Measurement of Dry Soot and Particulate Matter from Two-Stroke and Four-Stroke Snowmobiles 2010-32-0042

Recent increases in emissions regulations within the snowmobile industry have led to significant advancements in fuel, exhaust, and control systems on snowmobiles. However, particulate matter is currently an unregulated exhaust component of snowmobile engines. The measurement of dry soot as well as particulate matter from snowmobiles is the focus of this paper. Two industry-representative snowmobiles were chosen for this research which included a 2006 Yamaha Nytro carbureted four-stroke and a 2009 Ski-Doo MX-Z direct-injected two-stroke. Measurements for each snowmobile included gaseous emissions (CO₂, CO, NO_x, O₂, and THC), particulate matter collected on quartz filters, and dry soot measured using an AVL Micro Soot Sensor. Each snowmobile was tested over the industry-standard five-mode emissions certification test cycle to determine the emissions, dry soot, and particulate matter levels from idle to wide open throttle (full-load).

The carbureted four-stroke snowmobile was factory-calibrated rich of stoichiometric combustion to improve cold-start performance, increase power, and provide acceptable throttle response. The direct-injected two-stroke engine was susceptible to some short-circuiting of raw fuel to the exhaust system. For this reason, both snowmobiles produced relatively high levels of hydrocarbon emissions and particulate matter compared to modern automobile engines. The highest dry soot levels for both snowmobiles were recorded at full load conditions with the magnitude of the dry soot being quite similar for both vehicles. At the lower engine speeds and loads, dry soot levels were significantly higher for the direct-injected two-stroke engine compared to the carbureted four-stroke engine. While the two-stroke engine calibration was lean of stoichiometric at most operating conditions which led to reduced hydrocarbon and soot emissions compared to stoichiometric operation, the consumption of lubricating oil had a direct impact on dry soot emissions and led to higher emissions compared to the four-stroke engine.

The exhaust particulate matter was measured using an undiluted, hot quartz filter which was weighed before and after each run to determine particulate matter mass. The sample stream to the filter was not diluted and the temperature was not maintained at a specified value. Therefore, the measured particulate mass was an estimate of dry soot and hydrocarbon emissions, as quartz filters have an affinity for hydrocarbons. The mass flow rate of particulate matter determined from the filters was significantly higher than the dry soot results from the Micro Soot Sensor. The two-stroke and four-stroke engines were both observed to have high hydrocarbon emissions (10,000 - 30,000 ppmC1), which may have led to the discrepancy between the dry soot concentration and PM measurement techniques.