The research is focused on the ignition of solid fuels in a heated air flow. The experimental conditions correspond closely to solid fuel combustion in coal-fired boiler furnaces. Charcoal, wood, brown and bituminous coals were used as independent solid fuels and as fuel mixture components. The particle sizes of these fuels were less than 40 μm, 40–140 μm, 140–250 μm, 250–375 μm and 375–800 μm. They were ignited under the conditions of radiant-convective heating as they were moving in a heated air flow with a temperature of 500–800 °C and at a velocity of 5 m/s. The ignition delay time was the main investigated characteristic, recorded by a high-speed video camera. The induction period of bituminous coal shortens by 25–35% when 25–50% brown coal or wood in an air-dry state is added. The lowest ignition delay times were established for the fuel mixtures of bituminous coal with dry charcoal. The experimental curves of the ignition delay times of fuels and their mixtures versus the heated air temperature were presented as approximation equations. Based on the conducted research findings, a muffle burner design with a vortex structure of the fuel-air flow was proposed for the fuel oil-free start-up of coal-fired boilers. Display omitted •Oil-free start-up of coal-fired boilers can be put into practice.•Adding 25–50% of highly reactive components to the main solid fuel reduces ignition time by 25–35%.•Particle size of fuel mixtures should not exceed 250 μm.•They are reliably ignited within 0.1–0.2 s at an oxidizer flow temperature of 500–800 °C.•Design of a burner unit for fuel oil-free start-up of a coal-fired boiler was proposed.