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Old 02-01-2018, 04:31 PM   #41
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In my opinion, one of the stranger-looking production engines was the Chrysler Slant-6. My cousin had one in some little Plymouth (I believe) run-about he had in high school, and it looked like someone forgot to add the second bank of a V-8.
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Old 02-01-2018, 05:34 PM   #42
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... dividing the pressure and vibration between two crankshafts would allow smaller pistons and lighter weight.
It doesn't divide anything: the combustion chamber pressure will be the same as a conventionally configured engine. You can think of it as a 2.7 L 2-stroke V6 with the heads removed and the two banks placed against each other - cylinder pressure and force on each piston are the same.

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Who knows what another ten years of development can do.
Well, it's had 90 years of development already...
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Old 02-01-2018, 05:39 PM   #43
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It doesn't divide anything: the combustion chamber pressure will be the same as a conventionally configured engine. You can think of it as a 2.7 L 2-stroke V6 with the heads removed and the two banks placed against each other - cylinder pressure and force on each piston are the same.


Well, it's had 90 years of development already...
"Achates' opposed piston engine is a two-cycle, 2.7-liter, three-cylinder with six pistons arranged in a pair per cylinder, working against each other rather than each piston in its own cylinder working against a head and valves. Achates controls the engine's response curve by modulating pressures through both a supercharger and a turbo instead of varying valve lift and timing. No spark plugs, either -- the Achates design uses compression ignition like a diesel, but runs on gasoline. "

I'm betting it has much higher compression than our current gas engines...compression ignition.

I think SFDavis50 was referring to the pairs of pistons potentially cancelling out vibration due to opposing movement.
I sure would like to see a video of one running.
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Old 02-01-2018, 05:45 PM   #44
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In my opinion, one of the stranger-looking production engines was the Chrysler Slant-6. My cousin had one in some little Plymouth (I believe) run-about he had in high school, and it looked like someone forgot to add the second bank of a V-8.
Then there's the Porsche 2.5L 4-cylinder, used in the 944. It really was designed as half of Porsche's V8, and so the one cylinder bank slanted 45 degrees from vertical (to the right side).
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Old 02-01-2018, 05:55 PM   #45
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"Achates' opposed piston engine is a two-cycle, 2.7-liter, three-cylinder with six pistons arranged in a pair per cylinder, working against each other rather than each piston in its own cylinder working against a head and valves."
Right... there's no cylinder head. That doesn't change the force on each piston.

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I'm betting it has much higher compression than our current gas engines...compression ignition.
Probably higher, but maybe not much. My Mazda gas engine runs 14:1.

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I think SFDavis50 was referring to the pairs of pistons potentially cancelling out vibration due to opposing movement.
Aside from the whole pressure and force on the piston issue, yes, it's in primary balance. So are many conventional engines (including inline-4, inline-6, 90° V8, 4-cylinder boxer, and 6-cylinder boxer configurations). It has connecting rods on cranks rotating the same direction, so it has harmonic imbalance components.
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Old 02-01-2018, 07:12 PM   #46
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If we really want harmonic balance, how about retro-fitting a Bristol Hercules 14 cylinder, two row radial aircraft engine under the hood of an F-150? I'd pay good money to see that at a new car show!
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Old 02-01-2018, 08:09 PM   #47
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Be sure to get the extending wings option
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Old 02-01-2018, 10:21 PM   #48
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Mazda's SPCCI is 16:1, but it just has a low-boost supercharger. I'm guessing the Achates will need to run a bit lower compression ratio since it's twincharged.

I think the Achates would have lower peak piston speeds at a given RPM even if the pressure on the pistons is unchanged. Not that it'll do them much good with the dual crankshafts and linkage, though.
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Old 02-02-2018, 12:30 AM   #49
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I think the Achates would have lower peak piston speeds at a given RPM even if the pressure on the pistons is unchanged. Not that it'll do them much good with the dual crankshafts and linkage, though.
Piston speed is a simple function of the stroke, which I haven't seen for this particular engine (other than the displacement, specifications are lacking). There's nothing particularly short-stroke about the opposed-piston arrangement, but I don't think piston speed is much of a concern, anyway.

Although there are two cranks, they're both just spinning at the same speed as a conventionally configured engine would, so the rotational inertia will be high but speed capability isn't affected. The big single gear between the cranks(which also appears to run the supercharger via another gear) doesn't seem like much of a concern, either; certainly it's a lot better than wild arrangement of rocker arms in the old Commer TS3.
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Old 02-02-2018, 06:49 AM   #50
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Just noticed - looks like 8 main bearings, 4 per crank shaft. Solid.
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Old 02-02-2018, 01:42 PM   #51
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Just noticed - looks like 8 main bearings, 4 per crank shaft. Solid.
Although some old junk engines such as our Triumph Spitfire's lump are missing bearings (only three bearings in an inline four-cylinder, which should have five bearings), modern practice is to have a bearing on each side of every crankshaft throw. For engines with only one cylinder per throw (any inline), that's a lot of support. As far as each crank is concerned, this Achates Power engine is an inline three (albeit head-to-head with another inline-3), so it has four bearings per crank.

Subaru 4-cylinder "boxer" engines have four separate crank throws (because opposing pistons are 180 degrees out of phase, not together), and so that short engine jams in five main bearings. Porsche similarly has seven main bearings in their flat-six engines.
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Old 02-03-2018, 06:47 AM   #52
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There seems to be a tendency for some online authors to extrapolate from one test installation to an actual plan for Ford to use this engine; that's wildly inappropriate. To Cooley's credit, he has resisted this silliness; others have not.

Also, the jump from 25% to 45% thermal efficiency is neither realistic nor sufficient. Conventional gasoline engines have long been past 25%, and Mazda has demonstrated comparable performance to the Achates claims in an engine which is well on it's way into production: Skyactiv-X using Spark Controlled Compression Ignition or "SPCCI". Skyactiv-X has been demonstrated in near-production prototypes, and is due in the 2019 model year (so, coming off the production line later this year) Mazda 3.

Novel engine designs are fascinating, and I want them to succeed, but in reality they usually have problems which prove insurmountable in production use. In this case, the design isn't even novel: there have been many opposed piston engines, not just in labs but in production... mostly powering aircraft. The video sort of touches on this, but suggests that previous opposed-piston engines never made production; Achates - to their credit - clearly acknowledges the earlier engines in the text on their website. These designs certainly have issues - one of them is fitting in an effective spark plug, so a compression-ignition opposed-piston engine makes sense. It made sense when Junkers made their diesel Jumo 205 engines starting in 1932; that's what Achates has copied.
Remember the Wankel engine by Masda in the 70's?
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Old 02-03-2018, 08:42 AM   #53
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Remember the Wankel engine by Masda in the 70's?
See previous posts in this thread, especially in the #19-#25, range for a quick rotary engine review.
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Old 02-03-2018, 10:49 AM   #54
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Rotary engines were fun to play with my brother and me used to rebuild them in the late 70s. We called them the rubber and engines due to all the o rings they used for seal between the rotor housings an plates. Fun part was dropping RX4 engines into the RX2 bodies. Little screaming machines then ��
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Old 02-03-2018, 11:16 AM   #55
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Rotary engines were fun to play with my brother and me used to rebuild them in the late 70s. We called them the rubber and engines due to all the o rings they used for seal between the rotor housings an plates. Fun part was dropping RX4 engines into the RX2 bodies. Little screaming machines then ��
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Old 02-03-2018, 01:34 PM   #56
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It is interesting that Mazda tried the rotary, and is now pushing hard on the SPCCI design: it is a repeated theme of distinguishing itself by engine technology. This can work, and can make sense for a small company, but it can also be a fatal error due to the expense and risk. Both NSU (where Wankel and Paschke developed the engine which became the Mazda rotary) and Citroën went bankrupt, due in part to the failure of their rotary engine attempts. GM poured many millions into the rotary and never sold one; Chrysler put a huge effort into turbines, and has since gone bankrupt multiple times (although certainly not primarily due to their spending on turbine engines). None of the companies which built rotary snowmobile, motorcycle, or kart engines has succeeded with those products.

As much as we might want to cheer them on, any well-run auto manufacturer is very cautious of novel engines.
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Old 02-03-2018, 02:15 PM   #57
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... As much as we might want to cheer them on, any well-run auto manufacturer is very cautious of novel engines.
I think that's why John Deere was reluctant to venture into the jet engine powered tractor business!
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Old 02-03-2018, 03:14 PM   #58
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my favorite wankel powered car was an old friend's Tri-azda, which was a Triumph Spitfire powered by a MX 4 motor that was race built, with a big weber 4bbl downdraft carb, and a HUGE radiator laid over backwards filling most of the engine compartment (since the wankel itself was so tiny). this car was incredibly light, probably under 1500 lbs wet. the motor was mated to a conventional 4-speed transmission, and the gearing was such you could stay in 1st til about 50 then grab 2nd to well north of 100, or you could short shift it and it was quite tame in traffic. it wasn't real fast from 0-25, but above that hang on. it handled darn good for an oldie, too, with rally style sticky tires significantly wider than stock
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Old 02-03-2018, 03:48 PM   #59
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I think that's why John Deere was reluctant to venture into the jet engine powered tractor business!

Ironically, John Deere did try rotary engines.

They bought into it in 1984: John Deere Developing Family Of Rotary Engines
They bailed out seven years later: Deere Pulls Out Of The Rotary Engine Race
Deere's contributions to the technology, along with those of their predecessors at Curtis-Wright and successors at Rotary Power International apparently all ended up at Barger Tech.

Deere even proposed an aircraft engine, which is presumably a leftover from Curtis-Wright (who were primarily interested aircraft, while JD was into industrial and military applications).

Although it contains some interesting tidbits, and shows how many companies tried to produce this engine and failed to make it success, I wouldn't take the engine history on Barger Tech's site too seriously... they think that "Toyo Kogyo" was Toyota, while in fact it was the original name of what is now Mazda.

The rotary: poster child for the perils of novel engine investment.
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Old 02-03-2018, 04:08 PM   #60
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my favorite wankel powered car was an old friend's Tri-azda, which was a Triumph Spitfire powered by a MX 4 motor that was race built, with a big weber 4bbl downdraft carb, and a HUGE radiator laid over backwards filling most of the engine compartment (since the wankel itself was so tiny).
The Mazda engine is actually wider and about as long as the stock Spitfire engine... but it is lower.

A well-known example of this swap is the Ro-Spit, a project by Grassroots Motorsports magazine. There wasn't much Spitfire left in that thing by the time they were done; mechanically, it was all Mazda and other Triumph models.

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this car was incredibly light, probably under 1500 lbs wet.
Light, yes. Under 1500 pounds, not likely. Spitfires were over 1800 pounds originally, and the Mazda engine (which is mostly iron) is probably no lighter than the original lump. Rotary fans love to brag about the light weight, but scales show the truth.

By the way, we have a Triumph Spitfire in our garage.
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