Project at a Glance

Title: Emissions and demonstration of an emissions control technology for small 2-stroke utility engines

Principal Investigator / Author(s): Durbin, Thomas

Contractor: UC Riverside

Contract Number: 97-313

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels, Stationary Sources, Toxic Air Contaminants


Small utility engines contribute to emission inventories in California that are disproportionately high on brake-specific basis (mass of pollutants produced per unit work performed). The California Air Resources Board (ARB) has established emissions standards for handheld and non-handheld equipment powered by these small utility engines. A number of technologies have the potential for meeting these emissions standards, including four-stroke engines, fuel-injected two-stroke engines, stratified scavenging two-stroke engines, and two-stroke engines with catalytic aftertreatment devices. Manufacturers, however, have expressed concerns about the ability to achieve the desired performance in a cost-effective way.

In an effort to add to our knowledge regarding emissions from two-stroke utility engines and to demonstrate a potential control technology, the University of California, Riverside, Bourns College of Engineering - Center for Environmental Research and Technology (CE-CERT) tested four small two stroke utility engines; a 46 cc Tanaka (string trimmer), a 46 cc BKM-F1 modified Tanaka (string trimmer), a Stihl (string trimmer), and an Echo PB-210E (leaf blower). The unmodified Tanaka engine was tested as a baseline for the modified version, equipped with the BKM fuel / oil injection technology on an identical engine. The Stihl and Echo engines were tested in new condition and again after more than 100 operating hours. The program resulted in an assessment of emissions factors, fuel use, power, and durability for the engines tested. A summary of the results of this program is provided below.

* The BKM fuel / oil injection technology applied to the Tanaka two-stroke engine resulted in significant emissions reductions. The emission reductions were approximately 52% for carbon monoxide (CO), 70% for total hydrocarbons (THC), and 70% for particulate matter (PM). The BKM technology did result in nitrogen oxides (NOx) emissions increasing by nearly 200%. The ARB emission standards, however, are written in terms of THC + NOx. According to this metric, the BKM technology resulted in emission reductions in terms of THC + NOx of 67 %.
* The Echo engine was tested in new condition and after 100 hours of operation. Unfortunately, since this engine required maintenance during the course of accumulated operation, these emission results probably do not accurately reflect the absolute effects of the engine's deterioration on emissions. Specifically, this engine had lower emissions for CO and THC after operating for more than 100 hours, contrary to the expected emissions increase. The PM and NOx emissions did increase after 100 hours of accumulated operation, but it is difficult to determine how much of these increases can be attributed to engine deterioration.
* The Stihl engine was tested in new condition and after 162 hours of operation. The results show significant increases in CO and PM emissions levels after hour accumulation compared with the new condition. Specifically, CO emissions increased by more than 200% while PM emissions increased by about 250%. There was a small (20%) increase in THC emissions after the accumulated hours and a 64% reduction in NOx emissions.

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

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