Regulatory agencies are becoming increasingly concerned with particulate emissions as the health and environmental effects are becoming better understood. While much research has been performed on diesel engines, little is known about particulate matter (PM) emissions from natural gas internal combustion engines. In this project, tests were conducted on a Waukesha VGF F18 natural gas engine running at full load. $PM10$ combustion emissions were collected on teflon and quartz filters and a scanning mobility particle sizer was used to determine the particle size distribution. Tests were performed at 4–7% exhaust oxygen $(O2)$ levels. Overall, it was found that a large number of small particles were emitted from this engine. The total mass based PM emissions were found to be $0.0148gm∕bkWh$, which is slightly greater than the Tier-4 nonroad diesel particulate emission standard. Particle distributions revealed that the geometric mean diameter of the natural gas particles was approximately $30nm$ and did not change with air to fuel ratio. Particulate concentrations were found to decrease at leaner engine operating conditions. Results showed a strong correlation between the $NOx$ and particle concentrations, while an inverse correlation between CO and particle concentrations was revealed.

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