Research Projects

Project at a Glance

Project Status: complete

Title: Potential emissions and air quality effects of alternative fuels

Principal Investigator / Author(s): Austin, Thomas C

Contractor: Sierra Research, Inc.

Contract Number: SR89-03-04


Research Program Area: Atmospheric Processes


Abstract:

An analysis of available information on the emission characteristics and development status of alternatively-fueled vehicles indicates that:

* Methanol offers no clear advantage over gasoline in reducing vehicle emission levels. Projections of significant air quality benefits for methanol have been based on overly optimistic assumptions regarding the ability to control reactive organic emissions and oxides of nitrogen (NOx) emission from methanol combustion. Gasoline vehicles have already been certified at the emission levels projected for the use of "advanced technology" under a recent ARB-sponsored study by Carnegie Mellon University (CMU). In contrast, no methanol vehicle has ever demonstrated the level of emissions control assumed in the CMU study. Continued refinement of control technology should allow gasoline to retain its current advantage.
* The emission characteristics of natural gas compare favorably to gasoline, but the relatively low energy density and refueling time requirements of natural gas are a disadvantage in many light duty vehicle applications. Natural gas appears to be a more promissing alternative for transit buses and other vehicle fleets that use centralized fueling facilities (e.g., garbage trucks, certain delivery trucks, etc.).
* Liquified petroleum gas (LPG) provides some of the air quality advantages of natural gas with significantly higher energy density. However, the potential emission control benefits of LPG over gasoline are less than with natural gas.
* Methanol-fueled engines have lower particulate emissions than Diesel-fueled engines without traps, and some methanol-fueled engines also have lower NOx. However, catalytic control appears necessary to prevent increased emissions of formaldehyde compared to Diesel engines. Gasoline and compressed natural gas have at least as much potential to minimize emissions from heavy-duty vehicles. In addition, further development of particulate trap technology may allow Diesel-fueled vehicles to achieve particulate emissions comparable to methanol-fueled vehicles.

It has long been recognized that the organic compound emissions in the exhaust of methanol-fueled vehicles are less reactive than the organic emissions in the exhaust of gasoline-fueled vehicles. As a result, a number of air quality modeling studies have concluded that ozone.


 

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