A downhole steam generation apparatus and method of use are provided. The apparatus may include an injection section, a combustion section, and an evaporation section. The injection section may include a housing, injector elements, and injector plate. The combustion section may include a liner having channels disposed therethrough. The evaporation section may include conduits in fluid communication with the channels and the combustion chamber, and a nozzle operable to inject a fluid from the channels to the combustion chamber in droplet form. A method of use may include supplying fuel, oxidant, and fluid to the apparatus; combusting fuel and oxidant in a chamber while flowing the fluid through a plurality of channels disposed through a liner, thereby heating the fluid and cooling the liner; and injecting droplets of the heated fluid into the chamber and evaporating the droplets by combustion of the fuel and the oxidant to produce steam.