Engine History: The Sarich Orbital Engine – Sometimes A Dead End Can Lead Somewhere.

Image courtesy of the State Library of Western Australia


Perth, Western Australia, 1972. A locally born engineer/inventor named Ralph Sarich won Inventor of the Year on the ABC TV program “The Inventors” for his Orbital engine design.

The resulting media coverage and later investments by State governments and the large mining company BHP allowed him the funds to further develop the engine with a view to mass production.

Image courtesy of the State Library of Western Australia


The engine operated on the four-stroke principle, you can see the ports and the tops of the rockers above each of the seven chambers. The Orbital differs from the Wankel rotary engine in that the center rotor orbits around the  “crankshaft” rather than rotating, avoiding the high tip speeds that was always the bugbear of the Wankel engine. The sliding and hinging vanes separate each working chamber from the others. While it was light & compact for its capacity, it suffered  from poor “cylinder” & combustion chamber shapes and cooling issues which in the end prevented it from becoming a competitor to the traditional and well developed conventional piston engine.

Image courtesy of the State Library of Western Australia


Here Ralph Sarich himself on the left appears to be assisting with inserting the rotor into a prototype engine. You can clearly see the rockers operating the poppet valves; I believe this unit had a capacity of around 3.5 liters so it was clearly a very compact unit.

Image courtesy of the State Library of Western Australia


Photo of Sarich’s Orbital Engine Company in Balcatta, Western Australia in 1973. Centre right is a unit on the bench. Also you can see a much smaller 5 chamber unit on the bench to the left. During this further development, Sarich, ever the inventor, came up with a novel fuel injection system which at the same time as directly injecting the fuel also delivered a shot of compressed air, greatly increasing the atomization of the fuel and also providing a stratified charge. Unfortunately in the end the company could not overcome problems with the engine such as overheating and sealing of the sliding vane system.

It was eventually realized that this Orbital Combustion Process was the real innovation and subsequently the company pivoted from the original orbital engine concept to applying the OCP injection system to the two-stroke engine.

The conventional crankcase compressed, port scavenged two-stroke, while temptingly light, simple & blessed with a high power to weight ratio has always been hampered by poor combustion efficiency and poor emissions due to the fact that the fuel mixture along with lubricating oil is inhaled into the crankcase & then pushed via the transfer ports into the cylinder before compression. Despite careful design like loop scavenging some of the unburnt fuel mixture can inevitably escape before the exhaust port closes.

The chief advantage of the Orbital Combustion Process in a two-stroke engine is that a combustible air fuel mixture is directly injected only after the exhaust port is closed, this stratified charge burns clean without exhaust dilution. A small oil pump is added, which supplies lubricating oil directly to the big end and main bearings, further reducing (but not eliminating) oil contamination of combustion.

In 1998 Sarich announced he had signed a licensing deal with Ford Motor Company for the use of the technology.Ford and OCP built a batch of Fiestas with a 1.2 litre 3 cylinder two-stroke for fleet and journalist evaluation.

Ford was planning to market this model as the Orbital Ecosport

One of the few survivors of this batch resides in the Motor Museum of Western Australia near Perth.

Originally Orbital used a modified 3 cylinder Suzuki outboard motor to develop the system but eventually designed & built their own motor – see schematic above.

Another variation of the concept is this 6 cylinder supercharged version transplanted in to a BMW 3 series on display at the same museum.

In the end there were insufficient advantages in the OCP two-stroke to supplant the incumbent 4 stroke engine for automotive use, as around the same time electronic fuel injection in combination with more sophisticated sensors and controls meant that the efficiency of the traditional engine kept improving year on year.

But that was not the end of the Orbital Combustion Process two-stroke engine. In the outboard engine world, two-strokes were well established mainly because of their inherent power to weight ratio. OCP had licensed the technology to Mercury Marine were it was added to existing motors and was marketed as the Optimax engine on their higher power outboards.

In addition to this, Mercury also built a spark ignited diesel version of the Optimax V6 but it was only supplied for military use.

Orbital Engine Co still exists but now as Orbital UAV, developing and supplying a modular propulsion system for unarmed aerial vehicles (drones) using the OCP two-stroke but adapted for multifuel use in a similar manner to the Mercury diesel outboard. Orbital currently has a tie-up with a Boeing subsidiary and has recently announced a tie-up with Northrop Grumman to develop a hybrid propulsion system for VTOL UAV.

Orbital UAV still has its head office in Balcatta, the same suburb of Perth where it all began nearly 50 years ago.

Ralph Sarich sold out the bulk of his interests in the company in 1992, and would go on to become one of Australia’s wealthiest men.