Alex D. Colvin

Application of tunable diode laser spectroscopy to the real-time analysis of engine oil economy

Tunable Diode Laser Spectroscopy (TDLAS) of oil derived SO2 in automotive exhaust demonstrated acceptable repeatability in determination of oil consumption at steady state engine operating conditions. The response time of the instrument was approximately 30 sec, the time related to the flow rate of the sampling system. Instrument sensitivity is sufficient to measure SO2 levels of 0.1 to 1 ppm required to the oil consumption determination. Typical exhaust gas species were investigated for their interference effects and were observed to have less than a 10% interference on the SO2 signal for mixing ratios with SO2 typical of automotive exhaust. Water, on the other hand, did show a significant, but compensatible interference. Carbon deposition under rich engine conditions was observed and is expected to be a problem for any analytical device and is best solved by using a heated sampling line.

A proportional air-fuel ratio zirconia oxygen sensor

Abstract A novel time-sharing control circuit is used to convert a linear lean exhaust gas oxygen sensor into a proportional extended range (lean or rich exhaust) sensor. The time-sharing oscillator allows a single electrochemical cell to act as both the voltage sensor and as an oxygen pump, thus reducing the complexity of sensor geometry and fabrication compared to the universal exhaust gas oxygen (UEGO) sensor design. The control circuit has been demonstrated in the laboratory using two forms of commercially available ZrO2 cells: (1) a design with a small chamber that opens to the exhaust by a small hole; (2) a design that provides for a limited diffusion region by use of a porous ceramic layer over the outer electrode. The porous-layer design (or a ceramic coating with one or more holes) appears to be a potential candidate for a linear exhaust gas sensor where interest is primarily in a linear response around stoichiometry.

FAST-RESPONSE ZIRCONIA SENSOR-BASED INSTRUMENT FOR MEASUREMENT OF THE AIR/FUEL RATIO OF COMBUSTION EXHAUST

A fast-response zirconia sensor-based instrument has been developed to measure the air/fuel ratio (A/F) of combustion exhaust. This instrument uses a reduced-pressure sampling system which improves instrument response time (due to faster diffusion at lower pressures) and eliminates the need for a heated sample line. The measured response time of the described instrument is 170 ms (0-90%) for a step-change in oxygen concentration. The prototype instrument is easily calibrated in less than 2 min, requiring only nitrogen and room air for calibration. A complete description of the instrument is given. Results of tests comparing the instrument accuracy to a chemical balance technique are given. Also, a comparison study was conducted with the prototype instrument and a conventional zirconia sensor-based A/F monitor (Lamdascan, Sensors, Inc., Ann Arbor, Michigan) with respect to accuracy and response time.