Lubricating Oil Contribution to Direct-Injection Two Stroke Engine Particulate Emissions

Particulate emission measurements were performed on a direct-injection two-stroke engine that employed a lost-oil lubricating system. The particulate emissions were sampled using a partial-flow dilution system. Particulate mass emission rates were measured using a tapered element microbalance (TEOM), and the results were found to compare favorably with gravimetric tests performed simultaneously. The size distribution was measured using a scanning mobility particle sizer (SMPS), and the cumulative mass from the measured size distribution was found to agree well with the values measured by the TEOM. The particulate mass emission were found to be dominated by particulate matter derived from the engine oil. The particulate emissions were found to decrease substantially as the oil flow to the engine was reduced from the baseline case of 1:100 (oil-to-fuel mass ratio). Additionally, the reduction of the oil flow from the baseline case coincided with the removal of a secondary peak centered at 70 nm in the particle size distribution. It was determined that the oil flow rate had to be decreased to 1:450 in order for trends in the combustion-derived particulate matter to be observable. This level is comparable to levels seen in automotive four-stroke engines.