*Article* **Comparative Analysis of Flame Propagation and Flammability Limits of CH4/H2/Air Mixture with or without Nanosecond Plasma Discharges**

**Ghazanfar Mehdi , Maria Grazia De Giorgi \*, Sara Bonuso , Zubair Ali Shah, Giacomo Cinieri and Antonio Ficarella**

> Department of Engineering for Innovation, University of Salento, Via per Monteroni, 73100 Lecce, Italy **\*** Correspondence: mariagrazia.degiorgi@unisalento.it

**Abstract:** This study investigates the kinetic modeling of CH4/H2/Air mixture with nanosecond pulse discharge (NSPD) by varying H2/CH4 ratios from 0 to 20% at ambient pressure and temperature. A validated version of the plasma and chemical kinetic mechanisms was used. Two numerical tools, ZDPlasKin and CHEMKIN, were combined to analyze the thermal and kinetic effects of NSPD on flame speed enhancement. The addition of H2 and plasma excitation increased flame speed. The highest improvement (35%) was seen with 20% H2 and 1.2 mJ plasma energy input at φ = 1. Without plasma discharge, a 20% H2 blend only improved flame speed by 14% compared to 100% CH4. The study found that lean conditions at low flame temperature resulted in significant improvement in flame speed. With 20% H2 and NSPD, flame speed reached 37 cm/s at flame temperature of 2040 K at φ = 0.8. Similar results were observed with 0% and 5% H2 and a flame temperature of 2200 K at φ = 1. Lowering the flame temperature reduced NOx emissions. Combining 20% H2 and NSPD also increased the flammability limit to φ = 0.35 at a flame temperature of 1350 K, allowing for self-sustained combustion even at low temperatures.

**Keywords:** flame propagation; nanosecond plasma discharges; lean burning; ZDPlaskin; CHEMKIN
