Potential for energy and emissions of asymmetric twin-scroll turbocharged diesel engines combining inverse Brayton cycle system

Abstract

In this paper, a new combined cycle of asymmetric twin-scroll turbocharged diesel engine cycle and inverse Brayton cycle (IBC) for use is proposed. The use of a single asymmetric twin-scroll turbocharged diesel engine cycle is simple in structure and can improve the trade-off between low fuel consumption and nitrogen oxide emissions; however, both the engine exhaust gas recirculation (EGR) rate and the exhaust energy utilization should be further improved. A test bench experiment was performed to validate the numerical models of the single-cycle and combined-cycle approaches. Based on the models, the influence laws of the critical system parameters (turbine asymmetry and the IBC turbine throat area) on the engine performance characteristics were studied. The combined cycle was found to achieve improvements in both the engine EGR rate and the power. Given the same EGR rates at different engine speeds, the power improvement of the combined cycle was found to increase with increasing engine speed and decreasing turbine asymmetry, reaching a maximum of 5.00%. Moreover, further power improvements with an increasing IBC turbine throat area were observed, with the maximum power improvement of 5.78%. Compared with the power turbine, the combined cycle can utilize more waste heat at low and medium engine speeds; thus, the combined cycle is well-suited for use in heavy-duty diesel engines. The new combined cycle described in this report has great potential to provide substantial gains in both engine emissions and energy.