| Author |
Message |
Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, June 07, 2003 - 1:02 am: | |
Had a discussion with a hot-rod buddy today and he was asking me how diesel engines work. When I explained that they have no butterfly in the intake manifold, that they just gulp in as much air as possible and that engine power is controlled by how much fuel gets squirted in, he said "gee, that means that diesels run from very lean to maximum-rich, and even more when they make smoke.... so why when running lean don't they burn valves like gasoline engines do?
Good question, I couldn't answer.
My theories are three:
(1) the chemistry and energy content of diesel is different than gas and lean running diesel fuel doesn't burn as hot as gasoline
or
(2) lean running in gasoline engines often means preigniton which can't happen in diesels... preignition makes cars run hot because the explosion is too early in the cycle and works against the pistons instead of with them
or
(3)I'm missing the real answer entirely....
Any guru's that know the answer??
Cheers
Gary |
FAST FRED (67.75.96.138)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, June 07, 2003 - 5:42 am: | |
The gov keeps track of the RPM so the correct amount of fuel is injected for that load.
If too little fuel were injected the engine would simply slow down, not burn valves.
Lean burn is the next wave of diesel tech , problem is how to ignite the very lean mix.
Most Mfg of small stuff use a pre combustion chamber , small amount of fuel is rich enough to light in pre combustion chamber , and it squirts into combustion chamber to light rest .
Larger diesels (tanker sized) simply heat the fuel and inject at very close to ignition temp.
Injection pressures of 25,000 psi are now common in common rail systems.
FAST FRED |
scott cavanaugh (66.169.172.154)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, June 07, 2003 - 11:04 am: | |
Ok I have a question and I looked and searched via google and could not find a definitive answer. What is V-drive transmission, and what is a T-drive transmission? Even checked Allison's site and never found anything |
John Feld (150.199.209.26)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, June 07, 2003 - 1:46 pm: | |
A V-drive is where the driveshaft is off-set at an agle that forms a V between the transmission and rear-end. This is formed when the engine sits cross-wise to the frame, such as a Detroit in a bus rear mounted engine. The tranny output is to the side of the bus and the driveshaft angles back toward the center of the rear axle to connect.
A T-drive is what you would normally see in a rear drive automobile, the tranny output is center line to the vehicle and connects at a 90 degree line to the axle, thus forming a T configuration rather than a V. |
Henry R. Bergman, Jr. (Henryofcj) (209.210.116.27)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, June 07, 2003 - 3:10 pm: | |
Gary...I do not know the answer to your question. It is neat that our 25,000 to 30,000 pound coaches get 10 to 12 mpg at 60 mph and a stick built 454 powered cheapo motorhome weighing 12,000 pounds gets 6 mpg.
I think diesels are designed to run in a very lean condition. The exhaust always seems to have some left over oxygen in it. The fuel injection system is designed to provide just enough fuel to handle the load.
At idle, the amount of diesel fuel injected at high pressure is very little. Just enough to push the pistons down at idle speed. Diesels knock because they literally have to. The temperature of the compressed air is high enough...
...to ignite the sprayed fuel. I think also that gasoline burns much faster and hotter than diesel oil. Do wish someone who knows something about this will log on and set us straight. Good luck with your Turbo pluming. CROWNS FOREVER!! Henry of CJ |
Tom Caffrey (Pvcces) (64.114.233.182)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, June 07, 2003 - 10:58 pm: | |
Gas engines are designed to run a standard mix, regardless of load when they are working. This means that the valves never get to cool down in normal operation.
If you don't believe that, just check the temperature of the exhaust pipes on each after they have been setting idling for ten minutes. DON'T TOUCH THE GAS ENGINE ONE.
Diesel engines run on extremely lean mixes up to a standard mix when at full load, so their valves get a chance to cool off on anything less than a full load.
Gas engines don't normally use valve rotators, but heavy duty diesel engines do, so the valves do not leak as easily. Also, they are often better steel.
When gasoline is mixed with air leaner than standard, it burns slowly enough that much of the burning occurs very late in the cycle, just before and even after the valves open.
The loss of power from the lean mix leads to a heavier foot on the gas pedal, and more fuel burned. If the mix stays lean, then the valves are exposed to even more heat.
You might remember seeing aircraft started up in the war movies and seeing the slow lapping blue flame from the exhausts. You never see that with diesel, because even when it is ignited lean, it doesn't burn that slow.
I think that the difference is that with gas, the temperature of the flame front ignites neighboring mix. In the diesel, ignition is maintained by high air temperature thoughout the combustion chamber, so it can burn the smallest of charges.
Instead of a spark starting a fire in one place and spreading to the rest of the charge, the whole charge starts to burn nearly at once.
Just some thoughts based on my experience with these engines.
Tom Caffrey PD4106-2576
Suncatcher |
FAST FRED (67.75.112.35)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, June 08, 2003 - 5:38 am: | |
"Gas engines don't normally use valve rotators, but heavy duty diesel engines do, so the valves do not leak as easily. Also, they are often better steel. "
In medium duty engines like th RR uses the PISTONS rotate too, to even out the wear.
FAST FRED |
Peter Broadribb (Madbrit) (65.73.176.223)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, June 08, 2003 - 7:34 am: | |
Chevrolet has used exhaust valve rotators for years in their gas motors.
Peter. |
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