A novel layout to charge a single cylinder diesel engine using supercharging and impulse turbo-compounding

Abstract

The benefits of turbocharged internal combustion engines are well established in the literature and mass production. Despite the numerous advantages of turbocharging, commercial single-cylinder engines are generally not turbocharged. This is due to intermittent exhaust gas flow to the turbine, typical for a single-cylinder engine. The current work proposes a novel layout wherein a supercharger boosts the engine to reap the benefits of charging the single-cylinder engine. An impulse turbine salvages part of the exhaust energy from the pulsated flow. A one-dimensional simulation study of the novel supercharged and turbo-compounded single-cylinder engine was carried out, and critical parameters of an impulse turbine were designed. CFD simulation study was carried out to validate the performance of the impulse turbine and the novel layout. This study modified a light-duty naturally aspirated (NA) diesel engine currently in mass production into the supercharged version. A positive displacement supercharger was mechanically coupled to the base NA engine with a suitable belt drive, and steady-state experiments were performed with NA and supercharged versions. One-dimensional AVL boost simulation models were validated for the NA and supercharged engines for brake power, air flow rate and BSFC within a 3% deviation. Nozzles of varying exit diameters were employed at the exhaust pipe. One-dimensional simulations were conducted to predict the supercharged engine performance and the kinetic energy rate available at the exhaust nozzle exit. An optimal nozzle exit diameter was chosen. Base calculations for the impulse turbine were performed with the output from the 1D simulation tool to design the critical features of the blade and the power turbine. The designed impulse turbine was further simulated using a commercially available CFD simulation tool, CONVERGE. CFD results showed that the impulse turbine generated about 1.55 kW of power, equivalent to 39% turbine efficiency. Experimental analysis was conducted on the supercharged engine with the optimal nozzle and the simulated impulse turbine. Results showed significantly improved engine performance with the supercharged and impulse turbine compounded version compared to the base NA version. The brake power output and brake thermal efficiency increased by 34% and 3.8%, respectively. Soot and carbon monoxide (CO) emissions were 80% lower, while unburned hydrocarbon (HC) emissions were 45% lower. However, NO_x emissions were 60% higher, which can be curtailed by established NO_x reduction strategies. Thus, the proposed method of employing a supercharger and compounding an impulse turbine for a single-cylinder diesel engine proved beneficial with improved performance, reduced brake specific fuel consumption and reduced emissions except for NO_x.