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Tractor Talk Discussion Forum

Which Creates More Heat?

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in-too-deep

06-11-2006 09:20:28




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I've had this thought flying around my brain for quite some time. I figured this would be the place to get some input. Ok, start with a cold tractor engine. By cold I mean hasn't been run recently and everything is ambient temperature. Sufficient coolant, proper weight and amount of oil, etc. Now, start the engine. Is it the combustion of fuel in the cylinder or the friction of moving parts that creates more heat to warm the engine? I just can't decide which is hotter. I tend to lean to the combustion making the most heat, but please help. All opinions welcome.

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Jerry/MT

06-11-2006 23:11:08




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 Re: Which Creates More Heat? in reply to in-too-deep, 06-11-2006 09:20:28  
I'm doing this from memeory so I might not have all the numbers exactly right.
The average gas temperature at the start of the power stroke is probably about ~4000F and diminishes as the power stroke continues to 400oF or there abouts. Windages losses are maybe 10 % of the net power output so the temperature of combustion drives the overall heat input to the engine. The oil pickups heat from just being pumped as well from work being done agaist friction and from h components heated by combustion gases. it's a lot more complicated than this because the overall process is a transient until the engine comes up to stabilized operating temerature.
In a diesel it a little diffeerent because it runs with variable fuel to air ratio and hence a variable combustion temperature. An idling diesel take a along time to warm up becayue the temperatures are relatively low due to thelow f/a ratio. It'll warm up faster at part throttle.

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Jerry/MT

06-11-2006 23:08:28




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 Re: Which Creates More Heat? in reply to in-too-deep, 06-11-2006 09:20:28  
I'm doing this from memeory so I might not have all the numbers exactly right.
The average gas temperature at the start of the power stroke is probably about ~4000F and diminishes as the power stroke continues to 400oF or there abouts. Windages losses are maybe 10 % of the net power output so the temperature of combustion drives the overall heat input to the engine. The oil pickups heat from just being pumped as well from work being done agaist friction and from h components heated by combustion gases. it's a lot more complicated than this because the overall process is a transient until the engine comes up to stabilized operating temerature.

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NC Wayne

06-11-2006 14:06:34




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 Re: Which Creates More Heat? in reply to in-too-deep, 06-11-2006 09:20:28  
Remember, there is a difference in the heat of compression and the heat of combustion. In your case, considering the your asking about starting a tractor that is "cold" then the majority of the heat, at least initially, is going to be the heat from compression, not from combustion. The heat from combustion doesn't begin til the engine is actually running. Think about the older machines with pony start, especially ones like the old CAT dozers with the BIG inline engines. The starting process with them for "normal" ambient temps was to actuate the compression release to get the engine rolling fast and then kick it in for it to start. In that case the ambient temp was high enough that you didn't need anything more than the heat of a single compression stroke to make it hot enough for combustion. If the temps were cold then you put the pony transmission in low gear for the needed torque and turned the engine with compression on the cylinders for a few minutes. This allowed the heat of compression to warm the engine components enough that the "heat of compression" from a single stroke wasn't drawn down too cold to cause combustion. In many cases the pony was also responsible for warming the intake air, the oil, and the coolant, but the end result was always to get the component temps of the engine hot enough that a single compression stroke would creat enough compression heat to cause combustion. Just my .02

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john-mi

06-11-2006 13:35:57




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 Re: Which Creates More Heat? in reply to in-too-deep, 06-11-2006 09:20:28  
If you have a gas engine that is missing, you can feel the difference in temperture by feeling the spark plugs. So i would vote for combustion.



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Allan In NE

06-11-2006 11:27:22




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 Re: Which Creates More Heat? in reply to in-too-deep, 06-11-2006 09:20:28  
Hey Guy,

Friction in an internal combustion engine is "almost" non-existant. That is the oil's job.

Allan



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Coloken

06-11-2006 11:16:56




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 Re: Which Creates More Heat? in reply to in-too-deep, 06-11-2006 09:20:28  
The combustion by a large degree. The higher you can maintain the cylinder temperature, the better. Less heat (enery) transfered to the cooling media means less waste. thats why they went to high temp. thermostats.



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John No Mi

06-11-2006 10:05:31




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 Re: Which Creates More Heat? in reply to in-too-deep, 06-11-2006 09:20:28  
I believe it is the combustion that creates the most heat. Just grab the muffler a couple of min. after the tractor is started. If you have enough friction to cause heat mit would be very hard to start the engine.



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I Don't Know

06-11-2006 10:03:52




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 Re: Which Creates More Heat? in reply to in-too-deep, 06-11-2006 09:20:28  
May not answer your question, but it has to do with heat.

The following is an actual question given on a University of Washington Chemistry mid term. The answer by one student was "so profound" that the professor shared it with colleagues, via the Internet, which is, of course, why we now have the pleasure of enjoying it as well.

Bonus Question: Is He77 exothermic (gives off heat) or endothermic (absorbs heat)? Most of the students wrote proofs of their beliefs using Boyle's Law, (gas cools off when it expands and heats). One student wrote the following answer:

First, we need to know how the mass of He77 is changing in time. So we need to know the rate that souls are moving into Hell and the rate they are leaving. I think that we can safely assume that once a soul gets to He77, it will not leave. Therefore, no souls are leaving. As for how many souls are entering He77, let's look at the different religions that exist in the world today. Some of these religions state that if you are not a member of their religion, you will go to He77. Since there are more than one of these religions and since people do not belong to more than one religion, we can project that all souls go to He77. With birth and death rates as they are, we can expect the number of souls in He77 to increase exponentially.

Now, we look at the rate of change of the volume in He77 because Boyle's Law states that in order for the temperature and pressure in He77 to stay the same, the volume of He77 has to expand proportionately as souls are added. This gives two possibilities:

1. If He77 is expanding at a slower rate than the rate at which souls enter He77, then the temperature and pressure in He77 will increase until all He77 breaks loose. 2. If He77 is expanding at a rate faster than the increase of souls in He77, then the temperature and pressure will drop until He77 freezes over.

So which is it? If we accept the postulate given to me by Teresa during my Freshman year that: "it will be a cold day in He77 before I sleep with you," and take into account the fact that I still have not succeeded in having $exual relations with her, then #2 cannot be true, and thus I am sure that He77 is exothermic and will not freeze.

The student received the only "A" given.

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Olivergreen

06-11-2006 13:06:48




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 Re: Which Creates More Heat? in reply to I Don't Know, 06-11-2006 10:03:52  
My guiss or 2 cents worth is coming home late with a new tractor.



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