New 2-stroke Diesel engine, cool link to Engineering TV
Nice description of this new 2-stroke, double opposed boxer layout Diesel engine. I also like piston ports, no camshafts or conventional valves to deal with. With DARPA funding this and DOD interest, it could become a reality in military vehicles. Power to weight and powerplant volume (footprint) looks to be outstanding, if it goes, can you imagine the trickel-down of this design for cars?
It seems to be using something that I've thought would make sense: a "clutch" between the pairs of cylinders, so that you can run off of just two when you don't need all the power of four cylinders.
I wonder if it can be scaled (way) down to have 35-55HP units? [Edit: I guess that they can!]
(click on image for link to very informative video)
This thing looks awesome -- it can be run with just 1 module, or with 2 when you need more power; as each module is fully balanced. It is very efficient --about 40%, and has less heat output.
Typically long rods decrease loads on compontents, and like he said all of the connecting rods are either always push, or always pull, which would be a big advantage from a wear aspect.
What I'm wondering about is how the outer connecting rods will seal up, and how the outer pistons will wear; more the seal setup than anything, I'm guessing just a big cover over the entire thing . . . .
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This engine design replaces the crankshaft with two counter-rotating cams that have three lobes each -- mainly what this gets you is mechanical torque applied to the output shat at 20 degrees past TDC, which is far earlier than the 60 degrees past TDC that is typical for a conventional IC engine.
These are well into the testing phase, and look to be quite viable.
All things old are new again. The engine described on the Engineering TV link amounts to doubling the old Junkers Jumo or Fairbanks-Morse two stroke diesel engines.
The Junkers Jumo had a good power-to-weight ratio – so much so it was used on high-altitude reconnaissance planes in the 1940s. The Fairbanks-Morse was uber-reliable (there are seventy year old engines still running today making rated power) and would run on anything sorta oily.
The opposed-piston engine gets around one of the major manufacturing problems of the internal combustion engine: the complex cylinder head. The opposed engine simply uses another piston to provide the “equal and opposite” for the piston. I noticed the guy did pay special attention to a known weakness of piston-ported engines – heat buildup in the ports.
I have some reservations.
The Fairbanks-Morse and Junkers Jumo used a gear train to synchronize the motion of the pistons. This engine uses a Scotch yoke mechanism instead. The Scotch yoke is definitely less expensive, especially in the US where so few gear manufacturers survive, but the Scotch yoke is a notoriously weak mechanism that relies on a high-wear connection to the crankshaft. In most applications the Scotch yoke was out of general use before the second World War. Even I am not so old that I can even remember seeing a mass-produced Scotch yoke device. Maybe a Singer sewing machine of the 1950s. Early Singers used a Scotch yoke for the co-ordinated motion of their needle, but sewing machines are hardly high-stress machines.
I have absolutely no idea how you would package this engine in any vehicle other than a sidewheel paddle riverboat. The engine is long and low with the crank in the middle.
Trump card. It is a two-stroke diesel and sooner or later to be mass-produced it would have to meet Tier II emissions requirements. No chance whatsoever. Piston-ported two-strokers are notoriously dirty – emitting scads of unburned hydrocarbons (VOC), particulates, NOx, and carbon monoxide. That’s why they have all but disappeared from the market.
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Another feature of the Revetec engine is that 60% of downward force applied to the main journal via the crankshaft is deflected to rotational force increasing efficiency in the Revetec engine. The image to the left shows the bearings under the piston (Note: The second bearing on the reverse rotating cam is hidden behind the front bearing - side by side). As the piston pushes down on the bearing the load (shown in yellow) forces the trilobe cams to spread. The deflected force is deflected into the opposing counter-rotating trilobe cam. The contact angle between the point of bearing contact (shown in purple) produces the torque lever (shown in red). The trilobe and bearing sizes determine how long the high leverage occurs and is designed for each individual engine characteristic we are wanting to achieve.
The Revetec “trilobate” design is very different in regards to piston position in the compression and ignition areas. The down stroke is the same as a conventional engine. The difference is that the travel of the piston on the up stroke is reversed, meaning that at 90deg after BDC the piston moves over half the way up the stroke at the equivalent point of a crankshaft rotating 90degrees. This results in the piston travelling faster initially than a conventional engine. The result of this phenomenon is that when the cylinder is fired, the piston is closer to TDC than a conventional engine. This provides more fuel molecules between the spark plug. We then reduce the amount of fuel (leaner mixture) to provide the correct firing mixture. This feature is most noticeable between the 2,000-4,000rpm range, where most driving occurs. This feature also increases thermal efficiency within the chamber. Another feature of extended dwell is that in a conventional engine, it is normal to inject up to 60% more fuel on a cold start. We have been able to reduce this down to 7% more fuel, reducing cold start fuel consumption and emissions.
also, as a four stroke, the boxer 2 cylinder is as good as it gets. as a two stroke, it is indeed truly balanced. Very clever. The injectors leaving the intake to get just air long before fuel is sloppy, but does keep lube in cylinders for the design. I suppose that is the only engine on earth besides a diesel, that truly benefits from injection.
Trump card. It is a two-stroke diesel and sooner or later to be mass-produced it would have to meet Tier II emissions requirements. No chance whatsoever. Piston-ported two-strokers are notoriously dirty – emitting scads of unburned hydrocarbons (VOC), particulates, NOx, and carbon monoxide. That’s why they have all but disappeared from the market.
There are still 2 strokes still being produced where I work. Another thing is diesel exhaust is very easy to clean up. Simple salt water removes over 99% particulate (unburnt hyd.) Many boats are using this to become "Greener" The water based material is not acid because of the reaction with the salt and promotes algae/plant growth as a fertilizer.
Now lets see if anyone is willing to dump a 55 gallon drum of water every 4 hours or so? My father used to run a 2 stroke diesel in the mines, they used them because after cleaning with water the exhaust was less fatal in closed spaces as compared to gasoline emissions. He had to get fresh water every 2-4 hours.
Too bad they won't use the algae cleaners on major coal fired plants to go 0 emissions, not to mention the biodiesel that could be made from such a setup.
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