A device for pre-conditioning combustion air at an inlet path (2) to a combustion chamber (4), in which said inlet comprises a set (6) of two or more magnetic fields (8a, 8b, ..) arranged along said inlet path (2). Each magnetic field (8a) has a corresponding north pole (Na, Nb, ..) and a south pole (Sa, Sb, ...) and a magnetic moment vector (10a, 10b, ..) extending from said south pole portion (Sa, Sb, ..) to said north pole (Na, Nb, ..);characterized in that* the magnetic moment vectors (10a, 10b, ..) are arranged mainly perpendicularly with respect to said inlet path (2);* the magnetic moment vectors (10a, 10b, ..) are distributed consecutively along said inlet path (2);* the second or consecutive magnetic field (8b) are arranged with the second or consecutive magnetic moment vector's (10b, ..) pole (Nb (Sb), ..) with the opposite pole adjacent to the inlet path (2) relative to the first or preceding magnetic moment vector's (10a, ..) pole (Sa (Na), ..).