In-situ fuel concentration measurement near spark plug in spark-ignition engines by 3.39 μM infrared laser absorption method

Improving thermal efficiency and reducing the exhaust emissions of internal combustion engines have become crucial. Thus, it is important to determine the fuel concentration in the vicinity of the spark plug near the spark timing because initial combustion affects the following main combustion in spark-ignition engines. A fiber optic system linked to the optical sensor installed in the spark plug, by means of which light could pass through the combustion chamber, was developed to determine the fuel concentration near the spark plug using an IR absorption method. A He-Ne laser with a wavelength of 3.39 μm coinciding with the absorption line of hydrocarbons was utilized as a light source. By exchanging an ordinary spark plug for this spark plug with the optical sensor, successive measurement of fuel concentration before the spark timing near the spark plug was carried out in a port injection spark-ignition engine fueled with isooctane under the firing condition. The air/fuel ratio averaged for many cycles near the spark plug with this optical system agreed with that measured with a buret, which represented the mean value averaged over a protracted period. This sensor was also applied to determine air /fuel ratio quantitatively in a direct injection gasoline engine. As a result, it was clarified that the air/fuel ratio and its standard deviation near the spark plug had a strong relationship to the stable engine operation. Original is an abstract.