Achates Engines

[floyd]

Originally Posted by 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?

The engine shown in the video that I posted is BIG, Really BIG, as in maybe 10ft tall. Maybe a factor of its efficiency is a matter of scale.

[Raspy]

It does seem possible that the downside of the OP (Opposed Piston) engine may be it's breathing. As it runs faster it has less time to clear the spent gasses from the cylinder and can only do so through the ports with pressure from the intake system. This may mean a large parasitic loss to run the blower fast enough and at high enough pressure. and it may mean a gradually more and more contaminated mixture at higher and higher speeds.

Detroit Diesel two stroke engines are a similar design with a roots blower and scavenging ports. But just one piston per cylinder and with cylinder heads and valves. They respond well to turbocharging.

As far as the horsepower required to run the blower, and just as an interesting side note, I had a friend that had a dragster. It was powered by an older generation Chrysler Hemi with a blower. I remember him telling me the blower took 400 horsepower to run it! That was an extreme case, but interesting, I thought. In spite of that parasitic load, the engine was still producing around 3,000 horsepower!

I'm away now, but when I get home I'd like to study these things further and look at their history and the charts that Achates has come up with to see some trends in their behavior. This should speak to scaling the engines.

OP engines work wonderfully as slow ship engines, but light weight and high speed ones may present some serious limits. Dunno.

I was a throttleman in the Coast Guard for a while and ran two of these out at sea. In that application, the engines were stopped and then started in the other direction for reverse. They were started by injecting air into the cylinders through starting ports that were fed by an air distributor system that looked a lot like an ignition distributor on a conventional gas car engine. The timing of that distributor determined if the engine started in forward or reverse. As part of routine maintenance, we would take a reading on the rod bearing clearances. This was done by removing the fuel injector that pointed in right between the pistons at top dead center. The injector was removed from each cylinder and we slipped in a 1/4" diameter piece of round lead rod. Then the engine was rolled over to smash the rod between the pistons. Then we would use a micrometer to measure it's thickness and use that number to determine if the bearings were OK. One of the engines developed a grinding sound near the upper crankshaft and the vertical shaft interface, so we pulled the upper crank out at sea (!!) to have a look. That is when all hell broke loose and we got into an Atlantic storm. It's quite a story that I won't go into now.

[Raspy]

Originally Posted by floyd

The engine shown in the video that I posted is BIG, Really BIG, as in maybe 10ft tall. Maybe a factor of its efficiency is a matter of scale.

This is likely a part of the story. One very interesting characteristic of engine cylinder volume is how it is an exponential function. So, volume increases faster than surface area. This means there is a longer heat path to the cold cylinder walls and less cooling area for the gasses from those cold cylinder walls, as the volume increases in larger displacement engines This can lead to more complete combustion and definitely allows easier starting in diesels. The biggest diesel engine ever made happens to be the most efficient one too.

This relationship of volume to surface area shows up to an extreme degree in indirect injection diesels with pre-combustion chambers. The chambers are very small and are designed to improve combustion, but they have a high surface area to volume ratio, so the gasses inside cool too rapidly to allow easy staring. This is why so many diesels are hard to start.

For me, it's a very interesting topic.

[G_Hill]

Originally Posted by Raspy

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. ....snip.....

true. Apples to Apples, no diesel, no Turbo, no electrification, no regard for power band (another's comment/concern above) not considering what's in production, Achates can win at efficiency. 60% efficiency is only achieved with internal combustion & electric together - real world / mass production. Electric motors can achieve over 90% efficiency, coupled with an in-production 40% efficiency gas burner will yield 60% efficiency. But understanding OP's more narrow focus, & not meaning to diverge off-topic, Achates wins. Still .....
An excellent read as to why Achates is not running around today in cars & trucks - this might be useful to those who would like a good read;
https://www.greencarcongress.com/201...-20111102.html
Especially helpful, the design engineers feedback & rebuttals towards the
bottom of the article. "If" Achates high efficiency is limited to a certain RPM/Power Band (suggested in the above read) .... it may indeed make it into production by hybridization.
.

[Raspy]

Originally Posted by G_Hill

"If" Achates high efficiency is limited to a certain RPM/Power Band (suggested in the above read) .... it may indeed make it into production by hybridization.

Sounds like OP engines would be well matched to the new 10 speed automatics or a CVT, or as you suggest, running a generator in a hybrid

I don't like running a conventional piston engine with a CVT partly because newer engines run well over a wide RPM range and partly because of the way CVTs are programmed.

Part of my hope, as I've mentioned, is based on getting rid of the flailing valve train machinery of conventional engines and adding the advantages of a "two cycle" concept with low piston speed.

It would be really fun to drive one of the test mules.

[Lloyd (aka Santa) Coltman]

There was also a 3 cylinder (horizontal) opposed piston 2-stroke diesel engine (British Commer) that had large rockers linking rods to transmit force to a single bottom-mounted crankshaft, that was produced in the 1940s -50s. It was a 'Screaming Beast', as were the 3,4, and 6 cylinder GM 2 stroke diesels. Almost impossible to ride in the cab! Ask me how I know (but alert me to turn up my hearing aids, before you speak).