Measurements of OH* and CH* Chemiluminescence in Premixed Flames in a Constant Volume Combustion Bomb under Autoignition Conditions

The objectives of this paper are as follows: (1) To study parametrically OH* and CH* chemiluminescence trace evolution as a function of the initial pressure, temperature, and equivalence ratio of premixed flames of n-heptane, under autoignition conditions, in a constant volume combustion bomb. The signals of the electronically excited states of OH* (306 nm) and CH* (430 nm) have been detected through band-pass filters with two photomultiplier tubes placed in an optical access of the combustion bomb. (2) To determine the feasibility of using OH* and CH* chemiluminescence signals as active-control parameters for premixed flames. For this purpose, a correlation between OH* chemiluminescence emissions and the equivalence ratio and the rate of heat release during the combustion process is obtained, as well as a correlation between CH* chemiluminescence emissions and the adiabatic flame temperature. (3) To investigate the relationship between the OH* and CH* chemiluminescent emissions in premixed combustions of n-heptane, Leo-octane, and a mixture of 50% n-heptane and 50% toluene and the equivalence fuel/air ratio for a given initial temperature and pressure. To reach these objectives, measurements of OH* and CH* chemiluminescences from premixed flames of n-heptane with autoignition are reported at equivalence ratios ranging from 0.8 to 1.0, in a constant volume combustion bomb. The morphology of the curves and the relationships with parameters of interest during the combustion process (i.e., the rate of heat release, burned temperature, etc.) are studied. In addition, premixed combustions of iso-octane, n-heptane, and a mixture of n-heptane and toluene are also investigated at different fuel/air equivalence ratios for a given initial pressure and temperature, to assess the possibility of using the ratio between the OH* and CH* chemiluminescence signals to monitorize the equivalence ratio during the combustion, as other authors have considered previously.