AUSTIN, Texas—ASTM Subcommittee A on gasoline approved a ballot to limit the amount of manganese additive in gasoline to 0.25 mg/L in markets where vehicles meeting U.S. Tier 2, Euro 5 or more stringent emissions standards are required or in widespread use. Before this ASTM action, the lowest numerical limit was 2 mg /L, which applies to the European Union and major cities in China. There are some countries, such as Russia, Germany, etc., which do not allow manganese additives in fuel.
The proposed limit is embodied in Table 2 of the proposed revision to D4814, Standard Specification for Automotive Spark-Ignition Engine Fuel. This specification describes the various characteristics and requirements of automotive fuels for use over a wide range of operating conditions in ground vehicles equipped with spark-ignition engines.
The ballot will also have to be approved by ASTM Committee D02 on petroleum products, liquid fuels and lubricants before the proposed revision is adopted in the current ASTM standard. According to Honda’s Jeff Jetter, who is chairman of the ASTM Organometallic Task Force, committee-wide balloting will be done within six months.
The use of methylcyclopentadienyl manganese tricarbonyl or MMT has been a highly contentious issue for 40 years, Jetter said. Reaching a consensus within the task force was extremely challenging, he added. A “mutually acceptable ballot wording” was eventually reached in October, with many participants making concessions to reach consensus.
Currently, MMT is allowed in U.S. gasoline at a level equivalent to 1/32 grams per gallon (gpg) or 8.3 mg/L by the U.S. Environmental Protection Agency (EPA), which is thirty-three times higher than the proposed ASTM limit.
According to the EPA website, MMT added at 1/32 gpg “will not cause or contribute to regulated emissions failures of vehicles.” However, it also acknowledges that “Some have expressed concerns that the use of MMT may harm on-board diagnostic equipment (OBD) which monitors the performance of emissions control devices in the vehicle.” However, the EPA website said that “the data collected is inconclusive with regard to OBD.”
The ASTM Organometallic Task Force was formed to develop guidance in ASTM D4814 regarding appropriate concentration limits for organometallic compounds. The initial focus was on manganese, as all other organometallic additives are banned in the U.S. The task force used data from a Coordinating Research Council (CRC) report to draft the subcommittee ballot.
The CRC report, which was prepared by the Desert Research Institute based in the U.S. state of Nevada, concluded that “some vehicles are more susceptible to problems than others.” The report further said that “there is credible evidence that all of the above-mentioned problems [ primarily catalyst plugging and HC emissions increase, engine-out or tailpipe] can occur in Tier 2 vehicles—especially with long-term use that allows for greater manganese accumulation in the catalyst.”
“In particular, the in-use Canadian experience with Tier 2-type vehicles clearly demonstrated that use of MMT can cause consumer problems in select cases.”
A new CRC project focusing on other metallic additives is just starting, Jetter said. Metals of interest include sodium, silicon, phosphorus, calcium, iron, nickel, copper, zinc and tin. Also, lead at levels below the current ASTM D4814 limit will be included in the study.