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SEPilot
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RE: Piston Engine Fadec, Diesel Vs Avgas

Mon Nov 05, 2007 6:37 pm

Quoting Speedracer1407 (Reply 49):
Witness, for example, that when faced with the challenge of busting through the 400HP mark for the latest M3 to stay on par with their competition, BMW went to a 4 liter V8 and ended up with an engine that's actually lighter and more compact than the less powerful 3.2L I6 of the previous M3.

Exactly my point. The fact that most of the heavy truck engines are inline sixes to me speaks of inertia, not merit. Caterpillar, Cummins, and others have been building inline sixes for so long that it's habit (although Caterpillar builds smaller V-8's). Detroit Diesel was the only one who went seriously for V engines; their engines were considerably lighter for the output than any others, but being 2 cycle they had other problems. The -92 series initially had serious quality problems, which hurt them immensely, ultimately leading to GM selling them to Penske, who designed the -60 series. Why he stuck with inline instead of V I have no idea. I would have gone with V. By the way, a V-6 can be made just as smooth as an inline; it is trickier, though, as it requires a much more elaborate crank (unless you can make it 120 degrees, which is usually too bulky.)
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
speedbird2263
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RE: Piston Engine Fadec, Diesel Vs Avgas

Mon Nov 05, 2007 7:48 pm

Quoting Speedracer1407 (Reply 49):



Quoting SEPilot (Reply 50):

Both very good explanations on the subject  thumbsup . I forgot to take into account the many variables that surround the design and application. The fact that tradition is a variable shows that certain engine design choices are undoubtedly as a result of compromise.
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speedracer1407
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RE: Piston Engine Fadec, Diesel Vs Avgas

Tue Nov 06, 2007 2:51 am

Quoting Speedbird2263 (Reply 51):
The fact that tradition is a variable shows that certain engine design choices are undoubtedly as a result of compromise.

Indeed, but tradition is only part of it for BMW. The entire BMW lineup is uniquely positioned as premium/luxury cars that also possess superior rear wheel drive handling talents and driving fun. So for them, an inline6 makes great sense. They don't need to place that long block transversly or anything (unlike Volvo's truly bazaar usage of such an arrangement), so whatever engineering difficulties as far as packaging are minimized. In return, the utterly vibration-free operation of an inline6 combined with the glorious full-throttle snarl fulfill BMW's need to be both luxurious and exhilarating.

Actually, in automotive applications, I wish more makers would go with an inline 6. I'm reminded of my days working for a Mercedes dealership; my sole job was to transport new, used, and customer cars to and from other dealers and people's houses. Though the 1997 inline 6 E class benz's were no different from the V6 1998+s, the difference in character was huge. The old inline engine had a truly spine-tingling rip-snarl at high RPM, along with a seriously fun shove of power above 4000 RPM. By comparison, the V6 that replaced it sounded like a tractor at idle, had no sweet spot (a wide torque band isn't always fun), and moaned laboriously at high RPM. But the V6 was also lighter, more efficient, and made more usable power thanks to big torque at low RPM. Mercedes chose engineering sophistication and sensible design, just as any commercial/industrial engine manufacturer should. But the result was no fun at all.
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ex52tech
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RE: Piston Engine Fadec, Diesel Vs Avgas

Fri Nov 09, 2007 6:39 am

Quoting Sv2008 (Reply 24):
A straight six should be much lighter than a V8, and turbocharged, can produce the same power from a lower capacity. Another advatange is less friction (less cylinders), which means more power effectivley.

Exactly, for example the Mack E-9 V-8 weighs in at close to 2,700lb, (1090 cubic in.) it is wide, and burns considerably more fuel than the inline 6 cyl E-7.

The E-7 in line 6 weighs in at around 1,900 lb, and sips fuel compared to the V-8.

Quoting SEPilot (Reply 50):
Why he stuck with inline instead of V I have no idea. I would have gone with V.

Torque is the name of the game in heavy trucks. V-8s make their power at higher RPMs, which translates into no power to get the truck moving initally. L-6s make piles of torque at low RPMs, and don't need to be revved to make power. The manufacturers do not build in lines out of habbit, it is out of necessity.

I have driven trucks with 6V92, and 8V92 Detroit 2 stroke engines in them, and while they sound really cool, and are fun to drive, once you start pulling heavy loads through the hills, you will find yourself wishing for an inline 6cyl. 4 stroke engine.

Cat. and Cummins made V-8s, but went back to in line 6s for the heavy trucks, because the V-8s had to many strikes against them. The Mack V-8 was the only one in the U.S. that had any longevity, and that is only because it was just a brute. It was considerably bigger than the Cat., and Cummins V-8s
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Grunf
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RE: Piston Engine Fadec, Diesel Vs Avgas

Fri Nov 09, 2007 12:18 pm

Scania and Volvo inline-6:es deliver upwards 550hp from 12L with help of 4-valves, turbocharging/intercooling and turbo-compound. V8:s are only used on the very biggest haulers, and as far as I remember, only deliver a little more. I guess days of two-stroke V-designs in trucking is over as suitable power can be extracted from inline-6.

As you might guess, manufacturing V8 is more complicated as you need two cylinder heads, engine block requires more from CNC (as bores are angled), there are 8 pistons/rods, twin exhaust manifold etc. I6 block is just a lump of iron with longitudinal bores. When you churn out 100000 engines, small things start to count.
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RE: Piston Engine Fadec, Diesel Vs Avgas

Fri Nov 09, 2007 10:41 pm

Quoting Ex52tech (Reply 53):
Torque is the name of the game in heavy trucks. V-8s make their power at higher RPMs, which translates into no power to get the truck moving initally

That does not have to be the case; the ratio of the bore to the stroke is chiefly what determines this. Granted, it is easier to make a long stroke with an inline engine, and perhaps this is why they have prevailed.

Quoting Ex52tech (Reply 53):
I have driven trucks with 6V92, and 8V92 Detroit 2 stroke engines in them, and while they sound really cool, and are fun to drive, once you start pulling heavy loads through the hills, you will find yourself wishing for an inline 6cyl. 4 stroke engine.

So have I, by the way. The real issue is the fact that they are 2-stroke, not that they are V's. I have also driven a straight six Detroit (6-71); if you want a real dog you should try it. The 2-stroke Detroits are lousy on torque; always have been regardless of configuration.

Quoting Ex52tech (Reply 53):
Cat. and Cummins made V-8s, but went back to in line 6s for the heavy trucks, because the V-8s had to many strikes against them.

What were those strikes? As I said, the main problem I see is that it is harder to get a long stroke.

Quoting Grunf (Reply 54):
As you might guess, manufacturing V8 is more complicated as you need two cylinder heads, engine block requires more from CNC (as bores are angled), there are 8 pistons/rods, twin exhaust manifold etc. I6 block is just a lump of iron with longitudinal bores. When you churn out 100000 engines, small things start to count.

This is true, but if you can get more power with less weight it is worth it . The cylinder head argument doesn't hold, though, because I do not know of any currently produced heavy diesel straight six with only one cylinder head; they all have two or three because a single one is just too long, and has thermal expansion problems (leading to cracking.) With modern CNC mills the added machining is really quite minor; the total amount of machining is not much different.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
ex52tech
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RE: Piston Engine Fadec, Diesel Vs Avgas

Mon Nov 12, 2007 1:56 am

Quoting SEPilot (Reply 55):
What were those strikes?

Weight, fuel economy, and cost. If you have owned trucks, and I do, that pretty much says it all.

Quoting SEPilot (Reply 55):
The cylinder head argument doesn't hold, though, because I do not know of any currently produced heavy diesel straight six with only one cylinder head; they all have two or three because a single one is just too long, and has thermal expansion problems (leading to cracking.

How about a Series 60 Detroit 12.7L engine, The C-12 Cat had a single head, the C-15 has a single head, I have taken the heads off of all three, and they were all one piece. Yes the Cat engines have three valve covers, that is usually because the of the three Jakob's engine brakes. It is easier to keep three smaller valve covers sealed than one big one, as in the Series 60s. And I have wondered the same thing about cracking and thermal expansion with a one piece head, but there a lot of one piece heads on a lot of inline 6's.

Mack uses two heads on their E-7 inline 6 engines, and four on the E-9 V8. Then Volvo comes along and puts 6 individual heads on a lot of their engines, so go figure??

Quoting SEPilot (Reply 55):
I have also driven a straight six Detroit (6-71); if you want a real dog you should try it.

I drove a turbo charged, the gear driven supercharger goes without mention, 310 h.p. 6-71 Detroit in a General (GMC) dump truck for a few days, and yes it was a real dog. You have to keep them between 1800 and 2400 rpms if you want any power.
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RE: Piston Engine Fadec, Diesel Vs Avgas

Tue Nov 13, 2007 12:09 am

Quoting Ex52tech (Reply 56):
And I have wondered the same thing about cracking and thermal expansion with a one piece head, but there a lot of one piece heads on a lot of inline 6's.

I did not realize this; I worked recently at a company that installed Cat engines in their equipment (including C12's) and I did not notice that it was a single head. I assumed it was 3 heads because older Cat engines I was familiar with were, but I thank you for the correction.

Quoting Ex52tech (Reply 56):
What were those strikes?

Weight, fuel economy, and cost. If you have owned trucks, and I do, that pretty much says it all.

This may be the case; but as a mechanical design engineer I still believe it should be possible to design and build a heavy duty V-6 or V-8 that would be lighter and just as powerful as the inline 6's with similar torque and smoothness. There are problems, however, and it may well end up being more expensive. Just because nobody has succeeded in doing it means it is not easy; it does not mean it is impossible.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
ex52tech
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RE: Piston Engine Fadec, Diesel Vs Avgas

Tue Nov 13, 2007 4:23 am



Quoting SEPilot (Reply 57):
. I assumed it was 3 heads because older Cat engines I was familiar with were, but I thank you for the correction.

I thought the same thing until I tore a 1991 3406 Cat. down for a friend. The 3406 became the C-15, and even the 3406A had a single head, those engines are mid 80's vintage. The one thing that kills most of these older engines is emissions. The C-12 was de-tuned in 2003 from 430h.p. to 380h.p.so it could meet emissions, and they built the C-13 because it would meet emissions.
The C-12's are probably being used in other applications, but not in trucks any more.

Mack stopped bringing their E-9 V8 into the U.S. in the early 90s because it wouldn't meet emissions. They are still used in Australia though.

The N-14 Cummins went the same way, and that was one of the finest in-line 6's built, by far my favorite engine.

I have a friend that runs an E-9 V8 Mack in a 1992 CH model tractor, 550 h.p. I can pull away from him from a stop, 470h.p. E-7 Mack in-line 6, but not for long, and in the hills, he is just plain gone. He also gets 4 mpg to my 6.5 mpg., and I can carry more weight, which means I make more, and spend less on fuel. As much as I like that V8, I just couldn't afford it.

The biggest problem I could see with a diesel in an airplane is weight, I know they can be made lighter, but diesels like even temperature, and I could see the lighter alloys dissipating heat unevenly.
"Saddest thing I ever witnessed....an airplane being scrapped"
 
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RE: Piston Engine Fadec, Diesel Vs Avgas

Tue Nov 13, 2007 11:50 am



Quoting Ex52tech (Reply 58):
The biggest problem I could see with a diesel in an airplane is weight, I know they can be made lighter, but diesels like even temperature, and I could see the lighter alloys dissipating heat unevenly.

The other problem I see is vibration; the power strokes in a diesel are much more violent than in a gasoline engine. I heard that when Continental was working on theirs that was a huge problem; props didn't stand up. I'm not sure how Thielert and SMA are dealing with it, but they must have very substantial vibration dampers.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
A342
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RE: Piston Engine Fadec, Diesel Vs Avgas

Tue Nov 13, 2007 4:21 pm



Quoting SEPilot (Reply 59):
The other problem I see is vibration; the power strokes in a diesel are much more violent than in a gasoline engine. I heard that when Continental was working on theirs that was a huge problem; props didn't stand up. I'm not sure how Thielert and SMA are dealing with it, but they must have very substantial vibration dampers.

All flight reports I've read say the opposite. The Thielert diesels run much smoother than their gasoline counterparts.

Quoting Ex52tech (Reply 58):
I know they can be made lighter, but diesels like even temperature, and I could see the lighter alloys dissipating heat unevenly.

I've never heard of such problems with diesels that have an aluminium block, whether they are used in cars or in aircraft.
Exceptions confirm the rule.
 
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RE: Piston Engine Fadec, Diesel Vs Avgas

Tue Nov 13, 2007 5:27 pm



Quoting A342 (Reply 60):
The Thielert diesels run much smoother than their gasoline counterparts.

I would be very interested in finding out what they did to achieve this. I once attempted to use a VW diesel to power a stump grinder; due to the fact that it was belt driven the engine had to be rigidly bolted to the frame. The result was that the vibration caused the fuel injection lines to crack after a relatively short time because the vibration was so bad without the resilient engine mounts. An aircraft certainly can have resilient mounts for the engine, but the propeller is another matter. A torsional coupling can be made, but it would add weight. The other factor that helps is a heavy engine to begin with (which was part of what the VW engine lacked), but that is not practical for aircraft.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
A342
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RE: Piston Engine Fadec, Diesel Vs Avgas

Wed Nov 14, 2007 9:04 pm



Quoting SEPilot (Reply 61):
I would be very interested in finding out what they did to achieve this.

I don't know that in detail, but IIRC the props were specifically designed for the diesels.
Exceptions confirm the rule.

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