California Air Resources Board

Principal Investigator/Author: Tom Durbin

Contractor: University of California, Riverside

Subcontractor: California State University, Fresno

Contract Number: 19RD002

Project Status: Completed

Relevant CARB Programs: Mobile source Emissions Inventory, Mobile Source Emissions Research Program, Potential Amendments to Off-Road New Diesel Engine Emission Standards: Tier 5 Criteria Pollutants and CO2 Standards, FARMER Program

Topic Areas: Air Pollution Exposure, Heavy-Duty Vehicles, Heavy-Duty Vehicle Research, State Implementation Plans (SIPs),Particulate Matter (PM), PM2.5

Research Abstract:

Off-road diesel engines are widely used in agricultural goods production and supply and can contribute to poor air quality in non-attainment areas for particulate matter (PM) and ozone. Agriculture tractors are one of the most prevalent pieces of equipment in the agriculture industry that utilize diesel engines. To understand the impact of California agriculture tractors on air quality, it is important to develop accurate emissions inventories based on their activity patterns and associated emissions. The objective of this research was to collect real-world activity data from agricultural tractors, which could be used to improve the emission inventory and to inform policies and incentive programs in California. The activity data included both engine parameters collected using data loggers and engine hour records. In total, 208 tractors were monitored through either engine hour records or data loggers, with 103 of these tractors monitored with data loggers. These tractors represented a range of crop types (row and tree crops), horsepower (hp, <50 to 650 hp), and farm sizes (<250 to 21,000 acres). The study results will help ensure that the future development of emission inventories, policies, and incentive programs can reflect more information collected from real-world farm activities.

The results showed that the average annual hours of usage for agriculture tractors located in the San Joaquin Valley, California declined as a function of engine age/older engine technology. The annual hours of usage were 739 hours, 741 hours, 143 hours, 130 hours, and 60 hours, respectively, for Tier 4, Tier 3, Tier 2, Tier 1, and Tier 0 tractors. The results show that there is a large drop-off in annual engine hours for the older Tier 0 and 1 equipment, with a much smaller drop-off for the Tier 2 tractors.

The results showed that the tractors on average were used for about 4 hours per day. During that time, the average engine load was typically between 22 and 33% for the different categories, with an overall average load percent of 28%, with an average idle percentage of around 27%. Average daily fuel use rates were 20 gallons per day, with a maximum of about 40 gallons per day for the 300-650 hp categories, while Tier 1 and 2 tractors in the less than 300 hp category and Tier 3 and 4 tractors in the less than 175 hp category had fuel use rates below 10 gallons per day. Average fuel use rates were 4 gallons per hour, with a maximum of about 8 gallons per hour for the 300-650 hp categories, while the Tier 1-2 in the below 300 hp category and Tier 3-4 tractors in the below 175 hp category had fuel use rates of about 2 gallons per hour. Average diesel particle filter (DPF) outlet temperatures were at or above 250°C for both the tree and row crop categories and all of the different hp categories. Temperature distributions showed that the DPF outlet temperature is above 200°C for approximately 75% of the operational time, which in turn suggests that for 25% of the operating time, the DPF outlet temperature would not be sufficiently high to allow for the injection of urea into the selective catalytic reduction (SCR) to ensure it properly functions.

The in-use activity data covers a much broader range of operating conditions than are found in the certification cycles. In general, the distributions for the in-use data show that there is a more significant contribution at low load conditions than is captured in the certification cycles. Since low-load operations could lead to low DPF outlet temperatures and thus lower SCR efficiencies, further investigation into the emissions contribution during low loads is needed. This report also identifies recommendations for further research on the topic of in-use activity of off-road equipment used in agricultural applications.

Keywords: off-road, diesel engine, emissions, agriculture, tractors, activity data, data loggers, engine load

Final Report: Please email research@arb.ca.gov to request the Final Report generated by this research contract.