## Ecomotors Says Its OPOC Engine Could Deliver About 45% Greater Fuel Efficiency in a Class 8 Truck And With Tier 2 Bin 5 Emissions

##### 10 March 2010
 The EM100 base module showcased at the ARPA-E summit. Click to enlarge.

EcoMotors International, a Khosla-funded startup working to commercialize an opoc (opposed-piston, opposed-cylinder) engine family (earlier post), showcased its EM100 (100mm cylinder bore) base module implementation at the ARPA-E Energy Innovation Summit in Washington DC last week.

With a two-module application configured at the appropriate power level (to deliver a combined 480 hp), the opoc unit could deliver about 45% better fuel efficiency compared to a conventional heavy-duty diesel engine in a Class 8 truck, the company suggests, while delivering emissions at the US Tier 2 Bin 5 level (the 50-state level in the US for diesel light duty vehicles).

The opoc engine operates on the 2-cycle principle, generating one power stroke per crank revolution per cylinder. Each module consists of two opposing cylinders per module, with a crankshaft between them; each cylinder has two pistons moving in opposite directions. This design configuration eliminates the cylinder-head and valvetrain components of conventional engines, offering a more efficient, compact and simple core engine structure, the company says. The power density is more than 1 hp per pound of engine weight. The fully balanced opoc engine can be run on any liquid fuel.

 Cutaway diagram of the opoc engine. Click to enlarge.

The EM100 comes in different power configurations, said Jonathan Hurden, Chief Engineer - Engine programs, and with different emissions outcomes. The Ecomotors website describes a military spec version of the EM100 (no emissions requirement) with 325 hp (242 kW) of power and 664 lb-ft (900 N·m) of torque. The basic commercial power version of the engine offers 300 hp (223 kW) of power and 550 lb-ft (746 N·m) of torque, with a fuel economy improvement of 15% compared to a conventional engine, Hurden said. (These figures are all for diesel.)

Opoc modules can be combined through the use of an electrically controlled clutch, with select modules deactivated at different points in the operating cycle to optimize fuel consumption (cylinder deactivation, but on a module basis). The clutch assembly is housed between two engine modules, and is engaged when both modules are running to deliver power from both modules through the drivetrain.

When the power of the second module is not needed, the clutch is disengaged, allowing the second engine to stop completely. This not only improves fuel economy, it also eliminates parasitic power losses in the primary module. A dual module opoc offers a 45% improvement in fuel efficiency, according to EcoMotors. A dual module Class 8 truck would use two 240 hp (179 kW) modules (“because we don’t need more than 480 hp total”, Hurden said) and meet Tier 2 Bin 5 emissions requirements on diesel.

With no valvetrain, the opoc engine has 40% less friction than conventional valve-controlled engines. The engine design features 90% cylinder scavenging, a high-pressure fuel injection system, and an electrically controlled turbocharger, allowing it to run higher levels of EGR. Four features allow the opoc engine to achieve that high 90% scavenging:

• Asymmetric port timing
• Circumferential ports
• Uni-flow air charging
• Electronically-controlled turbocharging
 The turbocharger unit with electric motor. Click to enlarge.

The electrically controlled turbocharger (ECT) incorporates an electric motor into the turbo assembly. In essence, it provides a supercharger, driven by the electric motor, as an adjunct to the exhaust-driven turbocharger. Boost pressure can be created by the electric motor, the turbocharger, or both.

The ECT effectively eliminates turbo lag because the electric motor provides much faster turbine response, and also provides boost when there is low energy from the exhaust flow. The motor is actuated by an electronic controller, which can be integrated with the engine control unit. When it is being spun by the turbocharger, the electric motor acts as generator, producing electricity.

While some two-stroke engines suffer from high oil consumption, the opoc engine’s oil consumption is 0.2 grams per kilowatt-hour, as compared to 0.4 grams per kilowatt-hour of a standard four-stroke engine, according to Ecomotors. Because the opoc is a direct gas exchange engine, the only components exposed to combustion gases are the piston top, rings and cylinder wall—less than in a conventional four-stroke engine, where lubricated components such as valve stems are exposed.

Ecomotors is also developing a smaller version of the opoc, the EM65 (65mm bore diameter), with 75 hp per module, and targeted for light duty vehicle gasoline and flex-fuel applications.

This is a nice design, the linkage is a bit complex but the opposing mass keeps vibration down. I like the electric turbo and it they could add a hybrid drive this could really add some mileage to big rigs which use a LOT of fuel.

Could this be scaled down for flex fuel PHEVs? A (2x) 15 to 25 hp modules should be enough for extended range PHEVs.

It could be a nice one Harvey, it seems to produce good power at low RPMs and is efficient. Many different engine designs will reemerge from the drawing boards if EREVs become popular.

Such a design coupled with super-critic fuel injection as presented here 2 days ago could delay the EV car for quite a while. Sure it would make an attractive ICE for range extender.

That turbo is brilliant! It could be easily adapted to any diesel engine to improve performance and efficiency. The E-motor could be programed to prevent over-speed by generating power. That might allow a single model to fit a wider range of engine sizes.

-ALl...do you really believe that the truck engine manufacturers, whose customer's profitability is dependent on the fuel efficiency of thier rigs, are not providing the most efficient engines that they can at the allowable emissions level? Your typical Class 8 diesel engine offers >42% peak thermal efficiency and 40% over a relative wide portion of their operating range. It is a fiercely competitive business and they spend 100's of Millions of dollars in R&D per company per year to try to squeeze out single digit % improvements. The DOE has funded multi-million dollar contracts with the big engine manufacturers for more than a decade in hopes they they can demonstrate a 50% BTE engine without compromising emissions with little regard to cost but without success. a 45% increase in BTE is so far from realistic it is laughable. Moreover, ecomotors is making claims that can't be compared. Heavy Duty engines have a completely different emission cycle to meet than Tier II Bin 5 which is a Light Duty (passenger vehicle) spec because the two applications have very different duty cycles. It is not meaningful to say that an engine will improve efficiency relative to one target, and meet the emissions criteria of another target.
-As for the electric turbocharger, they are only about 20 years late to the party. Garrett and many others demonstrated this technology decades ago but it is neither a cost effective nor durabilty technology. Additionally, a HD diesel turbocharger compressor takes 10's of HP to drive it. You need massive quantities of stored electrical power and sophisticated power electronics to power it.

Just like Transonic Combustion, Khosla is making outrageous claims to try to get his money back after making foolish investments after real estate fell off a cliff.

What I do concede to Ecomotors is that they do have a good solution for applicaitons that want to run diesel fuel but with better power to weight ratio than can be expected from traditional diesel engines. Military makes a lot of sense to help them move towards a common fuel accross all applications, not to mention one which less prone to exploding at the hint of a flame. The original goal was to replace small gas turbines in UAV's but apparently it didn't meet the power/weight targets. It is also good for fixed speed applications where fixed port timing won't penalize volumetric efficiency and emissions. This could mean its a good option for a PHEV/EREV, but it will be hard to compete with a conventional gasoline ICE on a cost/kw basis which is the true figure of merit for this application. The cost of the batteries and power electronics leave very little money for OE's to spend buying fancy engines. an OPOC engine could be very cost effective, but the lack of significant production volume will place a heavy capital burden on anyone who tools it up.

UA

UA:

Small flex fuel gensets with this type of ICE could be mass produced at much lower cost (competitive with or cheaper than current GM Volt over-powered ICE unit) in China, India, Brazil, Mexico, Thailand, Turkey and many Eastern European countries,

A much lighter, more efficient genset could make extended range PHEVs cheaper and more efficient yet. That may be what the world needs for the next 1 to 2 decades or until such time as longer range affordable BEVs are mass produced.

This is quite a promising concept, however, I agree with UA that the claimed improvement of 45% over existing HD turbodiesels is quite exaggerated.

The improvement from lower combustion heat loss amounts to about 10-12% gain in efficiency (5% points gain out of 100%-point energy content of fuel). Then, there is also lower friction losses from the lack of valve train and the two-cycle operation that would amount to another 3-5% gain in efficiency (1.5-2.5 points gain out of 100 points energy content of fuel). Adding the two up, one will get ~15-17% gain in efficiency, or ~7-8 points gain. So, a HD diesel capable of 45% points/100% peak thermal efficiency would gain an additional 7 points, with a resultant thermal efficiency of 52-53%. A very impressive number, indeed!

Part-load efficiency gain would be even better, due to the lower friction losses that looms higher when the cylinder BMEP is reduced. I would predict an efficiency gain of 20% or higher for part-load operations.

The electric-boosted turbocharger only needs to be electrified during rapid acceleration from low loads. At other times, the exhaust gas will provide the energy. The saving from the cost of the valve train and fewer injectors (only one injector per pair of pistons) can justify the additional expense of an electric-boosted turbocharger.

Emission-wise, I see no disadvantage of this OPOC concept. The higher power-to-weight and displacement-to-weight and displacement-to-size ratio of the engine will allow low-temperature combustion regimes without resorting to riculously-high boost pressures, thus will allow high EGR and thus PCCI combustion with resultant much lower post-combustion NOx and HC and PM. Post-combustion exhaust treatment will be easier and less expensive to meet regulations.

A good look at the piston crown design shows a symmetrical layout which means it uses two injectors per cylinder.

I do agree that the claims are a little exaggerated as it is with most so called new engine developments. It does have its advantages in high power density and small size, so it definitely would have some well matched applications to use those advantages.

HarvyD
It is not clear what point you are using to justify your statement. Are you assuming the design is inherently lower cost or that production in low cost regions would drive the cost down? Most OE's are already sourcing and assembling in low cost regions, so this is not an advantage for OPOC. Either way, it is not exclusive to a particular engine architecture. Assuming it is cheaper, I agree that it would help make a PHEV more affordable, but only marginally. you have to put it all into perspective. Batteries cost ~$1000/kW-h. With 3 miles/kw-h, you need$10,000 in batteries just to go 30 miles with current SOC capability. At $50/kw and a 100 kw motor you have$500 in power electronics and only marginal vehicle performance. Add in the cost of the motor and generator and things only get worse. Considering that a simple gasoline ICE costs ~$500 in volume production, saving ~$100 or so due to a lack of valvetrain doesn't make much of a difference in the affordability of a PHEV. Unfortunately, without an order of magnitude improvement in battery technology, any vehilce that uses substantial electrical energy storage will struggle to compete for market share due to its inability to compete on a cost basis.

Roger
I think you are underestimating the cost of electrifying the turbocharger. There are 2 aspects: -A) the cost of the electric machine and integration. High speed, high temperature, high efficiency machines are highly engineered pieces and not available in volume production. You are looking at a ~3X increase in the cost of the turbocharger itself.
B)The cost of the rest of the system to support the electric motor. As stated before, even when considering this will only work during transients and relatively low engine power conditions, it still consumes a significant amount of power, on the order of ~10 kw to give a meaningful impact, at least on a CV engine of this power rating. This requires batteries with this kind of power draw capability and a means to charge it back up. It effectively requires to have a hybrid to support it which is prohibitive if you don't have this for other reasons. This poses an interesting delimma. If you have a hybrid, what is a better way to handle vehicle transients, by using the motor or by suppliementing the turbocharger? At any rate, because eletrical turbochargers are not new, it seems that at least until now, the engine manufacturers have not found the benefit worth the additional cost. Perhaps this will change, but I would not jumpt to conclusions based on Ecomotor's press releases.

@UA,
The electric motor in the turbocharger can double as a generator as well, in order to harness excess power from the turbocharger at higher power setting, thereby acting as an electric turbo-compounder, and perhaps even reduce the need for or eliminate altogether a turbo waste gate if the electric components are robust enough to handle the excess exhaust energy. In this case, I would recommend another electric motor coupled to the drive train or to the engine, or a more robust electric starter/motor/generator to put the excess exhaust energy back to the wheels when the battery is fully charged.

With an electric turbo-boost/turbo-compounder system and braking energy recuperator all integrated, higher peak thermal efficiency in the order of 56%-58%, and overall efficiency in city driving can even be further improved. This will make the extra cost of the electric-boosted turbocharger even more palatable.

This isn't a new design. Try Googling "Doxford marine opposed piston" for the marine engine, or "Commer TS3 Rootes Lister" for the truck version.

How do I know?

I drove a Commer TS3 (on its last legs, then) water tanker as a student in the late 60's, and well remember the opposed-piston oddities of that model: rattly crank-piston rockers (the motion was taken from piston to crank by rockers, with a total of five bearing surfaces - plenty of opportunity for slap and knock), an engine note that can only be described as a mosquito on speed, and the difficulties of starting a worn engine which relied on a worn supoercharger for cylinder scavenging.

Old wine, new bottle.

UA:

What I was trying to point out is that locally produced PHEVs will not be affordable or competitive unless many major components and sub-assemblies are outsourced; that would have to include batteries and chargers, gensets, e-motors, wheels and tires, brakes, control systems, HVAC systems, power steering, radio-GPS-Com systems, LED lights assemblies, seats, steering wheels, doors with heat resistant window glass installed, hoods, truck covers, frames, wiring harnesses, etc etc.

The local employees could restrict their interventions to automated final assembly works and paint.

NB: Batteries may be produced locally if half a dozen very large fully automated mass production plants are built near (the PHEV/BEV) final assembly plants.

ANOTHER new engine with unrealistic promises for efficiency, low cost and low weight.

The linkage (which must carry all the power) is a bit complex.

The electric turbo adds more complexity - and a genset does not need electrical turbo assist for acceleration - they are constant speed.

Promises promises.

A small version of this engine from a differently named company with the same people was already tested as a range extender and portable generator that I mentioned for years in prior posts. Because diesel is easier to produce from crude oil and because it does not evaporate and degrade as fast as gasoline, diesel should become the fuel of the future for moving vehicles when the electric batteries have run low after thirty or so miles for passenger vehicles. The particulate filters and catalytic converters now available will clean up the exhaust sufficiently. Nothing can be done perfectly and the exhaust will still contain CO2.

Very small versions of this engine should be used in range extenders in the TH!NK and the TESLA.

An air bearing electric turbosupercharger for fuel cells was built by MITI, and should be considered for this machine. Both the flywheel integrated starter alternator and the electric turbo supercharger should be converted to the lighter weight more reliable switched reluctance motor technology.

A version of this machine should also be built that does not require electronics. The balanced smooth motion allows higher speeds and higher energy density for range extenders which are rarely used.

The limited number of pistons in this engine reduces the friction and a combined flywheel alternator starter can put excess energy from the turbocharger generator into the shaft or electric energy can be borrowed from the flywheel to quickly ramp up turbocharging.

Two cycle large diesel engines with no valves but port valving with opposed pistons are still used in various naval vessels in the form of the DELTAC engine. They were also used in a number of diesel locomotives in the UK. If they had been redesigned for reliability in exchange for a little extra weight they would be still used in locomotives. A prototype version that incorporated a small jet engine instead of a turbo charger in anticipation of the OPOC put out more power than the cranks of the prototype could withstand. Such a combination of jet and piston engine can give the best power and efficiency of any engine of the same weight.

Now all that remains is to increase the efficiency with a version of the Kitson-Still locomotive diesel engine. Imagine a diesel truck that has its engine running only when it is traveling more than five miles an hour and has no gears to shift. Actually since roads are steeper than railroads, there might be a need for gears.

The Junkers Jumo airplane engine also had opposed pistons with cylinder port valving as did many diesel powered US submarines and a few locomotives with simlar engines from the Fairbanks-Morse company.

One of the most interesting valve ported engines was the free piston Pescara engine that compressed and heated gas with a pair of cylinder ported diesel pistons but drove the driveshaft with a turbine on the compressed air. It also had piston supercharging before turbo superchargers had been perfected. Because of the very high pressure ratio available, this engine could use very cheap fuel oil long before standard diesels were built to use it. The scavaging of oposed piston engines is very efficient and can also be used for cooling as it was in the Pescara engine. ..HG..

I should have said Napier-Deltic. ..HG..

@ Roger
What you said is sound in principal, and without crunching the math it seems like a good solution, unfortunately in practice it doesn't work out to be very effective, at least when you have to consider emissions compliance, automotive cost levels and consumer durability expectations. If you have access to GT Power, try setting up a model with turbocompounding and see what happens to PMEP when you try to extract power from the exhaust using a turbine. If you don't have GT Power, just set up the equations in a spreadsheet to simulate a turbocharged engine. What you'll see is that pumping work penalty imposed on the engine by a compounding turbine is very similar to the power extracted by that turbine, resulting in a relatively small net gain in power. The relative impact is fairly sensitive to operating load, with the benefit increasing as load is increased, but at part load operation, it tends to be a net deficit. Now consider the relative inefficiency of eletrical power transmission (80-85% after generation, rectification, conditioning, consumption) and it becomes rather difficult to see much benefit. With a modern diesel ICE, with +40% BTE and relatively low emissions, you're looking at 3-5% improvement at the best operating point. Multiple that by 0.9 if you want to do it electrically. Consider that most of your fuel is consumed <60% load in a commercial vehicle and the impact to cycle average fuel economy is marginal. At the end of the day, the payback on the technology is much closer to 5yrs than the 2yrs that consumers use as the measure for financial sensibility. This is why you don't see many turbocomounded engines in the market today even though the technology, much like OPOC dates back to WWII.

@ Roger
What you said is sound in principal, and without crunching the math it seems like a good solution, unfortunately in practice it doesn't work out to be very effective, at least when you have to consider emissions compliance, automotive cost levels and consumer durability expectations. If you have access to GT Power, try setting up a model with turbocompounding and see what happens to PMEP when you try to extract power from the exhaust using a turbine. If you don't have GT Power, just set up the equations in a spreadsheet to simulate a turbocharged engine. What you'll see is that pumping work penalty imposed on the engine by a compounding turbine is very similar to the power extracted by that turbine, resulting in a relatively small net gain in power. The relative impact is fairly sensitive to operating load, with the benefit increasing as load is increased, but at part load operation, it tends to be a net deficit. Now consider the relative inefficiency of eletrical power transmission (80-85% after generation, rectification, conditioning, consumption) and it becomes rather difficult to see much benefit. With a modern diesel ICE, with +40% BTE and relatively low emissions, you're looking at 3-5% improvement at the best operating point. Multiple that by 0.9 if you want to do it electrically. Consider that most of your fuel is consumed <60% load in a commercial vehicle and the impact to cycle average fuel economy is marginal. At the end of the day, the payback on the technology is much closer to 5yrs than the 2yrs that consumers use as the measure for financial sensibility. This is why you don't see many turbocomounded engines in the market today even though the technology, much like OPOC dates back to WWII.

@ Harvey
All of those components you mentioned are already being manufactured in emerging regions (low cost). If you live in the Western World, just look around. nobody manufactures here anymore, except for high tech, but even that is pretty much been outsourced. In a global market you simply can't compete if you aren't using the most cost effective means to produce your product/service. Outsourcing is not something of the future in the Auto industry. it is the current reality and the benefits in brings in low cost vehicles is already factored in to both conventional and PHEV's for the most part. When outsourcing isn't used, heavy automation is to take out the cost of high labor rates. Capitol costs for tools are relatively insensitive to location for a given manufacturing process and quality level which is how Japan and Germany continue to manufacture. The main difference then between labor intensive manufacturing in low cost regions and highly automated high cost region manufacturing is the relative quality and the overhead for the machines. At any rate, I'm afraid I can't agree with your claim that PHEV's will be cost competitive when the components and labor are outsourced. That happened +10 yrs ago.

@ Henry Gibson

You are right that this isn't a groundbraking technology by any stretch, either by using opposed pistons or piston porting, but be careful to take information out of context and apply it to another time or application. Fuel cells have very different needs than ICE's. What made sense for a bomber in the 40s may not apply to a ground vehicle today. The same can also be said for marine and rail, civilian and military, or yesterday vs today. There is no universally superior engine design. Each has their positive and negative attributes and the industry ultimately finds what makes the most sense for their customers for that time. If someone comes along with a truly better mousetrap and the manufacturer can make money selling it, you can be certain that it will be for sale.

@UA,

--First, when you inputing the spreadsheet, please keep in mind that this OPOC engine loses less heat to the combustion chamber wall (no head) in the expansion process in comparison to a typical diesel engine, and hence more energy will be available in the exhaust when generating the same BMEP.

--Second, please be reminded that this OPOC engine is modular in nature, with at least 2 modules for HD version, in which only 1 module need to run during cruise at lower power setting, but optimal load so as to give sufficient energy to the exhaust compounding turbine. This is totally different and more advantageous than a typical 6-cylinder Big-rig engine in which the whole thing must run, but at lower load and lower BMEP during cruise for all the cylinders.

--Third, I was not complete in my description of the exhaust layout. There will need to be a separate turbine use for powering the motor/generator that is separate from the turbine powering the centrifugal compressor for optimal functioning in order to do away with the turbine waste gate. But, one motor/generator can do dual function.

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