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Project at a Glance

Project Status: complete

Report Published May 1994:

Title: Performance of analysis and research tasks for the California smog check program

Contractor: Sierra Research, Inc.

Contract Number: a164-074

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels


An onboard data acquisition system has been designed, installed and tested in a 1991-model Chevrolet Lumina, to collect engine and vehicle operation data, including tailpipe pollutant concentrations. The systems measures and records manifold air pressure, manifold air temperature, engine RPM, throttle position and coolant temperature, all on a second-by-second basis. Lateral and longitudinal acceleration and oxygen sensor voltage are measured at 10 hertz and averages are calculated and recorded at 1 hertz. Vehicle speed is measured at 1 hertz and can be differentiated and substracted from longitudinal acceleration to estimate grade. Additional digital data are sampled and recorded to document gear changes or change in status of the "service engine soon" indicator. A portable gas analyzer is used to measure and record concentrations of hydrocarbons, carbon dioxide, carbon monoxide and oxygen in engine exhaust. In conjunction with the measurements of manifold air pressure and engine speed, the concentration data can be converted to mass emissions. With the exception of the added accelerometers and exhaust gas analyzer, the system samples data exclusively from OEM system sensors. The exhaust gas analyzer requires periodic maintenance, but the remainder of the data acquisition system can be operated automatically upon vehicle ignition. The data acquisition system includes an 80,386-based, DOS-compatible computer with a custom-modified power supply and start up circuitry, a 7 MB battery-backed static RAM card (for computer start up and data collection without mechanical disks) which is effectively doubled using software data compression, an IBM PC-compatible analog to digital converter / digital counter board and custom accessory box and a commercial data acquisition program. While not required in normal data collection, the system can be operated with video monitor for real time display of most data, and a compact keyboard and mechanical floppy disk drive can be used for data or program exchange. Sample data and calculations are provided to show how road grade and second by second mass emissions can be estimated from the measured parameters.


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

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