Fuel reformulation has benefits, but may not reduce NOx emissions

A new report by the International Energy Agency (IEA) details the results of a comprehensive survey of European automotive fuels. The report was published by the IEA Automotive Fuels Information Service and distributed by IEA operating agent Innas BV, Breda, The Netherlands.

Current fuel reformulation trends lead to reduced emissions of carbon monoxide, hydrocarbons, and benzene from automobiles. Results for NOx emissions, however, are contradictory and inconclusive.

Part 1 of the two-volume report focuses on raw materials and conversion. Part 2 looks at distribution and use. According to IEA, the report "presents an overview of important aspects of raw materials and their conversion to automotive fuels."

In addition to traditional fuels, the report includes sections on alternative fuels such as natural gas, hydrogen, ethers, and fuels derived from biological sources. The books also contain a detailed analysis of refinery and automotive emissions.

Refinery emissions depend on the refinery processing scheme. Cat cracking refineries, for example, emit significantly greater quantities of sulfur than hydroskimming or thermal cracking refineries.

In addition, the report includes data from tests of the effects of fuel reformulation on automobile emissions.

Refinery emissions

Energy consumption and emissions vary according to the type of refinery operation. IEA selected data from three refineries representing three basic processing schemes: hydroskimming (separation only); thermal cracking; and catalytic cracking. The cat cracking refinery is a modern, complex refinery.

The hydroskimming refinery processes 4.7 million metric ton/year (mt/y) of crude. The thermal cracking refinery inputs 3.6 million mt/y, and the cat cracking refinery, 8.0 million mt/y.

Table 1 [23419 bytes] shows the energy consumption per year for the three refineries. IEA cautions that these data represent a single year, and should not be used to draw far-reaching conclusions.

Table 2 [30511 bytes] shows emissions per ton of crude processed for the three refineries. Of the three processing schemes, cat cracking plants emit the greatest quantity of sulfur and hydrocarbons, while thermal cracking refineries emit more NOx and CO.

Automotive emissions

In the last decade, two organizations have performed major studies on the effects of gasoline composition and vehicle design on automobile emissions. The two groups are:

In the U.S., the Auto/Oil Air Quality Improvement Research Program
In Europe, the European Programme on Emissions, Fuels, and Engine Technologies.

Each of these programs was undertaken by a consortium of automobile manufacturers and oil companies. IEA summarized the results of these tests and other experiments conducted by independent companies and researchers.

Table 3 [37410 bytes] summarizes changes in seven pollutants for vehicles equipped with catalytic converters. The fuel characteristics studied were: aromatics, oxygenate, olefins, and sulfur concentrations; distillation characteristics; and vapor pressure. Table 4 [30161 bytes] shows the results for noncatalyst cars.

In general, measured changes in NOx emissions as a result of common fuel reformulation measures were contradictory, and thus inconclusive. Carbon monoxide is generally reduced by changes in fuel quality, as are emissions of hydrocarbons and benzene. Most of the other results were inconclusive.

IEA tempers these results by reminding the reader that, "The greatest reduction of air pollution by gasoline cars can be realized by changes in vehicle technology." The influence of fuel composition on emissions is small, compared to the effects of changes in vehicle and engine design.

"Especially the use of heated catalysts can reduce [hydrocarbon] emissions during cold starts to a great extent," according to IEA. "The installation of carbon canisters in the fuel tank will reduce the evaporative emissions by up to 90% for a well functioning system," concludes the report.