Investigations on Supercharging and Turbo-Compounding of a Single Cylinder Diesel Engine

Despite the advantages of turbocharging in improved engine performance and reduced exhaust emissions, commercial single-cylinder engines used for automotive applications remain naturally aspirated (NA) and are not generally turbocharged. This is due to the shortcomings with pulsated and intermittent exhaust gas flow into the turbine and the phase lag between the intake and exhaust stroke. In the present study, experimental investigations are initially carried out with a suitable turbocharger closely coupled to a single-cylinder diesel engine. Results indicated that the engine power dropped significantly by 40% for the turbocharged engine compared to the NA version even though the air mass flow rate was increased by at least 1.5 times with turbocharging. A novel approach of decoupling the turbine and the compressor and coupling them separately to the engine is proposed to address these limitations. Also, an impulse turbine is chosen for this application, better suited to extract energy during the pulsated exhaust flow. Commercially available AVL Boost software was used to carry out the simulation studies to understand the improvement in overall engine performance with the proposed novel approach compared to the base naturally aspirated engine. Different nozzle area ratios were analyzed to estimate the kinetic energy available at the nozzle exit. An optimum nozzle area ratio of 1:2 for the impulse turbine was arrived, which provided better net engine performance. The net effect of the supercharged and turbo-compounded engine resulted in an improved performance with 43% higher brake power output and 3% higher brake thermal efficiency at the rated power conditions. Thus, the present approach reaped the benefits of charging the single-cylinder diesel engine, which was otherwise impossible by the conventional turbocharging method.