Achates Engines

[Civilguy]

Here's two links to videos concerning a new engine based on an old design and claiming the potential for a lot of good things. There's a lot more information to be found online.

They have developed a 2.7L OP Engine delivering 37 combined mpg, 270 HP and 429 ft/lb torque(!) which has been fitted into an F150 as a test bed. Cummins is also working with Achates on a 1,000 HP military engine, (which is probably a wee bit more than I am personally in the market for).

Radical new engine makes a run at reality

https://www.cnet.com/roadshow/videos...un-at-reality/

The history of the Achates Engine – as told by entrepreneur Dr. James Lemke

https://goo.gl/u5swHS

[Al and Cindy K]

Thanks for posting - interesting reads.

Al

[Bruce Olive]

Interesting. Thanks for posting.

[Raspy]

Mike,

Here's my take on it.

The opposed piston design has been around a long time and was very successful as a Fairbanks-Morse ship engine using diesel fuel. Using gasoline, I don't know how they plan to ignite the fuel by compression only, but that seems to be what they are saying.

Claiming up to 30% more efficiency seems a bit optimistic as current gas engines seem to be getting around 35% and Achates seems to be advertising a little over 40% in his video. Part of Mr. Lemkes pitch is that nobody would believe that a two stroke could be made to run clean. But that is a misleading point. This is a two-stroke only in that it fires every revolution, but not that it is lubricated by the fuel and scavenged by crankcase pressure. So, there is no issue with having to burn lube oil with the fuel. Thus, no pollution problem. And since it is scavenged by a blower, it won't be as sensitive to speed changes or need a tuned exhaust as much as a naturally aspirated two stroke. It should not be so peaky in it's power band as a typical two-stroke, and it should be torquey because it fires every revolution with two cranks pushing.

I like the ability to design the combustion chamber shape for best efficiency, the reduction of cold exposed surface area to the combustion, and the reduced stroke to dispalcement ratio, even with a long affective stroke, with both pistons moving away from each other. Since the most efficient number of cylinders is three, but being a two-stroke, it might run as smoothly as a six cylinder in-line four stroke. Very nice and simple.

The advantage of having no valve train is huge. And with it's short stroke, and possibly, large port design, it might turn out to be a real revver, depending on how the fuel is delivered. If it's compression ignition, the fuel can't be delivered until they want the power stroke to start and that limits the speed the engine can run. I don't see the advantage of attempting compression ignition with gasoline, especially since there are no inherent hot spots in an opposed piston design that might lead to pinging, meaning they should be able to raise the compression ratio beyond what is considered normal now and inject the fuel in the intake port or way earlier than at the ignition point for timing purposes. This would allow higher reving and better efficiency at high speeds, I think. If it is intended to run slower, they could inject the fuel right at a spark plug and achieve an extreme lean burn.

It will need a supercharger to run, but may get a turbocharger to feed the supercharger and reduce the parasitic loss, raising efficiency a bit more.

It will be fun to see the test mules, when the time comes.

Your thoughts?

[floyd]

forty years ago I took a temporary assignment with Fairbanks Morse (my brother was the field rep) to work on field pumping station engines, Same basic thing except HUGE in comparison they could run on multiple fuels, but they mostly ran on natural gas produced in the field... Diesel fuel when used on locomotive applications. They were not a new thing then and they are still in use today.

https://www.youtube.com/watch?v=JSVOSX1MqCY

[Civilguy]

Originally Posted by Raspy

Your thoughts?

My thoughts? As far as the engineering and O&M aspects go, you guys are way over my pay grade!

Agreed, the opposed-piston design is not new. I recall reading Dick O'Kane's Clear the Bridge which included many passages extolling the virtues of the Fairbanks Morse "rock-crushers" in the Tang, a Balao-class submarine fitted with four 38 8-1/8 engines. Lemke credits those that preceded him and speaks of the technology remaining substantially unchanged for some 70 years.

Reading up on the Junkers Jumo 205 engine, one shaft ran some 11 degrees behind the other to facilitate porting the intake and exhaust. So, there was certainly some inefficiency there. It appears the new Achate engines may not have that lag, but that's admittedly just based on looking at their published graphics. I easily could have missed any lag.

There is a brief video online of an F150 which has been fitted with the engine, accompanied by a write-up mentioning that Aramco will be involved in the development of additional test beds.

https://www.trucks.com/2018/01/15/de...pickup-engine/

I hadn't recalled that Lemke said nobody would believe that a two stroke could be made to run clean (which he did at 4:53). I had only recalled it as their first, reflexive, objection.

His mention of efficiency gains was actually "about 20 to 30% more efficient than any diesel ever made" (6:31). They filed a paper with SAE in 2014 citing "over 30% fuel economy improvement when compared to an equivalent four-stroke diesel engine".

An interesting aspect to me was John Walton's recounting the story of respective "war chests" for litigation. Though some might thrive on that sort of thing, it's not the part of the project that I'd want to be involved in.

Anyway, the whole concept seems pretty intriguing to me, as do most things mechanical. But, my being intrigued doesn't really equate with having much understanding, I fear.

[Raspy]

Mike,

I'm interested too. We are reaching the limit on efficiency with conventional piston engines and are also up against the need for a much better valve train. The whole flailing belt or chain, cams and poppet valves works well, with over 100 years of careful refinement, but is way to complicated and troublesome. A power stroke only every other revolution means so much effort is used up just for scavenging. And so much mechanical friction losses per power stroke.

A clean running two-stroke with ports instead of poppet valves sidesteps all of that. Plus fewer parts, possibly higher revving, more efficient combustion chambers and more even combustion chamber heat, which can help with emissions and pre-ignition. Sheesh, the list goes on and on.

You mentioned the Junkers engine where one shaft ran 11 degrees behind the other, "so, there was certainly some inefficiency there". Not sure what you mean. The exhaust ports are uncovered before the scavenging ports, in order to drop the cylinder pressure to facilitate the fresh air clearing the cylinder. This could be done with crankshaft timing or port location. Timing might be the better way because it keeps each piston's power stroke the same, but I don't know why this feature is indicative of inefficiency. It seems similar to the exhaust valve opening before bottom dead center on the power stroke in a conventional piston engine. Turns out this situation that seems wasteful actually make the engine more powerful, but less efficient. That is where the Atkinson concept fits in with various designs that can vary the power stroke as compared to the intake stroke, and become more efficient at the expense of power. But that begins to speak about why piston engines are so inefficient. Some 1/3 of the fuel's energy goes out the exhaust, another 1/3 goes into the cooling system and the rest becomes useful work, approximately.

Interesting stuff.

Thanks for the link.

[G_Hill]

A modern hybrid electric can already run up to 60% efficiency, & that's not even considering a plug-in version. Most of the Sparkletts & Arrowhead delivery trucks (pretty decent size around here) around SoCal are already hybrid electric. There's a reason for that choice. Efficiency, Clean, & long term running cost.

[floyd]

With two pistons per cylinder... wouldn't that make it a 4 stroke?

[Mike Magee]

I'm not sure how they keep the emissions clean. When the piston rings slide past the intake and exhaust openings, I'd think the lube oil would get into the cylinder mixture and burned to soot, and unburned oil would blow out the exhaust.

[Raspy]

Originally Posted by Mike Magee

I'm not sure how they keep the emissions clean. When the piston rings slide past the intake and exhaust openings, I'd think the lube oil would get into the cylinder mixture and burned to soot, and unburned oil would blow out the exhaust.

That is a good question. It appears the Achates engine has oil control rings near the bottom of the pistons that never pass the ports. Seems like a tricky balance to get enough oil to the upper rings without having any go out the exhaust ports.

here's a pic of the Achates design:

[Raspy]

Originally Posted by G_Hill

A modern hybrid electric can already run up to 60% efficiency, & that's not even considering a plug-in version. Most of the Sparkletts & Arrowhead delivery trucks (pretty decent size around here) around SoCal are already hybrid electric. There's a reason for that choice. Efficiency, Clean, & long term running cost.

Not sure how you are calculating efficiency. Supplementing gas engine power with an electric assist doesn't mean the engine itself is more efficient with the fuel it burns, or put another way, if a conventional gas/elect hybrid calculates to 60% in your example, then the Achates would calculate higher because it is a more efficient engine. Meaning, it delivers more work per fuel burned, than a conventional four stroke engine.

[Civilguy]

Originally Posted by Raspy

Mike,
You mentioned the Junkers engine where one shaft ran 11 degrees behind the other, "so, there was certainly some inefficiency there". Not sure what you mean.

John,

Thinking about it, I wouldn't be able to tell whether or how the lag would effect either the efficiency or the power.

Folks at Achates have spent years on this specific project, building on an older design that went through an initial inspiration phase followed by additional refinement before apparently going quiescent for some 70 years. The more recent work has included CFD modeling, which is pretty heady stuff in itself. Knowledge is accumulated through trial and error and practice.

So, ultimately, I guess I'm just riffing without any real underlying knowledge here.

[starbrightsteve]

I’m wondering why this engine has been dormant for so many years. Some sort of a world record was set back in the thirties using the design and then nothing comes of it. Why did the the engine design we now have in cars and trucks become the standard?

[Al and Cindy K]

Steve, I don't think the technology has been dormant. Based on post #5 above (thanks Floyd), I did a bit more looking and found that Fairbanks Morse seems to have continued development of opposed piston engines and now offer a 12 cylinder, 1000+ cubic inch, 33'x10'x10' genset weighing in @ 95,000 lbs. https://www.fairbanksmorse.com/trident-op Wonder how many eggs this thing would power?

[Steve Carlson]

95,000 pounds!

I think even a full size semi is limited to 80,000 pounds.

[Mike Magee]

My son (engineer) thinks the basic design (opposed-piston, 2 cycle) is best suited for stationary applications where it isn't subject to a wide range of RPM. I'm sure it took a great deal of refinement work and ingenuity to bring it to the point where Achates has it now, going into actual trucks for testing.

[G_Hill]

Originally Posted by Raspy

Not sure how you are calculating efficiency. Supplementing gas engine power with an electric assist doesn't mean the engine itself is more efficient with the fuel it burns, or put another way, if a conventional gas/elect hybrid calculates to 60% in your example, then the Achates would calculate higher because it is a more efficient engine. Meaning, it delivers more work per fuel burned, than a conventional four stroke engine.

most hybrid electric vehicles take advantage of the Atkinson engine designs.
https://www.caranddriver.com/news/a1...-its-benefits/
Very efficient but lower in HP. That deficiency can be / is made up, by The Torque from electric motors. Both the Atkinson & Otto cycle engines have been around forever as well.
Achates like diesel, are more expensive. Look at the illustration. You have 2 crankshafts. That means more gears. That means more journals, etc. More parts. Doesn't necessarily mean it's bad - being more costly to build, presuming it's going to run for a long long time.
.

[Raspy]

Originally Posted by G_Hill

most hybrid electric vehicles take advantage of the Atkinson engine designs.
https://www.caranddriver.com/news/a1...-its-benefits/
Very efficient but lower in HP. That deficiency can be / is made up, by The Torque from electric motors. Both the Atkinson & Otto cycle engines have been around forever as well.
Achates like diesel, are more expensive. Look at the illustration. You have 2 crankshafts. That means more gears. That means more journals, etc. More parts. Doesn't necessarily mean it's bad - being more costly to build, presuming it's going to run for a long long time.
.

I'm trying to compare apples to apples. Gas engine efficiency in two different engine designs, not whether an electric motor can assist a gas engine of one design and then compare that to a pure gas engine of another design. I don't know of any gas engines that have achieved 60% efficiency. Please post one.

Assuming the Achates is more costly because it has two crankshafts, may be a false assumption. I don't know. The elimination of the cylinder head, the valves, cam and cam drive system removes a lot of complexity and parasitic losses. And with those things goes the less than optimal combustion chamber design, hot spots and high piston speeds. It seems like a pretty good trade off to me and the preliminary efficiency gains shown in Achates testing seem to prove it. One of the weakest parts in modern piston engines is the cam drive and valve mechanisms. This it typically a belt or chain. Belts have a limited service life and must be changed. If they are used in an interference engine, like Fiats, the engine will self destruct if the belt breaks. This has been the death of many an engine. Better manufacturer's, like Mercedes, or Chrysler with the Pentastar engine, use chains. But these two are not the final answer. Cummins uses gears, but their engines are simple pushrod engines and not designed for higher speeds. Small block OHV V8s have been refined to be OK and Chrysler Hemis took the design a bit further by setting the cam higher in the valley to shorten the pushrods. But all of them have complicated valve trains that become the limit on RPM. The Yamaha five valve may be the best design of all for breathing and RPM, but it is even more complicated. Designers have been trying to improve or eliminate the valve problems for decades and nothing better than the simple poppet valve and camshaft has been developed. Electric valves have been the holy grail, but can't yet rival the mechanical system. Typical two stoke engines eliminate the valves, but have pollution problems and can't be made to run as torquey and reliably as four stroke engines. Then, setting aside the complicated nature of the valve system, valves also come as a four stroke design that only fires on every other stroke. So much friction and piston speed goes on for each power stroke. Then, a fresh look at the opposed piston design, shows a lot of spinning mass, a required blower, two cranks with connecting gears. But it also reveals lower piston speed, no valve train, excellent combustion chamber design with no hot spots, a power stroke on every revolution, the ability to have very high compression, and the need for only three cylinders instead of six. And, tests seem to prove they are more efficient. When used as part of a hybrid system they may be even better.

If you took all of the current four cycle gasoline engines and were able to eliminate the entire cam, cam drive, valve and valve train mechanisms, and the cylinder heads and gaskets (especially on V type engines), they would, on average, last a lot longer. The OP engines have none of those things. Gears last a very long time. Roots type blowers do too, since they have no sliding parts.

I want to see where this technology goes.

[Paul O.]

This thread topic has been quite interesting to read.

Originally Posted by Raspy

...

I want to see where this technology goes.

Well, it has survived in a small niche for 70+ years, and it will do so for a long time, I believe.