Small utility engines represent an important contribution to the emissions inventory and have been subjected to increasingly stringent regulations in recent years. For this project, a Tanaka two-
stroke engine was tested in its original condition and with a modified
fuel/oil injection system. The modified
fuel/oil injection system applied to the Tanaka two-
stroke engine resulted in significant emissions reductions of approximately 52% for
carbon monoxide (CO), 70% for total
hydrocarbons (
THC), 70% for
particulate matter (PM), and 67% for the regulated
THC +
nitrogen oxides metric. This technology met the California Air Resources Board's 2000 model-year regulations for all
pollutants, with the exception of slightly higher PM emissions. Two additional two-
stroke engines were tested under a new condition and after at least 100 hr of use to examine the effects of deterioration on in-use, two-
stroke engines. For one engine, CO and PM emissions more than tripled after 162 hr of operation in the field, with smaller increases also observed for
THC (20%). For the second engine, significant repairs were required throughout the 100 operating hours, which counteracted the effects of the emissions deterioration and resulted in lower CO and
THC emissions.