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On-road Vehicles and Engines

Alternative Fuel Conversion

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  • Advisory Circulars
  • Applications for Certification
  • Certificates of Conformity
  • Certificate Summary Information
  • Manufacturer Guidance Letters
  • Verify System Documentation

NOTE: You will need Adobe Acrobat Reader, available as a free download, to view some of the files on this page. See EPA's PDF page to learn more about PDF, and for a link to the free Acrobat Reader.

This page provides links to information about alternative fuel vehicle and engine conversions. Conversion systems modify vehicles and engines so that they can run on different fuels than the ones for which they were originally designed. Most alternative fuel conversions involve reconfiguring a gasoline or diesel vehicle or engine to operate on natural gas, propane, alcohols, or electricity, or on a blend of conventional and alternative fuels. Use of clean alternative fuels opens new fuel supply choices and can help consumers address concerns about fuel costs, energy security, and emissions.

Any change to the original configuration of a certified vehicle or engine, including alternative fuel conversion, is a potential violation of the Clean Air Act section 203(a)(3) prohibition against tampering (42 U.S.C. §7522 (a)(3)). The tampering prohibition is important because poorly designed modifications can increase emissions. However, EPA has established protocols through which conversion manufacturers may seek exemption from the tampering prohibition by demonstrating that emission controls in the converted vehicle or engine will continue to function properly and that pollution will not increase as a result of conversion. Please see the Final Rule and Information for Clean Alternative Fuel Conversion Manufacturers for detailed information about these protocols.

On this page you will find:


Final Rule

Proposed Rule

Information for Clean Alternative Fuel Conversion Manufacturers

EPA Notification and Data Submission Procedures Guidance Letters Other Information

Conversion Manufacturer Webinar

EPA presented a webinar on the Clean Alternative Fuel Vehicle and Engine Conversions Final Rule on April 27, 2011. Topics included an overview of the new rule, a review of the new regulations, and an explanation of how to use the new instructions document and data submission templates.

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Information for Consumers

The benefits of conversion will vary depending on your situation and your objectives. Please educate yourself thoroughly before altering your vehicle or engine to run on an alternative fuel or before buying a converted vehicle or engine. Here are some factors to be aware of if you are considering fuel conversion:

    Environmental Impact and Benefits: Some fuels have a reputation of being inherently “clean” but in today’s vehicles and engines, it is not the fuel alone but rather the sophisticated integration of engine, fueling, exhaust and evaporative emission control system designs that determine how clean a vehicle will be. Fuel conversion systems must retain a sophisticated and integrated design logic and functionality in order for emissions to remain low. Conversion to alternative fuels can be environmentally beneficial, but conversion does not necessarily reduce pollution. Manufacturers of EPA-compliant fuel conversion systems must demonstrate that the converted vehicle or engine meets the same standards as the original vehicle or engine, or, for older vehicles and engines, that emissions do not increase as a result of conversion.

    Cost and Range: The cost of running a vehicle on an alternative fuel will depend on fuel price and on how far you can travel on each unit of fuel. The amount of fuel you need will depend on the fuel’s energy density, and on whether the converted vehicle is optimized to take advantage of the alternative fuel characteristics. Operating costs may be either higher or lower for a conversion than for the original configuration. Alternative fuel prices tend to fluctuate considerably more from region to region than gasoline and diesel fuel prices. The U.S. Department of Energy maintains an up-to-date report on alternative fuel prices around the country at http://www.afdc.energy.gov/afdc/price_report.html.

    Electricity, gaseous fuels, and alcohol fuels are generally less energy dense than gasoline and diesel fuel. Depending on how much alternative fuel you can store onboard, you may not be able to travel as many miles on a “fill-up” and may need to refuel more frequently.

    Fuel Availability: As with fuel price, alternative fuel availability varies greatly from region to region. The U.S. Department of Energy maintains an alternative fueling station locator at http://www.afdc.energy.gov/afdc/fuels/stations.html.

    Warranty: Consumers considering conversion should investigate warranty implications in advance. Warranty liability for certain failed components in a converted vehicle or engine may transfer from the original equipment manufacturer to the conversion manufacturer. Generally, the conversion manufacturer maintains liability for problems that occur as a result of conversion, while the original manufacturer retains responsibility for the performance of any covered parts or systems that retain their original function following conversion and are unaffected by the conversion. Consumers should be aware that liability in a given conversion situation may not be clear, creating potential for confusion and even for dispute over which manufacturer is responsible for repair.

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EPA-Compliant Conversion Systems

Certified Clean Alternative Fuel Conversion Systems

The conversion systems on this list have been certified by EPA as meeting applicable emission standards and are exempt from the Clean Air Act tampering prohibition. Certified conversion systems may be applied to new, intermediate age, or outside useful life vehicles/engines covered by the conversion certificate. Please note that this is not a comprehensive list of certified systems.  Certified conversions that do not appear on this list may also be exempt from the tampering prohibition. EPA will add conversion systems to this list upon request of the conversion manufacturer. Please check back periodically for updates.

You can use the Document Index System to search for certified clean alternative fuel conversion systems appropriate for use on light duty vehicles and chassis-certified heavy duty vehicles. From the Document Index System home screen, select “Certificates of Conformity” as the Compliance Document Type and select “Alternative Fuel Conversions” as the Industry. Detailed search instructions are provided in EPA’s October, 2010 guidance letter for fuel converters. See the response to Question #12.

To find certified clean alternative fuel conversion systems for heavy-duty highway engines, you may search the lists of certificates that are available in the on-highway engine certification data section at https://www.epa.gov/otaq/certdata.htm. Please note that the certificate lists do not distinguish original manufacturer and clean alternative fuel conversion certificates. To find the conversion certificates, you must either look for the conversion fuel you are interested in or for the name of a specific conversion manufacturer. Please contact Fakhri Hamady for assistance.

Intermediate Age Clean Alternative Fuel Conversion Systems

Conversion systems that are compliant under the intermediate age program may be applied to intermediate age or to outside useful life vehicles/engines covered by the converter’s compliance demonstration and notification package. Please check back periodically for updates.

Outside Useful Life Clean Alternative Fuel Conversion Systems

Conversion systems that are compliant under the outside useful life program may only be applied to vehicles/engines that have exceeded their regulatory useful life and that are covered by the converter’s compliance demonstration and notification package. Please check back periodically for updates.

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Other EPA Links

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External Links

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For further information or assistance, please contact the Compliance Information Hotline at (734) 214-4343 or email: complianceinfo@epa.gov.

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