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Old 05-29-2001, 05:01 PM
Join Date: May 2001
Posts: 3
Orbital Combustion Engine... what happened?

An Australian friend tipped me off today that one of the local heroes from Perth is a man named Ralph Sarich, who invented a two-stroke engine suitable for use in motorcars that didn't have the typical pollution troubles of normal two-stroke engines.

Quoting from
The Orbital Engine Corporation Limited's innovative technology invented by Ralph Sarich in 1972 has focused world attention on the merits of two-cycle engines by overcoming their traditional high hydrocarbon and carbon monoxide emissions. Compared to the conventional four stroke engine, the ingenious two-cycle orbital combustion process (OCP) engine is 50% lighter, takes up 70% less space, and consumes 30% less fuel. The power source is not only suitable for motorcars, but also many other applications including inboard and outboard marine engines.

Now, if this is all true, and this engine was available almost 30 years ago, why have I never heard of a car with an Orbital patent engine? What auto maker wouldn't like to throw a lighter, cheaper, more economical engine into their vehicles?

I must be missing something.
Old 05-29-2001, 05:14 PM
Join Date: May 2001
Location: England
Posts: 57,536
Orbital engines have been around a long time, there are a number of drawbacks:
1: The piston is a kind of rounded triangle shape and is very prone to wear at the corners.
2: They are properly known as Wankel engines, and that's not a name that's going to win hearts
3: Hi Opal
Old 05-29-2001, 05:59 PM
Join Date: Apr 2000
Location: Pasadena, CA
Posts: 752
IIRC, they worked like a wonder for about 30000 miles, and then the o-rings (?) needed to be replaced. The only problem was that unlike its' regular engine brethren, the entire engine had to be disassembled, which made the practice, and thus the engine, unfeasible.

I don't have a cite though...
So hardcore you have to be 31 to see!
Old 05-29-2001, 06:23 PM
Charter Member
Join Date: Nov 1999
Location: Seattle, WA, USA
Posts: 3,733
Mangetout, I don't think that the Wankel rotary engine could really be described as a two-cycle, so I'm sure it wasn't what the OP was referring to. On top of that, they were used extensively by Mazda for years (I don't think they're still making any rotary models, but I'm not sure). The rotor didn't wear too badly at the corners, as it had a sort of wing gadget there that actually did the rubbing against the chamber sides. The wing (no idea what it is called) had to be periodically replaced, just like piston rings in 'normal' engines.
Old 05-29-2001, 07:16 PM
Join Date: Dec 1999
Location: Spokane, WA, USA
Posts: 7,213
It's called an apex seal.
Old 05-29-2001, 07:20 PM
Join Date: Sep 2000
Posts: 551

It doesn't look all that revolutionary to me.
Old 05-29-2001, 07:22 PM
Join Date: Dec 1999
Location: Bay Area
Posts: 269
On top of that, they were used extensively by Mazda for years (I don't think they're still making any rotary models, but I'm not sure).
I believe that the FC and FD model RX-7s are still being produced in Japan. The RX-Evolv coming out soon will use a rotary engine.

IIRC, if the engine ever knocked or overheated once it had to be totally rebuilt. They have a very bad wrap and it's not uncommon to find a car with 40k or 50k miles that's already had an engine replacement.
Old 05-29-2001, 07:25 PM
Join Date: May 2001
Posts: 3
No, Not the Wankel Rotary Engine...

As far as I know the rotary engine was actually used in a few mass-produced cars. I heard one once, and it made a really peculiar noise.

The Orbital engine is something different entirely. You can find the patent info here:

It's really really obscure. Nobody I know outside of Australia ever heard of it before I asked.

The popular theories among my friends, in order of enthusiasm:

1. It's an amazing super-engine and the auto makers suppressed it in collusion with the oil producers.

2. It's got some drawback that nobody knows about since nobody's ever heard of it.

3. Versions of it are in use, just cunningly redesigned to get around Orbital's patent.

4. Nobody's heard of it so why should anyone use it?
Old 05-29-2001, 07:30 PM
Join Date: May 2001
Posts: 3
Oh, and here's another source of info... gives a quick overview of how a 2-stroke engine works and how it differs from the typical internal combustion engine. It mentions the Orbital engine very briefly at the end, but doesn't go into any real detail.
Old 05-29-2001, 07:49 PM
Straight Dope Science Advisory Board
Join Date: Apr 2001
Location: Connecticut
Posts: 1,698
Not sure if this relates to teh OP's engine, but the June 2001 issue of Scientific American has an article about "Homogeneous-Charge Compression-Ignition" (HCCI) engines. It appears to be a two-cycle engine, compression-ignition followed by power-exhaust, and is described as more-efficient and cleaner burning. Nothing more than prototypes yet. Maybe the rest of the auto industry is catching up to Mr. Sarich. A summary of the current issue is available at:
Old 05-29-2001, 11:43 PM
Join Date: Jan 2001
Location: Somers Point, NJ
Posts: 5,895
I remember hearing about the orbital engine about ten years interesting feature was the variable compression ratio.
Anyway, the reason it was called an orbital was that instead the pistons reciprocating in individual cylinders, the engine had several cylinders inside the crankcase, which "orbited" the centrally located crankshaft.
Old 05-30-2001, 12:45 AM
Join Date: Mar 2000
Posts: 8,165
I believe there is an Australian company called Orbital which has come up with a design for a two-stroke engine which may be what you are talking about.

This engine uses pre-mix of fuel air which is then compressed and direct injected to the combustion chamber.

It is unlike other 2-strokes in that the crankcase is not used for precompression but rather a separate pump which is driven from the crankshaft.

This menas that it can have a sump and the lub oil does not have to be mixed into the fual to lubricate the min bearings which leads to much cleaner emissions.

The use of injection allow for variable timing which reduces emissions of hydrocarbons.

Aprilia, the Italian bike manufacturer, has licensed the technology and is shortly going to sell scotters equipped with such motors. They also have plans to use it for a much larger engine.

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