General Motors plans to have 335 hybrid buses like this one operating in North American cities by the end of the year. Two leading technologies used in fuel-efficient vehicles seem destined to unite. Industry experts say joining hybrid motors with diesel engines would result in the greenest mainstream vehicles ever, and the initial tests are promising.
Hybrid vehicles, which use an electric motor powered by batteries to assist a gasoline engine, have proven popular with consumers because of the lower fuel costs and reduced emissions, according to Dan Kahn, road test editor at automotive website Edmunds.com. Vehicles powered by diesel fuel – which contains up to 20 percent more energy than gasoline, according to the Diesel Technology Forum – are another fuel-efficient option, Kahn said.
For example, the 2004 Toyota Prius is rated at 60 miles per gallon by the Environmental Protection Agency, while the Volkswagen Jetta diesel is rated at 38 mpg, compared to the 24 mpg of a Jetta with a gasoline engine.
Combining the technologies is “our best shot right now at creating a truly environmentally friendly vehicle,” Kahn said. Because the technologies are complementary, their integration is “the next logical step in the chain.”
Diesel engines are good for providing the torque needed to haul heavy loads, while hybrid motors can assist with sudden acceleration by drawing electricity from the batteries, according to Kahn.
John Heywood, director of the Sloan Automotive Laboratory at MIT, said that integrating hybrid technology could enhance the fuel efficiency of a diesel engine by up to 10 miles per gallon.
“That’s about the upper limit,” he said, based on his research into hybrid-diesel engines.
Demand for both hybrid and diesel vehicles has outstripped supply during the last year. Toyota will double the number of Prius hybrids it manufactures for the U.S. market in 2005 to meet demand, and based on the success of the Civic Hybrid, Honda will begin selling the Accord Hybrid in December. Mercedes-Benz recently increased production of its E320 CDI diesel sedan for the U.S. market to meet demand.
To date, no auto manufacturers have publicly committed to producing hybrid-diesel passenger vehicles. However, hybrid-diesel buses are now transporting thousands of commuters each day, and two auto manufacturers said they are leaving the door open to migrating the technology to commercial vehicles.
Brad Beauchamp, General Motors‘ fleet account executive for government, said that school buses and large utility vehicles such as refuse trucks are likely candidates to incorporate hybrid-diesel technology.
“It will likely come from the heavy end down,” said Beauchamp, explaining that diesel vehicles that tow heavy loads and make frequent stops would benefit from hybrid motors. For consumer vehicles, Beauchamp said that hybrid-diesel technology would likely first appear in GM’s pickup trucks.
“A hybrid-diesel is not something that we (Toyota) would eliminate as a candidate” for the U.S. market, said Paul Nolasco, Toyota’s assistant manager for public affairs. Toyota manufactures a hybrid-diesel flatbed truck for sale in Japan, Nolasco said, and the company “doesn’t want to rule anything out.”
Nolasco acknowledged that it would be a challenge to integrate the two technologies into a vehicle that would be attractively priced for consumers.
“Technically we could do it for a passenger vehicle, but the trouble is to make it small enough and cost-effective enough,” he said.
While the technologies provide complementary benefits in performance, “the question is cost, because consumers have to pay a double premium,” according to Dan Benjamin, an analyst at ABI Research. Benjamin said that installing diesel engines and adding hybrid systems each increase the cost of a vehicle by a few thousand dollars, so price “will be an issue for the rest of the decade.”
Hybrid-diesel buses are currently proving the viability of the technology in a dozen metropolitan areas, including New York, Philadelphia, Seattle and Portland, Oregon. In Seattle, more than 100 hybrid diesel buses are currently in use and performing well, according to Michael Voris, supervisor of fleet procurement for King County Metro Transit.
Voris said the buses benefit urban areas that have air-quality concerns because they have much lower emissions. The buses, which first hit the streets in June, can run on battery power when stopped, which is great for reducing pollution on a Seattle route that includes a 1.2-mile tunnel, he said.
“All of the drivers I have talked to (about the hybrid diesels) have been very pleased,” Voris said. “I have not heard of any complaints about the buses not having enough power.”
The hybrid-diesel buses in Seattle are getting about 7.5 mpg, a 50 percent improvement over the buses they replaced, according to Tim Grewe, the chief engineer of rear wheel drive and hybrids at General Motors, which helped to design the buses. He said the company is shrinking the hybrid technology so that it will fit in a gasoline engine Chevy Tahoe that will go into production in 2007, but did not have a time line for combining the system with a diesel engine. Grewe said the technology could make its way into GM’s diesel trucks for sale in Europe, but did provide a time line.
Hybrid-diesel technology is “a perfect setup for a city bus,” said Edmunds.com’s Kahn. “They make frequent stops, allowing the batteries to be recharged using regenerative braking,” he said. “Because they save fuel, the bean counters are happy, and because of the lower emissions, the enviros are happy too.”
That two of the world’s largest automakers are developing technology for hybrid-diesel buses signifies that they are interested in seeing the technology succeed, according to Kahn. In addition to GM, Orion Bus Industries, which is owned by DaimlerChrysler, manufactures hybrid-diesel buses that are in service in New York.
Kahn said that the ultimate green machine would be a hybrid-diesel car running on biodiesel, which is made from plants such as soybeans.