An assembly for producing electric power, including a housing at a first end of which a first substantially cylindrical portion housing a first combustion chamber is formed, and at a second end of which a second substantially cylindrical portion housing a second combustion chamber is formed, wherein a first piston is housed within said first portion of said housing and delimits said first combustion chamber, said first piston being housed free within said first portion of said housing and being arranged to reciprocate therein, and wherein a second piston is housed within said second portion of said housing and delimits said second combustion chamber, said second piston being housed free within said second portion of said housing and being arranged to reciprocate therein, said first piston being connected to a first end of a first rod carrying at its opposed end a third piston and said second piston is connected to a first end of a second rod, carrying at its opposed end a fourth piston, said third piston and said fourth piston defining, together with the walls of said housing, a third combustion chamber formed in an intermediate portion of said housing, said first rod has fastened thereto one or more first supports carrying sets of first magnets or first induction coils, facing sets of stationary first induction coils or stationary first magnets, and said second rod has fastened thereto one or more second supports carrying sets of second magnets or second induction coils which face sets of stationary second induction coils or stationary second magnets, characterized in that said first combustion chamber: is equipped with fuel injection means and with ignition means for fuel ignition; is also equipped with an inlet port in communication with an inlet duct for introducing air into said first combustion chamber, said inlet duct being in communication with an intake duct (11 a) equipped with an intake valve; and is also equipped with an outlet port in communication with an exhaust duct for the outflow of exhaust gases from said first combustion chamber; and wherein said second combustion chamber: is equipped with fuel injection means and with ignition means for fuel ignition; is also equipped with an inlet port in communication with an inlet duct for introducing air into said second combustion chamber, said inlet duct being in communication with an intake duct equipped with an intake valve; and is further equipped with an outlet port in communication with an exhaust duct for the outflow of exhaust gases from said second combustion chamber, wherein said third combustion chamber: is equipped with fuel injection means and with ignition means for fuel ignition; is also equipped with two inlet ports (8c, 8d) in communication with respective inlet ducts (9c, 9d) for introducing air into said third combustion chamber, one of said inlet ducts being in communication with said intake duct of said first combustion chamber through an intake valve, and the other of said inlet ducts being in communication with said intake duct of said second combustion chamber through an intake valve; and is further equipped with two outlet ports (12c, 12d) in communication with said exhaust duct of said first combustion chamber and with said exhaust duct of said second combustion chamber, respectively, for the outflow of exhaust gases from said third combustion chamber. is equipped with fuel injection means and with ignition means for fuel ignition; is also equipped with an inlet port in communication with an inlet duct for introducing air into said second combustion chamber, said inlet duct being in communication with an intake duct equipped with an intake valve; and is further equipped with an outlet port in communication with an exhaust duct for the outflow of exhaust gases from said second combustion chamber, wherein said third combustion chamber: is equipped with fuel injection means and with ignition means for fuel ignition; is also equipped with two inlet ports (8c, 8d) in communication with respective inlet ducts (9c, 9d) for introducing air into said third combustion chamber, one of said inlet ducts being in communication with said intake duct of said first combustion chamber through an intake valve, and the other of said inlet ducts being in communication with said intake duct of said second combustion chamber through an intake valve; and is further equipped with two outlet ports (12c, 12d) in communication with said exhaust duct of said first combustion chamber and with said exhaust duct of said second combustion chamber, respectively, for the outflow of exhaust gases from said third combustion chamber. is equipped with fuel injection means and with ignition means for fuel ignition; is also equipped with two inlet ports (8c, 8d) in communication with respective inlet ducts (9c, 9d) for introducing air into said third combustion chamber, one of said inlet ducts being in communication with said intake duct of said first combustion chamber through an intake valve, and the other of said inlet ducts being in communication with said intake duct of said second combustion chamber through an intake valve; and is further equipped with two outlet ports (12c, 12d) in communication with said exhaust duct of said first combustion chamber and with said exhaust duct of said second combustion chamber, respectively, for the outflow of exhaust gases from said third combustion chamber.