DiGas dual-fuel system is cost-effective, highly scalable, safe for engine, easy and fast to install. The system is tailored for a wide range of locomotive engines, providing diesel like power performance, but without the harmful emissions and particulate matter. It applies the principle of “port injection” (gas injected through the existing air-intake valves) for aftermarket engines and direct injection for new engines with high compression ratio. This approach means no significant adjustments to engine design are required and high reliability is retained. The system is comprised of functional modular blocks, contained in a universal infrastructure network.