Supercharging with Turbo-Compounding - A Novel Strategy to Boost Single Cylinder Diesel Engines

Mass-production single-cylinder engines are generally not turbocharged due to pulsated exhaust flow. Hence, about one-third of the fuel chemical energy is wasted in the engine exhaust. To extract the exhaust energy and boost the single-cylinder engines, a novel supercharging with a turbo-compounding strategy is proposed in the present work, wherein an impulse turbine extracts energy from the pulsated exhaust gas flow. Employing an impulse turbine for a vehicular application, especially on a single-cylinder engine, has never been commercially attempted. Hence, the design of the impulse turbine assumes higher importance. A nozzle, designed as a stator part of the impulse turbine and placed at the exhaust port to accelerate the flow velocity, was included as part of the layout in the present work. The layout was analyzed using the commercial software AVL BOOST. Different nozzle exit diameters were considered to analyze their effect on the exhaust back pressure and engine performance. A suitable nozzle exit diameter was chosen based on simulation results. The simulated exit conditions of the nozzle were used as inputs for velocity triangle calculations. Based on these calculations, major design features of the impulse turbine, such as blade speed, nozzle exit diameter and stator exit angle, were established. The key parameters were thus designed for the impulse turbine. The designed impulse turbine resulted in about 91% impulse turbine efficiency at rated power conditions. The proposed layout with the designed impulse turbine delivered 68% higher brake power output and improved the engine efficiency by 9.36% compared to the naturally aspirated stock engine.