The ignition characteristics of heated C2H2counterflowing against heated air were numerically investigated in the presence of additives such as NO, F2, and H2C2H4and 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−1to 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 F2and H2were also found to promote ignition, but to a lesser extent compared to NO. Results also show that with the addition of F2in the presence of NO, ignition promotion is further enhanced. The system becomes hypergolic for F2and NO concentrations larger than 25,000 ppm. The present investigations suggest that the use of C2H2. NO, and F2may permit ignition at conditions of relevance to SCRAMJET's.