Academic journal article Environmental Health Perspectives

Fuel for the Long Haul? Diesel in America. (Focus)

Academic journal article Environmental Health Perspectives

Fuel for the Long Haul? Diesel in America. (Focus)

Article excerpt

Brawny diesel engines have helped drive the world economy for more than a century. From an economic and operational perspective, there's little reason to expect that will change anytime soon. Diesel's big draws are power, durability, and an inherent advantage over gasoline: higher energy content and resulting fuel efficiency.

But studies beginning nearly 50 years ago and continuing today increasingly point to adverse health effects from diesel exhaust, especially the particulates that pour from the tailpipe or form later in the atmosphere. Exposure to ambient diesel particulate matter (DPM) containing such contaminants as sulfur oxides, volatile organic compounds, and aromatic hydrocarbons occurs in nearly every county in the eastern half of the United States and in many western counties, says the U.S. Environmental Protection Agency (EPA) in its National-Scale Air Toxics Assessment (NATA), released in May 2002 [see "U.S. Air Only Fair," p. A452 this issue].

To help stem the adverse health effects of diesel emissions, which some public health agencies now consider the source of at least 70% of the total toxic risk posed by air pollutants, U.S. regulators have been requiring cleaner diesel engines for several decades. As a result, the total mass of particulate emissions from a new or retrofitted engine has been sharply reduced.

But millions of older diesel engines that haven't been cleaned up are still running in the United States. And many questions remain about exactly what other tiny pollutants the new fuels and emission control methods may be creating. Researchers at several private and public facilities are scouring the data and designing new experiments, looking for answers.

While the results of their probes trickle in, sometimes with contradictory findings, new rounds of regulations for on-road diesel engines will take effect in the United States in 2002, 2004, 2007, and 2010, following recent court decisions and settlements. Other regulations, including those for off-road uses such as irrigation pumps and marine vessels, are still in the formative stages, but may play just as big a role in reducing diesel particulates as on-road engine regulations. "That's the next big bite of the apple," says Paul Billings, the American Lung Association's assistant vice president for government relations. About two-thirds of DPM comes from off-road sources, according to the EPA's 1999 National Air Quality and Emissions Trends Report.

While many people are pushing for and developing cleaner diesel engines, alternative energy sources such as hydrogen-powered fuel cells may prove to be a healthier long-term solution if they can match up in power, durability, and efficiency. Manufacturers are creeping closer to success with automobiles, light trucks, and even buses. But the diesel industry isn't about to wither away. "I don't think there will ever be a technology that replaces diesel," says Allen Schaeffer, executive director of the Diesel Technology Forum, a Frederick, Maryland-based organization that advocates for more than a dozen major diesel engine, fuel, and technology companies.

Durable Power and Particulates

The diesel engine is edging into its second century; German engineer Rudolf Diesel patented his design in 1892. Diesel experimented with many fuel types, including powdered coal, but an engine explosion helped convince him that liquid fuels might be a bit safer. Peanut oil was one of his early choices, but petroleum products soon dominated the diesel engine market.

Diesel engines are similar to gasoline engines in many ways. Both depend on internal combustion of a fuel to drive pistons, which then transmit their energy to a crankshaft and eventually to wheels, pulleys, or other power outlets. But the heat for diesel combustion comes from compression of the fuel, not ignition as in a gasoline engine. …

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