New Swedish study compares exhaust emissions from ethanol and biogas with those from petrol
8 May 2008
The exhaust emissions from cars fuelled by ethanol (E85) and biogas have been compared with the emissions from petrol-fuelled cars in a comprehensive study funded by the Swedish Road Administration. The study has been conducted in a research co-operation between AVL MTC, Ecotraffic ERD3 and Stockholm University.
Emissions were tested at +22°C and -7°C, and the study covered potentially hazardous exhaust components such as aldehydes, alkenes, polycyclic aromatic hydrocarbons (PAH) and particles (number, size distribution and mass).
The results showed that the emissions of several exhaust emission components (such as PAH) were higher for E85 than for petrol at the lower temperature, -7°C. PAH emissions increased with increasing ethanol content in the petrol. However, at +22°C, the differences in emissions were smaller, and often lower for E85 than for petrol.
The levels of aldehydes were higher for E85 than for petrol at practically all tested conditions. The emissions of, for example, light aromatics and alkenes were lower than for petrol at the higher temperature. At the lower temperature, higher levels of several emission components that are not regulated in emission norms were measured for E85. These higher levels are principally seen during a cold start. The “winter quality” of ethanol fuel (E70) gave lower levels than E85. Electric engine block heaters were not used in this study, but previous tests have showed positive results when such heaters have been used.
Today, E85 cars are typically petrol cars that have been modified to use
E85. Further development will be needed to fully utilise the properties
of the fuel. The study also shows the necessity for exhaust emission limits
at low ambient temperatures for these vehicles.
Biogas operation should generally provide great emission advantages during
cold start, since the fuel is already in gaseous state and does not have
to be evaporated as with liquid fuels. However, most gaseous-fuelled
cars on the market start on petrol. Therefore, the biogas
cars cannot reach their full potential for low emissions.
In a separate sub-project, on-board measurements were conducted on nine biogas-fuelled cars and one E85 car to assess the catalyst durability regarding methane oxidation. The on-board measurements showed that catalyst durability for methane oxidation is a problem on biogas cars after 40000 km. The newer biogas cars and the E85 car had low levels of methane in the exhaust.
