Chemiluminescence of electronically excited species during the self-ignition of acetylene behind reflected shock waves.

Acetylene is an effective additive to various rocket fuels. Acetam, an equilibrium highly concentrated solution of acetylene in liquid ammonia, is a promising fuel for use in liquid−propellant jet engines. To gain insights into the processes occurring in such systems and provide means for predicting their characteristics, the self-ignition of model acetylene−oxygen−argon mixtures is experimentally and theoretically studied. The experiments are performed behind reflected shock waves in a temperature range from 1100 to 1870 K at a total gas concentration of [M] ≈ 1.0 × 10−5 mol/cm3, with chemiluminescence signals from electronically excited C 2 * (λ ≅ 516 nm), CH* (429 nm), CO 2 *(363 nm), and OH* (308 nm) recorded. Numerical simulations within the framework of various detailed kinetic mechanisms closely reproduce the measured temperature dependences of the ignition delay time for the tested mixtures, but in some cases fail to satisfactorily describe the time profiles of the emission signals from C 2 *, CH*, CO 2 *, and OH*. The performed numerical simulations make it possible to explain the observed characteristic features of the emission profiles of electronically excited C 2 *, CH*, CO 2 *, and OH* during the self-ignition of C 2 H 2 –O 2 −Ar mixtures. Sensitivity analysis demonstrates that the existence and characteristics of the preignition stage in the CO 2 * and OH* emission signals are largely determined by the kinetic behavior of intermediate species, such as the ketene molecule and CH 2 radical. Based on the results obtained, a new detailed kinetic mechanism has been proposed for describing processes in the combustion products of acetylene-containing propellants, in particular chemiluminescent glow, which are of considerable interest for the development of new technologies for astronautics and aeronautics. • Results of shock-tube acetylene autoignition are presented. • A detailed kinetic mechanisms capable of describing acetylene ignition delay is developed. • The problems of simulation of chemiluminescence are discussed. • The importance of the kinetics of intermediate products are demonstrated. [ABSTRACT FROM AUTHOR]