In situ Measurement of Fuel Concentration of Hydrocarbon near Spark Plug in an Engine Cylinder by 3.392μm Inframed Laser Absorption Method (Discussion of Applicability with Homogeneous Methane-Air Mixture)

Abstract

A fiber optic system linked to the optical sensor installed in the spark plug, in which light can pass through the combustion chamber, was developed to determine the fuel concentration near the spark-plug successively using an infrared absorption method. A He-Ne laser with a wavelength of 3.392 μm that coincides with the absorption line of hydrocarbons was used as a light source. By exchanging an ordinary spark plug into this spark plug with the optical sensor, sucessive measurement of fuel concentration before the spark timing near the spark-plug was performed in a spark-ignition engine inducted with homogeneously mixed method methane-air. The fuel concentration was determined from law of Lambert-Beer in consideration for the effects of pressure and temperature on molar absorption coefficient of methane.