Americans love their trucks — the bigger, the better. Pick-ups, sport utility vehicles and 18-wheelers move people and goods around our cities and across the country. In the process, we burn more fuel and emit more pollutants into the atmosphere than any other nation on earth.

I drive a Jeep Cherokee and I love its power, cargo room and 4-wheel-drive capability. Frequent and high priced stops at my local filling station, however, make my truck less than the ideal vehicle. I don’t enjoy being a hypocrite driving a symbol of America’s undying thirst for energy, meanwhile claiming to be concerned about global warming and climate change.

Is there an answer for those of us who love our trucks, yet want to be more energy efficient? In a few years, the answer could be yes.

The Environmental Protection Agency has set new emissions standards and fuel quality rules in the last several years that may put more diesel engines in pick-ups and SUVs within the decade. Common in heavy-duty trucks, diesel engines are viewed by most of the driving public as noisy, dirty nuisances. Driving behind one can be an ear-rattling, lung-choking experience, but diesel also represents one of the quickest and easiest ways to reduce petroleum consumption in passenger vehicles in the short term.

“Diesel has a role to play,” said Kathy Graham, a public relations representative with DaimlerChrysler AG. “It is a bridge to get us to future technology.”

The Good: Fuel Efficiency

Diesel engines are more fuel-efficient than gasoline engines for two reasons. In a gasoline powered engine, air and gas are mixed before entering the engine cylinder where combustion takes place. The air and gas mixture is compressed in the cylinder and then ignited by the spark plug. Compressing the mixture is what provides the power. The more the air and gas are compressed, the greater the combustion following ignition. The limitation with this design is if the mixture is too compressed, the heat and pressure that has built up can spontaneously ignite, which produces “knocking” in the engine.

In a diesel engine, fuel is added to compressed air directly in the cylinder. The air in a diesel engine can be compressed up to twice as much as air in a gasoline engine. The heat and pressure of the compressed air spontaneously ignites when the fuel is added, eliminating the need for a spark plug. Each time the piston is turned in a diesel engine, the resulting power is greater than in a gasoline engine because more energy is released. Add diesel fuel’s greater energy potential — it is more energy-rich than gasoline because it contains more carbon molecules in longer chains — with a higher combustion ratio and more power is created from less fuel.

This greater efficiency also leads to reductions in emissions of the primary greenhouse gas, carbon dioxide.

“Anytime you reduce the amount of fuel you use, you reduce the emissions,” said Jason Helgren, a University of Wisconsin mechanical engineering student who worked on the Future Truck competition during his four years in Madison. “They go hand-in-hand.”

Helgren and other students took a Ford Explorer, powered by a diesel-electric hybrid engine, and were able to meet strict California standards for ultra low emission vehicles, achieve nearly 40 miles per gallon fuel efficiency, and maintain similar performance to an unmodified Explorer. Their entry won first place at the 2002 competition. Helgren said his team chose a diesel engine because of its fuel efficiency and because more low-end torque is produced.

“It doesn’t feel like you’re losing any performance,” Helgren said.

The Bad: Emissions

Although diesel powered vehicles have reduced emissions of carbon dioxide, diesel is a major contributor of nitrogen oxide (NOX) and particulate matter (PM) emissions to the atmosphere. The EPA reports that nearly one-third of NOX emissions and one-quarter of PM emissions come from highway diesel vehicles. Emissions of NOX to the atmosphere contribute to smog and acid rain, and increased emissions of PM have been linked to a variety of respiratory problems, including lung cancer.

This paradox of increased fuel efficiency at the cost of increased pollution can be seen in the EPA’s annual mileage estimates for 2002 model year cars. Volkswagen is currently the only automaker selling diesel powered passenger cars in the U.S. The only vehicles to achieve better fuel efficiency in the EPA tests were the Honda Insight and the Toyota Prius, both gasoline-electric hybrids. The same report ranks the Volkswagen diesels as some of the worst polluting cars sold today.

According to Loren Beard, senior man ?ager for energy programs at DaimlerChrysler, hybrids may not be the right solution for light trucks and SUVs because of performance issues.

“We’re still exploring hybrids and fuel-cell technology,” Beard said. “But diesel represents the best chance for improving fuel economy in SUVs.”
Bridging the gap

The EPA recognizes the possibilities with diesel technology and has set new rules to improve diesel emissions. Jeffrey Holmstead, assistant administrator for the EPA, speaking at a recent world fuels conference, endorsed the use of diesel fuel as a way to both reduce U.S. dependency on oil and reduce emissions of carbon dioxide.

“Clean diesel is one of the most effective strategies to address fuel efficiency and energy needs,” Holmstead said.

It will be several years before the potential of “clean diesel” can be realized. The first step was the enactment of new EPA emissions rules that will begin to go into effect in 2004. Signed in December 1999, “Tier 2” standards aim to reduce “ozone-forming gases” and will mandate that all vehicles meet the same lower emissions standards. This is especially important because it requires that all cars and trucks, including previously less-regulated SUVs, will eventually have to have the same emissions of NOX and PM, no matter what type or size of engine drives the vehicle. The standards for SUVs will be phased-in starting in 2008.

The second step occurred in January 2001 when the EPA signed a final rule that will reduce the amount of sulfur in diesel fuel starting in mid 2006. Sulfur damages high-efficiency emission control devices that will be needed to reduce the emissions of NOX and PM, according to the EPA. When these regulations begin to go into effect, automakers can look to bring diesel technology to the U.S. DaimlerChrysler currently sells several American models powered by diesel engines in Europe, including the PT Cruiser, Grand Cherokee and Liberty, according to DaimlerChrysler’s Beard.

Until diesel technology can develop new methods of controlling exhaust on par with gasoline technology, the promise of greater fuel efficiency will have to come from another technology.

“We believe businesses should have flexibility,” said David Gard, an energy policy specialist with the Michigan Environmental Council. “As long as they meet emission standards, we don’t care what technology they use to propel the vehicle.”

Helgren said more research has gone into developing catalysts and after treatment devices to control harmful emissions for gasoline engines than for diesel engines. But that is beginning to change.

“Common rail injection in diesels is analogous to port fuel injection in gasoline engines,” Beard said.

These new fuel injection systems allow for greater control of the quantity and timing of fuel released to the diesel cylinder and will bring emissions levels down to current gasoline standards. Coupled with low-sulfur fuel and treatment devices, Beard said diesel powered vehicles will be able to meet Tier 2 standards.

“People think of diesel as dirty, which can be true,” Helgren said. “But it doesn’t have to be."