Oil & Fuel Diesel torque difference mostly myth?

[Henro]

<font color="blue"> My whole point in starting this thread was just because of how surprised I was that it was even close and the research that showed why it was close.
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I guess I should keep my mouth shut, since I have just been looking in on this thread when I stop in my workshop to do something, but what research are you referring to, getut?

I know you mentioned peak numbers, but they really don't tell the story...sorry if I missed it the first time through the thread...I will read again after the sun goes down... /forums/images/graemlins/smile.gif

At the end of the day though, it is not what turns the shaft, but how the shaft is turned that tells the story... /forums/images/graemlins/grin.gif

Performance curves (not peak numbers) tell that story...

 

[getut]

Ya peak is what I keep mentioning and I know that the diesel is still best... its just that when a diesel is made to be small and high RPM... the checkbox items that usually distinguish a diesel are much LESS of a factor. They aren't as far ahead in torque as I thought before researching it.

I'm talking about my own research on the internet. I had never really thought about it before and had just assumed that "diesel" itself meant torque. It seems that isn't the case. It is in fact only the dimensions that are normally associated with a diesel that make it that way. In other words... make a gas engine with some of the same features normally associated with diesels (big beefy parts with high mass, long stroke, and slow RPM) and blammo.. you have high torque. It isn't the DIESEL that makes the high torque.. just the features that diesels TYPICALLY (but not always) possess. Again... I realize that all things even, the diesel still wins. I have never disputed that. Its just that the little small high RPM diesels don't possess a very large advantage over a similar gas engine. That is what surprised me.

I'm not absolutely sure that the cost difference is worth the small gains associated with a diesel, when the diesel is made with characteristics typically associated with a gas engine such as the high RPM and relatively short stroke. I wouldn't even be thinking twice about the cost difference if that tremendous torque difference were there (again.. peak torque).

 

[DirtHauler]

I have a buddy who owns a Dodge Cummins dually, he decided he wanted a "little" more punch. All he did was install a set of "marine" injectors, turn up the pump a little and tweak the timing, now he's got like 650 + ft. lbs. of torque at around 2400 rpm. This thing will throw you back thru the rear window! Good thing he has a friend at the tire shop /forums/images/graemlins/laugh.gif

 

[Henro]

Here is an interesting link that relates to this thread...

A simulated dynamometer test of two different engines

Enjoy... /forums/images/graemlins/smile.gif

 

[Cliff_Johns]

Henro,
Excellent link. great animation and explaination.
Cliff

 

[KiotiJohn]

I know you've said diesel still wins, but you continue to say the the torque is not that much better than with gas. When you put the two identically sized, HP'd engines side by side with the same weight, the same load and start pulling, you're going to FEEL the difference because the gas engine cannot maintain the torque under load that the diesel can. That's the dange in going by peak torque. Peak torque is like peak wattage in speakers, it means very little.
In your research, I doubt that you found the torque curves for those gas engines. If you had, you wouldn't need to even question whether the diesel and gas engines have a large gap in torque or not. The gas engine falls off tremendously under load while at some point, the diesel torque increases. No questioin about it. John

 

[Syncro]

Geeze... what an interesting thread to say the least. On the subject of torque, how about the steam tractor that developed maximum torque at zero rpm? Interesting because at 0 rpm horsepower would also be zero since hp is a function of time. Hmmm /forums/images/graemlins/grin.gif

 

[Egon]

It's the same for an electric motor!

Egon /forums/images/graemlins/grin.gif

 

[bugstruck]

Egon, Learn me something here. I understand, generically at least, maybe 80 or 90 percent of the theory being bounced around on the gas vs. diesel torque thing. But your post and the one prior just clocked me. Are one or both of you stating that max. torque for steam or electric motors occurs at zero work? I am beyond lost on that. /forums/images/graemlins/confused.gif Help!!

 

[Henro]

<font color="blue"> Are one or both of you stating that max. torque for steam or electric motors occurs at zero work? I am beyond lost on that. Help!! </font>

Bugstruck,

With a DC electric motor, like those used in heavy industry, the torque is a function of the magnetic forces acting between the magnetic field of the armature windings and the magnetic field of the "field" winding. So if the motor is stalled due to something holding it back, the torque is the same as if the motor is turning.

In a normal application, the motor will have a constant strength magnetic field set up within it by its field windings.

Voltage is applied to the armature terminals and armature current flows as the result. Interaction between the magnetic fields that result from this electrical current, and the magnetic field resulting from the field current, causes torque to be developed at the armature shaft.

In the case of the DC electric motor this torque is not max at zero speed but pretty much over the range of operation, as long as the magnetic field within the motor frame is held constant by the field winding current.

The interesting thing in DC motor application is that there are two operating ranges. The first is called "constang torque" and that is the range that the motor operates in, with full field current holding the magnetic field within the motor constant, and with variable voltage applied to the armature terminals as the way of changing speed. More voltage means more speed, unless the load connected to the armature shaft is great enough to keep the shaft from turning.

IF one needs more speed than can be gotten from the voltage applied to the motor terminals, then it is possible to weaken the motor field. When this is done, the DC elcetric motor enters a range called "constant HP" operation. This is because the voltage and current holds constant, but the speed changes...

Guess I got carried away... /forums/images/graemlins/blush.gif ... sorry

Anyway, in the electric motor the action is the same as holding two magnets close to one another...south to north...you feel the pull as long as you want to hold them in position. South to south (or north to north) and you feel the push, again as long as you want to hold them...

If those magnets were on a stick connected to a shaft, and you were holding the end of the shaft, you would feel torque as long as you wanted to hold the shaft in that position... /forums/images/graemlins/smile.gif

Hence, torque at zero speed... /forums/images/graemlins/cool.gif