E&MU: Could Gasoline Overtake Diesel as Power of Choice?

For decades, diesel engines — prized for their durability and pulling power — have dominated broad segments of the heavy truck and equipment markets. As gasoline prices rose in the 1970s, diesels made quick inroads in light-duty markets as well.But now, just as gas prices seem poised, once again, to enhance the attractiveness of diesel technologies, strict emission standards from the Environmental Protection Agency present daunting obstacles.For the foreseeable future, the U.S. light- and medium-duty truck market likely will remain relatively unchanged, with diesel engines the power plant of choice for heavier vehicles and more strenuous workloads and gasoline engines better suited to lighter vehicles and commuter applications, said Charles Freese, executive director of diesel engineering for GM Powertrain.But that arrangement hasn’t stopped would-be competitors from looking — and planning — ahead.“It is possible that the Environmental Protection Agency’s post-2010 emission goals will severely restrict the efficiency and cost advantages currently enjoyed by today’s diesel engine,” said a release from the Southwest Research Institute (SwRI), a sprawling complex situated on 1,200 acres of farmland on the outskirts of San Antonio. “With improved combustion technology, the gasoline engine will be able to better compete in the heavy-duty market.”The institute announced in the release a cooperative research program — the HEDGE (High-Efficiency, Dilute Gasoline Engine) Consortium — aimed at developing a high-efficiency gasoline engine suitable for heavy-duty applications. And while the project is still in its early stages, the motivation is clear. “I’m not selling this as next year’s solution to the problems we’re facing,” said Charles Roberts, manager of advanced combustion and emission in SwRI’s Department of Engine Research. “We’re building a gasoline engine that’s based upon existing technologies, so it’s not some giant breakthrough. But we’re stacking [those technologies] up in new ways where we’re leveraging the advantages of each one.” For example, HEDGE technology uses cooled exhaust gas recirculation at concentrations above 30%, which make it difficult for a traditional ignition system to light the combustion mixture. So, SwRI also is working to develop a new, more efficient igniter and ignition system.“With successful ignition, the high-EGR engine can run at increased compression ratios without knocking [and can] achieve marked improvements in fuel economy, while the low-flame temperatures result in very low engine-out nitrogen oxide levels,” Roberts said. “Because the fuel-air mixture is primarily premixed, particulate matter emissions are also very low. And finally, to achieve load levels on par with today’s diesel engines, the HEDGE engine must utilize boosting technologies, such as turbochargers or superchargers. “This technology can be applied to either lean-burn or stoichiometric engines,” Roberts said, “and the engine-out NOx from the demonstration engines has been low enough that, in either case, the expected aftertreatment requirements are limited to proven technologies like oxidation catalysts or three-way catalysts.”He describes his work as strictly research and development. There is no guarantee that HEDGE technology will ever reach production. The best measure of success to date may be the interest his work has generated from industry heavyweights. Three years into the project, the HEDGE Consortium counts among its membership Cummins, DaimlerChrysler, Ford, Honda, Nissan, Renault, Volvo and Volkswagen.“We have to wait and see how successful the gasoline engine research is at achieving the torque, power and fuel efficiency expected from light- and medium-duty applications,” Roberts said. “We’ve been able to show in the laboratory that we can run at diesel fuel economies [and] at loads that are close enough to diesel full-load that the diesel companies are watching.”But diesel still has tricks up its sleeve, and industry insiders aren’t ready to concede — either to the competition or to the EPA.“There’s no question that 2010 represents a significant emissions milestone for the diesel industry,” said Allen Schaeffer, executive director of the Diesel Technology Forum, Frederick, Md.The forum comprises representatives of leading vehicle and engine manufacturers, key component suppliers, petroleum refineries and emissions control device manufacturers. “Those engines will be 98% lower in emissions — both for NOx and particulate matter — than are the ones sold today,” Schaeffer said.“However, even with these changes, diesel engines will still retain the unique characteristics that make them the engine of choice in the light- and medium-duty truck category — power to do work, reliability, durability, resale value and economical operation. . . . So, while emissions changes will make diesel engines more expensive, I don’t think that will result in a shift away to another fuel type or technology,” Schaeffer said.Jeff Weikert, executive engineer of midrange engineering for Cummins Inc., agreed.“Achieving the 2010 standard will take effort, but it isn’t impossible,” Weikert said. “The advances in combustion modeling and the learning that have come from that work show real insight into how to reduce the production of emissions in the combustion chamber. “The continued advancement and learning in aftertreatment systems show real promise,” he said. “These solutions will be developed, and there will be competitive products in 2010. Diesel will continue to provide the best torque-per-liter of power, cost-effectively and with lower operating costs.”For example, GM Powertrain’s Freese cited the new light-duty diesel engine that GM announced last August. The engine — a dual-overhead cam, four-valve V-8 that, in demonstration, ran at 330 horsepower and 520 pound-feet of torque — can fit in the same space as a small-block V-8 gasoline engine. It uses a NOx aftertreatment system with a diesel particulate filter to meet the stringent 2010 emission standards and achieve compliance in all 50 states.But Freese acknowledged the challenges that the 2010 standards will impose on the industry and called attention to the more daunting challenges facing the light- and medium-duty markets.“In 2010, for heavy-duty vehicles, you’re looking at a big, big reduction in NOx, but that’s measured on an engine dynamometer, which means that, although those reductions are very aggressive, you can go in and certify an engine once and then put it into any vehicle you want,” Freese said. “That’s a different standard than light-duty, where emissions will be measured at the tailpipe.”Thus, an engine that meets emission standards in a light vehicle or under light loads might fail to meet standards in a heavier vehicle or in a more severe work environment. To further complicate the situation, California’s stringent LEV (low-emission vehicle) II standards — which already have been adopted by a handful of other states — are even tougher than the EPA’s and prohibit sales of nonconforming vehicles, Freese said. By ignoring the LEV II standards, a manufacturer could effectively limit its market.But gasoline engines impose their own challenges on the light- and medium-duty market.“[The gasoline engine] has the capability to meet all of these emissions standards inherent in the design, and catalyst technology is very well developed to reduce emissions at the tailpipe,” Freese said. “The challenge on the gasoline engine is what you can do that will further increase its fuel efficiency while still being able to match the emissions levels that are required.“On the reciprocal side is the diesel engine. It is inherently fuel-efficient, so the trick is to put technologies into it that bring down the emissions without sacrificing the fuel economy. And that’s really what it’s all about.”As time passes, many of the technologies actually start to overlap, Freese said. There is growing demand for turbochargers on gasoline engines — engines that are also starting to use direct injection, sometimes borrowing directly from diesel technology. Even combustion strategies seem destined to align, as both gasoline and diesel technologies move toward homogeneous charge compression ignition, a hybrid of the traditional spark ignition typical in gasoline engines and the compression ignition process found in diesels.“I guess, in the very long term, you could even say that these engines might converge, but to know the exact timing of that, you’d have to probably have a larger and clearer crystal ball than I’ve got,” Freese said.The writer is a freelance journalist in Kensington, Md. This story appeared in the March/April 2007 issue of Equipment & Maintenance Update, a supplement to the March 19 print edition of Transport Topics. 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