A Study on the Application of the Two–Color Method to the Measurement of Flame Temperature and Soot Concentration in Diesel Engines

Results are presented of optical measurement of the flame temperature and KL factor (soot concentration) in a direct injection diesel engine using the two-color method. In the latter stages of combustion, the infrared two-color method gave a lower value than the visible two-color method, the difference being enhanced with crank angle advancement. The KL factor value obtained by the visible method was about half that of the infrared method. These differences were caused by the alpha index (wavelength dependency of flame emissivity) change in the infrared region during the combustion period; the effect at both wave lengths of uneven distributions of temperature and soot concentration along the optical path; and the effect of the reflection of the opposite wall on the infrared method. The optical characteristics and other instrumentation problems of the two-color method at both wavelengths are also discussed.