Opposed piston engines are two-stroke engines. Regulations(mostly emissions) eliminated most two-stroke engines. Attempts have been made to make them compliant. So far nothing has brought them back. Gearing crankshafts together has always been ahnj engineering challenge. According to Andy Granatelli that was the fatal flaw with the H-16. If you like the H-16 engine, check out the Napier Sabre H-24 sleeve valve engine. The idea was to improve cylinder scavenging. There were variations of the design with crankshaft rotated 90 degrees. That caused the pistons to cover and uncover the intake and exhaust ports at different times. Asymmetrical timing has the potential to further improve scavenging and power. Although the idea was based on good thinking, a comparable engine of conventional design and displacement could produce more power, and was also not limited by a relatively weak connecting rod.
Not quite, a year ago or so, Ricardo presented the solution for the two-stroke engines to make them compliant with off-road emission regulations, in the form of a redesigned carb, where the mixture was stratified, injected only on a section of the intake, thus creating a rich and poor layer in the flow. This design greatly reduced the emissions of the two-stroke, and I believe they are now into production with chainsaws and such using that technology. Must look it up for actual data, but I have the articles somewhere. I agree, the gearing of multiple cranks was always an issue and what ultimately killed quite a few ambitious designs. It's hard enough to smooth one's torque output, let alone combine several... As for the sleeve-valve engines, that's another complicated idea but one that gave a very smooth and silent powerplant. Cheers, Eddie
Several solutions have been worked out for small engines, but those aren't required to meet the same standards as cars. Orbital spent years working on new generation two-strokes for cars. Last I heard they still were. Direct cylinder injection seems to be a must have. I don't know much detail about what they have done, but I noticed no one is selling two-stroke cars.
-------------------------- I remember those. Guys used to refer to them as "Twingles". 1n the '1960's, Sears-Roebuck in the U.S and Simpson-Sears in Canada sold a motorcycle with 250cc engine like that. The bikes were made in Austria by Puch. but badged as "Allstates" for sale in the U.S. and Canada, You could order one in the Sears catalog. Mart3406 ============================
<center>You want weird?? How about this one - a Commer TC3 diesel that was widely in British trucks for many years. It was a 3 cylinder, 2-stroke diesel, with 6 opposed pistons operating on a single crankshaft through a set of rocker arms and a second set of connecting rods! Mart3406 --------------------------------- http://www.sa.hillman.org.au/TS3.htm Commer TS3 Two Stroke Diesel Engine This page was previously featured at Harrington Coachwork. It is displayed here by permission of Nick Webster, author and webmaster of www.thcoachwork.dsl.pipex.com. </center> Have you got it yet? The engine has three cylinders situated above and across the plane of the crankshaft. Each cylinder contains two pistons with the crown facing inwards. On each side the pistons are linked to the crankshaft via a short connecting rod, a substantial rocker arm and a secondary connecting rod. Unlike a petrol engine, a two stroke diesel cannot use crankcase pressure to boost the air supply, because it would tend to combust any oil that was entrapped in the air. A Roots (not Rootes) blower (i.e. rotating lobe type) is situated on the front of the engine and supplies the combustion air. The total displacement is only 3.25 litres, but the engine develops 90 B.H.P. Contemporary four stroke engines, for example the Gardner 5LW produced this kind of power from 8 litres. The engine was introduced in 1954 and power outputs were progressively increased. The engine was discontinued when the Rootes Group was taken over by Chrysler in 1968. At the time a four cylinder prototype version was under test and this never made it to production. An example of the TS4 can be seen in the Leyland Historic Commercial Museum in Lancashire, England. A schematic view of the operation of the engine is given, below. <table valign="center" width="100%" border="0" cellspacing="0"><tbody><tr> <td width="245"></td> <td>[FONT=Times New Roman,Times]Figure 1 shows the pistons commencing their compression stroke. The exhaust piston has a slight lead over the air piston, thus the exhaust ports are closed whilst filtered air is still entering through the air ports. The design of the latter causes the air to swirl as it enters the cylinder to aid complete combustion. In normal operation the blower increases the pressure of the inlet air chest to about 6 p.s.i. above atmospheric. When the inlet ports close, compression commences. [/FONT]</td> </tr></tbody></table> <table valign="center" width="100%" border="0" cellspacing="0"><tbody><tr> <td width="245"></td> <td>[FONT=Times New Roman,Times]Figure 2 Shows the pistons at inner dead centre (this is equivalent to top dead centre on a vertical engine). Shortly before the pistons reach this position an atomized spray of fuel oil is injected into the cylinder and this is ignited by the intense heat generated by the compression of the air charge. The resulting pressure forces the pistons apart to provide the power stroke.[/FONT]</td> </tr></tbody></table> <table valign="center" width="100%" border="0" cellspacing="0"><tbody><tr> <td width="245"></td> <td>[FONT=Times New Roman,Times] In Figure 3 the pistons are approaching outer dead centre (the equivalent of bottom dead centre on a vertical engine). The exhaust ports open first and the exhaust gases are released causing an initial drop in pressure within the cylinder, known as "blow down."[/FONT]</td> </tr></tbody></table> <table valign="center" width="100%" border="0" cellspacing="0"><tbody><tr> <td width="245"></td> <td>[FONT=Times New Roman,Times] In Figure 4 the pistons have reached the extreme of their outward movement and the air ports are open. Blow down ends and air from the blower swirls into the cylinder towards the exhaust ports, thereby scavenging the exhaust gases. This continues until the pistons have passed on through outer dead centre position, the exhaust ports close and the pistons start another compression stroke. The cycle is then repeated.[/FONT]</td> </tr></tbody></table> <table valign="center" width="100%" border="0" cellspacing="0"><tbody><tr><td width="245"></td> <td>[FONT=Times New Roman,Times][SIZE=+1] Finally, you consult the Roobarb & Custard school of animation and end up with a working model something like this. *(Click on the picture to animate) [/SIZE][/FONT][FONT=Times New Roman,Times][SIZE=+1]====================[/SIZE][/FONT] </td></tr></tbody></table>
I've seen quite a few of these layouts, and then some. One of my favourite books is "Motori endotermici" (or "Endothermic engines" in English), by Dante Giacosa, who worked on the projects office at Fiat for 40 years (and being head of said office for most of that time). A very accomplished engineer, and creator of some quite revolutionary cars. This book was first published in the 50's and updated often. My copy is a 1964 edition, and the amount of knowledge and versatility of the subjects covered is amazing. Anything from a marine slow diesel for an ocean liner to a jet engine for an aircraft, passing through stationary engines for generators or small high-speed two-strokes, it's all there, backed by the theory and many practical case studies. It's all in Italian, mind you... Not sure it ever got translated to english. There's quite a lot of info on layouts, and some of the engines shown beggar belief. We're quite an inventive bunch, or at least our ancestors were. Here's a few sketches on the cover, this is what mine looks like: A fine book and worth every cent! This is one of my car bibles! Cheers, Eddie P.S.: I've just found out that this is now on its 15th edition, updated by another engineer, and it is still considered the work of reference for automotive studies in Italy today.
-------------------- Hmmm?? Thinking and trying to figure out how that picture could possibly relate to, and somehow remind you of 'an old girlfriend you dated in college', leaves me with some very disturbing (and possibly obscene and at the very least, highly enjoyable.....er, I mean, 'highly immoral') images in my minds eye.....and for that, I thank you!!!
---------------------------- OMC invested heavily in Orbital technology and used it on their last series of Evinrude and Johnson brand 2-stroke outboards. At the time though, it apparently still wasn't fully developed and reliability problems with the system were just one more of the many problems that all came together at about the same time to drive OMC into bankruptcy. Mart3406 ==================
These engines are cool! I have loved mechanical things since I started my spark plug collection! (about 20 years ago). I always wanted to develop my own engine, but that would have been a BIG waste of time- it's all been done now! I disassembled a new style AC compressor and have its guts on my shelf. It is an excellent addition to my mechanical sculptures.
The Jalopy Journal
