Ethanol Emissions Testing: Executive Summary

Executive summary

This is the final report of work undertaken on behalf of the UK Department for Transport, local Government and the Regions (DTLR) by AEA Technology plc under contract number PPAD 9/107/15. The contract had two main objectives. The first was to provide an indication of the potential impact of using ethanol/petrol blends in the latest petrol cars on 'real world' tailpipe emissions for a wide range of regulated and non-regulated air pollutants and greenhouse gases.

The second was to provide data that could be used to generate emissions factors for the latest petrol-fuelled cars.

The work was carried out on five vehicles representative of current UK use.

Where warranted by the quality of the emissions data sets, a statistical analysis was undertaken on the results to establish the levels of confidence that could be ascribed to the quantitative effects observed.

The main conclusions on the effect of 10% ethanol additions to petrol were that:

• PM and CO emissions were significantly reduced;
• for some of the vehicles tested, CO2 emissions were significantly reduced;
• overall it led to a small deterioration in fuel economy (although this was not significant at the 95% confidence level);
• NOx emissions were not significantly influenced;
• for some of the vehicles tested, acetaldehyde emissions were significantly increased.

The observed effects of ethanol addition were consistent with the anticipated effects on combustion chemistry and the response of different vehicle technologies to these. In particular, the two vehicles that showed the greatest enhancement of fuel economy were those with modern engine management systems incorporating knock sensors which would confer the ability to optimise timing in response to an octane number increase.

In the course of the work lessons were learned on the appropriateness of the test methodologies adopted and on the comparative performance of different analysis methods used for the unregulated emissions measurements. Recommendations are made for improving the statistical significance of the results from future programmes.

The main report and appendices are available from the links below.