Stroke of Fortune

Another future postponed. Today we look at an engine technology from the early 1990’s which, for a short time at least, looked like a certainty.

Posterchild for Orbital, the 1993 Pininfarina Ethos. Image credit: hooniverse

Where do ideas go to die? Are blueprints simply rolled up and secreted away, to be dusted off by historians in decades hence or are there engineers in a quiet workshop somewhere in Australia (or Toyota City) still burning with religious fervour for what now appears to have been something of a lost cause?

Founded by engineer, Ralph Sarich, the Orbital Engine Corporation was based in Perth and during the early 1990’s attracted the interest of a number of big name manufacturers for a clever reworking of the time-honoured but somewhat flawed two-stroke engine design. For a short period of time, it sounded tantalisingly like the future, but seemed to have quietly died without eulogy, leaving many wondering exactly why.

There were a number of inherent problems with traditional two-stroke engines as fitted to the likes of early Saabs, DKWs, Trabants and Wartburgs. Amongst them were issues surrounding symmetrical port timing, which allowed unburnt air / fuel to escape through the exhaust port, contaminated unpurged gases affecting clean combustion and the crankshaft lubricating oil (which needed to be added to the petrol) being drawn through the transfer port to be burnt along with the fuel.

Schematic of a basic 2-stroke cycle. Image credit: amsoil

The combined effects added up to a power unit with admirable advantages in compactness, lightness, simplicity and cheapness in manufacture, but with potentially malign traits of noxious emissions, power losses and poor running characteristics. Many of these issues were addressed, if not entirely dismissed by the (predominantly Japanese) motor cycle manufacturers, but given the lack of interest in two-strokes within the mainstream motorcar industry, these developments had not been incorporated into a suitable two-stroke car engine design.

The Orbital two-stroke was different in that direct air-assisted low pressure sequential fuel injection ensured that a strictly monitored amount of fuel was injected only after all ports were closed by the action of the piston, eliminating the scourge of incomplete combustion. The plume of injected droplets was said to provide a natural charge stratification (where the ratio of fuel to air within the combustion chamber is optimised), giving a claimed immunity to detonation (knock) and giving rise to fewer oxides of nitrogen (NOx) being produced, especially at light-load conditions. Also key to this was the use of electronic engine management and a catalytic converter.

Built in two forms; the lower powered versions which employed traditional internal scavenging through the crankcase, (the underside of the piston acting as a pump), using a highly developed lubricating oil which was injected into the crankcase through reed valves on induction. Any oil mist burnt during combustion was oxidised by the catalyst, obviating the once familiar plumes of blue smoke. More powerful versions would employ an external scavenger – in the form of an engine-driven supercharger.

Orbital 2-stroke cutaway. Image credit: the autochannel

Claims by Orbital were ambitious: fuel savings of 15% compared with contemporary four-stroke rivals and exhaust emissions in advance of those then required for the ultra low emissions vehicles being considered by the US state of California at the time. NOx emissions were claimed to be far less than that of a conventional, non-catalysed engine, while in hydrocarbon terms, exhaust gases were claimed to be cleaner than the air being drawn into the intake in many cities.

Couple this to an engine configuration which was, like-for-like, 40% lighter, 50% more compact and around 17% cheaper to make and the argument in favour of Orbital appeared highly convincing. Having successfully demonstrated the promising characteristics of the power unit to the World’s motor industry, licencing arrangements were promptly made with Ford, GM and Fiat, amongst others. Ford at one stage had around 25 test vehicles running Orbital-based two-strokes, mostly Fiestas and Australian market Festivas. Chrysler were also believed to be working on a two-stroke at the time, but to their own design.

The three cylinder Orbital 2-stroke fitted to a Ford Fiesta. Image credit: motorpasion

In 1993, Pininfarina showed two Orbital concepts (Ethos 1 and 2), to demonstrate how the two-stroke could be packaged in a compact and lightweight mid-engined 2-seater. Arguably the last truly intelligent and attractive concept from Cambiano, the delightful little Ethos twins charmed the World’s press and lent the Orbital engine a degree of sex appeal it hitherto lacked.

But the real business of work was taking place in Australia, in the US and in Europe where fleets of Orbital powered family hatchbacks were evaluated. Part of this regime involved the UK’s Surrey police force taking delivery of an Orbital-equipped Fiesta for 15 months and 30,000 miles, where it acquitted itself rather well.

The primary power plant (as fitted to Fiestas) was a 1.2 litre three cylinder developing 80 bhp at 5000 rpm and 90 lbs/ft of torque at 4000 rpm. A 800cc twin and a supercharged 2.0 litre in-line six were also developed, as indeed was a 330 bhp 3.2 litre V6, believed to have been taken up with some seriousness by Jaguar.

Dear Leonard. Setright gives the Orbital the once over. Image: Car

In 1994, the eminent LJK Setright penned a laudatory piece on both the Orbital two-stroke and concurrent developments from Toyota (and Ricardo) which combined camshaft driven poppet valves for both inlet and exhaust porting with an externally scavenged two-stroke cycle. The results, especially from the Anglo-Japanese design appeared to set the industry upon an innovative and potentially exciting course in engine design. Ford talked of Orbital production by 1995. Then it all went silent.

While it appears Orbital’s claims for the power unit were entirely credible, it’s believed that Ford engineers found it incredibly difficult to successfully marry them all in practice. So while an Orbital could be made to run incredibly smoothly, economically, or cleanly, it’s been suggested it was nigh-impossible to make it do all three simultaneously.

Furthermore, the likely level of investment required for two-stroke was probably deemed prohibitive by cost-obsessed carmakers. Another nail in Orbital’s coffin (in Europe at least) was the rise of the high speed diesel, in particular Volkswagen’s turbocharged 1.9 litre ‘Umwelt’ unit. And with EU politicians pushing for lower CO2 emissions, a grubby deal appears likely to have been done which diverted resources towards diesel engine development.

Another way of looking at it perhaps is this. The four-stroke Otto cycle engine has been the predominant configuration, perhaps because it’s repeatedly proven itself as the least flawed compromise. Add to this a risk-averse industry who are in the business of, if not always making money, at least not losing vast quantities of it. The two-stroke, be it Orbital, Chrysler or Toyota’s seemingly revolutionary concept, may have held promise, but against the zeitgeist, probably hadn’t a chance.

But if Toyota’s recent projections are correct, the internal combustion engine has a good three decades of development left in it, which leaves a lot of scope for clever solutions. So who knows, with petrol fuelled engines having to get smaller and ever more efficient, perhaps the Japanese car giant still has something up its sleeve. Could we yet see the two-stroke’s rise?

Author: Eóin Doyle

Founding Editor. Content Provider.

7 thoughts on “Stroke of Fortune”

  1. Allegedly some version of the Orbital engine used in the Fiesta test cars was said to be have been planned for the Ford Ka, only for Ford to opt for the Kent / Endura-E engine.

    It is indeed a shame nothing became of the various direct-injected two-stroke projects of the period, could easily envision such engines powering featherweight Superminis to Kei Cars (Peugeot 106, Citroen Saxo, Rover 100, Nissan Micra K11, Ford Ka, Daihatsu Cuore, etc) though not completely sold on the improved two-stroke engines being upscaled into 4-cylinder to 8-cylinder engines let alone being misused in the same way downsized turbocharged engines currently are in powering larger heavier cars.

    Is it known whether Rover via Honda or BMW were investigating two-stroke projects of their own?

    Some Japanese companies even developed two-stroke diesel engines for automotive use during this period such as Daihatsu, Yamaha and possibly even Nissan as well.

    Daihatsu (albeit not including other two-stroke diesels) – http://forums.tdiclub.com/showthread.php?t=3864
    Yamaha – https://global.yamaha-motor.com/news/1999/0323/super-diesel.html

  2. An engine with low nitrous oxide raw emissions as the Orbital invariably has a low thermodynamic efficiency, resulting in high fuel consumption.
    Problem is that Eurocrats can’t make up their mind whether they want to save the Earth through low carbon dioxide levels or have low other pollutant levels.

    Under changing loads the two stroke suffers from the same inefficient gas flow as the Wankel, leading to hunting on the overrun and uneven power delivery under constant partial load. Both effects are negligible in a motorcycle where loads and revs constantly change.

    Funny thing is the thermodynamic engines with the highest efficiency known to mankind, marine diesels, invariably are two strokes. They just have nothing in common with two stroke designs used in cars or motorcycles with four cam operated variable lift exhaust valves and forced induction directly through the intake port in the cylinder wall. These engines just happen to run under constant load at 120 (slow marine engine) or 150 (fast marine engine) rpm…

    1. Interestingly, this appears to be the lines along which Toyota and Ricardo were working in the mid-90s, according to LJKS. Setright also espoused the use of an exhaust turbine in addition to the mechanical supercharger/scavenger to further aid expansion of combustion gases and to help keep boost pressure constant.

      As an eminent engineer told me once, thermal efficiency is all about expansion ratio.

      In the end I suppose it all comes down to bangs per buck…

    2. The two strokes‘ Achilles heel is their bad effective expansion ratio as opposed to the geometrical expamsion ratio.
      As soon as any port in the cylinder wall opens, all combustion pressure is lost and expansion ends. Thus a typical two stroke only has sixty to seventy percent of the effective expansion ratio of a four stroke because for the rest of the piston stroke there is always some open port.
      As a two stroke has a combustion stroke at every revolution these inefficient pulses happen twice as often as in a four stroke and the engine delivers 120 to 140 percent of a comparable four stroke’s power at 200 percent of the fuel consumption.
      Part oft he problem are symmetrical port timings where any piston controlled port opens as many degrees before TDC as it closes after TDC.
      When valves are used the timing can be set at will, greatly improving the engine’s efficiency but greatly increasing its cost- With forced induction (ever seen the turbo of a marine diesel?) small inlet port openings can be used but the engine can’t be started with the supercharger standing still – not a problem in a marine installation where compressed air is used for starting the engine.
      Any marine diesel is designed exactly like a four stroke with the additional complexity of port openings in the cylinder wall (as well as two piece con rods, compressed air starters and heated fuel systems for crude oil).
      But if you want an engine with 90,000 kW at 120 rpm there’s no way around it…

  3. Interesting. I know Chrysler was developing a two-stroke small engine around the same time, too. It was originally supposed to debut in the Gen 1 (1994) Dodge Neon, but was axed a little before release.

  4. The positive-scavenge two-stroke diesel engine with exhaust valves of the 4 cycle variety was a GM/Winton invention back in the 1930s. US fleet submarines had 4x 1200 hp V16 engines in WW2. And GM-sourced locomotives had similar designs. You can download official US Navy maintenance manuals for details. Their trade mark was eventually Detroit Diesel, and thank god their screaming engines are no longer used in buses here. Talk about noisy! But efficient in their latest giant marine versions by Wartsila etc. as mentioned above, but remember a lot of that comes from preheaters/heat exchangers. No room for those things in cars, plenty on ships, where despite international agreements, pollution control is nowhere near as strict as on vehicles, allowing higher combustion temperatures for higher efficiency and increased nitrogen dioxide (not nitrous oxide which is laughing gas) and NOx emissions.

    Orbital is still around as a company, supplying N20 drone engines for Boeing Unmanned Aerial Vehicles. They’re working through a US $90 million contract as we write. But at 25 % efficiency, (330g/kWh) hour, the little aircooled engine is best known for its ability to digest almost any fuel. I have had updates since 1996 by email from Orbital. That lot never give up preaching their gospel, the persisent blighters, and there are still outboard motors using their fuel-injection method. So not all is lost at Orbital as a company, except the silly original rotary mechanism.

    When a Toyota Camry tests 54 mpg Imp at a 75 mph cruise by Car & Driver, and claims 200 g/kWh (40%) thermal efficiency, the two stroke petrol cannot compete. Toyota’s truck diesels are 44 % efficient – most automotive diesels are 41 to 43. However, Ford only claims about 34% for their Ecoboost 3.5l petrol – time for these other makers to catch up with Toyota! The Honda 1.5l turbo is close.

  5. Another carmaker who explored direct-injected Two-Strokes was by PSA via the IAPAC Compressed Air Assisted Fuel Injection, which produced a 74 hp 1230cc 3-cylinder two-stroke engine at 5000 RPM and 92 lb⋅ft at 3000 RPM.

    The two articles below were what could so far be found on this Two-Stroke project.
    https://www.sae.org/publications/technical-papers/content/960363/
    https://epdf.tips/catalysis-and-automotive-pollution-control-iii-studies-in-surface-science-and-ca.html

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