Described herein is a microgenerator of electrical energy with a high power density, which uses an internal-combustion micromotor with two combustion chambers set opposite to one another, within which a piston is displaced with reciprocating motion. The piston is at least in part made of magnetic material and is wound with a coil, within which is generated an electric current by induction. The fuel, the oxidant, and preferably a catalyst, are injected into each of the two combustion chambers by means of injectors that are substantially of the same type as those used in ink-jet printer heads. The dimensions of the device are comparable to those of a 1.5-V NiCd battery of a traditional standard type.