diesel rpms
10-17-2011, 10:31 PM
#2
howstuffworks will probably give you more answers than you'll get here.
do a google on two stroke and four stroke diesel, and also on torque rise.
what determines max rpm's is the mass of the piston and the stroke of the engine. The useful rpm range or where max torque is generated is then decided by the camshaft profile if on a 4 stroke with intake valves. if it's a 2-stroke I believe it's largely dependent on boost pressure. And all diesels are basically direct injection, the fuel injector squirts diesel into the combustion chamber or pre-chamber which is pressurized at over 500 psi.
Gasoline engines with 93 octane fuel will detonate once the fuel/air mixture is pressured over 200 psi, because of the heat generated from pressurization.
do a google on two stroke and four stroke diesel, and also on torque rise.
what determines max rpm's is the mass of the piston and the stroke of the engine. The useful rpm range or where max torque is generated is then decided by the camshaft profile if on a 4 stroke with intake valves. if it's a 2-stroke I believe it's largely dependent on boost pressure. And all diesels are basically direct injection, the fuel injector squirts diesel into the combustion chamber or pre-chamber which is pressurized at over 500 psi.
Gasoline engines with 93 octane fuel will detonate once the fuel/air mixture is pressured over 200 psi, because of the heat generated from pressurization.
10-22-2011, 09:13 PM
#3
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Have you ever taken a diesel apart? You will quickly realize why. The components in it are huge due to the severe detonation a diesel goes through so the reciprocating mass is terrible which limits RPM. Also the journals are big so there is a lot of parasitic loss on the crank. Next the cylinder heads are usually terrible so even with 30 psi of boost the heads cant get the air in with high PRM.
10-26-2011, 11:06 AM
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A friend of mine has a 01 TDI JETTA and spins that to 6500rpm. It is awesome. It never stops pulling. He is worried to spin it higher though even though it is still making power.
10-27-2011, 10:15 PM
#7
The diesel world is changing fast. Especially the small diesel world. Mazda's new twin turbo diesel that is coming to the states in late 2013 is spinning over 5600 rpms (40 mpg, 170hp, 310tq) not bad if you ask me. But as said above most big diesels are limited due to there main goal (durability) Parts are heavy and tough made to last and take a pounding. Look at the LB7 duramax and 12/24 valve cummins engines out there. You can take one that is producing 230 horses at the wheels and with some miner mods make close to 500 on the pavement and they still last. I have owned 4 diesels over 200,000 miles and one with almost 400,000. All of them had stock bottom ends and ever suffered any major mechanic problems and that was due to over heating (cracked cylinder head).
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11-15-2011, 05:35 PM
#8
I have wondered this question myself. I find it hard to believe that the rotating mass is the limiting factor of RPM's. You have two engines one stock LS1and another LS1 with the same H/C/I combo with the lightest rotating mass possible, the one with the lightest rotating mass will accelerate to a give RPM fast but it will not turn a higher RPM. Im no engineer but to me the cylinder pressure will be the limiting factor or even piston speed for that matter. I could be wrong. I wish someone a lot smarter would chime in on this
11-15-2011, 10:28 PM
#9
Put a 1LB rock on a string and swing it around. Now put a 5lb rock on the same string and swing it around. The 1lb rock will have little trouble tilll you get up to faster RPM's when the string can't handle the inertia mass. The 5lb rock wont take near as much RPM before it breaks the string cause of the rotating mass's weight. My .02
11-16-2011, 10:38 AM
#10
You can't rev a diesel engine too high because of the direct injection of the diesel fuel to the cylinder. It takes a certain period of time to inject the fuel and then there is an ignition delay, then a couple of periods of combustion, one rapid the other steady. You can't make the burn process speed up, so if you speed up the engine rpm, you now have less time to complete the burn and not end up wasting most of your power when the piston is already on the downward stroke.
There is a few things that the injector must do.
- Be accurate in the delivery amount of fuel
- Start Injection at the correct time
- Must properly atomize the fuel throughout injection time
- The droplets of fuel that are atomized must penetrate the combustion chamber evenly but not impinge on the surfaces
- Injection must end abruptly and completely
Remember these systems operate up to 15,000 PSI and above. I'm sure some of these systems have to worry about cutting the metal like a waterjet.
Here is a diagram of diesel injection events.
There is a few things that the injector must do.
- Be accurate in the delivery amount of fuel
- Start Injection at the correct time
- Must properly atomize the fuel throughout injection time
- The droplets of fuel that are atomized must penetrate the combustion chamber evenly but not impinge on the surfaces
- Injection must end abruptly and completely
Remember these systems operate up to 15,000 PSI and above. I'm sure some of these systems have to worry about cutting the metal like a waterjet.
Here is a diagram of diesel injection events.
11-16-2011, 11:15 AM
#13
Nope, unlike your gas engine the fuel is not in the chamber during the intake stroke. The limits are and will always be how fast you can get it into the chamber at exactly the right time and exactly the right amount.
11-18-2011, 11:46 AM
#17
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You can't rev a diesel engine too high because of the direct injection of the diesel fuel to the cylinder. It takes a certain period of time to inject the fuel and then there is an ignition delay, then a couple of periods of combustion, one rapid the other steady. You can't make the burn process speed up, so if you speed up the engine rpm, you now have less time to complete the burn and not end up wasting most of your power when the piston is already on the downward stroke.
There is a few things that the injector must do.
- Be accurate in the delivery amount of fuel
- Start Injection at the correct time
- Must properly atomize the fuel throughout injection time
- The droplets of fuel that are atomized must penetrate the combustion chamber evenly but not impinge on the surfaces
- Injection must end abruptly and completely
Remember these systems operate up to 15,000 PSI and above. I'm sure some of these systems have to worry about cutting the metal like a waterjet.
Here is a diagram of diesel injection events.
There is a few things that the injector must do.
- Be accurate in the delivery amount of fuel
- Start Injection at the correct time
- Must properly atomize the fuel throughout injection time
- The droplets of fuel that are atomized must penetrate the combustion chamber evenly but not impinge on the surfaces
- Injection must end abruptly and completely
Remember these systems operate up to 15,000 PSI and above. I'm sure some of these systems have to worry about cutting the metal like a waterjet.
Here is a diagram of diesel injection events.
It has always amazed me that diesel engines could be run in races such as Le Mans and be competitive. Noice is on point here. Here is a few things said about the Audi R10 raced at Le Mans.
The new Audi prototype was the R10, a V12, twin-turbocharged, direct-injected diesel. For the 2005 and 2006 seasons, the 5.5-liter engine produced 650 hp and 737 lb-ft of torque.
The results were almost immediate, proving that diesels could win at Le Mans. Audi pilot Rinaldo Capello put an R10 on the 2006 Le Mans pole with a 3:31.211 lap at 144.57 mph. While lap speeds for the diesels weren't considerably faster than those of the gasoline-powered cars they replaced, the diesels could go longer between fuel stops.
The R10 went on to win the 24 Hours of Le Mans in 2006, 2007 and 2008.
The R10 featured Audi's TDI diesel engine technology (turbocharged direct injection). According to Dr. Ullrich Baretzky, the Head of Audi Motorsports Engine Development, what Audi learns on the track has an influence on its production vehicles. For example, Baretzky told PM, "fuel-injection pressure levels are key to engine efficiency. In 2004, when we started the development of the R10, our diesel road cars had an injection pressure of 1600 bar",he says. "We are now running over 2200 bar in the R15, and our road cars, starting in 2008, used increased pressures of 2000 bar. It took only four years for what we learned on the racetrack to be in our diesel road cars," Baretzky says, "And the process continues."
The results were almost immediate, proving that diesels could win at Le Mans. Audi pilot Rinaldo Capello put an R10 on the 2006 Le Mans pole with a 3:31.211 lap at 144.57 mph. While lap speeds for the diesels weren't considerably faster than those of the gasoline-powered cars they replaced, the diesels could go longer between fuel stops.
The R10 went on to win the 24 Hours of Le Mans in 2006, 2007 and 2008.
The R10 featured Audi's TDI diesel engine technology (turbocharged direct injection). According to Dr. Ullrich Baretzky, the Head of Audi Motorsports Engine Development, what Audi learns on the track has an influence on its production vehicles. For example, Baretzky told PM, "fuel-injection pressure levels are key to engine efficiency. In 2004, when we started the development of the R10, our diesel road cars had an injection pressure of 1600 bar",he says. "We are now running over 2200 bar in the R15, and our road cars, starting in 2008, used increased pressures of 2000 bar. It took only four years for what we learned on the racetrack to be in our diesel road cars," Baretzky says, "And the process continues."
Might be on topic. Might not be. Still thought I should share.
11-18-2011, 01:06 PM
#18
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I was under the impression that the harmonics of the diesel would destroy itself above a said RPM. I had been looking up information on my 12v dodge, and found some that said that if you spun higher than 4200 it would only be once time because the engine would beat itself.
Time to go read up on diesels again......
Time to go read up on diesels again......
11-21-2011, 08:28 PM
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I understand the "lead time" vs combustion time available for a diesel, but at what point does that honestly become an issue? Power level (ie fuel quantity) dictates this almost as much as the RPM itself.
Seeing how a pulling truck is grossly over fueled, and some turn 5-6k, (depending on the class ofcourse) the rpm limit of a diesel, dictated by fueling alone, must be far, far north of 6k.
Now, those huge lifters and heavy *** valves, with mediocre spring rates would cause an issue earlier on than harmonics or fuel timing.
Seeing how a pulling truck is grossly over fueled, and some turn 5-6k, (depending on the class ofcourse) the rpm limit of a diesel, dictated by fueling alone, must be far, far north of 6k.
Now, those huge lifters and heavy *** valves, with mediocre spring rates would cause an issue earlier on than harmonics or fuel timing.
Last edited by Mighty Whitey; 11-21-2011 at 08:43 PM. Reason: Damn you auto correct!
12-04-2011, 10:33 AM
#20
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I have wondered this question myself. I find it hard to believe that the rotating mass is the limiting factor of RPM's. You have two engines one stock LS1and another LS1 with the same H/C/I combo with the lightest rotating mass possible, the one with the lightest rotating mass will accelerate to a give RPM fast but it will not turn a higher RPM. Im no engineer but to me the cylinder pressure will be the limiting factor or even piston speed for that matter. I could be wrong. I wish someone a lot smarter would chime in on this
Diesel is a slow burning fuel. Plain and simple. It needs injected very precisely both in quantity and more importantly timing. Modern diesels can rev harder than some older ones purely because the modern common rail inject at very high pressures, with extremely precise control.
On older mechanical engines it was difficult to achieve this.