I was happy to be invited to speak at the Emissions 2013 conference this week. Not only did it give me a chance to visit Ann Arbor, where I received my undergraduate education, but I was able to hear from some of the leading experts on the topic of vehicle emissions mitigation.
In addition to papers on the reduction of conventional emissions—oxides of nitrogen (NOx), particulate matter (PM), unburned hydrocarbons (HC) and carbon monoxide (CO)—the conference featured several papers on vehicle carbon capture.
This illustrates a dilemma regulators face to achieve clean air. Mandates to reduce vehicle emissions often increase operating and capital costs. As emissions standards get tougher, fuel economy usually decreases (due to calibration adjustments made to eliminate emission formation and the increased work required for the air handling system) and costs increase. If emissions mandates push operating and capital costs too high, too quickly, users hang on to their older, grandfathered, more-polluting equipment.
Regulators in different countries have decided to balance the tradeoff between fuel efficiency and emissions differently. The U.S. has the toughest emissions standards in the world, which has improved air quality to a remarkable degree. Europe has put more emphasis on carbon dioxide (CO2) reduction than the U.S., so vehicles there have slightly less stringent emissions standards. Developing countries, in general, are more sensitive to the operating and capital costs of equipment, and air quality often suffers (but note that China just announced an accelerated timetable for adopting very stringent emissions standards).
The opposed-piston, two-stroke (OP2S) engine offers a way out of this dilemma. We’ve previously described the fuel economy benefits of this architecture, but there are also significant advantages with regard to emissions.
First, as described in the technical paper, Thermodynamic Benefits of Opposed-Piston Two-Stroke Engines, the OP2S engine features lean combustion without excessive pumping work. Moreover, our design of the combustion system—with opposed injectors spraying across the cylinder bore—provides long λ=1 isosurfaces. The design of the piston crowns converts swirl into tumble at the moment of autoignition, providing excellent mixing and keeping combustion away from the combustion chamber surfaces. In sum, a lot of air and excellent mixing minimizes PM formation.
Second, the OP2S engine has advantages in reduced NOx formation, as described by Dr. Gerhard Regner in a previous blog post.
Finally, we’ve developed a technique for rapid catalyst light off after a cold start. This gets the catalyst to an effective operating temperature quickly.
The measured performance and emissions data show low NOx, very low PM and very low brake-specific fuel consumption (BSFC) across the speed-load map. Moreover, since the OP2S engine eliminates the cylinder head (one of the most expensive parts of a conventional engine) and the valve train (which contributes the most to the part count of the engine), the OP2S engine has a lower manufacturing cost than a conventional engine in similar volumes.
Lower emissions, lower fuel consumption and lower manufacturing costs—that is a formula that regulators and customers around the globe can appreciate.

Clean Diesel Engine Emissions