Achates Power wins $9M from ARPA-E to develop gasoline compression ignition medium-duty multi-cylinder opposed-piston engine
Achates Power, the developer of a family of two-stroke compression-ignition opposed-piston engines (earlier post), has been selected by APRA-E under its OPEN 2015 solicitation (earlier post) for an award of more than $9 million to develop a multi-cylinder opposed piston engine operating with compression ignition that uses gasoline as the fuel.
The unthrottled nature of the compression ignition process provides high engine efficiency while achieving compliant exhaust emissions with conventional, low-cost aftertreatment. This—in addition to the opposed engine architecture—could increase fuel efficiency by 40-50% over the comparable spark-ignited gasoline engine, Achates said.
This engine will also be more efficient than conventional diesel engines, but without the additional cost incurred by diesel fuel injection and complex exhaust aftertreatment.
Past work has demonstrated that using gasoline in diesel engines has the potential to achieve very high efficiency while reducing the cost of diesel engines by lowering injection pressures and requiring less expensive exhaust aftertreatment. Broadly, this approach is termed Gasoline Compression Ignition (GCI). (Earlier post.)
Further, opposed piston engines (OPE) offer a number of fundamental efficiency enablers compared to four-stroke engines:
- Lower heat transfer
- Leaner combustion
- Optimally phased and faster combustion at equivalent pressure rise rate
- Lower pumping work
Achates Power, founded in 2004, currently has six announced development projects underway spanning a variety of applications of its CI opposed-piston engine architecture, from light-to-heavy duty—all diesel. (Earlier post.) As demonstrated through more than 6,000 hours of dynamometer testing, the Achates Power engine addresses proposed efficiency targets by providing a 20 to 30% in fuel economy over current advanced diesel engines. The Achates Engine is EPA 2010 and Euro VI compliant. (Earlier post.)
Although Achates’s work to date has been with diesel, its fundamental approach is suited for advanced combustion regimes using other fuels as well. In 2011, Achates CEO Dave Johnson told Green Car Congress:
If you think about Rolf Reitz from the University of Wisconsin, and his reactivity controlled compression ignition [RCCI, earlier post], basically the industry has looked at the academic studies around dual fuel and said, really cool. I understand, I get it, but man, you’re really blowing my mind in terms of actually implementing this. But if you think about that, and I think he made some pretty compelling arguments, the thing about our technology, because we have these opposed pistons, we can put multiple fuel injectors around the cylinder much easier than a conventional engine can put multiple injectors in the cylinder head. So let’s say we develop that technology...I think we can apply it more easily in our engine. So sure, if that offers 3% more or 5% more, sure, bring it on.
Fast forward a few years, and Rishi Venugopal, then a Senior Staff Engineer at Achates Power (he has subsequently left the company) noted that the OP engine synergistically offers numerous advantages for advanced combustion concepts, such as RCCI and GCI.
Achates Power’s uniflow-scavenged opposed-piston architecture is essentially a flow-through device when the port windows are open, and can be designed for partial scavenging of the cylinder—thereby retaining significant amounts of exhaust gas residuals. This “hot EGR” mixture in the cylinder is much more reactive than the trapped charge in a conventional four-stroke engine and is thus suited for the ignition and combustion of higher octane and lower reactivity fuels, such as gasoline and natural gas.
Partially scavenging the cylinder also reduces pumping losses, which tend to be significant at lower loads.
Direct injection of multiple fuels can be incorporated with relative ease due to the packaging opportunities Johnson noted before. Injection patterns can also be extensively optimized to tune performance and emissions for the fuels and applications of interest.
The Achates award was one of 41 announced by US Energy Secretary Ernest Moniz under ARPA-E’s OPEN 2015 program for a total of $125 million in awards. Open solicitations—also issued in 2009 and 2012—serve as an open call to scientists and engineers for transformational technologies across the entire scope of ARPA-E’s energy mission.
Through both open and focused solicitations, ARPA-E funds innovative technologies that display promise for both technical and commercial impact, but are too early for private-sector investment.