Near Infrared Absorption Sensor for In-Vehicle Determination of Automotive Fuel Composition

The use of methanol as an automotive fuel can be expected to become significant in North America during the 1990's. Methanol fuel will be sold as 85%/15% MeOH/gasoline mixture. Limited availability of methanol fuel in some parts of North America will require methanol vehicles to be dynamically adaptable to fuel compositions ranging from 85% methanol to 100% gasoline. One approach to meeting such a requirement is a sensor that is mounted somewhere in the vehicle's fuel handling system that determines the concentration of methanol in the fuel flowing to the engine. The output of the sensor is supplied to the computer controlled engine management system that sets engine operating parameters. A sensor based on near infrared absorbance is the subject of this paper. The device is constructed around a novel combination of commercially available components including a light source, optical filters, detectors, and signal processing electronics with the purpose of monitoring the absorbance of light at selected wavelengths in the near infrared spectral region. Prior to sensor construction, laboratory experiments demonstrated the appropriate wavelengths for the determination of methanol concentration in fuel mixtures. The paper will describe the laboratory experiments, the specifications that need to be met for an automotive fuel sensor, the construction of prototypes, and the results from laboratory and invehicle testing of the prototype devices.