Dolphin powered bike... a different kind of 2 stroke

Johnincali

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MEASURE TWICE

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Has anyone come across a good theory of operation of this engine. I noticed that unlike a regular two stroke engine, a spark plug in each cylinder, this kind specifically has a cylinder without a spark plug to I guess draw in and ready a charge mixture that transfers to an second cylinder with a spark plug. It idles slower than a normal two stroke engine that is for sure.

MT
 

Agreen

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Is that an air compressor you modified into a dolphin replica?! It looks convincing at first, then I realized it doesn't look 100% (still, quite convincing though) like the drawing.
 

MotorBicycleRacing

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Hi John
Where abouts in CA are you located?
Your bike is very cool, if you bring it out to the Sat Oct 22nd Socal Motor Bicycle Racing event it will be a big hit.

If you come on Friday 21st you can cruise it around the track at Grange Motor Circuit in Apple Valley, CA
 

MEASURE TWICE

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So I guess after seeing the post after the first one, I looked for faux. Well guess hose clamps on a rubber hose between cylinders could be OK if it does not get too hot and transfers carb input not exhuast.

Even if it is faux and this is a 4 stroke engine, does the Dolphin 2 Stroke actually idle slow in reality because of the design?

MT
 

Agreen

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It's still a 2 stroke, the 2nd cylinder is a charge chamber. It just doesn't utilize crankcase compression. If it were a 4 stroke it would have valves. The only valve this engine has is a check valve above the power cylinder.

And I did a little research on that design. There is apparently only one left in existence, and it's not on his bicycle.
 

Slogger

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It's a converted air compressor (says so in the video header).
That's quite an achievement, getting it to run at all. You guys are nuts!
:)
 

Johnincali

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Hello all, Thanks for the comments... if interested you can read about the Dolphin engine here... http://www.oldengine.org/members/diesel/misc/ricardo.htm

or here.... http://www.oldengine.org/members/diesel/misc/ricardo.htm

Ricardo designed it in 1904 when he was just 17 years old... it was know for it's smooth running and high torque.. Around 1908 they made a car called a Dolphin that used the engine... it was also popular in boats.. Never hear of one in a motorcycle though...

The engine operates like any other 2 stroke except that it is uniflow and uses a piston to charge / scavenge the cylinder... I like to build different kinds of engines and I couldn't find any video of a running Dolphin so I thought it would be a neat one to make... yes the engine is made from a 2 cylinder single stage air compressor.. both pistons are on the same crank throw.. I replace the power cylinder with one from a Harley... Agreen, there is actually 2 valves...one near the spark plug and another just behind the carburetor. I've also made some modifications / improvements to the original design like moving the location of the carb and also changed the combustion chamber...

All the best, John
 
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Johnincali

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here's a picture of the original Dolphin...


you can read about the Dolphin engine here... http://www.oldengine.org/members/diesel/misc/ricardo.htm

or here.... http://www.oldengine.org/members/diesel/misc/ricardo.htm

Ricardo designed it in 1904 when he was just 17 years old... it was know for it's smooth running and high torque.. Around 1908 they made a car called a Dolphin that used the engine... it was also popular in boats.. Never hear of one in a motorcycle though...

I also added a 2 speed....
 
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MEASURE TWICE

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Thanks for that link.

https://www.youtube.com/watch?v=BwLQ-Zfk36Y

A marine version and hear it does idle very slow.

Most 2 stroke cycle engines have a much higher idle speed.

I did see another book on Google Books see this at page 16 near the bottom 1/3 of the page.

https://books.google.com/books?id=6...ustion engines constantine arcoumanis&f=false

Now on page 16 see the area where it mentions of the rate of burn speed by the changing of turbulence in the cylinder by changing the diameter of the tube between then two cylinders. The more turbulence it was said made faster burn. A compromise between fast and slow burn got a quiet engine with good fuel usage. Maybe this is how I can hear the difference between a normal 2 stroke engine and this type where it can idle very slow.

MT

One more Youtube video of one of these engines in a boat.

https://www.youtube.com/watch?v=zeXplu6kSUE
 
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Johnincali

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Hi MT, Those engines are typical 2 stroke boat engines manufactured by a company called Dolphin in the 1950's and 60's ... They are not the same as the original dolphin type engine that uses a piston to charge the cylinder... http://www.dolphinengines.co.uk/history.php

Also I think most of the reason the Dolphin runs smooth is because it uses top / down uniflow scavenging... this causes the fuel / air near the spark plug to be in an ideal state for combustion. Ricardo also used a narrow passage to ensure the engine idled smoothly but IMO a narrow passage is also wasteful and not the best answer. I developed a different combustion chamber design which also allows for smooth running.

Most small carbureted 2 strokes use ether cross or loop scavenging which tends to not idle smooth... they also loose a portion of the unburned fuel out the exhaust which makes them not good from an emissions standpoint.

http://www.airplanesandrockets.com/motors/inside-the-two-cycle-engine-feb-1968-aam.htm

Modern low emission engines like the E tech and Orbital use a system that injects the fuel after the exhaust port is covered.

https://www.youtube.com/watch?v=eu3NEPSBfUs
 
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