• • Pingshuo coal ash has Si+Al >85% and Si/Al <1.5, with FT >1550 °C, necessitating flux addition for entrained-flow gasification.
• • Adding 20% calcium-sodium composite flux (CaO/Na2O = 3:7) reduces FT to 1377 °C and 1279 °C for two coal ashes, outperforming single CaO or Na2O additions.
• • Composite flux induces formation of low-melting minerals (nepheline, albite, gehlenite) and inhibits mullite, enabling low-temperature eutectic melting.
• • MD simulations show that below 1600 K, Na+ enhances atomic diffusion (higher MSD) and disrupts silicate networks, facilitating Ca2+ coordination with [AlO4]5- and further breaking Si-O-Si bonds.