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Questions for the diesel folk


Nate1647545505

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There have always been questions floating around my head about diesel fuel.

 

If the stuff can withstand so much abuse without premature ignition, why is it not looked at for incredibly high horsepwer applications???

 

Would diesel fuel be able to be ignited with say, a direct injection engine with a high compression ratio and turbocharger by use of a spark plug?

 

Why are the outlets on Diesel turbo's so damn big compared to petrol engines??

 

Why does diesel lose torque with RPM even in racing applications without the humingo stroke and are made for racing {Audi TDI Lemans car}?

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It is used for incredibly high horsepower applications..... think bigger then cars.

 

You know, I tried.

 

Audi's Lemans car made 1000ft/lbs and only 600hp. Surely you would want something that sustained HP for gearing and for the sake of not putting 1000+ft lbs through your tranny.

 

I could be wrong though, any examples you can post up?

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You know, I tried.

 

Audi's Lemans car made 1000ft/lbs and only 600hp. Surely you would want something that sustained HP for gearing and for the sake of not putting 1000+ft lbs through your tranny.

 

I could be wrong though, any examples you can post up?

 

It's not 1000 ft/lbs, it's 1000 Nm. That equals about 808 ft/lbs. Just thought I'd fix that for ya.

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There have always been questions floating around my head about diesel fuel.

 

If the stuff can withstand so much abuse without premature ignition, why is it not looked at for incredibly high horsepwer applications???

 

Would diesel fuel be able to be ignited with say, a direct injection engine with a high compression ratio and turbocharger by use of a spark plug?

 

Why are the outlets on Diesel turbo's so damn big compared to petrol engines??

 

Why does diesel lose torque with RPM even in racing applications without the humingo stroke and are made for racing {Audi TDI Lemans car}?

 

I believe that diesel is actually the opposite... it's supposed to preignite. The engines basically run on detonation. Some of the principles in diesels are real interesting, all you have to do to make more power on most diesels is to just add more fuel. Diesels don't actually have throttle bodies, when you push the pedal it just injects more fuel into the engine giving it more power.

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There have always been questions floating around my head about diesel fuel.

 

If the stuff can withstand so much abuse without premature ignition, why is it not looked at for incredibly high horsepwer applications???

 

Would diesel fuel be able to be ignited with say, a direct injection engine with a high compression ratio and turbocharger by use of a spark plug?

 

Why are the outlets on Diesel turbo's so damn big compared to petrol engines??

 

Why does diesel lose torque with RPM even in racing applications without the humingo stroke and are made for racing {Audi TDI Lemans car}?

 

I would say the biggest reason for low rpm and low hp at high rpm is because of the inertia. Diesel cranks have much more inertia than say gas engine of similiar size. The counterweights on the diesel crank are much wider and span a larger angle.

 

Think about tractor pull motors, they are looking for maximum sustaining torque. They don't have to worry about the time to accelerate the engine. They can spend all day getting the engine up to speed before they make a pull. Distance, not time, is important. Higher inertia is harder to accelerate but at the same time, harder to decelerate once up to speed (M=I*alpha, M = Torque, I = inertia, alpha = angular acceleration). Cranks for those bad boys are huge and heavy!

 

Although inertia may not be the main/only reason, it definitly is a factor. I know very little about diesels in general so I can't even say why larger inertia is better for the diesel cycle. Although hopefully someone else can chime in and add to that.

 

Hopefully some insight.

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There's some good info here already. A couple notes,

 

Glow plugs are only used to start the engine. Once the engine is warm, the extremely high rate of compression causes the fuel to ignite, think detonation. They are very inefficent when cold, thats why many semi's don't get shut off unless they are going to sit for a day or longer. Light duty trucks usually have block warmers so you can plug it in at night.

 

Low compression diesel engines can rev higher, but aren't as efficient. That's why diesel's make massive amounts of torque, but not so much hp. The higher the compression, the stronger the burn, the more force applied to the piston to push it back down. If you aren't getting enough compression in a diesel, you could rev it to the sky and it still won't help.

 

http://www.truckinohio.net/filedump/mike/Cumminsrod1.jpg

 

As you can see, diesel trucks have huge internals. This is another reason why they don't rev very high, that shit is heavy and hard to move. The Cummins has the largest pistons and rods, and it's an inline 6. It's also the most powerful and reliable of the three, but I would guess that it has the lowest redline. I would GUESS that the Powerstroke rev's the highest, but it's also the least reliable of the three.

 

Diesel can't be run rich or lean, it will detonate either way. That's why they love boost. However, more fuel to a point helps out too. Too much fuel is just a waste, however it won't hurt the engine in the least.

 

Diesel's don't need backpressure like gas engines do. I'm not sure how the valves work, or the injection for that matter, but I do know that you can't get too big of an exhaust pipe on them. I think it's also a cleaner burning fuel, diesel's only started being required to have cats within the last few years, and it was because the diesel used in America is high in sulpher. Europe doesn't have that problem.

 

If I think of anything else I'll add it later.

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diesel fuel in injected on the compression stroke just before TDC and the tempatures from the heated air cause the fuel to burn. i don't know about the ford or dodge but the duramax is 16.8:1 cr. runs about 32psi of boost and is 310hp 610ft. lbs. the brand new duramax is 360 horse and 650 ft. lbs. fuel pressure dropped from 28,000 to 26,000 witch makes the engine quiter.
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There have always been questions floating around my head about diesel fuel.

 

If the stuff can withstand so much abuse without premature ignition, why is it not looked at for incredibly high horsepwer applications???

Some of the super stock methanol tractor pulling engines are around the 24:1 ratio. They've got more money in one engine than I've ever seen in my life tho.

 

Would diesel fuel be able to be ignited with say, a direct injection engine with a high compression ratio and turbocharger by use of a spark plug?

Diesel's notoriously hard to ignite. There are Natural gas pipeline pumps that run with spark plugs, but diesel doesn't appear to work that way.

 

Why are the outlets on Diesel turbo's so damn big compared to petrol engines??

They suck alot. Stock light truck applications push 20psi/650cfm daily. Modified apps run twice as much or more. Also, the diesel's biggest enemy is exhaust temp. Generally the bigger the exhaust housing is, the lower the EGT's you can run towing a heavy load.

 

brandon.

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Guest chpmnsws6
There have always been questions floating around my head about diesel fuel.

 

If the stuff can withstand so much abuse without premature ignition, why is it not looked at for incredibly high horsepwer applications???

 

Would diesel fuel be able to be ignited with say, a direct injection engine with a high compression ratio and turbocharger by use of a spark plug?

 

Why are the outlets on Diesel turbo's so damn big compared to petrol engines??

 

Why does diesel lose torque with RPM even in racing applications without the humingo stroke and are made for racing {Audi TDI Lemans car}?

 

 

Stock EGR engines are now making upwards of 600hp and 1300+ foot pounds of torque

 

Smaller diesels do use spark plugs. Mid sized use glow plugs for initial fire up, and full sized diesels do not even use glow plugs.

 

Diesels use more air then a gasser, just less fuel, as they use every bit of fuel then the typical gasser.

 

We lose HP with RPM as the diesel gets "winded" to quickly.

 

 

With to much fuel, you will wash the cylinder walls, raise EGT's, and very easily harm the engine.

 

Once people forget about the unreliable GM 6.2 and the thoughts of diesels being loud and dirty, you will see many more diesel engines in everything from your corner carver or drag car to your econo hybrid vehicle. They have now made the diesel engine nearly as quiet as a gas engine.

 

Also- In the old days it was better to let the engine sit and idle but with todays tolerances and such, it is more harmful to let the engine run as you need some heat in the cylinder or else the fuel will bypass the engine and contaminate the engine oil (thinning it out and deluting the many additives in diesel oil)

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another cool notesw on diesels

unlike when you add gasoline to a gas engine it will lower the EGTs, when you add deseil to a desiel engine it raises the EGT, and the air will lower it and also make it have less smoke.

to get more power to a deisel you add more fuel (unlike a gas engine where you have to figure a way to add more air) you just cant let the EGTs get to high.

on a deisel when you have the cumbustion process after it is ignited deisel fuel continues to be added when the piston travels down the stroke, this is one reason it is to the advantage to have a long stroke, as you have more time to add fuel to it and make massive torque.

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Here in Korea alot of the engines are diesel. They range from small to large and just about every "truck" has a diesel in it. The US is about the only country in the world that hasn't really accepted diesels do to false myths about them. Like someone said once we forget about the GM 6.2 and 6.5 the better off we will be.
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