Question

charcoal or coal burn with glow not flame why

Answer 1

Charcoal is a solid fuel. This is the reason that it can't vaporious on heating. so that's why coal not burn by producing flame..

Answer 2

Coal or charcoal does not produce flame when burnt because it does not vapourizes, only those substances which vapourizes on burning produce flame like wax , natural gas. Substances that undergoes rapid combustion have lower ignition temperature and coal and charcoal do not vaporize while burning that's why does not produce flame.