Performance Results and Design Considerations for a New In-Use Testing Instrument

In response to the appearance of formal regulations, CFR part 1065 subpart J, a new in-use emission measurement system was developed, the OBS 2000. The OBS 2200 uses partial-vacuum analyzers. The heated flame ionization detector (HFID), heated chemiluminescence detector (HCLD) and heated non-dispersive infrared analyzer (HNDIR) are all upstream of the sample pump. This design decreases the response time of the analyzers, lowers power consumption and minimizes the overall dimensions of the system by avoiding the use of a heated sample pump. The size of the heated zones is also minimized to reduce power usage. Typical power consumption of analyzer unit is less than 500 W. The overall dimension of the main unit is 350mm (W) × 330mm (H) × 500mm (D). Analyzer linearity checks as required by new regulations [1] for all available ranges will be presented along with cut point accuracies relative to full scale and percentage of point. Oxygen interference and relative response of several hydrocarbon components, including methane, will be presented. CO₂ and H₂O quenching for the HCLD will be demonstrated for the instrument. Quenching results will be shown after compensating with the CO₂ and H₂O concentration measured by the HNDIR, as allowed in the new US regulations.

In addition to the main unit, a tailpipe attachment unit (TAU) is used. The flow measurement is done with a factory calibrated pitot tube exhaust flow meter in the TAU. Tailpipe pressure and temperature are recorded within two inches of the sampling location in the TAU. A variety of TAU diameters were evaluated. In addition to exhaust flow the system records the ambient temperature, humidity and pressure. A built in global positioning system (GPS) records position and supplies an independent velocity measurement. The interface for recording engine data is the J1939 or J1708 protocols. All control of the instrument is through a laptop computer. A basic description of the calculations and operational features will also be presented.