Last week, I had the privilege of presenting our light-duty diesel engine’s latest performance and emissions results at the SAE High Efficiency IC Engine Symposium and SAE World Congress. It’s always an honor to share our work with automotive executives, analysts, academics and engineers. And, it’s even more meaningful when those same individuals realize the potential our engine has to revolutionize passenger and commercial vehicle transportation.
The focus of the two presentations was a detailed benchmark studycomparing our opposed-piston architecture to a next-generation diesel engine equipped with the most advanced technologies. This 2.8L, four-cylinder, four-stroke engine is part of a U.S. Department of Energy (DOE)-funded project that is being developed to show the potential of meeting upcoming emissions regulations. The goal of the DOE project is to develop the engine to meet emissions levels within reach of Tier 3 or LEV III emissions regulations. By 2025, these standards will require OEMs to have a fleet average emissions level of 0.030 g/mi NMOG+NOx (non-methane organic gas+nitrogen oxide) for all light-duty vehicles below 8,500 lbs. gross vehicle weight. When comparing our engine design to the DOE-funded engine, we successfully demonstrated:
- A 30% fuel economy improvement without hybridization or other costly vehicle enhancements
- The potential to meet the fully phased-in Tier 3 standards
- This improvement—which is the average of both LA-4 (city) and highway driving cycles—is even more significant than what Achates Power has already shown for medium- and heavy-duty applications. The reason: the lower the speed and load operating modes (characteristic of light-duty applications) and the lower the engine-out NOx (required to achieve Tier 3 emissions standards), the greater the fuel efficiency advantage delivered by our opposed-piston engine.
In addition to a significant fuel economy gain, the Achates Power engine also demonstrated improvements in NOx and Soot. The NOx, particulate matter (PM) and hydrocarbon (HC) levels achieved with the Achates Power architecture meet the engine-out targets that the DOE project team estimated would allow the vehicle to attain the fully phased-in Tier 3 emissions with the appropriate aftertreatment. In the LA-4 driving cycle, the Achates Power opposed-piston engine produced NOx levels of 0.47 g/mi while the benchmark engine produced 0.82 g/mi. In the highway driving cycle, the gap between the two increased—0.34 g/mi of NOx for the Achates Power engine and 0.94 g/mi of NOx for the DOE-funded engine.
- Exceptional exhaust temperature management for catalyst light-off
As described in an earlier blog, the Achates Power opposed-piston engine features a patent-pending temperature control strategy for reaching higher exhaust temperatures during catalyst light-off than are possible with conventional, four-stroke diesel engines. This is especially important since more than 50% of the tailpipe emissions in an FTP-75 test are produced in the first 200 seconds of operation after a cold start with a conventional diesel engine.
- Excellent vibration characteristics
Noise, vibration and harshness (NVH) are critical for any application, but they are especially important to light-duty vehicles like the one studied. The magnitude of the Achates Power engine’s vibration forces—the focus of a future blog post—are significantly lower than those of a modern, four-stroke gasoline V6 engine. Since the DOE-funded four-cylinder diesel engine would not provide a useful comparison (as the balance shafts effectively cancel all forces and moments internally), we benchmarked our design against the award-winning Honda 3.5L SOHC 60° V6. While the vibration moments of our engine are not perfectly balanced, they are several orders of magnitude below Honda’s design.
- Seamless integration into existing vehicles
The Achates Power engine was evaluated for packaging into a light-duty pickup truck. Despite having different dimensions than the benchmark, there are no packaging concerns nor are vehicle modifications required. This study clearly demonstrates that the final CAFE 2025 light-truck fuel economy regulation has the potential to be met, and exceeded, by simply applying Achates Power technology. Using our opposed-piston engine, OEMs can comply with the regulations—and they can do so without additional investment in other vehicle technologies. With a game-changing solution like ours—one that meets the toughest global emissions standards, delivers significant fuel savings, fits into existing vehicles and delivers a smooth ride—OEMs have a clear path forward, and one that does not add cost compared to a conventional light-duty diesel engine. I’m sure you cannot wait to learn which companies will introduce our opposed-piston engine to their fleets first. Stay tuned to this blog and we will continue to highlight our customers’ announcements as they make them. For a short summary of the SAE World Congress paper, click here. You can also find the complete technical paper on the SAE website.
I’m extremely interested in which light duty pickup truck (1/2 ton)manufacturer is about to introduce your opposed piston diesel. That will be the truck that I purchase especially because of fuel economy and engine longevity i.e. million mile engine, no valves, push rods, lifters & cam shafts, direct gear linkage between piston crank shafts. Maybe the automobile manufacturers will wake up to the consumers needs for a solidly built vehicle that can be maintained and road worthy for 25 years while still making a secondary profit on maintenance and parts. Designed obsolescence is a bad working model to follow.
I find it amazing that engineers had the insight to recognize the advantages of opposed piston engines 70 to 100 years ago – imagine what they could have done with modern electronic control systems.
How much emphasis do you place on smooth running engines VS efficiency? More cylinders for a given displacement generally makes for a smoother running engine, but less efficient engine. This, while larger cylinder bores are more thermally efficient due to smaller surface area to volume ratio.
Now, apart from no cylinder head heat loss, your opposed piston engine design contributes significantly to smooth running: Inertial loads are cancelled and crankshaft torques are balanced for paired pistons, during the compression and expansion (power) strokes, before the ports are exposed.
However, because of the pressure differential required to scavenge the cylinders in the short time available, the piston nearest the inlet port will experience a greater gas load than its paired piston nearest the exhaust port, while the ports are open. The instantaneous torque and attendant structural loads would thus be different for the paired crank shafts, repeating every revolution.
My question is, does this imbalanced gas pressure during aspiration and exhaust contribute noticeable engine vibration? If enough cylinder pairs are used, such that torque ripple due to combustion pressure is acceptable then perhaps vibration from scavenging can be ignored? Adding cylinders with small displacement engines means smaller cylinder bores or a shorter stroke. However, this would decrease efficiency because of increased heat loss and mechanical friction. As such, the potential problem will appear with small displacement engines first, if it exists.
Now a question about efficiency: One of the major advancements in modern engines is variable valve timing, because it enables better cylinder filling at all speeds, to yield a wider usable torque band and improved efficiency.
Opposed piston 2-stroke diesel engines have fixed valve timing and duration due to port location and port length in the piston travel axis. Does the inability to vary valve timing represent a significant efficiency loss, or:
a) Is that potential loss more than offset by the power saved by not needing to drive a valve train?
b) Or, would variable valve timing have limited value anyway because the engine speed range is so narrow?
c) Or, is variable valve timing and duration largely irrelevant because forced induction is used?
How much power is consumed to drive forced induction? I am sure that is a function of air pressure and volume, as well as quantity wasted to ensure appropriate levels of exhaust scavenging. Also, while cooler inlet air is more dense and carries more oxygen for better combustion and more nitrogen for better expansion, a heat exchanger that uses lost exhaust heat may add efficiency under certain running conditions. Perhaps modulating inlet air pressure and thus volume could be made to work as a variable heat exchanger. Thus, full scavenging could be used under full load when the maximum amount of fuel is burnt, and yet allow some “exhaust gas re-circulation” inside the cylinders under lower loads that need less oxygen.
So many factors – so many questions…
Thanks for your time.
I meant to add this point my comment above:
While a large flywheel could be used to smooth out torque delivery and damp vibration, instead of using more cylinders, heavy flywheels are practical only for static power generation plants or similar applications.
For road vehicle applications, a large flywheel hurts efficiency because of carrying around extra weight and it kills acceleration, especially in first and second gear because the gearing would multiply flywheel inertia.
The video link in my previous post shows the rough machining of the crankshaft for an opposed piston engine of sorts – of my own design. I am trained as an ME, and while I dabble in engine design as a hobby, I have been involved in the development and testing of solid rocket motors, and with mass production of automotive suspension components.
That said, I would love to work on full-size engines, and happen to live in San Diego…
Now, if you had a chain drive connecting the two crankshafts, you could have a dual sided tensioner and change the phase angle between cranks by moving the tensioner; effectively altering “valve timing”…