by Jim Kerr

MMT, Methylcyclopentadienyl Manganese Tricarbonyl, has been a controversial fuel additive for many years. In Canada, most of our fuel includes MMT as an octane enhancer to help prevent engine pinging or knock. In the United States, MMT has been banned in the past but is now allowed in some parts of the country. Even though it is allowed, MMT is still not in common use in the U.S.

Ethyl Corporation, the sole manufacturer of MMT claims that MMT is beneficial to reducing vehicle emissions. While MMT is an octane enhancer and may provide some advantages studies by the automotive industry would indicate otherwise.

Over 30 papers have been published by the Society of Automotive Engineers (SAE) on MMT fuel additives. Many of these have indicated MMT increased tailpipe emissions, spark plug fouling, catalyst damage and impairment of On Board Diagnostic systems. While it is claimed these studies were not of enough depth to indicate accurate results, the latest study released in 2002 has the statistical controls and research methods to accurately determine the effects on MMT additive on vehicle emissions.

Conducted jointly by the Alliance of Automobile Manufacturers, the Association of International Automobile Manufacturers and the Canadian Vehicle Manufacturers’ Association, this eight million dollar study is the most comprehensive study on the effects of MMT on vehicle emissions to date.

The test used 56 vehicles from 6 major automotive manufacturers. Side by side testing was performed on two pairs of matched vehicles, with half of the vehicles using fuel with MMT additive and the others without MMT. Emission levels were tested several times during the evaluation program, during which the vehicles accumulated up to 160,000 kilometres. A total of 5,840,000 kilometres were driven during the six year test.

Between 4000 and 50,000 miles, MMT fuelled vehicles had hydrocarbon emissions averaging 13% higher than non-MMT fuelled vehicles. CO was about 6% higher but NOx was reduced by 10%. Spark plugs in two of the test vehicles fuelled with MMT misfired to the point of turning on the Malfunction Indicator Light (MIL). Evaluation of the plugs by Delphi, the plug manufacturer, found that reddish brown deposits were on the tips of the plugs exposed to MMT. Delphi theorised that the manganese oxide deposits on the plugs are conductive under high heat, causing the plugs to track down the insulator and misfire. Several other vehicles also experienced sparkplug misfires but not severe enough to turn on the MIL.

Fuel economy tests were also performed during the study. City fuel economy for vehicles using fuel with MMT were consistently lower than for vehicles not using MMT. The difference at 15,000 miles was .35 mpg U.S. and increased to .48 mpg U.S at 35,000 miles. Highway fuel economy was lowered by .2 mpg U.S. This is a significant reduction in economy over the life of an automobile.

Who does one believe? Ethyl Corporation claims MMT is beneficial and they have the research to back up their claims. The auto industry research shows MMT causes vehicle problems, higher emissions and lower fuel economy. Both have a lot to loose. If MMT continues to be added to fuel, the auto manufacturers will have to spend huge amounts of money to design emission systems compatible with MMT. If MMT is banned, the refining of fuel could be more costly or other octane enhancers will be required and Ethyl Corporation would not be able to sell MMT.

The Canadian Government did try to ban MMT. In 1996, Environment Canada announced that it would control MMT under a trade bill, Bill C-29 (the Manganese-based Fuel Additive Act), claiming that MMT can impair the on-board diagnostics and air pollution control devices of vehicles and thus indirectly harm the health of Canadians. In 1997 this bill came into effect, banning importation and inter-provincial movement of MMT. However, in 1998, Bill C-29 was rescinded after a panel formed under the Agreement on Internal Trade found that this bill was inconsistent with the government’s obligations under the Agreement on International Trade. Ethyl Corporation had also challenged Bill C-29 and the government’s right to restrict trade.

In an out of court settlement with Environment Canada, Ethyl Corporation received a $13 million settlement for “reasonable cost and profit” lost because of the implementation of C-29.

Is MMT all right or is this really political posturing to support economic trade? I tend to believe the validity of the automotive industry’s study.

Finally, studies by Health and Welfare Canada (now Health Canada), on the health effects of MMT in fuel found no significant health effects associated with exposure to manganese exhaust emissions. Meanwhile, other Canadian researchers and the U.S. environmental Protection Agency disagree with Health Canada. It would appear that more scientifically based research is needed to find the real truth on the health effects of using MMT in fuel. The controversy continues.

Connect with