Along with the regulation of heavy-duty diesel emission levels starting in 2007, EPA has set the target of sulfur levels in diesel fuel for a 97% reduction from the current 500 ppm level to 15 ppm for diesel fuel sold at service stations beginning on September 1, 2006. After-treatment equipment such as catalyzers and filters, in other words, technology for controlling emission levels of NOx and PM-will be indispensable in satisfying the requirements of the major revisions in the regulation of emissions from heavy-duty diesel engines due to take effect in 2007. Considering the deterioration of these devices caused by sulfur contained in diesel fuel as well as the sulfate PM they generate, EPA promotes the reduction of diesel fuel sulfur content prior to the new regulations coming into effect.
The Clean Diesel Independent Review Panel (CDIRP), a subcommittee of the Clean Air Act Advisory Committee, has studied the feasibility of implementing the above described heavy-duty emission regulation in 2007 given the technological challenges inherent both in reducing emissions and in ensuring the availability of low-sulfur diesel fuel, and has concluded that 15 ppm, low-sulfur diesel fuel is feasible.
As the sulfur content of diesel fuel is reduced, one further problem that will be addressed is sulfur content and other additives contained in lubricants, which could potentially have a detrimental effect on after-treatment equipment. The generation of ash by the additives is a potential cause of clogging in DPF, resulting in frequent maintenance and increased operating costs. Although there is at present no movement for specific regulation of these substances, close monitoring of future trends is necessary.
Recently in the US, there has also been a sudden interest in the use of vegetable (soybean, corn, etc.) and animal oil in the production of "biodiesel" fuel, which is said to be effective in reducing emission levels of hydrocarbons and particulate matter. Thus, the use biodiesel fuel is likely to garner interest not just from those involved in energy policy but also from those involved in agricultural policy as well, and in fact, 1998 revisions to the Energy Policy Act recognize biodiesel fuel as an option in the application of alternative fuel vehicles as required of fleet owners. In March of 2003, ASTM D6751 was issued by the American Society for Testing Materials as a standard for biodiesel fuel.
Still, most manufacturers have yet to approve the use of biodiesel fuel in their vehicles due to the fact that its effect on the durability of fuel system elements has yet to be verified. Although oxidation during long-term storage also remains a concern, it remains an issue worthy of attention.