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pictsidhe

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Aircraft engines are fairly constant speed. The Evinrude 2 strokes are similar if not better economy than 4 stroke outboards. I found a dyno test of one. BSFC of 0.45 at the prop for about 30hp. They really shine at idle.
 

tspear

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Aircraft engines are fairly constant speed. The Evinrude 2 strokes are similar if not better economy than 4 stroke outboards. I found a dyno test of one. BSFC of 0.45 at the prop for about 30hp. They really shine at idle.
.45 is actually rather poor. That is likely running ROP on any of the old certified avgas engines.
Further, unless the engine is turbo normalized (or uses a super charger to normalize manifold pressure) then engines actually operate across a fairly wide power band.

Tim
 

Swampyankee

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Besides the world's most efficient engine is a 2 stroke, there's millions of 2 stroke engines running around that are incredibly more powerful per pound than 4 strokes. Anywhere from double to 4 times the hp per lb dependent on cylinder capacity.

It makes me wonder why these myths and lore about 2 strokes continue, admittedly the antiquated pieces of miserable 1960's tech 2 stroke rubbish that flyers use doesn't help, but dirtbike, snowmobile and jet ski users know better.

2 stroke's fail when compared to a 4 stroke is emissions output and space for the exhaust, but both have been turned around in recent years.

165 hp at 90 lbs, what more could you want ...

https://www.rotax.com/en/products/rotax-powertrains/details/rotax-850-e-tec.html

Mercury and Evinrude 2 stroke outboards not only meet Californian emissions law, they are now cleaner than many of their 4 stroke counterparts.
The world's most efficient engine is a two-stroke, crosshead, turbocharged diesel with an operating speed of about 100 rpm, and a stroke of well over a meter. A basic consideration is that these super-large engines are designed for efficiency. For typical two-stroke gasoline engines, efficiency is low on the the list.
 

cheapracer

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Now find a two stroke engine which is used in a variable speed application which beats the performance of a four stroke (again, diesel only). I have yet to see one of these unicorns...
Well I do know of a few, get back to you later.

I need to get back to my engine soon also, and as of 2 nights ago (due to this very thread, that's why i get involved, makes my brain tick) I realised how I can circumnavigate both Hooper's and this Group's patents, I am going to seriously consider this 'stepped piston' layout.


. For typical two-stroke gasoline engines, efficiency is low on the the list.
Could you define "typical" for me please?
 

cheapracer

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Lo & behold ! http://www.launchpnt.com/portfolio/transportation/electromechanical-valve-actuator . Poppet valve two stroke without cams, rockers or anything else with infinite valve duration & phasing. Even the ability to run both 4 stroke & 2 stroke modes on the same engine. https://youtu.be/ZYEjAv0hFug
BMW spent many millions and many years trying and couldn't get it reliable enough for mass production, and gave up.

One of the Euro Supercars, Koenigsegg, has the option on it's V12, buts that's ok for a limited producer who's customers understand the risk.
 

Swampyankee

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Well I do know of a few, get back to you later.

I need to get back to my engine soon also, and as of 2 nights ago (due to this very thread, that's why i get involved, makes my brain tick) I realised how I can circumnavigate both Hooper's and this Group's patents, I am going to seriously consider this 'stepped piston' layout.




Could you define "typical" for me please?
Most common, i.e., crankcase scavenged, low-power, used on something like a weed wacker or a motor scooter.
 

cheapracer

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Most common, i.e., crankcase scavenged, low-power, used on something like a weed wacker or a motor scooter.
Maybe true, but who cares? Those engines are in the don't care efficiency bracket, you pay $1 or $2 to cut your grass or ride down to the shops, meh.

[video=youtube;tZvIw83uZgY]https://www.youtube.com/watch?v=tZvIw83uZgY[/video]
 
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cheapracer

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Most common, i.e., crankcase scavenged, low-power, used on something like a weed wacker or a motor scooter.
Maybe true, but who cares? Those engines are in the don't care efficiency bracket, you pay $1 or $2 to cut your grass or ride down to the shops, meh.

[video=youtube;tZvIw83uZgY]https://www.youtube.com/watch?v=tZvIw83uZgY[/video]
 
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tspear

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Maybe true, but who cares? Those engines are in the don't care efficiency bracket, you pay $1 or $2 to cut your grass or ride down to the shops, meh.

[video=youtube;tZvIw83uZgY]https://www.youtube.com/watch?v=tZvIw83uZgY[/video]
Props and where is the 40HP measured. It has been a really long time, but way back when Yamaha outboard motors used to measure HP at the prop while Mercury measured at the camshaft. As a result the Yamaha engines were actually "bigger" and stronger then the Mercury engines.

Tim
 
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RJW

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Have any of you guys seen this before? Looks pretty interesting.
Looks like a nice motor. I wonder how they get that dual-mesh, dual-idler gearbox to work? Setting up dual idlers for equal tooth loading in a light gearbox designed for aircraft use is no easy task.

Rob
 

cheapracer

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Snowmobiles, power boats, lawn equipment... Short duration usage patterns, where there is a significant concern about weight.

Tim
Well the fact is that for small diesels a 4 stroke is easier to manufacturer as a ported cylinder has problems with the rate of compression after the exhaust closes, and a scavenge port with it's ports very low in the cylinder requires a supercharger to run.

Note that the scavenged 2 stroke would still be superior weight per hp, but not by enough to warrant the extra costs.

There is a few attempts to solve these problems and I am very keen on the XRDi - http://www.xrdi.com/Home_Page.php
 

cheapracer

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Props and where is the 40HP measured. It has been a really long time, but way back when Yamaha outboard motors used to measure HP at the prop while Mercury measured at the camshaft. As a result the Yamaha engines were actually "bigger" and stronger then the Mercury engines.

Tim
The only thing that matters is how fast it goes, how much fuel it used and how much it weighs.

The model 2 strokes beat the 4 strokes in all 3 regardless of what numbers are on the cowling.
 

pictsidhe

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.45 is actually rather poor. That is likely running ROP on any of the old certified avgas engines.
Further, unless the engine is turbo normalized (or uses a super charger to normalize manifold pressure) then engines actually operate across a fairly wide power band.

Tim
0.45 from 30hp twin, measured after a 90° gearbox, running on 87 octane mogas, not avgas. Seems promising to me.
 

Staggermania

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It seems to me that the stepped piston is doing the same job as the supercharger/compressor/blower that the Detroit 2-stroke diesels use?
Is the stepped piston more efficient? Not understanding the advantage this design has.
 

PMD

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Achates seems to have smashed the diesel 2 cycle barrier for efficiency. They have a fair number of engines running and seem to be very near production for automotive 2.7, but not sure if that will be the compression ignition or spark version.

Seriously: given modern HPCR injection hardware and technology, opposed piston diesel engines are the future of aircraft, outboards and much more.
 

cheapracer

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It seems to me that the stepped piston is doing the same job as the supercharger/compressor/blower that the Detroit 2-stroke diesels use?
Is the stepped piston more efficient? Not understanding the advantage this design has.

It has a normal bottom end, same as any 4 stroke. It takes power to run a supercharger, besides the additional weight, drive system ect..


Achates seems to have smashed the diesel 2 cycle barrier for efficiency. They have a fair number of engines running and seem to be very near production for automotive 2.7, but not sure if that will be the compression ignition or spark version.

Seriously: given modern HPCR injection hardware and technology, opposed piston diesel engines are the future of aircraft, outboards and much more.
Just in time as everything is turning to electric power ...
 

Staggermania

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It has a normal bottom end, same as any 4 stroke. It takes power to run a supercharger, besides the additional weight, drive system ect../QUOTE]

Sure, I can see that. The charge is still being compressed,however which requires power. I wonder, also, if the stepped setup is more difficult to cast/machine, maybe negating some of the gains?
Dont get me wrong, I think it is a pretty neat and simple setup. I like it.

The achates is pretty cool. Only criticism, at this point, is it is pretty tall.

Found this...

http://www.hybrid-engine-hope.com/hope-two_stroke_engine
 
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