Off-Road Diesel Vehicles

Emission control technologies developed and commercialized for on-road applications – diesel oxidation catalysts, particulate filters, selective catalytic reduction, and lower sulfur content diesel fuel – are now being developed for use on heavy-duty off-road vehicles. While many have been used for several years, others are newer to the market and all effectively reduce particulate matter (PM), nitrogen oxide (NOx), carbon monoxide (CO), and/or hydrocarbons (HC). Similar to on-road use of these technologies, research continues to show that they perform best, and achieve the greatest emissions reductions, when used with ultra-low sulfur diesel fuel (ULSD).

Proposed standards announced by the U.S. Environmental Protection Agency (EPA) in April 2003 for off-road diesel engines in construction, agriculture, and industry will result in fewer emissions from new engines and the use of ULSD fuel. Off-road diesel engines built since 1996 have had to comply with modest standards focusing on NOx emissions, with little attention to PM. EPA estimates that engines addressed by the proposed standards currently account for about 44 percent of total PM and about 12 percent of total NOx emissions nationwide. EPA proposed standards – similar to the requirements for truck and bus diesel engines, which take effect in 2004 – will reduce PM and NOx emissions (125,000 and 825,000 tons, respectively) – by more than 90 percent beginning in 2007. For the first time ever, advanced emission control systems will be incorporated into off-road diesel equipment.

The table below shows the proposed emission standards and when they would apply for different sizes of engines:

Off-Road Emission Control Technologies

Under the proposed emission standards, engine manufacturers are expected to use high-efficiency control systems to substantially reduce both NOx and PM emissions. As such, the principal focus of manufacturers will be on diesel oxidation catalysts (DOCs) and catalyzed diesel particulate filters (DPFs) to control PM, as well as selective catalytic reduction (SCR) and lean NOx adsorption technologies to lower NOx. (See the insert on “Emission Control Technologies” for more information.)

Recognizing that the off-road standards are premised on the transfer of technology being developed for engines to meet the diesel engine standards for trucks and buses that take effect in 2007, the standards do take effect four years later. According to EPA’s Draft Regulatory Impact Analysis, “[t]his time lag…is necessary in order to allow time for engine and equipment manufacturers to further develop these on-highway technologies for nonroad engines and to align this program with nonroad Tier 3 emission standards that begin to go into effect in 2006.”

The estimated costs vary widely for equipment of different sizes and for different applications. For the vast majority of equipment, the cost of meeting emission standards will be roughly one to two percent compared with the typical retail price. Costs could range higher for some types of equipment. For example, EPA estimates that for a 175-horsepower bulldozer, it will cost an additional $2,600 to add the advanced emission control systems to the engine and to design the bulldozer to accommodate the modified engine. A new 175-horsepower bulldozer costs approximately $230,000, so the increased costs are about one percent of the total purchase price. In addition, engines running on ULSD will have reduced maintenance expenses that EPA estimates will be equivalent to reducing the cost of the fuel by 3.3 cents per gallon.

Ultra-Low Sulfur Diesel Fuel

The sulfur content of diesel fuel will be dramatically phased down from its current uncontrolled level of 3,400 parts per million (ppm), the national average, to 500 ppm beginning in 2007 and then to 15 ppm in 2010. In addition to maximizing the performance of NOx and PM emission control technologies on new engines, the low sulfur content will result in reductions in PM from existing engines. (See insert on “Alternatives to Conventional Number 2 Diesel” for more information.)

Lessons Learned from the Field

In November 1998, Massachusetts launched the Clean Air Construction Initiative (CACI) to reduce air emissions generated by heavy-duty construction equipment used in the largest public works project in order to tunnel the highway system under downtown Boston. Representing one of the largest concentrations of off-road, heavy-duty diesel engines in an urban setting, the Central Artery/Tunnel Project, or “Big Dig,” will achieve emissions reductions that are the equivalent to removing 1,300 diesel buses for one full year.

One of the project’s principal goals was to transfer emission control technologies used in trucks and buses to the construction industry. Under the initial plan, 70 pieces (approximately 25 percent of the permanent construction equipment) of contractor-owned equipment, such as front-end loaders, backhoes, cranes, and excavators were retrofitted with oxidation catalysts, particulate filters, or both. With an average retrofit cost of $2,500 per vehicle, the resulting cost-effectiveness ratio has been about $1,000 per ton of pollution removed. This represents a relatively low cost for an air pollution measure, however, the $2,500 cost per vehicle may be significant to fleet operators.

Due to the positive air quality benefits achieved by the oxidation catalysts, the “Big Dig” Project has elected to expand its retrofit program and require that all off-road diesel equipment used until the end of the project be equipped with oxidation catalysts. Additionally, every contractor is required to keep their equipment properly tuned. No adverse operational problems or additional maintenance costs have been experienced by “Big Dig” construction equipment retrofitted with oxidation catalysts.

Preliminary estimates of area-wide emission reductions from the retrofitted equipment amount to approximately 36 tons per year of CO, 12 tons per year of HC, and 3 tons per year of PM.

Sources

U.S. Environmental Protection Agency – www.epa.gov/otaq