Technologies Make Diesels Less Dirty

Diesel engines have long been the technology of choice for high fuel-consuming vehicles such as buses, transport trucks and heavy-duty construction equipment. Although they are more efficient and longer lasting than gas-powered engines, diesels have a dark side when it comes to creating urban smog and particulate matter.

A typical diesel-powered vehicle emits one-and-a-half to two times as much nitrogen oxide into the air as a comparable gas vehicle. When nitrogen oxide and volatile organic compounds react in sunlight and stagnant air, they form ground-level ozone—the main component of smog. Diesels are also major contributors to urban particulate matter, which can carry carcinogens and cause respiratory health problems in people.

Canada's federal Ministers of Health and the Environment have declared particulate matter smaller than 10 microns in diameter (PM10) as toxic to human health and the environment under the Canadian Environmental Protection Act. Such tiny particles are a health risk because they can be inhaled deep into the lungs.

As part of its clean air agenda the federal government has proposed regulations to mandate low-sulphur diesel for on-road vehicles by mid-2006, and will soon propose stringent new emission regulations for on-road diesel vehicles and engines. Combined, the low-sulphur fuel and the emission regulations will reduce particulate matter emissions from new diesel vehicles by 90 per cent over current regulated levels.

Environment Canada also works closely with manufacturers, fleet operators and others across North America to develop and verify after-market technologies using chassis dynamometers and other advanced sampling and analysis equipment at its Environmental Technology Centre in Ottawa.

Recent technology development work has included cooperating with consortia in Ontario, Quebec and New York State to examine emissions from diesel-electric hybrid buses. Such hybrids have been proven to produce lower emissions of all types because they are equipped with advanced controls that allow them to recapture wasted energy, and to operate in the most fuel-efficient and least polluting mode. The Department has also been involved in emissions testing on New York City buses using ultra-low-sulphur fuel and equipped with a particulate filter system. Over the first eight months of operation, the buses showed a greater than 90-per-cent reduction in emissions of particulate matter, carbon monoxide and hydrocarbons.

Since construction equipment is a significant contributor to total nitrogen oxide emissions, many tests have also been carried out on heavy-duty non-road equipment, such as bulldozers, dump trucks and backhoes. Trials carried out in New England on equipment retrofitted with various exhaust-emission control technologies showed that they can achieve substantial in-use emission reductions.

For example, diesel oxidation catalysts—which use the temperature of the exhaust to convert carbon monoxide and hydrocarbons to carbon dioxide and water and to oxidize the organic fraction of the particles—reduced particulate matter by an average of 23 per cent. Other engines equipped with catalyzed particle filters showed reductions of up to 97 per cent for particles and 66 per cent for carbon monoxide and hydrocarbons.

Emissions tests carried out on diesel construction equipment in Houston, Texas, confirmed that vehicles using a new blend composed of diesel fuel, purified water and an additive package exhibited nitrogen oxide reductions of up to 41 per cent and particulate matter reductions of up to 69 per cent—all without requiring any changes to their existing engines. Particle filters and catalyst systems also fared well when added to in-use vehicles, cutting nitrogen oxide emissions by up to 81 per cent, total particulate matter by up to 83 per cent, and carbon monoxide emissions by up to 95 per cent.

The results of these and other tests offer strong proof that many after-market technologies may be added to in-use diesel engines to significantly reduce their production of harmful emissions. If such technologies were applied to even a small portion of the diesel vehicles in Canada and the United States today, they would help to reduce the risk of smog-related health problems.

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