New diesel unveiled

[rv6ejguy]

Originally Posted by kgood

Ok Ross and Ted,
I've been thinking about this.... and I read part of one of the articles L Adamson provided, where it said that two engines producing the same HP at the same RPM, would produce the same torque.

Given my two comparisons: my 300 hp gas suburban vs my 300 hp Diesel pickup - and the Cat powered heavy haul rig vs the same rig with a 550 hp Chevy -

Are you saying that if I were to create some type of optimal gearbox for the gasoline engine - a torque multiplier -, then run the engine at the RPM required to achieve rated hp (300 or 550 in these examples), that the gas-powered rig would pull the same load up the same grade at the same speed as the diesel does? If that's what you're saying, then I think I get it. Not a very practical or reliable thing to do, but doable in theory I suppose, leaving efficiency and power loss from the gear train out of the discussion.

Let me know if I'm thinking straight. It would not make me a convert to the SI Gospel Fellowship, but I may be starting to understand what you're trying to tell me

Kurt

I'm glad you kept an open mind through all of this discussion. This shows you REALLY DO want to understand the concept. Nobody expects you to convert to SI engines. What you have achieved in both your 9 and at Bonneville is very impressive in my mind. I'm a firm believer in driving and flying what turns your crank. Clearly you love diesels which is fine by me.

Getting back to the discussion, in fact, just putting a 3 to 1 gearbox aft of the 502 atmo Chevy would allow it to do almost the same job as the 928 inch turbocharged CAT engine running 40 psi boost. The Chevy would output around 1700 lb./ ft. to the main transmission. As Ted pointed out, it is not going to last anywhere near as long as a 2900 lb. giant loafing along at 1500 rpm and part load and it needs to be kept within a narrow upper rpm band.

Ted hits on the other points about design and intended application well. The CAT is practical for heavy duty truck use but would be a poor choice for a Lancair IVP for instance, just as the Chevy would be a poor choice for the semi.

Ted reiterates my stance on CI, torque etc. My whole objection to people stating that CI engines have superior torque merely because they are diesels just rubs me the wrong way because it is simply not true. Modern turbo diesels have high torque because they are heavily boosted, simple as that. If we apply even half the boost pressure to the same size, same stroke SI engine, we'll always have both more torque and more hp as we can see in any of the examples. HP does the work, not torque.

People continually compare a 6.5L turbo CI engine to a 6.5L atmo SI engine and come to conclusion it has more torque and even more hp in some cases- well of course it does since it is running 2-3 atmospheres of boost- a no brainer. Add even one atmosphere of boost to the same SI engine and it will trounce the diesel in both respects. The SSC Aero is an example of what relatively low boost does to a well designed 6L class production SI engine- 1200/1200 hp and torque is far in excess of any comparable size diesel running even double the boost pressure.

No one disputes the superior BSFC of CI engines. When this can be combined with low weight, longevity and comparable cost to SI engines, they make a fine choice for aircraft. The weight part does not matter much in road use and I'd be the first to admit that some of the modern turbo CI engines in auto and truck use today work very well and are vastly different and better from the stuff available 20-25 years ago. Diesels continue to intrigue me, I don't hate them- well maybe the smell part but even that has pretty much gone away lately.

[JohnK]

Originally Posted by rv6ejguy

Well the reason there are so many discussions about torque and hp on the internet is because lay people continue to post nonsense and ignore the science and physics. ...

"Physics BS", well what can I say about that? On this planet at least, the laws of physics are pretty well established, repeatable and apply to all of us and all things last time I checked.

I think that this misconception about torque is due in large part to the abstract nature of "power"; it is a difficult concept to grasp without formal training in physics. Torque, on the other hand, is more concrete and readily understood by anyone, and is therefore more naturally applied as the explanation for how and why things work.

By the way, in case your interested, much more lively (and rude!) discussions on this topic are available in the various truck and towing forums.

John

[L.Adamson]

Originally Posted by rv6ejguy

Modern turbo diesels have high torque because they are heavily boosted, simple as that.

I need to get a friend of mine in on this discussion. He's a two time RV builder, prefers Lycomings or clones, but best of all (in regards to this subject), he spent decades with Union Pacific as an instructor for the mechanics of diesel engines. This morning at breakfast, he was able to quote exact figures off the top of his head, including BTU's, compression ratios, turbo boosting, etc.

But he did say one thing, and to quote him on it. In regards to diesel engines..... "torque is everything!"

I also got the impression that at sea-level altitudes, the boost wasn't doing much for a diesel engine, just as within an airplane with turbo boost. And that the high compression of a diesel was much of the factor in terms of torque. And at the same time, because of the higher BTU content of diesel fuel, and the fact that less rpms are required to do the same job.........the diesel will always win in the fuel use department as well as longivity of the engine.

But don't quote me on all this (in case I have misunderstandings)............except his "torque is everything!" statement.

L.Adamson --- RV6A

[rv6ejguy]

Originally Posted by JohnK

I think that this misconception about torque is due in large part to the abstract nature of "power"; it is a difficult concept to grasp without formal training in physics. Torque, on the other hand, is more concrete and readily understood by anyone, and is therefore more naturally applied as the explanation for how and why things work.

By the way, in case your interested, much more lively (and rude!) discussions on this topic are available in the various truck and towing forums.

John

I was reading some of these last night for entertainment. Like I said, well entrenched belief in the CI culture.

If you are towing something with a truck a long distance, SI engines are not the best choice simply because they'd burn a lot more fuel getting the job done and there are few production SI turbo powered trucks made anyway.

I've never had a problem saying that turbo CI trucks are not good for towing and get better mileage doing it than an SI engine- total reality The part that bugs me is where people think that torque is all important and comparable CI engines have more torque than SI engines.

[rv6ejguy]

Originally Posted by L.Adamson

I need to get a friend of mine in on this discussion. He's a two time RV builder, prefers Lycomings or clones, but best of all (in regards to this subject), he spent decades with Union Pacific as an instructor for the mechanics of diesel engines. This morning at breakfast, he was able to quote exact figures off the top of his head, including BTU's, compression ratios, turbo boosting, etc.

But he did say one thing, and to quote him on it. In regards to diesel engines..... "torque is everything!"

I also got the impression that at sea-level altitudes, the boost wasn't doing much for a diesel engine, just as within an airplane with turbo boost. And that the high compression of a diesel was much of the factor in terms of torque. And at the same time, because of the higher BTU content of diesel fuel, and the fact that less rpms are required to do the same job.........the diesel will always win in the fuel use department as well as longivity of the engine.

But don't quote me on all this (in case I have misunderstandings)............except his "torque is everything!" statement.

L.Adamson --- RV6A

Actually the low rpm is not a real advantage here except for longevity and in a loco application, engine weight is no factor in design. A higher revving engine could be geared to do the same job but at the expense of longevity- but this makes no sense to use in this application.

Actually the very high CR in CI engines does not do much for torque as we have seen. I searched a lot over the last few days and could not find a single case where a comparable sized CI engine had more torque than an SI engine. If you can find some examples, let me know. High CRs use a lot more energy to compress the charge and there is a rapidly diminishing hp gain as CRs climb above 12 or so- the curve is very flat.

A diesel needs to be larger and run more boost in fact to do the same work as an SI engine. Many people who come from the CI industry/ world just won't believe this.

Torque IS a factor in determining hp and therefore WORK that an engine can perform. It is a simple fact that the more torque any engine produces at a given rpm, the more hp it also has. If people are impressed that some big CI engine produces 3000 lb./ft. at 1200 rpm, they should only be impressed because it is producing 685 hp at such low rpm. Its specific hp output is actually pretty pathetic for a 1500 cubic inch engine but this is precisely the type of engine design best suited for a boat, heavy truck or locomotive. As such, your friend's statement that "torque is everything" is true from one perspective but scientifically incorrect. A modern atmo F1 engine with say 200 lb./ft. geared down 16 to one from 20,000 rpm could perform the same "work" as this massive turbo diesel at 1200 rpm in reality.

[L.Adamson]

Originally Posted by rv6ejguy

I've never had a problem saying that turbo CI trucks are not good for towing and get better mileage doing it than an SI engine- total reality The part that bugs me is where people think that torque is all important and comparable CI engines have more torque than SI engines.

Yes, I do think torque is all important...........in regards to pickups & towing. I get bugged about modern liquid cooled engines in GA airplanes. I really do, as I have not seen one that compares anywhere close to 70 year old technology for simplicity & reliability. My favorite aircraft of all time is the "liquid cooled" P-51 Mustang, and I prefer my liquid cooled Honda motorcycle engine over that of a Harley because liquid cooling is more sutible for ground bound vehicles. Air cooled Harleys sound better though, and Lycs sound better than high reving liquid cooled in airplanes. Of course, that is my opinion, along with some others. My Honda is a six cylinder Valkyrie bought new in 98'.

When WII ended, large commercial aircraft stuck with air cooled radials, and dispensed with the liquid cooled variety. In terms of RV's, it just happens that my air cooled Lycoming at 180 HP/2700 rpm/ & 350 lb.ft. of torque is getting off the ground & climbing faster than the Subaru H6 at 212 HP/ 4400 RPM / 210-247 lb. ft. torque & maximum rpm of 6000.

In this case, is it the torque of the larger displacement airplane engine, or what? I don't have the real answer to this one. Yet, I'll take my diesel pickup over a comparible SI pickup anyday (or, I suppose they really don't make comparibles). My thoughts are due to actual experience over the years. Heavy duty pickups are a part of my job, and I've been driving them for almost 45 years. So yes, I too get bugged when someone try's to tell me different, based on engineering principles, and just a small bit of experience with the actual product. If horsepower is what counts, then that H6 should be flying circles around my prehistoric engined RV, yet it doesn't, and may never. Why is that? I'm rather curious. But for the record, I much prefer SI for my airplane.........at this point.

L.Adamson ---- RV6A

[L.Adamson]

Originally Posted by rv6ejguy

Actually the very high CR in CI engines does not do much for torque as we have seen. I searched a lot over the last few days and could not find a single case where a comparable sized CI engine had more torque than an SI engine. If you can find some examples, let me know.

http://www.autoblog.com/2010/03/10/g...atings-releas/

Not bad for an engine stuck on the front of a standard sized pickup, and has more towing ability & better fuel economy at the same time. That really IS, the diesel advantage.

L.Adamson

[ajay]

Nice looking truck. I guess GM can still do some things right, the LS series engine is another!

Originally Posted by L.Adamson

http://www.autoblog.com/2010/03/10/g...atings-releas/

Not bad for an engine stuck on the front of a standard sized pickup, and has more towing ability & better fuel economy at the same time. That really IS, the diesel advantage.

L.Adamson

[kgood]

Originally Posted by rv6ejguy

Actually the very high CR in CI engines does not do much for torque as we have seen. I searched a lot over the last few days and could not find a single case where a comparable sized CI engine had more torque than an SI engine. If you can find some examples, let me know. High CRs use a lot more energy to compress the charge and there is a rapidly diminishing hp gain as CRs climb above 12 or so- the curve is very flat.

A diesel needs to be larger and run more boost in fact to do the same work as an SI engine. Many people who come from the CI industry/ world just won't believe this.

Ross, you're forgetting two-stroke. I challenge you to find a "stock" 5.2L SI atmo engine that produces 470 ft/lb, like the 318 inch atmo diesel does. Yeah, you're right, it's not apples to apples cuz it's a 2-stroke, but it really works well, and there's no down-side (other than the smell). When most of us think of two-strokes, we think of motorcycle engines and outboards with their associated quirks, like low life-span, mixing oil, fouling plugs, etc. But the diesel two strokes have none of these issues. And they're extremely reliable.

That's why I'm so excited about them for aircraft engines. As you say, they would be ideal for aircraft if they can meet the criteria (simplicity, direct drive, efficient, low parts count, low weight). All of these have been achieved. Its just a matter of time before the "right" package comes out.

I'm agreeing with all the physic and mathematics you provide, along with all of your theoretical examples of SI engines being able to perform on par with CI engines in the right circumstances. Problem is, no one's producing the truck engines you describe. They're building diesels with incredible pulling power, reliability, and efficiency for the "work" they do. Why don't they produce these incredible SI engines and drive trains they would require to do the same work as a diesel? My guess would be "no market".

Now, if your "work" is getting a light vehicle through the 1/4 mile in big hurry, then SI is the best tool, because in this application, HP is king.

So, as you point out, it's all about the type of "work" you wish to perform. In my experience, the SI engine works great for intermittent pulls and bursts of speed, whereas the CI engine works best for the long pull under a steady load. You have pointed all of this out. But when you look at the two "jobs", which is more like an airplane's work? IMHO, it's the "long pull under a steady load". That's why, as L Adamson points out, Lycomings and the like are designed to have more Diesel-like characteristics, ie slow-turning, lower hp, higher torque, and simplicity. Yes, as you say, high-revving, higher hp, lower torque SI engines can be converted to work in these applications (with their associated gearboxes, turbos, etc), but, at least for now, they struggle to match the traditional engines. (but you keep working at it and you'll get there, and I'll respect you for it!)

Just some of my thoughts for tonight....
Kurt

[PCHunt]

Somehow it seems that "efficiency" may be being left out of this Truck discussion.

Trucks need to be efficient to be financially viable. So a compromise might be made to give up some "performance" for "efficiency". For example, a trucker might be willing to be forced to slow down to 40mph going up a hill in order to be able to run a smaller, more cost-efficient engine over the life of the truck. OTOH, a passenger car owner might not be willing to make that compromise, and therefore would choose to buy a larger engine than he might need otherwise.

Sorta like the choice between a 150 hp carbureted Lyc, vs. a 200 hp angle-valve FI Lyc, let's say. I think the term is "Life-Cycle cost".

Physics may well decide which engine is superior in any given application, but economics drives the decision-maker.