Scientific Studies Show the Clean-Air and Safety Benefits of Diesel Engine Technology

Guide to Scientific Research on Diesel and Natural Gas Engines

Scientific research confirms that advanced, low-emitting engine technology and ultra-low-sulfur fuel make diesel trucks and buses as clean as or cleaner than natural gas. Research of relative fire risk also shows that diesel is safer than natural gas. Use this brief guide to research on diesel emissions and fire safety to learn more about the advantages of diesel.

Independent Research Shows That Natural Gas Buses Have Higher Emission Levels¹

Exhaust emissions from natural gas school buses contain higher levels of air pollutants and substances identified by the California Air Resources Board as “toxic air contaminants” than those from school buses powered by advanced-technology, low-emitting diesel engines.

That is the chief finding by an independent research laboratory presented recently to a Society of Automotive Engineers conference. The research compares emissions from a popular model natural gas bus with emissions from diesel school buses.

California Government Research Shows That Natural Gas Exhaust Contains High Levels of Pollutants²

California’s Air Resources Board conducted two studies in 2001-02 comparing emissions from diesel and natural gas transit buses. In 8 of 11 categories tested, a low-emitting diesel bus powered by ultra-low-sulfur fuel and equipped with a particulate trap produced lower levels of pollutants than a similar transit bus powered by natural gas.

The natural gas bus discharged more particulate mass, hydrocarbons, carbon monoxide, and mutagenic material than the low-emitting diesel bus. These findings were confirmed in a parallel study conducted by a broad group of government, academic and industry research partners (Department of Energy, National Renewal Energy Laboratory, California Air Resources Board, South Coast Air Quality Management District, West Virginia University, UC Riverside, Desert Research Institute, BP, Engelhard and Johnson-Matthey).

Test numbers show that adding oxidation devices to natural gas buses and running them on a special, not-yet-available fuel does help reduce some emissions. Other emissions, however, are still higher than those from diesel buses equipped with particulate traps and running on low-sulfur diesel fuel that is already being sold in California and is mandated for national availability by a new federal rule.