Yong Yin

Parameter Study of a Brayton Cycle Waste Heat Recovery System for Turbocharged Diesel Engines

A Brayton cycle waste heat recovery (WHR) system for turbocharged diesel engines was described and the performance of a diesel engine integrated with this system was investigated. The waste heat recovery system is integrated with the turbocharging system of the diesel engine, with the turbocharger compressor working as the Brayton cycle compressor simultaneously.The combined cycle of diesel cycle and Brayton cycle was simulated using the engine cycle simulation code GT-Suite 7.0, and the performance of the Brayton cycle WHR engine was investigated. The turbocharging turbine and the Brayton cycle turbine were designed and their performances were simulated with turbine through-flow model. The mass-flow rates of the diesel cycle and the Brayton cycle have a great influence on their power outputs, which are determined by the turbocharger performance greatly. The influence of the charging turbine geometric parameters on the performance of the Brayton cycle WHR system was discussed. Results show that there is a tradeoff in performance between high and low engine-speed operating conditions with the investigated parameters variation, and different geometric dimensions should be selected when different common operating conditions are considered.Copyright

Through Flow Matching of Power Turbine for a Turbo-Compounded Diesel Engine

Turbo-compounding (TC) is a possible solution to make transportation more ecological. Matching the engine with an appropriate power turbine is the key for the turbo-compounded engine performance optimization. Conventionally, the matching work is based on a turbine map. The influences of the turbine geometry parameters on the engine performance are taken into account.A new matching method based on the turbine through flow model is presented in this paper. The influences of geometry parameters of the power turbine on the diesel engine performance are investigated. The research focuses on the effects of inlet blade radius and height, exit blade angle and tip radius of the power turbine on the engine BSFC and torque. Results show that the outlet blade angle and tip radius have stronger impacts on BSFC and torque of the engine than the inlet blade radius and height. Further studies show that the engine cycle and air mass flow rate are more sensitive to the outlet blade tip radius and angle than the inlet blade radius and height.Copyright

Performance Analysis of an Electric Turbocompounding System for a Hybrid Vehicle Diesel Engine

Waste heat recovery (WHR) is one of the main approaches to improve the internal combustion engine (ICE) overall efficiency and reduce emissions. The electric turbocompounding (ETC) technology is considered as a promising WHR technology for vehicle engines due to its compactness and light weight. In order to improve the overall fuel efficiency of the engine at practical operating conditions, the impacts of the implementation of the ETC system should be investigated not only at engine full load conditions, but also under practical driving cycles.In this paper, an ETC system was designed for a 4.75 L diesel engine, in which a power turbine was installed down-stream to the turbocharger turbine. A performance simulation model of the ETC engine was developed on the basis of the diesel engine model, which was validated against engine performance experimental data. The control strategies of the wastegate of turbocharger turbine, the wastegate of power turbine and the operating torque of generator were determined. The relative variation in BSFC was studied under full range of operating conditions, and results show that the maximum improvement of fuel economy is 6.7% at an engine speed of 1000 rpm and 70% of full load, in comparison with the baseline diesel engine. Main factors lead to the performance differences between the ETC engine and the baseline engine were analyzed. Furthermore, the performance of the ETC engine under the C-WTVC driving cycle was investigated. Results show that the implementation of the ETC system resulted in a 1.2% fuel consumption reduction under the C-WTVC driving cycle.Copyright

Design of Counter-Rotating Turbine to Improve the Off-Design Performance of Turbo-Compounding Systems

Engine turbo-compounding (TC) is an effective technology to improve the engine efficiency and cut down CO2 emission. A power turbine downstream of the conventional turbocharger turbine is used to recover the exhaust energy and transfer it into mechanical work. However, the performance of turbo-compound system deteriorates seriously at engine off-design points. It is mainly caused by the fact that the designs of turbocharger turbine and power turbine are independent from each other, failing to consider the effects of upstream swirls on the downstream power turbine performance.Analysis showed that the off-design conditions, off-design incidence loss, transition duct loss and non-uniformity inlet loss contributed to the deterioration performance of power turbine at off-design conditions. Among these reasons, the incidence loss played significant effect on power turbine’s performance. The current research aims to improve the turbo-compounding performance at engine off-design conditions by counter-rotating turbine (CRT) configuration. CRT consists of a radial-flow turbocharger turbine and an axial-flow power turbine with counter-rotating direction. The main purpose is to decrease the incidence loss and turning loss in the power turbine stator by CRT. Performance comparisons between the counter- and co-rotating turbines have also been conducted.First, meanline analysis was carried out to investigate the influences of design parameters on the velocity triangles and turbine performance. Analysis shows that counter-rotating turbine requires the design of high reaction radial turbine. Then, the 1D preliminary design starts and it is followed by 3D detail design. Finally, the computational fluids dynamic (CFD) method was used to evaluate the counter-rotating turbines performance. Results show that the designed counter-rotating turbine improves the off-design performance effectively, with 3.8% increase of power turbine efficiency points at 1200rpm condition. Further analysis on the flow field was conducted and it was found that the flow angle distribution at upstream turbine exit was highly non-uniformity along the span. To weaken the non-uniformity may be a potential way to further improve the performance of turbo-compounding systems.Copyright