This was probably just a slip of the keyboard so to speak, but since HP~FORCExVELOCITY or HP~TQxRPM the statement above should read the same "torque" at a greater speed where speed means the shaft's RPM.

I think the most humorous explanation of HP & TQ that's available on the internet is the 3 part series which starts here with posts #2, #3 & #4...

The true story of how HP and TQ were actually discovered...Part 1 of 3
HP, TQ, Dynos, a new beginning... - TheDieselGarage.com

... and the easiest to understand explanation of HP & TQ that's available on the internet is the 5 part series which continues with posts #5, #7, #8, #9, & #10. I even made my wife read these posts to both proof read the words and to see how much of it she could follow!

 

not sure what direction this thread went, but:

How is banks getting diesel #2 to work at more than 3000 rpm? It was my understanding one of the rpm limits is caused by the rate of combustion and flame rate propagation of a relatively slow burning fuel.

Now otoh, if they are exploding it due to really high compression........

 

No problem with RPM and #2...

My friend had a VW Rabbit that would routinely hit 5500 RPM just because it was a worthless, gutless POS.

 

Just like gasoline, diesel must be atomized to burn quicker and more complete. Diesel is a heavier fuel, so it takes higher injection pressures to atomize than it does for gasoline. As diesel technology has progressed, injection pressures have increased tremendously (older diesels had injection pressures of 2000 psi and less, newer common-rails are upwards of closer to 40,000 psi). These pressures allow for a better atomization, meaning smaller fuel droplets. Also, injection timing and fueling has come a long way. Injectors today can fire more fuel in less amount of time, and with electronically controlled injection you can pinpoint exactly when you want the injection event to occur.

The problem with achieving higher RPM's is limited to the computer. On the PSD's, the IDM is the limiting factor, as you can't fuel enough at higher RPM's to make any power. People have gotten Powerstroke HEUI injectors to fire at an equivalent engine speed of 6000 RPM's on the bench, but no one has done it in an actual PSD engine yet. If someone can figure out a way around the IDM, then higher RPM's on the Powerstroke will be possible.

Of course, achieving higher RPM's on a diesel also requires other mods. Nothing like trying to run high RPM's on stock valve springs. Do that and you'll have a nice valve shape indented on the top of your pistons.

 

Well at least you figured out what I meant.

 

I'll put some numbers together later but I agree that straight #2 diesel fuel definitely imposes an upper limit for engine RPM.

Piston HP is proportional to the TIME rate at which a combustion generated FORCE can do useful WORK=FORCExDISTANCE on a piston. In order to do a substantial amount of WORK on a piston a fuel-air mixture needs to combust and release its heat ENERGY pressure generated FORCE at a TIME rate that's faster than the TIME rate at which the top of the piston is moving away from the source of the combustion generated FORCE. The TIME rate at which the top of a piston moves is the piston speed which depends on RPM.

So a fuel's rate of combustion does set an upper RPM limit for useful HP production and it's one of the several parameters that determine the shape of an engine's FWHP vs RPM curve. Straight #2 diesel fuel has a slower rate of combustion than gasoline and this effect alone limits diesel engine RPM.

Diesel fuel also exhibits a fairly long time delay for auto-ignition. Since heat of compression is needed for auto-ignition to occur, and since the piston has to be approaching TDC on the compression stroke in order to generate enough heat of compression to trigger auto-ignition, the amount of effective ignition advance that's necessary at higher RPM can't be obtained with straight #2 diesel fuel, and this effect also limits diesel engine RPM.

I'll give some more details on this topic later but for now take a look at this neat video...

Diesel Injection Flame
Diesel Injection Flame- Video

...I've hit the replay a number of times studying the combustion process. The auto-ignition time delay isn't visible in this video but I'll give some graphs of auto-ignition time delay later.

 

Pretty interesting thread you have ErnestEugene! Since I am limited on my internet capabilities I will just state what I know to add. I see the words exploding and Auto-ignition. There are better ways of describing what is going on in this complex subject of combustion. My experiences, Auto-ignition and Pre-ignition are the same thing (pre-ignition can cause damage also). In the gasoline world. In the diesel world, the fuel is auto-igniting, although not occurring until just a tad before TDC from the compression heat raising the fuels temperature for burning to begin if nothing is wrong. BUT, what would you call it if it were to happen before it (fuel ignition point desired) is wanted? Would you call it auto-igniting still? That is what will confuse people. My belief is if you have some form (inaudible or audible) of detonation in a diesel engine that ignition source had to come from a hot spot on the piston crown. Carbon buildup or a spot (maybe lean area in the chamber) transferred more heat to that area raising the surface temperature causing or going to possibly cause a “pre-desired” fuel ignition point. Now that word *exploding*, that makes me think of detonation in a heartbeat. We are not exploding anything in the internal combustion engine. How fast the flame propagates is holding hands with in-chamber temperature. Detonation happens in the coolest part of the chamber majority of the time. Where are those areas? Under the injector nosel and the perimeter of the piston next to the cylinder wall. I have never seen the side of a piston damaged before in a diesel, but, I have seen a big gaping hole right in the middle of the crown many times Next, if we have too cold of intake air, too cold of fuel we will not be lighting the fuel period until the temp raises enough. If it is cold, you all know what we get -> post combustion with white exhaust smoke until engine temp rises and fuel ignites at the correct time. In any engine, lower compression from a worn-out or damaged part can cause a slower burn and produce less power from loss of compression. So will too hot of an air charge This also applies to density of the fuel from being heated too much (too much fuel- perhaps a Quenching action is causing the cooler chamber temperatures? - I will try and explain later).. Also, what if the air charge is too hot? Could that be a detonation culprit once the fuel is injected? Instantaneous ignition, I believe it can be. Now if they (Banks) use the less volatility diesel fuel, then could that be saying he is holding off a possible problem during the combustion cycle???maybe? and using NOS to assist with the burn Hmmm I am curious!As for limiting the rpms, we have to look at rotating assembly weight, port flow and obstructions such as the turbocharger. If we could have a TC that acts like a straight through pipe but still has a boost characteristic, we would achieve a higher rpm level more quickly. But we don’t. Getting back to that “quench” comment I made. What comes to mind is a old worn injector tip. What happens when a tip has a lot of miles? Sprays too much fuel from enlarged fuel ports and in odd directions. If there is excessive fuel present as the piston is coming towards TDC at the perimeter. As it comes up, you are compressing the fuel into a tight spot. Now with the cylinder head flat and tight piston to head clearances. Where is that fuel going? Towards the center of the chamber where the fuel burn is located causing a cooling effect producing less heat expansion of the fuel combustion. Now as the piston goes back down the cylinder its pulling that A/F back into that area, what was once a tight area, to burn further and more complete. In turn this quenching results with unburned fuel and carbon buildup. Equaling a less thermal efficient engine without assistance. The Quench chambers of the '70s for gasoline engines I believe were done away with because of cooling too much. Causing emissions to be terribly high. I do not know how much, if any quench is used in a diesel engine. I have not found anything yet on it. But I wanted to use that as an example.