Edumacate me???

[SteveAnsley]

OK - here are some questions I just curious about and have not seen a direct reference to.

Some may seem very basic and be stupid but... .



1. Cummins Motor - Crank, rods, pistons; are they cast or forged?

I've seen the rod comparison picture, just curious as to if they're cast or forged.



2. Why does a diesel take so long to generate heat in the block?

Diesel has a higher BTU rating compared to gas, I assume it's the heavier casting of the block that helps dissipate the heat. Or, is it something else?



3. Clearance lights - what's the legal reason/indicator?

I think I remember something about the cab lights are required if the width of the vehicle or trailer excedes 80" - yes/no?

SRW 1 tons and 3/4 tons w/ the camper package will have the cab lights because of the 'option/ability' to tow a trailier that will exceed 'X' width?

DRW are required to have the 3 lights on the rear, correct?



Sorry, I'm just a general idiate that likes to 'why' some things are the way they are.

 

[MCummings]

I can't reallyl help you with #1, but I can give you some #2... lol, anyway.



A Diesel takes longer to generate heat in teh block, because there is less heat being created in teh clylinders. Diesel's generally idle between 200-400*F , where as a gasoline motor can idle over 1,000*F. To heat the water to 180 or 200 degrees would take a long time, since that's what the motor is running at, not counting the intake stroke, or the radiator, and fan constantly trying to cool the engine back down.



It's not really the actual size of the motor, nor the size of the radiator, both of which can be 2x bigger than a similar sized gasoline engine, but to the fact, that a diesel creates less heat durin operation.



Hook your truck up to a trailer, and get cookin' down the road at 70MPH and watch how fast teh temp can come up. Within a mile or two, you can have full operataing temp when loaded down if started from a cold stop.







I'm gonna guess at #1, and say cast, since the Fordged rods in '01+ PowerStroke are known for easy failure.



#3, Clearance lights, in Tx, I think it's 80" wide and over, either the truck or trailer, and you have to have them, although most DOT/DPS officers won't recognize, or remember this. Out of sight, out of mind.





Merrick

 

[DogDiesel]

Heat Transfer - item 2

Heat becomes a thermal loss or cooling by these process of transfer:

1. Radiation 2. Convection 3. Advection 4. Dissapation 5. Absorbsion

1. Heat radiating is largely heat loss from one mass to surrounding receptor (Air for ground vehicle- water for floating things). Quite clearly the larger surface area (engine) mass cools by radiation faster than a smaller mass. Air cooled engines depend greatly on radiation to transfer heat.



2. Convection is the internal movement of currents within fluids (i. e. liquids and gases). It cannot occur in solids due to the atoms not being able to flow freely.



3. Advection is the process in which mass or heat is transported by the currents or motion in the fluid. In the case where the advected substance is heat, the heat itself may cause fluid motion, so the problem of heat transport (and transport of other substances in the fluid due to it) may become quite complicated.



4. Dissapation is transfer (in engines) of heat from one metal to another.

5. As one medium dissapates heat, another must absorb hold or transfer (dissapate-radiate-advect-convect... ).



Conductive heat transfer is proportional to the temperature difference between materials. If an engine metal is at 300°C and the air is at 0°C, then there is a 300°C temperature difference for cooling. An air-cooled engine uses all of this difference.



In contrast, a liquid-cooled engine might dump heat from the engine to a liquid, heating the liquid to 150°C which is then cooled with 0°C air. Thus, in each step, the liquid-cooled engine has half the temperature difference and so may need as much as twice the cooling area.



Why it takes so long is normally, the mass of diesel engines is greater than petrol engine. Additionally, thermal rates of burn as stated above cause many diesel engines to slobber at idle from incomplete fuel burn, as diesels achieve best combustion temps at points above idle speeds.



I remembered these principles from diesel class in the early 80s, so I used Wikipedia and memory of terms to put this together. This could generate comments. Ok

Good.

Wayne

 

[JApol]

Another reason why it's slow is that you have ~1000 lbs of cast iron to heat and ~ 7 gallons of fluid to heat.

 

[MCummings]

Conductive heat transfer is proportional to the temperature difference between materials. If an engine metal is at 300°C and the air is at 0°C, then there is a 300°C temperature difference for cooling. An air-cooled engine uses all of this difference.



In contrast, a liquid-cooled engine might dump heat from the engine to a liquid, heating the liquid to 150°C which is then cooled with 0°C air. Thus, in each step, the liquid-cooled engine has half the temperature difference and so may need as much as twice the cooling area.

That's awesome Wayne.



Gasser exhaust temp at idle 1,000*F.

Therefore dumping huge amounts of heat into the water, that will need cooled by the radiator. (about 800*F needs to be dissapaited)



Diesel exhaust temp at idle ~300*F.

Only about 100*F needs to be dissapaited.





You need to take into account that the exhaust heat is removed by the cylinder walls, pistons, incoming air, all the exhaust system (exhaust valve, head, manifold, turbo, exhaust pipe), untill it is released into the atmosphere.



The hotter your exhaust gasses are, the faster the water will be heated up from the motor.



That's just one of the factors. Also take into account that the 5. 9L Cummins does not have a throttle plate and has more airflow, allowing more cooling of the cylinders.



Merrick

 

[Cattletrkr]

If I may hijack for a sec here:

A customer rode with me today and he has a pulling tractor that was getting some work done at a big name diesel shop (I guess) and they were telling him that the ISB has Mercedes heads. Only the block is Cummins. Any truth to that. Sounded a lot like "ford owns cummings" to me...

 

[CogginsP]

We are missing the fact that the cooling systems built for the Cummins are built for extremely high operating temperatures and basically built for towing. Thats why I think it takes so long to heat up.

 

[05mxdiesel]

I'm gonna guess at #1, and say cast, since the Fordged rods in '01+ PowerStroke are known for easy failure.



Merrick

I think you mean the powered metal rods in the 01+ powerstrokes that can't hold up to much power.

 

[JJuday]

Pistons are normally cast, rods are a toss up in some areas as I think some are cast and some are forged, as for the cranks, they are mostly forged steel or machined.

 

[RustyJC]

I don't have much time, but I'll tackle your second question. A diesel engine is unthrottled. It always runs with as much air as is available. At idle, this means that the air/fuel ratio may be 100:1 or higher. All of the excess air that's not involved in the combustion process acts as a heat sink. If you look at the EGTs of a cold diesel engine at idle, they may be 200 to 250 degF. At that temperature, there's not a lot of thermal gradient between the cylinder temperatures and the temperature of the engine block, heads and coolant, and with the greater mass of cast iron and volume of coolant as compared to a typical gasser, the diesel is going to take significantly longer to build heat.



To illustrate the above, by energizing the exhaust brake, EGTs can be raised to 450 to 500 degF at idle. This results in significantly faster warmup.



Rusty

 

[AKaiser]

"The Cummins turbodiesel also provides an average of 350,000 miles before an overhaul is needed, thanks partly to gallery cooled, high-strength aluminum pistons;high-strength Inconel® exhaust valves and high-cobalt Stellite® exhaust valve seats, a high-strength exhaust manifold with multi-layer gasket between head and manifold; and forged steel, fracture-split connecting rods. " from Allpar.

 

[MCummings]

mxdiesel,



Yes, that's what I was meaning.



Rusty, you are correct, except that, the 6. 7L Cummins and 6. 4L International (Twin turbo) now have EGR valves, and throttle plates, so idle EGT's are much higher, and I feel that we will see much faster warm up times.



Merrick

 

[RustyJC]

mxdiesel,



Yes, that's what I was meaning.



Rusty, you are correct, except that, the 6. 7L Cummins and 6. 4L International (Twin turbo) now have EGR valves, and throttle plates, so idle EGT's are much higher, and I feel that we will see much faster warm up times.



Merrick

Yes, but they're not throttle plates in the traditional sense. They're there to force the engine to inhale more cooled exhaust gas and less air. In other words, it doesn't change the amount of gaseous matter flowing into the cylinder as much as it changes the composition of the gaseous matter.



Rusty

 

[mhenon]

Heat becomes a thermal loss or cooling by these process of transfer:

1. Radiation 2. Convection 3. Advection 4. Dissapation 5. Absorbsion

1. Heat radiating is largely heat loss from one mass to surrounding receptor (Air for ground vehicle- water for floating things). Quite clearly the larger surface area (engine) mass cools by radiation faster than a smaller mass. Air cooled engines depend greatly on radiation to transfer heat.



2. Convection is the internal movement of currents within fluids (i. e. liquids and gases). It cannot occur in solids due to the atoms not being able to flow freely.



3. Advection is the process in which mass or heat is transported by the currents or motion in the fluid. In the case where the advected substance is heat, the heat itself may cause fluid motion, so the problem of heat transport (and transport of other substances in the fluid due to it) may become quite complicated.



4. Dissapation is transfer (in engines) of heat from one metal to another.

5. As one medium dissapates heat, another must absorb hold or transfer (dissapate-radiate-advect-convect... ).



Conductive heat transfer is proportional to the temperature difference between materials. If an engine metal is at 300°C and the air is at 0°C, then there is a 300°C temperature difference for cooling. An air-cooled engine uses all of this difference.



In contrast, a liquid-cooled engine might dump heat from the engine to a liquid, heating the liquid to 150°C which is then cooled with 0°C air. Thus, in each step, the liquid-cooled engine has half the temperature difference and so may need as much as twice the cooling area.



Why it takes so long is normally, the mass of diesel engines is greater than petrol engine. Additionally, thermal rates of burn as stated above cause many diesel engines to slobber at idle from incomplete fuel burn, as diesels achieve best combustion temps at points above idle speeds.



I remembered these principles from diesel class in the early 80s, so I used Wikipedia and memory of terms to put this together. This could generate comments. Ok

Good.

Wayne

That's a great post Wayne. You can always learn something on this site.

The info above is exactly why I plug in any time the temps get close to freezing.

Mike

 

[MCummings]

Yes, but they're not throttle plates in the traditional sense. They're there to force the engine to inhale more cooled exhaust gas and less air. In other words, it doesn't change the amount of gaseous matter flowing into the cylinder as much as it changes the composition of the gaseous matter.



Rusty

hmmm. .



Rusty, I wonder if the throttle plate might be used in conjunction with the exhaust brake to provide additional braking? If you could raise EGT to 1,000*F at idle, the Cat, DPF, and water temps would all come up to temp and stabilize much faster lessening "warm up wear" that would be normally seen on engines that spend alot of time "warming up" before the owners put them to work.



What do you think? Time to get Marco (MADS) on the ball?



Merrick

 

[jwgary]

Heat becomes a thermal loss or cooling by these process of transfer:
1. Radiation 2. Convection 3. Advection 4. Dissapation 5. Absorbsion
This could generate comments. Ok
Good.
Wayne

And it has generated comments. I'll try to make it a little simpler. Some of the aforementioned terms are combinations of the 3 modes of heat transfer: Conduction, Convection, and Radiation.

Conduction is the transfer of heat from one body to another. You use an oven mitt to prevent conductive heat transfer from occuring between your pizza pan and your hand. The amount of heat transfer is dependent on the temperature difference between objects and the thermal conductivity of each. Metals have high conductivity and plastics are lower. This can also be thought of as heat resistance like the R-factor of a home's insulation.

Convection is heat transfer to a fluid that is moving. Natural convection is what you see when you heat water on the stove and you can see stuff floating and moving around as the hot and cold portions move to replace each other. Forced convection is when you have something actively moving the fluid like a fan or pump to increase the heat transfer rate. Again you are dependent on the conductivity of the materials since you have direct conduction at the fluid/solid interface, but then it is carried away allowing for faster heat transfer. Water is a much beter conductor of heat than air which is why water cooled engies are usually found when you need to cool a larger ingine in a smaller space.

Radiation is heat transfer without a medium. This is the way we get solar energy and why the outside of a light bulb is hot even though there is no air inside. Ratiative heat transfer is dependent on temperature difference, distance and emissivity of the object. Flat, dark surfaces have higher emissivity than bright, shiny ones do. The under-hood area is mostly heated by radiation.

All three depend on the amount of surface area. A large-bore I-6 has less surface area than a small-bore V8 so it transfers less heat from the combustion products. That, combined with the lower combustion temperatures (especially at idle) makes the diesel (with a more massive and slower thermally responsive block) heat up slower.

Whew! I feel better now. I hope this has cleared up things a little more.

Note: I tried to post this yesterday, but my server locked up.

 

[DogDiesel]

No intent to SIMPLIFY

The addition of advection to explain movement of fluids in convection process and also the topic of absorbsion (all) was added to the block of instruction, to simply teach. There were never any intent to simplify or summarize. If there is a dieselholic who learned something; it was all good.

Hoo-ah if you got it...





Wayne