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Project Status: complete

Title: Evaluation of the feasibility, cost-effectiveness, and necessity of equipping small off-road diesel engines with advanced PM and/or NOX aftertreatment

Principal Investigator / Author(s): Durbin, Thomas

Contractor: UC Riverside

Contract Number: 14-300

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels


Current (Tier 4) emission standards for off-road engines generally do not require aftertreatment to reduce PM emissions for engines smaller than 25 hp, or NOX aftertreatment for engines smaller than 75 hp. These engines comprise an increasing share of the statewide inventories of these pollutants, however, and represent a potential future path for further reductions of these emissions. The objective of this contract was to evaluate the potential effectiveness, feasibility, and cost-effectiveness of implementing regulations on mobile off-road diesel engines with rated powers of less than 50 hp that will require the use of advanced emission control strategies, such as diesel particulate filters (DPFs) and selective catalytic reduction (SCR). A DPF was installed on a 20-hp transportation refrigeration unit (TRU) and a 25-hp excavator; both reduced PM emissions by over 97 percent both before and after a 1000-hr field demonstration. A SCR and a selective continuously regenerating technology (SCRT) system were installed on a 37-hp ride mower and a 49-hp skid steer, respectively; these reduced NOx by 50 to 80 percent depending on the duty cycle, which most likely impacted SCR temperature and the dosing of diesel exhaust fluid in the SCR and SCRT. These results demonstrate that the addition of advanced aftertreatment to off-road engines smaller than 75 hp could reduce statewide off-road PM and NOX emissions by 0.2 and 15 - 23 tons per day, respectively. This represents two percent and 11 - 16 percent, respectively, of the total off-road emissions of these pollutants, and 0.2 percent and 1.4 - 2.2 percent of their total mobile source emissions. Furthermore, approximately 29 and 22 percent of statewide NOx from off-road diesel engines is emitted in the San Joaquin Valley (SJV) and SoCAB, respectively, where reductions are needed to meet NAAQS from PM and O3. The estimated total cost of these reductions is $29,000 / ton for PM reduction and $733 - $1039 / ton for NOx reduction. This price range for NOx is lower than approximately 70 to 80 percent of estimates from previous CARB NOx rulemaking efforts.


For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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