An infrared fiber-optic spark plug probe has been developed that will measure the instantaneous fuel-air ratio of the unburned fuel-air mixture near the spark plug in the cylinder of a production automobile engine. The heart of the device is a probe that is placed into the spark plug hole of an engine. It can house both a spark electrode and a pair of optical fibers. Radiation from an infrared source in supplied to one fiber, while the other fiber carries the absorption signal from the probe to a detector and data acquisition equipment. The probe measures variatios in the light transmitted through a regio surrounding the spark gap due to fluctuations in the fuel concentration in this region. It can record variations in the air-fuel ratio in an engine cylinder at high enough rates to show how engine operating conditions affect the mixing inside the engine cylinder.
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