Wednesday, 18 January 2017

Opposed-piston – promises, promises, promises

Opposed-piston engines for road vehicles have proved to be a moving target. Mystifying and elusive. Promises are made and not fulfilled. But now it looks as though there could be light at the end of the tunnel. But still the light at the end of the tunnel is set for 2018.
Here we go, here we go, here we go. Achates Power Inc. of San Diego, California, this month announced development of an engine for a Light-Duty Truck demonstration vehicle, which will surpass CAFE 2025 regulations.
The Opposed-Piston Engine, will be 30-50 per cent more efficient than comparable engines, reduce emissions and cost less than alternative technologies under development for meeting CAFÉ, claims Achates Power.
The new Achates Power 2.7-litre Opposed-Piston Engine will achieve 270bhp, 650Nm, and the vehicle will achieve 37 mile/gal, above the 33 mile/gal fully phased-in CAFE 2025 requirement for a full-size, light-duty pick-up truck.
The output curiously is exactly given 100bhp/litre. This suggests more is available.
The demonstration engine will be integrated into a drivable prototype in 2018; development engines will also be available for automakers.
Achates Power claims it has engine programmes under development with 12 leading engine manufacturers, including work with Cummins Inc. on the Advanced Combat Engine for the US Army, and an Opposed-Piston, Gasoline Compression Ignition Engine for the US Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) in partnership with Argonne National Laboratory and Delphi Automotive, and Fairbanks Morse.
Achates Power has to disclose Cummins as this is Federally-funded programme, but it has to be assumed other big names could be in the list anxious to tap into whatever Achates Power has to offer.
“While we continue to work on our customer programmes, and research and development programs (like Gasoline Compression Ignition), we are excited to showcase the fuel efficiency, low emissions and outstanding driving characteristics of our Opposed-Piston Engines,” said David Johnson, president and chief executive officer of Achates Power.
                                        No other technical solution

“There is no technical solution to respond to the proposed 2025 CAFE regulation that is as cost effective, compatible with our existing vehicles and fuels, ready for production and adaptable to future renewable fuels as our Opposed-Piston Engines,” claims Johnson. who added that of the nine automakers who have signed on as development partners, at least one of them has begun tooling up to build an opposed-piston engine in volume. If this claim is true then the implications for the future could be significant.
No mention has been made of materials for the opposed-piston two-stroke diesel engine but it is known that Achates Power, and other engine developers have looked closely at Compacted Graphite Iron (CGI) as a possible material for the crucial cylinder block which needs to be capable of coping with over 100 bhp/litre.
The EPA’s draft Technical Assessment Report released in 2016 forecast cost increases to integrate fuel saving technology, using this information and a related National Academy of Sciences report, Achates Power determined that including the Opposed-Piston Engine in the roadmap to achieve CAFE will be at least $1,000 less expensive. This again implies major implications IF the engine can be delivered as per the forecast specificaton.
Achates Power claims the Opposed-Piston Engine uses fewer parts, including the eliminating the cylinder head(s) and related components, eliminating the valve train and related components, and a reduction in the after-treatment system size and cost, among other things.
A comparison between the 2.7-litre OP Engine and a comparable V6 with supercharger shows a part reduction of more than 60 per cent, enabling an approximate 10 per cent cost reduction. The 2.7-litre could drop into a Ford F-150 pick-up truck.
Way back in 2014, a technical paper at the SAE World Congress aimed at showing how Achates Power would be able to meet CAFE 2025 regulations in a Full-Size Truck was given by Fabien Redon, vice president, technology development at Achates Power.
He then claimed: “In 2018 we will have a demonstration vehicle that proves an internal combustion engine is able to cost effectively meet the CAFE standard, does not require the adoption of costly vehicle modifications, infrastructure upgrades, or a change in how the driver operates or maintains the vehicle.”
                                   13 years in development
Achates Power has spent 13 years improving the opposed-piston engine, a historically efficient engine originally developed in the late 1800’s.  
Just to recap, the Achates Power Opposed-Piston Engine features two pistons per cylinder, working in opposite reciprocating action; the Opposed-Piston Engine does not need cylinder heads, which are a major contributor to heat losses in conventional engines.
Junkers Motoren in Germany in the 1920s pioneered opposed piston two-stroke engines. It six-cylinder, 12-piston two-stroke work culminated in the Junkers 205 used in World War 2.  The 205 developed 870 bhp or 647 kW from 16.63 litres giving a specific power of 53 bhp/litre or 39 kW/litre. The engine had a specific weight of 1.09 kW/litre. Junkers Motoren also designed 12- and 24 cylinder engines of which the latter was built. Automotive and aero engine maker  Napier Ltd of Acton, west London in the UK, developed opposed-piston engines including its famous Deltic for rail and marine use. Rootes Motors also offered an opposed-piston two-stroke diesel engine - the famous three-cylinder T3 for commercial vehicle applications.
Achates Power claims that ports in cylinder walls replace the complex poppet valves and friction-creating valve trains of conventional engines. The intake ports at one end of the cylinder and exhaust ports at the other are opened by the piston motion and enable efficient uniflow air scavenging. Napier also used uniflow scavenging.
The two-stroke, compression ignition engine has been engineered to achieve superior thermal efficiency by the virtue of its lower heat losses, higher expansion ratio, lean combustion and reduced pumping losses.
“The OP Engine confirms what the industry already knows; the technology needed to exceed these standards and deliver fuel economy and cost savings to customers is currently available, and works with existing infrastructure and fuels,” said Johnson, a former Ford Motor Company engineer, who added “Any vehicle that has an internal combustion engine today will use this engine.”
“We have a development programme underway to create the engine and look forward to coming back to the North American International Auto Show in 2018 to show our progress and we’re even more excited to drive the vehicle later that year,” he claimed.
According to, Johnson has hinted that of the nine both automotive and truck clients are in the mix. Several industry insiders contacted by said they were aware of, and intrigued by, Achates research, though there remains plenty of scepticism. “We’ve heard about plenty of breakthrough engines that ultimately never amounted to anything,” said Bob Lutz, the now-retired global product development director for General Motors.
Well, we shall see.

COMMENT. Anyone who has listened to a Youtube video of a Rootes T3 opposed-piston engine will sincerely hope that Achates Power’s engine does nor replicate that noise. Engine noise will be as paramount as power, torque, fuel economy and above all emissions. Orbital Engine’s work with two-stroke gasoline engines never achieved the results expected by Ford. 


Willy Persson said...

Motortrend is claming that at least one customer is already busy making the tooling.

"But the bigger bombshell was his announcement that of the nine automakers who have signed on as development partners, at least one of them has begun tooling up to build an opposed-piston engine in volume."

It may be close

Alan Bunting said...

An opposed-piston engine, especially a two-stroke, brings significant weight reductions compared with a conventional reciprocating engine of similar performance. That is a big plus for truck applications, where every kilo saved translates into extra payload productivity. Its lower overall dimensions can also be exploited. Assuming a horizontal configuration, it has the potential to allow a more roomy cab in European-type forward-control trucks; that in turn can allow easier cross-cab access - important for urban delivery operations.
However, the big question mark for any heavy-duty two-stroke diesel, as anyone who recalls GM, Rootes or Foden units of 50-odd years ago will testify, is noise. In Europe there are tough legislated 'drive by' decibel limits which are only just achievable by some current heavy trucks. Greater engine encapsulation is an obvious palliative, but that brings increased engine cooling challenges.
So we shouldn't perhaps be holding our breath awaiting the first opposed-piston engined vehicle to go on commercial sale.

Willy Persson said...

EM's opoc® engine does not have a cylinder head or valve train, which are the sources of much of the airborne and structure borne noise from conventional engines. In addition, opoc is symmetrical – both sides are essentially the same, and are balanced.

Fewer parts means less noise, and balanced operation means reduced vibration. All of this means more end-user comfort. The use of of CGI is also contributing to less noise. A typical CGI engine is 1-1,5 dBA lower than one in greyiron.