Diesel Horsepower

[JimBinMI]

Hey all,

How do you equate the horsepower of a diesel engine to that of a gas engine? Is there a formula that can be used? Obviously the 18.5 hp 3 cyl. diesel I now have is way more powerful that the 16 hp 1 cyl. gas that I had before.

Oh, and before anyone asks, you can just use diesel, period, without making the adjustment for NH being stronger than the others! /w3tcompact/icons/laugh.gif

JimBinMI

The world without Blue would be too Orange!

 

[Bird]

JimBinMi, there's always been much I don't understand about power and ratings, but I think I'm safe in saying that 1 hp is 1 hp, whether gas or diesel, so I guess you could say it's a direct equation. However, the number of foot pounds of torque produced is quite different; a diesel with comparable horsepower will produce more torque or twisting force. And then, of course, the engines may be used in situations in which the gearing is considerably different and that will make a big difference in the apparent power. Now, someone tell me if I understood something wrong, or if someone can explain better./w3tcompact/icons/smile.gif

Bird

 

[JimBinMI]

Bird,

Thanks, that's a start! /w3tcompact/icons/smile.gif

JimBinMI

The world without Blue would be too Orange!

 

[MChalkley]

Jim - there's no difference in horsepower. Horsepower is a calculated quantity with a precise definition no matter what kind of engine is producing it.

But there is a major difference in the operating characteristics between gas and diesel engines: torque. The horsepower of an engine is calculated using the engine's torque, its rpm and a number I'll have to go look up.

The reason you're thinking that a diesel's hp will do more work than a gas engine's equivalent hp is because the diesel is producing much more torque to have the same calculated hp because of it's much lower rpm. So a diesel with 15 hp @ 2800 rpm has much more pulling power than a gas engine with 15 hp at 4000 rpm.

If you need the exact numbers, I'll dig them up. Or someone else will post them first, probably.

Mark

 

[MChalkley]

Bird, we're posting in stereo again, I see. /w3tcompact/icons/laugh.gif

Mark

 

[Bird]

Yep, Mark, the messages get posted on here faster than I can read them sometimes./w3tcompact/icons/laugh.gif And would you believe, it's thundering and raining like the dickens again? I love it!/w3tcompact/icons/laugh.gif

Bird

 

[MChalkley]

Congratulations! I hope you got enough to do some good. It rained harder here than it did during last year's hurricane. We didn't get near as much total rain, but more per hour. I went out for a couple hours just before it got dark and repaired some of the damage to the road, but there's 4 or 5 more hours of work left. And now there's another one rolling in. Like I said, never a dull moment.

Mark

 

[Bird]

It quit raining again and I just went out to check the rain gauge and I figure I've gotten 3.17" in the last 24 hours. It's been well over a year since that happened. I only got 20.4" for the whole year of 1999.

Bird

 

[TomG]

It's been awhile since my high school physics days, and my high school hot rodding days for that matter. But, here goes. Somebody correct me if I get it wrong.

Torque is expressed in foot-pounds. Horsepower is expressed as foot pounds per second. The measures are related, but torque is a static idea while horsepower is dynamic. The measures are calculations, and the calculations are the same for all power sources--gas, diesel, electric motor etc.

Other things being equal, you can't have more torque without having more horsepower. However, in terms of using the power, it makes a difference how the torque is distributed across time. For example, one way of expressing horsepower is 1 HP = 550 foot pounds per second. An engine that banged out 550 foot pounds once a second (='s 1HP) and has little inertia would perform very different from an engine that banged out 55 foot pounds 10 times a second (also 1HP) and contained substantial inertia. Inertia changes the way power is distributed across time.

Also, as noted, there's a bunch a factors, such as 'ability to resist changes in load' that affect how an engine actually works on the ground. These factors vary widely between gas and diesel engines. Basically, horse poser and torque are pretty simple measurement ideas. Neither captures the sense of 'what will this thing do on the ground' very well. There are other measurement ideas, such as power curve and break horsepower that capture other aspects of how the machine actually works. However, no set of measures captures the idea very well. It's sort of like the comments on Consumer Reports. No set of measures rolled into a rating index is going to do a very good job of answering the question 'How am I going to like this product' for most people?

Anyway, tractor owners seem to be more poetic than scientific. What I want to know is: 'When I push the 3ph level down, what feeling to I get on this machine compared to that machine?' Knowing a bunch of science-like horsepower and torque measures isn't going to answer that.

 

[Bird]

Too dense for me; or should I say I'm too dense for that?/w3tcompact/icons/laugh.gif

Bird