Instantaneous Unburned Oil Consumption Measurement in a Diesel Engine Using SO2 Tracer Technique

The contribution of lubricating oil to diesel engine particulate emissions is of concern not only because of stringent particulate emissions standards but also because of engine-to-engine variability. Unburned oil contributes directly to the particulate soluble organic fraction. A real-time oil consumption measurement technique previously developed was further refined to also measure real-time unburned oil consumption. The technique uses high sulfur oil, low sulfur fuel, and fast response, sensitive SO₂ detection instrumentation.

Total and unburned oil consumption maps over the engine operating range are presented. Results show that both total and unburned oil consumption generally increase as speed and load are increased. Unburned oil consumption shows some peaks at intermediate speed, high-load conditions. Oil consumption from individual cylinders was measured and shown to be approximately equal. The sum of oil consumption from all six cylinders is nearly equal to the total except at low speeds. This difference at low speeds is thought to be due to turbocharger seal leakage.

Oil consumption maps were numerically integrated over the US Federal Transient Test Procedure to show that oil consumption during transients and motoring might be a significant contributor to the total over the cycle. Controlled step transients consisting of step changes in load and speed were tested to identify problem conditions. It is shown that certain transients such as step decreases in speed might be more significant contributors to unburned oil consumption than other transients such as step increases in speed or load. It is suspected that the high transient unburned oil is due to unstable component dynamics during transients. A program is under way to simultaneously measure component dynamics and oil consumption to establish any correlation between the two phenomena.