mark kibort

Torque doesnt dictate anything, unless it is matched with an RPM. Again, torque (or force) over a distance is only work. Power takes it a step even further, being the rate of doing work!
Torque is a component of HP, and is meaningless unless you attach an RPM to it.

HP or Power WILL determine what the acceleration force/torque will be

Acceleration = power/(mass x velocity) is a combination of newtonian identies.
This says that acceleration is directly proportional to Power.

Now, you can substitute this for Acceleration= F/M However, YOU need to be looking at the "F" at the rear tires, not at the engine. Hp will dictate this. AND, this Force can indicate HP as well, as it is a component of it.

Its not a chicken an egg discussion. The energy is produced from the combustion of fuel. The energy has the capacity to do work at a certain rate over a period of time (i.e. think kw-hours like with your energy bill, or for our discussion, hp-seconds)
You now have the potential to create a force at a rapid speed, or a greater force at a slower speed. eitherway, the power will determine the force, small or large depending on how it is produced.

So, yes, you can always calculate power by knowing rpm(velocity) and torque(force), but it is power that will dictate the true net force at the rear tires acting on the car, regardless of the comparative engine torque values

mk




.[QUOTE=doc2s]

Congo

The P1 regs give 37.5 % more engine displacement (5.5 liters) for turbodiesels than turbo'd gasoline engines (4.0 liters) and 6.0 liters for n/a'd engines.

Pescarolo says the new 5.5 liter Judd V-10, called the GV5.5 S2, has 640 hp at 7,000 rpm. The additional 1/2 liter brings more power earlier in the power band.

http://www.mulsannescorner.com/juddgv510.html

http://www.engdev.com/

http://www.pescarolo.com/images/2007/dp2007.pdf

Ulrich Baretzky is the head of engine technology at Audi Sport. The following is from the April, 2006 issue of Car & Driver:

"Baretzky wasn't forthcoming about precise dimensions or mass. But he did suggest that the diesel V-12 would weigh about 50 percent more than the 385-pound R8 V-8. If so, the diesel should weigh about 580 pounds."

insite

[QUOTE=doc2s]you're not comparing apples to apples. in a car, the force we're interested in is at the contact patch. this is dictated by power. power can consit more heavily of torque or of RPM; it doesn't matter. the transmission deals with the WAY the power is delivered, but power output still dictates the maximum force at the wheels.

mark kibort

A+

mk

QUOTE=insite]

Mike Murphy

Now that we got all the HP vs. Torque issues out of the way...

It has been said that one main reason why a diesel engine cannot rev is due to the long stroke, which I understand and it makes sense to me. What if, however, you were to compress the air well before it entered the combustion chamber? A healthy 50psi supercharger might do the trick. Compression ratio would be lowered to, say 12:1 and you would have enough heat to ignite the diesel fuel during compression. In this case, you could then build the diesel engine to rev much higher because there is less stroke and piston velocity. Therefore, I believe you would have a more powerful engine compared to a gasoline engine if you didn't have to account for the emissions issue of particulate waste.

NNH

I recall reading that a major element in the lower rev limit for diesels is that it's hard to maintain the extremely high injection pressure needed for accurate fueling, beyond a certain rev limit. If so, that sounds like "just" an engineering challenge that will eventually be addressed.
OTOH, if the90 is right about the flame speed, then we'll hit a brick wall at a little over 100bhp/litre.

insite

simple physics. if you can maintain peak torque and increase the rev limit from 5000 to 8000RPM, power would increase by 60%. the power increase given equal torque is a linear relation to RPM. if you make 100HP at 4000RPM, the same torque at 8000RPM would be 200HP.

A.Wayne

While , bore /stroke ratios will effect the max RPM, It is not enough to limit the BHP..It would appear the limit of diesel engines making power at High RPM , would be Cylinder pressure , if you had some sort of a rotary chamber you could control the cylinder pressure as RPM increases , creating more power....

adrial

I asked my buddy that recently took an Internal Combustion Engines class...here is his answer (he is referring to diesels here):

"At high revs you can't effectively burn all the fuel in the time allowed to transfer it effectively into the crank. This is why swirl and tumble are huge things in diesel motors. They need a lot of in chamber movement/velocity. "

kurt M

How about a cross between the two? Diesels don't have any ignition advance.
Use the diesel method but also use spark plugs to initiate a flame front as needed? Computers can ajust for anything. Set things up to fire the plugs when rpm needs require faster flame fronts. Use more than one plug per cyl and fire then all same time or in sequence which ever is better to increase burn rates. Best of both, diesel frame twisting torque and a gasoline like ignition advance system to increase the RPM range. (This is too simple there has to be good reasons it won't work)

ed devinney

Ask and ye shall receive: Mercedes DiesOtto engine

1.8L, 238hp and 400 N-m, claiming almost 40mpg in an S-class sized car. I'll believe that when I see it but interesting none the less.

Mike Murphy

I have heard that as well, but here is my disconnect: "Diesel burns significantly faster than gasoline." So if a gas engine can burn quick enough to run 15,000 RPM, then you'd think that a diesel engine could go even faster. Hence, theoretically, it should be able to produce more power.

krC2S

sorry guys this is all wrong..doc2s is correct

please read what newton law is and does not say anything about power it's force/torque


power is just an outcome of force x speed that's it...a force is what causes something to move

and yes i am a mechanical engineer so i am not making this up

Mike Frye

Not sure if I agree with the basic premise here. I think you'll be seeing some turbo diesels on the track (from the rear ) very soon. Watch the industry... it's coming.

Mike Murphy

No offense, but since you are a mechanical engineer, then can you please give your input on the original topic? I have a background in engineering also, so I'm just dying for someone to properly explain why a diesel engine cannot produce power at a high rpm. I don't need any explanation on power vs torque vs rpm or anything like that.