Effects of Additives on the Non-Premixed Ignition of Ethylene in Air

Abstract

The ignition characteristics of heated C₂H₂ counterflowing against heated air were numerically investigated in the presence of additives such as NO, F₂, and H₂ C₂H₄ and air temperatures were chosen to resemble conditions relevant to high-Mach number, air-breathing propulsion. The numerical simulations were conducted along the stagnation streamline of the counterflow and included detailed descriptions of chemical kinetics and molecular transport. Addition of NO, at concentrations of about 10,000 ppm (1%), results in a substantial increase of ignition strain rates, from 300s⁻¹ to values up to 32,000s⁻¹, This ignition promotion is caused by enhanced radical production, initiated through the interaction between NO and HO₂. Further increases in NO amount lead to reduced improvements. Small additions of F₂ and H₂ were also found to promote ignition, but to a lesser extent compared to NO. Results also show that with the addition of F₂ in the presence of NO, ignition promotion is further enhanced. The system becomes hypergolic for F₂ and NO concentrations larger than 25,000 ppm. The present investigations suggest that the use of C₂H₂. NO, and F₂ may permit ignition at conditions of relevance to SCRAMJET's.