SAE 2013 Energy Savings and Emission Reduction Forum
Technical Session Schedule
Thursday, November 7
Technical Session: Thermal Efficiencies, Including Waste Heat Recovery
(Session Code: ESER2)
Room Site N5 Room M47 10:00
A significant driver for the development of future commercial vehicles is likely to be the introduction of fuel consumption related legislation in various regions around the world. The application of a waste heat recovery system to the powertrain of such vehicles is seen as a possible step, amongst many, to help them achieve the required fuel economy.
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|Reducing Fuel Consumption and Emissions with the Opposed-Piston Engine
Global automotive manufacturers are under tremendous pressure to reduce fuel consumption and emissions without sacrificing safety, performance or cost. To do this, many are focused on enhancing the efficiency of conventional engines while others are looking to “alternative” technologies, including the opposed-piston, two-stroke (OP2S) architecture.
First manufactured in the late 1800s, the OP2S engine set records for fuel efficiency and power density that, in combination, have never been matched. In addition, these engines were known for their inherent thermal efficiency advantages over four-stroke powertrains:
• A 30 percent smaller surface area-to-volume ratio
• Leaner combustion
• Optimally phased and faster combustion at equivalent pressure rise rates
• No dedicated pumping stroke
Despite these advantages, however, the OP2S historically suffered from high NOx and soot as well as poor oil control. With the passage of the Clean Air Act and other global emissions standards, production for on-road applications was eventually halted.
Over the last nine years, Achates Power has leveraged the latest technologies and engineering methods to successfully modernize the OP2S—developing a powertrain that has demonstrated the following when compared to leading, conventional medium-duty diesel engines:
• 21 percent lower cycle average brake-specific fuel consumption
• Similar engine-out emissions levels
• Less than 0.1 percent fuel-specific oil consumption
• Reduced cost, weight and complexity
After more than 4,000 hours of dynamometer testing, the engine’s brake thermal efficiency is projected to be 48.5 percent for medium-duty applications and 51.5 percent for heavy-duty applications.
Included in this paper is a:
• Brief historical look at opposed-piston engines and their fundamental architectural advantages (thermodynamics, pumping work, transient operation and combustion)
• In-depth discussion of how the engine can deliver better efficiency than a four-stroke, without the substantial expense of waste heat recovery
• Detailed analysis of the engine’s performance and results and how these results will impact China and other countries
In addition, the paper highlights several fundamental challenges of OP2S engines as well as provides insight into how issues such as wrist pin durability and piston and cylinder thermal management have been addressed.
Laurence Fromm, Achates Power Inc.