Combustion Chamber Gas Temperatures by a Benzene Light-Absorption Technique

Several techniques have been presented in the literature for measuring mixture temperatures in internal combustion engines during the compression process up to the time of knock. This paper describes a new method based on the light-absorbing properties of benzene vapor and presents engine data based on this technique.

The ultraviolet light absorption coefficient of benzene vapor has been measured over a temperature range of 300-1400 K (80-2060 F). This absorption coefficient, which is very sensitive to temperature, is a function of temperature to the eighth power at room temperatures and decreases smoothly to a fourth power function at approximately 1000 K (1340 F).

The extreme sensitivity of the absorption coefficient to temperature allows precise determination of gas temperatures during the early part of the compression process in a Cooperative Fuel Research (CFR) engine and throughout compression of the fuel/air mixture. The data quantitatively support an analytical prediction that heat transfer from the chamber wall to the inlet mixture, during the intake stroke, causes increased compression temperature histories.