12-10-2017, 11:26 AM
The Hydrogen Program of Sandia National Laboratories is developing internal combustion engine generators for use in hybrid series vehicles and stationary power units. The program consists of two approaches: to investigate the use of hydrogen in a conventional crankshaft driven engine and in an advanced free piston configuration. The conventional engine program has taken the lead in using the unique spark capability to ignite homogeneous hydrogen fuel / air mixtures at low equivalency ratios (f ≈ 0.4) to achieve low NOx emissions and high thermal efficiency. The goal is to translate the indicated thermal efficiency of single cylinder engines into multi-cylinder configurations, achieving at least a 40% thermal efficiency of brakes. When coupled to an electric generator, the efficiency of converting fuel to electricity would be approximately 37%. A modified Perkins 3.152 diesel engine (850 cm3 per cylinder) is currently being tested and has achieved an indicated thermal efficiency of 45% in preliminary operations. The advanced design of the free piston utilizes a new approach to the combustion of the IC engine. A double-tipped free piston is used for compression to ignite homogeneous fuel / air mixtures as it oscillates within a closed cylinder. Through this oscillation, the electric energy is generated in a linear alternator that also acts to control the movement of the piston by the active adjustment of the electromagnetic forces that the piston feels. Electricity is the output of this motor, and electronic control of the compression ratio is achieved with extreme mechanical simplicity. The new load is introduced into the engine in a modern two-stroke fashion. Initial testing in a single-cycle experiment has validated the potential of this alternative combustion system, as it has produced an indicated thermal efficiency of 56% with essentially zero NOx emissions. The development of these advanced generators continues.