Skip to main content

Achates Power Opposed-Piston engine more fuel efficient than four-stroke diesels

Published data from extensive testing shows Achates Power engine is 20 percent more fuel efficient than a recently introduced, state-of-the-art, four-stroke diesel engine.


According to the news release dated Nov.1, 2011, Achates Power, a developer of radically improved internal combustion engines that increase fuel efficiency, reduce greenhouse gas emissions at lower cost, today announced its highest engine efficiency test results.

The results demonstrate a 20 percent improvement in fuel efficiency when compared to a recently introduced, award-winning, state-of-the-art, four-stroke diesel engine.

Recall that this is the same company that Torque News interviewed in August in Traverse City at the CAR MBS 2011 conference. Read: Achates Power addresses commercial truck mileage and emission standards

This latest milestone represents a seven percent gain since September 2010. Furthermore, Achates Power has demonstrated newly increased engine fuel efficiency results in every quarter of 2011, beginning with a 13 percent efficiency advantage presented at the Symposium on International Automotive Technology (SIAT) in January, a 15.5 percent efficiency advantage in June, and a 19 percent efficiency advantage presented at the SAE Commercial Vehicle Engineering Congress (ComVEC) in September.

Brake thermal efficiency of 45.1 percent has also been demonstrated at the best engine operating point with an overall calibration that meets the stringent U.S. EPA 2010 emissions standard.

“Achates Power’s published technical results are demonstrated and validated from dynamometer tests of running engines, and have been validated by numerous third-party, independent sources,” said David Johnson, CEO, Achates Power. “No other independent engine developer has matched this level of reported data and results. As commercial and passenger vehicle manufacturers continue to seek improved fuel economy, our data speaks for itself and sets Achates Power apart in the market as a key player in the future of clean, efficient and cost-effective vehicle transportation.”

As Confirmed by Dynamometer Testing

The Achates Power opposed-piston architecture with the two-stroke cycle has improved brake thermal efficiency resulting from a combination of the following four effects:

1) Reduced heat transfer due to the more favorable combustion chamber area/volume ratio of the opposed-piston architecture;
2) Increased ratio of specific heats due to the leaner operating conditions of the two-stroke cycle;
3) Decreased combustion duration achievable within maximum pressure rise rate limits due to the more rapid expansion of the in-cylinder volume-per-crank degree angle; and
4) Reduced pumping work as only a portion of the residual gases in the cylinder need to be scavenged at each cycle.

The thermodynamic rationale for these results is documented in the SAE International Paper 2011-01-2216, presented at SAE ComVEC on Sept. 14, 2011. The most recent 20 percent fuel efficiency improvement is from ongoing enhancements, including the latest hardware upgrades and calibration improvements and more than 2,500 hours of testing at the company’s San Diego facility.

When compared to the published performance data of one of the best medium-duty clean diesel engines in the world, the Achates Power engine demonstrates:

1) 20 percent lower cycle average brake-specific fuel consumption
2) Similar engine-out emissions levels
3) Less than 0.1 percent fuel-specific oil consumption
4) Reduced cost, weight and complexity

Disinguished Compliments

Dr. Paul Miles (Ph.D., Cornell), a Distinguished Member of the Technical Staff at Sandia National Laboratories and co-chair of SAE powertrain activities, applauds the methods Achates Power employs to determine engine performance, fuel consumption and emissions characteristics.

“Achates Power employs industry-standard instrumentation and methods to benchmark its engines at multiple engine load and speed points representative of regulatory test cycles,” he said. “The single-cylinder results are then carefully extrapolated to expected multi-cylinder results using a rigorous interface model. These are real-world numbers. The outstanding fuel economy and emissions it reports are a testimony to the effectiveness of the fundamental research and development work I have seen at its San Diego facility.”

“Through the application of rigorous science and engineering methods, Achates Power has overcome historical two-stroke engine challenges,” said Dr. David Foster (Ph.D., MIT), a professor of mechanical engineering at the University of Wisconsin-Madison, an Achates Power technical advisory board (TAB) member, and an expert in the field of internal combustion and fluid dynamics. “Achates Power uses sophisticated models and powerful computers to analytically solve the complex combustion processes of the opposed-piston, two-stroke cycle.”

More About Achates Power

Achates Power has built state-of-the-art laboratory facilities utilizing leading-edge testing, simulation and analysis tools; developed more than 1,000 patentable innovations; demonstrated the superior performance of its engines; and garnered the attention of top manufacturers around the world. The company has a highly-regarded TAB that includes National Academy of Engineering members and SAE Fellows with more than 200 years of combined experience.

Achates Power was founded in 2004 by Dr. James Lemke, a serial entrepreneur and influential physicist who has more than 100 patents. The initial came investment from the late John Walton, son of Sam Walton, the founder of Wal-Mart.

The company is now backed by Sequoia Capital Partners, RockPort Capital Partners, Madrone Capital Partners, InterWest Partners and Triangle Peak Partners.

Achates Power ( is based in San Diego where it has more than 40 in-house engineers and scientists with proven technical know-how and expertise, coupled with the industry’s leading-edge testing, simulation and analysis tools. Achates Power has also received widespread recognition from groups such as Business Week, AlwaysOn, The Guardian and Cleantech Group for its leadership in the Clean Tech sector.

About the Reporter: After 39 years in the auto industry as a design engineer, Frank Sherosky now trades stocks, futures and writes articles, books and ebooks like, "Perfecting Corporate Character," "Awaken Your Speculator Mind", and "Millennial World Order" via He may be contacted here by email: Fr[email protected] and followed in Twitter under @Authorfranks

Additional Reading:
The Battery Show 2011 Message: Many forms of intelligent energy management
Altair Engineering helps automakers develop the right shape for lighter stronger parts
CAR MBS 2011 reveals auto industry still uncertain on next IC Engine choices
2011 CAR MBS Day 2 addresses Advanced Powertrains session
2011 CAR Management Briefing Seminar looks at connected vehicles vs safety
Detroit 2.011 Autobeat Insider Conference addresses auto industry's new best practices
Scuderi Group releases results of split-cycle engine simulations
Raytheon: Cyclone Power's combustion engine game changer
Scuderi says 50-plus mpg achievable with turbocharged split-cycle air-hybrid engine