The breadth and coverage of analytical expertise in the IEA Technology Collaboration Programmes (TCPs) are unique assets that underpin IEA efforts to support innovation for energy security, economic growth and environmental protection. The 39 TCPs operating today involve about 6 000 experts from government, industry and research organisations in more than 50 countries1.

Advanced Motor Fuels (AMF TCP)


Analysing heavy duty vehicle efficiencies and emissions

The primary goal of the AMF TCP is to facilitate the market introduction of advanced motor fuels and related vehicle technologies. This TCP provides an effective platform for fuel analyses and reporting of GHG emissions tested and measured in engines. 

Emissions from heavy duty vehicle engines operated with diesel or diesel in combination with methane.*

Reducing the environmental impact of fossil fuels usage for transport, the largest contributor to CO2 emissions, is a policy priority for a growing number of countries worldwide. Alternative motor fuels can provide an effective solution to improve the fuel economy.

Alternates include substituting diesel fuel with a synthetic fuel or hydro-treated vegetable oils, or by modifying heavy duty vehicle (HDV) engines to operate on other fuels such as natural gas or plant-based natural gas (bio-methane). While fuel efficiencies of passenger vehicles continue to increase, and alternative fuels comprise an increasing share of fuels consumed, improved efficiencies of HDVs is lagging and few alternatives to diesel are currently available.

For these reasons one study of the AMF investigated the current status of the fuel efficiency and emission performance for commercially available (new or retrofit) diesel dual-fuel (DDF) engines of HDVs, including benchmarking of the emissions performance and certification schemes. HDV testing was carried out in Canada, Finland and Sweden (and with contributions from Japan, Germany and the EC) under a variety of driving conditions on the road as well as in laboratories on chassis dynamometers under well specified conditions. CO2 and CO2-equivalent emissions (CO2 plus methane emissions multiplied by its global warming potential) were measured on different types of HDV engines fuelled by diesel alone or diesel “dual-fuel” (diesel combined with methane).

Even if the carbon content per unit energy of methane is lower than in diesel fuel, tests on five different vehicles showed that CO2 equivalent emissions were lower for dual-fuel engines operating solely on diesel compared to when operated on a mix of diesel and methane (vehicles 3, 4 and 5 in graph). This was found to be due to a combination of lower fuel efficiency and the occurrence of “methane slip”, i.e. the emission of methane that is not combusted in the engine from the tailpipe. Engines fuelled solely with methane (vehicles 1 and 2) had a lower fuel efficiency than diesel engines, which led to higher CO2 emissions, but with minor methane slip. The vehicle manufacturers of the HDVs tested in the study were informed of the results. This analysis shows that further development is needed for dual-fuel engines to reach adequate on-road performance regarding fuel efficiency and/or exhaust emissions.

These and other findings, compiled in the AMF TCP final report, Enhanced Emissions Performance and Fuel Efficiency for Heavy-Duty Methane-Fuelled Engines, have contributed to development of a certification scheme for diesel dual-fuel engines.

* Graph adapted from data provided by the AMF TCP


  • Alcohol: application in compression-ignition engines
  • Alcohol fuels: unregulated pollutants
  • Commercial vehicles: fuel and technology alternatives
  • Dimethyl ether specifications
  • Ethanol and butanol: direct-injection, spark ignition engines
  • Hydro treated oils and fats for engines
  • Internal combustion engines: exhaust gas and particles
  • Methane emissions control
  • On-road vehicles: natural gas pathways
  • Off-road engines: fuel and technology alternatives
  • Passenger cars: fuel performance evaluation


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