that often means a main bearing on each side of a rod as a gas engine youi will be more likely to find a pair of rods between main bearings. Because of the higher pressures on top of the piston more stuff gets by and I think oil change intervels have that factored in.

The governor on a modern diesel, well any of the ones I have used say 1989 or 2006 is just so incredibly better than the 1950's gasoline governors I have used.

I am waiting for natural gas tractor myself. There were quite a few propane, (not sure if Deere made any) years ago.

I expect those fuel air mixure numbera a few posts back are by weight.

Strangely it seems that the big engines in cargo ships are two cycle diesels. I don't know of any two cycle diesel Deere stuff but detroit diesel usually means two cycle. I am not real current on what is in what lately.

fran
 

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Discussion Starter · #9 ·
The reason why people idle their engines for a while after they work them hard is to cool the turbo. When you work a diesel engine, your turbo is pushing high PSI's to the intake and all the hot exhaust is running through the turbo. By idling it, you are cooling the entire turbo and its oiling system. If you turned off a hot engine, your oil could "coke" or create sludge in your turbo lines. Those lines are needed to feed fresh oil to the turbo.

Think of it just like your cooling system on your tractor. If you shut off a very hot engine, you can boil coolant because it can no longer circulate and go through the cooling process. Your oil is the same way, but it will create a film or burn on items rather than boil in most cases.

I forgot your other question....:morning2:
Brian, my little 41 hp Yanmar on the 990 does not have a turbo on it. So does that mean I have no need to idle it after working it hard? Your other points about the coolant and oil would say I should still idle it but those points could be the same for a gasoline engine unless I am missing something which I may well be.
 

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Discussion Starter · #10 ·
Rob its not really the fuel that gives you more torque but the operating principals. The diesel operates totally different than a gasoline engine just like a 2 cycle gas operates different than a 4 cycle gas engine.

Stroke and compression are typically very different. If you are wondering why everything isnt just diesel to start with its because a diesel is very heavy duty and was cost prohibitive in most applications. But now things are changing and they are becoming cheaper to build so you are seeing them in smaller applications.

I often wonder if we are going to start seeing cheaper built diesels that will have similar longevity to a gas.
It is really design then that makes diesels better. It also sounds like diesel fuel (which I believe is a lower grade or less refined grade of oil than gasoline) has its advantages as well when it comes to these engines except for the fact it costs more and my guess that is because of taxes more than anything. It probably costs less to refine but again I am only going by hearsay and not known facts. Why did they pick diesel instead of gas for these designed engines?
 

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Discussion Starter · #11 ·
If you get into thermodynamics say at a first college level course and study the carnot cycle engine and do your calculus or at least can follow the instructors calculus it turns out that effeciency goes up as the compression ratio goes up. That has got to figure into the why more effecient. Typically longer stroke might as well. As best as I know there is no butterfly type valve in a diesel intake so think of the gas engine as sucking against a vacuum most all of the time.

Whether a diesel is really more long lasting than a gasoline engine with a governor so it stays in the same rpm range for the same displacement might well be up for a fair discussion. The gasoline burning by products are more corrosive at least I have read that. Because of the higher compression of the diesel it has to be designed for it and that often means a main bearing on each side of a rod as a gas engine youi will be more likely to find a pair of rods between main bearings. Because of the higher pressures on top of the piston more stuff gets by and I think oil change intervels have that factored in.

The governor on a modern diesel, well any of the ones I have used say 1989 or 2006 is just so incredibly better than the 1950's gasoline governors I have used.

I am waiting for natural gas tractor myself. There were quite a few propane, (not sure if Deere made any) years ago.

I expect those fuel air mixure numbera a few posts back are by weight.

Strangely it seems that the big engines in cargo ships are two cycle diesels. I don't know of any two cycle diesel Deere stuff but detroit diesel usually means two cycle. I am not real current on what is in what lately.

fran
Fran, I believe I saw somewhere recently that JD did make a propane engine. Maybe it was on some other forum.

This is interesting info.
 

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Like I said, two different animals. Its about how the fuel ignites.

Fuels are pretty complex. Even in gas engines. Higher compression gas engines require slower burning fuel. AKA higher octane.
 

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Discussion Starter · #13 ·
Like I said, two different animals. Its about how the fuel ignites.

Fuels are pretty complex. Even in gas engines. Higher compression gas engines require slower burning fuel. AKA higher octane.
So it truly is a combination of the fuel type and the engine design as I am understanding it. There is a whole science to engine design combined with fuel type and then its application. That is what I believe I am learning here and that tractor duties are greatly benefited by a diesel engine as apposed to a gasoline engine.

With the engine being different you have a complete set of different needs in the maintenance realm and the types of coolants/lubricants than you have in a gasoline engine. I have been learning that with doing all the maintenance on this 7 y/o 990.
 

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Brian, my little 41 hp Yanmar on the 990 does not have a turbo on it. So does that mean I have no need to idle it after working it hard? Your other points about the coolant and oil would say I should still idle it but those points could be the same for a gasoline engine unless I am missing something which I may well be.
Well, I think almost any engine can benefit from a short idle after getting hot or hard work. BUT, most diesels you see that are idling after they come off the highway or out of the field are mostly due to trying to release the heat from the turbo and somewhat from the engine. There are programmers that you can purchase that will turn off the engine when the exhaust temps reach XXX temp (usually 800 or 900 degrees) or after so many minutes. So would I idle it for a minute after I got out of the field, yes, as I believe that starting the cooling process while running is a good thing. But you do not have a turbo that is almost red hot, so not as important as it is with a turbo, but still important.

When I grew up, I was taught to never turn off any motor after it was used. Even out little trimming mower or weed wacker would get an idle for a little after the job was done. But when I was using diesels (most with turbos) I was taught to run them at a lower rpm for about 5 times the amount of time I would a gas engine.
 

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Rob its not really the fuel that gives you more torque but the operating principals. The diesel operates totally different than a gasoline engine just like a 2 cycle gas operates different than a 4 cycle gas engine.

Stroke and compression are typically very different. If you are wondering why everything isnt just diesel to start with its because a diesel is very heavy duty and was cost prohibitive in most applications. But now things are changing and they are becoming cheaper to build so you are seeing them in smaller applications.

I often wonder if we are going to start seeing cheaper built diesels that will have similar longevity to a gas.
This is the best answer to your second question. Without going into the physics behind how the engine actually works, it's near impossible to explain. If you'd like, I'd doe some research/googling on how the engines actually work. A lot more info than what can be put in a single post:thumbup1gif:
 
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