An Active Control Methodology to Improve Pulsatile Turbocharger Operating Conditions and Performance

Abstract As a critical component of an Internal Combustion Engine (ICE), a turbocharger suffers highly pulsatile airflow from the exhaust pipe, which determines the turbocharger performance is very different from that under steady and quasi-steady conditions. Faced with the theoretical and computational challenges associated with the optimization of the inlet and outlet conditions of the turbocharger, this paper presents an active control methodology (ACM) to improve turbocharger operating conditions and performance based on the redistribution of air mass flow and fuel flow. Considering the poor-efficiency of constant pressure turbocharging system and high structural-dependent pulse turbocharging system, the ACM proposes 3 essential steps: extract partial compressed air from the compressor outlet, then heat the compressed air with the appropriate amount of fuel in a burner and finally supply the high-pressure and high-temperature gas to the turbine inlet. These three control steps are executed in every cycle of the engine operating period, which can achieve cycle-level active control for turbine inlet compressor outlet conditions and finally achieve the purpose of overall performance amelioration for turbocharger and engine. In this paper, a two-cylinders two-stroke turbocharged diesel engine with this active control system (ACS) is modeled using 1-D modeling software to validate the effectiveness of the methodology. System performance simulations are conducted with exemplifications of control strategies and 5 different extraction pipe diameters in the 1-D simulation model. Results show that 7mm is the optimal pipe size for the ACS corresponding to the adapted control strategies, which is supported by the 62.5% wider surge margin of the compressor and better instantaneous performance of the turbine. The presented ACM combines the features of high energy utilization for pulse exhaust and stable operating conditions for the turbocharger, which can achieve a wider surge margin and better engine performance. This paper provides an initial and rather unique insight for designing and optimizing the high-performance turbocharging system for engines.