A typical gaseous fuel multi-point injection system of modern S.I. engines is composed of the following main elements (see Fig. 1): the gas tank (11), the pressure regulator and the filter (5 and 6), and the fuel rail (12) which feeds each injector (8). In the setup of Fig. 1 the fuel is injected into the inlet duct (port injection). The regulator reduces the gas pressure from the high level in the tank (10 bar for LPG while CNG is stored at around 200 bar) to the low level in the fuel rail (about 10 bar for CNG and 2 bar for LPG).