Search Results (11)

The turbocharging of hydrogen fuel cell systems (FCSs) has recently become a prominent research area, aiming to improve FCS efficiency to help decarbonise the energy and transport sectors. This work compares the performance of an electrically assisted variable-geometry turbocharger (VGT) with a fixed-geometry turbocharger (FGT) by optimising both the sizing of the components and their operating points, ensuring both designs are compared at their respective peak performance. A MATLAB-Simulink reduced-order model is used first to identify the most efficient components that match the fuel cell air path requirements. Maps representing the compressor and turbines are then evaluated in a 1D flow model to optimise cathode pressure and stoichiometry operating targets for net system efficiency, using an accelerated genetic algorithm (A-GA). Good agreement was observed between the two models’ trends with a less than 10.5% difference between their normalised e-motor power across all operating points. Under optimised conditions, the VGT showed a less than 0.25% increase in fuel cell system efficiency compared to the use of an FGT. However, a sensitivity study demonstrates significantly lower sensitivity when operating at non-ideal flows and pressures for the VGT when compared to the FGT, suggesting that VGTs may provide a higher level of tolerance under variable environmental conditions such as ambient temperature, humidity, and transient loading. Overall, it is concluded that the efficiency benefits of VGT are marginal, and therefore not necessarily significant enough to justify the additional cost and complexity that they introduce. Full article

The present paper studies the degradation of an ethylene propylene diene monomer (EPDM) due to aging within an environment resembling the conditions inside the turbine stage of an electrically assisted turbocharger for fuel cell applications, with a special focus on the influence of the system resonance. Aging experiments were conducted on EPDM O-rings of different thicknesses and compression levels, evaluating their degradation and determining its impact on system functionality. The study also quantified changes in system resonance and created an Arrhenius law-based forecast model. The unique activation energy for the degradation processes was identified, providing insight into the optimal dimension and compression of EPDM O-rings. Full article

The objective of this study is to understand how each variable impacts the optimal configuration of a marine diesel engine equipped with an electric hybrid air-charging system that allows energy assistance and recovery. The aim is to minimize CO₂ emissions by reducing fuel consumption. The hybrid system offers flexibility in adjusting parameters from both the engine and air-charging system. It is compared with the baseline engine, which uses a free-floating turbocharger. The results show a significant improvement at low engine loads, where the baseline engine struggles to provide sufficient air. While turbine speed has little influence, compressor power reduces fuel consumption at low loads. However, at mid loads, resizing the turbomachine is necessary for further improvements. At high loads, full optimization of all variables is required to reduce fuel consumption. The electric hybrid system is particularly effective in tugboat-like conditions, where low loads dominate, but less impactful for ro-pax ferries. Despite the potential of the hybrid system, a fully optimized turbocharger could provide greater benefits due to reduced losses. Future studies could explore combining the adaptability of the hybrid system with a highly efficient turbocharger to reduce emissions across all load conditions. Full article

The implementation of increasingly stringent emissions and efficiency targets has seen engine downsizing and other complementary technologies increase in prevalence throughout the automotive sector. In order to facilitate ongoing improvements associated with the use of these strategies, delivering enhancements to the performance and stability of the turbocharger compressor when operating at low mass flow rates is of paramount importance. In spite of this, a few concepts (either active or passive) targeting such aims have successfully transitioned into use in automotive turbochargers, due primarily to the requirement for a very wide compressor-operating range. In order to overcome the operational limitations associated with existing pre-swirl generation devices such as inlet guide vanes, this study developed a concept comprising of an electrically driven axial fan mounted upstream of a standard automotive turbocharger centrifugal compressor. Rather than targeting a direct contribution to compressor boost pressure, the fan was designed to act as a variable pre-swirl generation device capable of being operated completely independently of the centrifugal impeller. It was envisioned that this architecture would allow efficient generation of the large pre-swirl angles needed for compressor surge margin extension and efficiency enhancement at low mass flow rate-operating points, while also facilitating the delivery of zero pre-swirl at higher mass flow rates to ensure no detrimental impact on performance at the rated power point of the engine. Having progressed through 1-D and 3-D aerodynamic modelling phases to understand the potential of the system, detailed component design and hardware manufacture were completed to enable an extensive experimental test campaign to be conducted. The experimental results were scrutinized to validate the numerical findings and to test the surge margin extension potential of the device. Compressor efficiency improvements of up to 3.0% pts were witnessed at the target-operating conditions. Full article

This paper presents a method for the performance analysis of high-speed electric machines supplied with pulse-width modulated voltage source inverters by utilizing a fast analytical model. By applying a strict mathematical procedure, effective expressions for the calculation of rotor eddy current losses and electromagnetic torque are derived. Results obtained by the approach suggested in this study are verified by the finite element model, and it is shown that the proposed method is superior in comparison to the finite element method in terms of computation time. The proposed method enables fast parameter variation analysis, which is demonstrated by changing the inverter switching frequency and electric conductivity of the rotor and analyzing the effects of these changes on rotor eddy current losses. The presented work separately models effects of the permanent magnet and pulse-width modulated stator currents, making it suitable for the analysis of both high-speed permanent magnet machines and high-speed induction machines. Full article

To improve the performance of electrically assisted turbochargers (EATs), the influences of the hub profile and the casing profile on EAT performance were numerically studied by controlling the upper and lower endwall profiles. An artificial neural network and a genetic algorithm were used to optimize the endwall profile, considering the total pressure ratio and the isentropic efficiency at the peak efficiency point. Different performances of the prototype EAT and the optimized EAT under variable clearance sizes were discussed. The endwall profile affects an EAT by making the main flow structure in the endwall area decelerate and then accelerate due to the expansion and contraction of the meridional surface, which weakens the secondary leakage flow of the prototype EAT and changes the momentum ratio of the clearance leakage flow and the separation flow in the suction surface corner area. Because the tip region flow has a more significant influence on EAT performance, the optimal casing scheme has a better effect than the hub scheme. The optimization design can increase the isentropic efficiency of the maximum efficiency point by 1.5%, the total pressure ratio by 0.67%, the mass flow rate by 1.2%, and the general margin by 6.4%. Full article

Due to the increasing demand for better fuel economy and increasingly stringent emissions regulations, engine manufacturers have paid attention towards engine downsizing as the most suitable technology to meet these requirements. This study sheds light on the technology currently available or under development that enables engine downsizing in passenger cars. Pros and cons, and any recently published literature of these systems, will be considered. The study clearly shows that no certain boosting method is superior. Selection of the best boosting method depends largely on the application and complexity of the system. Full article

The electrically assisted turbocharger (EAT) shows promise in simultaneously improving the boost response and reducing the fuel consumption of engines with assist. In this paper, experimental results show that 7.8% fuel economy (FE) benefit and 52.1% improvement in transient boost response can be achieved with EAT assist. EAT also drives the need for a new feedback variable for the air system control, instead of the exhaust recirculation gas (EGR) rate that is widely used in conventional turbocharged engines (nominal system). Steady-state results show that EAT assist allows wider turbine vane open and reduces pre-turbine pressure, which in turn elevates the engine volumetric efficiency hence the engine air flow rate at fixed boost pressure. Increased engine air flow rate, together with the reduced fuel amount necessary to meet the torque demand with assist, leads to the increase of the oxygen concentration in the exhaust gas (EGR gas dilution). Additionally, transient results demonstrate that the enhanced air supply from the compressor and the diluted EGR gas result in a spike in the oxygen concentration in the intake manifold (X_oim) during tip-in, even though there is no spike in the EGR rate response profile. Consequently, there is Nitrogen Oxides (NOx) emission spike, although the response of boost pressure and EGR rate is smooth (no spike is seen). Therefore, in contrast to EGR rate, X_oim is found to be a better choice for the feedback variable. Additionally, a disturbance observer-based X_oim controller is developed to attenuate the disturbances from the turbine vane position variation. Simulation results on a high-fidelity GT-SUTIE model show over 43% improvement in disturbance rejection capability in terms of recovery time, relative to the conventional proportional-integral-differential (PID) controller. This X_oim-based disturbance rejection control solution is beneficial in the practical application of the EAT system. Full article

For the purposes of design of a turbocharger centrifugal compressor, a one-dimensional modelling method has been developed and applied specifically to electrically-assisted turbochargers (EAT). For this purpose, a mix of authoritative loss models was applied to determine the compressor losses. Furthermore, an engine equipped with an electrically-assisted turbocharger was modelled using commercial engine simulation software (GT-Power) to assess the performance of the engine equipped with the designed compressor. A commercial 1.5 L gasoline, in-line, 3-cylinder engine was selected for modeling. In addition, the simulations have been performed for an engine speed range between 1000 and 5000 rpm. The design target was an electric turbocharger compressor that could meet the boosting requirements of the engine with noticeable improvement in a transient response. The results from the simulations indicated that the EAT improved the overall performance of the engine when compared to the equivalent conventional turbocharged engine model. Moreover, the electrically-assisted turbochargers (EAT) equipped engine with power outputs of 1 kW and 5 kW EAT was increased by an average of 5.96% and 15.4%, respectively. This ranged from 1000 rpm to 3000 rpm engine speed. For the EAT model of 1 kW and 5 kW, the overall net reduction of the BSFC was 0.53% and 1.45%, respectively, from the initial baseline engine model. Full article

Mass-produced, off-the-shelf automotive air compressors cannot be directly used for boosting a fuel cell vehicle (FCV) application in the same way that they are used in internal combustion engines, since the requirements are different. These include a high pressure ratio, a low mass flow rate, a high efficiency requirement, and a compact size. From the established fuel cell types, the most promising for application in passenger cars or light commercial vehicle applications is the proton exchange membrane fuel cell (PEMFC), operating at around 80 °C. In this case, an electric-assisted turbocharger (E-turbocharger) and electric supercharger (single or two-stage) are more suitable than screw and scroll compressors. In order to determine which type of these boosting options is the most suitable for FCV application and assess their individual merits, a co-simulation of FCV powertrains between GT-SUITE and MATLAB/SIMULINK is realised to compare vehicle performance on the Worldwide Harmonised Light Vehicle Test Procedure (WLTP) driving cycle. The results showed that the vehicle equipped with an E-turbocharger had higher performance than the vehicle equipped with a two-stage compressor in the aspects of electric system efficiency (+1.6%) and driving range (+3.7%); however, for the same maximal output power, the vehicle’s stack was 12.5% heavier and larger. Then, due to the existence of the turbine, the E-turbocharger led to higher performance than the single-stage compressor for the same stack size. The solid oxide fuel cell is also promising for transportation application, especially for a use as range extender. The results show that a 24-kWh electric vehicle can increase its driving range by 252% due to a 5 kW solid oxide fuel cell (SOFC) stack and a gas turbine recovery system. The WLTP driving range depends on the charge cycle, but with a pure hydrogen tank of 6.2 kg, the vehicle can reach more than 600 km. Full article

Modern downsized internal combustion engines benefit from high-efficiency turbocharging systems for increasing their volumetric efficiency. However, despite the efficiency increase, turbochargers often lack fast transient response due to the nature of the energy exchange with the engine, which deteriorates the vehicle’s drivability. An electrically-assisted turbocharger can be used for improving the transient response without any parasitic losses to the engine while providing energy recovery for increasing overall system efficiency. The present study provides a detailed numerical investigation on the potential of e-turbocharging to control load and if possible replace the wastegate valve. A parametric study of the optimum compressor/turbine sizing and wastegate area was performed for maximum torque, fast response time and energy regeneration across the real driving conditions speed/load area of the engine. The results showed that the implementation of a motor-generator could contribute to reducing the response time of the engine by up to 90% while improving its thermal efficiency and generating up to 6.6 kWh of energy. Suppressing the wastegate can only be achieved when a larger turbine is implemented, which as a result deteriorates the engine’s response and leads to energy provision demands at low engine speeds. Full article