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Thermoelectric generators (TEGs) have become a promising technology for vehicle exhaust heat recovery. Although the complex vehicle driving conditions may lead to significant variation of TEG performance, such influence was rarely paid attention to. In this study, a numerical model of thermoelectric generator (TEG) based on vehicle waste heat recovery is developed. When the acceleration duration is short, the hot side temperature increases quickly at first with an overshoot phenomenon. When the acceleration durations increase or the acceleration range becomes smaller, the overshoot phenomenon becomes weaker. The change of the voltage and power generally follows the same trend. The performance variation of TEGs becomes more significant with faster acceleration or deceleration. The transient response of the hot and cold side temperatures, voltage and power in deceleration is less significant than acceleration, because in deceleration, the cold side temperature increases first due to the weakened heat convection. For the step change of vehicle speed, when the speed is low, the voltage and power curves and the speed curve are more consistent, and a longer step duration leads to better consistency. A higher road grade can increase the power output of TEG significantly, and lead to a faster transient response. The Japanese 10–15 cycle, New European Driving Cycle (NEDC) and Urban Driving Dynamometer Schedule (UDDS) are selected to evaluate the impact of different driving cycles. The results suggest that a highly frequent change of driving condition may have a negative effect on the TEG performance.

Thermoelectric generators (TEGs) have become a promising technology for vehicle exhaust heat recovery. Although the complex vehicle driving conditions may lead to significant variation of TEG performance, such influence was rarely paid attention to. In this study, a numerical model of thermoelectric generator (TEG) based on vehicle waste heat recovery is developed. When the acceleration duration is short, the hot side temperature increases quickly at first with an overshoot phenomenon. When the acceleration durations increase or the acceleration range becomes smaller, the overshoot phenomenon becomes weaker. The change of the voltage and power generally follows the same trend. The performance variation of TEGs becomes more significant with faster acceleration or deceleration. The transient response of the hot and cold side temperatures, voltage and power in deceleration is less significant than acceleration, because in deceleration, the cold side temperature increases first due to the weakened heat convection. For the step change of vehicle speed, when the speed is low, the voltage and power curves and the speed curve are more consistent, and a longer step duration leads to better consistency. A higher road grade can increase the power output of TEG significantly, and lead to a faster transient response. The Japanese 10–15 cycle, New European Driving Cycle (NEDC) and Urban Driving Dynamometer Schedule (UDDS) are selected to evaluate the impact of different driving cycles. The results suggest that a highly frequent change of driving condition may have a negative effect on the TEG performance.

With the rapid growth and development of proton-exchange membrane fuel cell (PEMFC) technology, there has been increasing demand for clean and sustainable global energy applications. Of the many device-level and infrastructure challenges that need to be overcome before wide commercialization can be realized, one of the most critical ones is increasing the PEMFC power density, and ambitious goals have been proposed globally. For example, the short- and long-term power density goals of Japan's New Energy and Industrial Technology Development Organization are 6 kilowatts per litre by 2030 and 9 kilowatts per litre by 2040, respectively. To this end, here we propose technical development directions for next-generation high-power-density PEMFCs. We present the latest ideas for improvements in the membrane electrode assembly and its components with regard to water and thermal management and materials. These concepts are expected to be implemented in next-generation PEMFCs to achieve high power density.

With the rapid growth and development of proton-exchange membrane fuel cell (PEMFC) technology, there has been increasing demand for clean and sustainable global energy applications. Of the many device-level and infrastructure challenges that need to be overcome before wide commercialization can be realized, one of the most critical ones is increasing the PEMFC power density, and ambitious goals have been proposed globally. For example, the short- and long-term power density goals of Japan's New Energy and Industrial Technology Development Organization are 6 kilowatts per litre by 2030 and 9 kilowatts per litre by 2040, respectively. To this end, here we propose technical development directions for next-generation high-power-density PEMFCs. We present the latest ideas for improvements in the membrane electrode assembly and its components with regard to water and thermal management and materials. These concepts are expected to be implemented in next-generation PEMFCs to achieve high power density.

In this study, the performance of two high-temperature proton exchange membrane fuel cell (HT-PEMFC) systems has been investigated by using the method of exergy analysis under different operating conditions, one of the systems is directly fueled by hydrogen (direct hydrogen system), and another by methane (natural gas) with steam methane reforming (reformed hydrogen system). The results indicate that for both systems, a higher fuel cell operating temperature tends to increase the efficiency and power output of the system. However, higher inlet air relative humidity and operating pressure has insignificant influence on improving the quality of both systems. Fuel cell stack is the place where exergy loss is the highest, which means more efforts should be focused on improving the energy exchange efficiency and decreasing the irreversibility of fuel cell to increase the system efficiency.

In this study, the performance of two high-temperature proton exchange membrane fuel cell (HT-PEMFC) systems has been investigated by using the method of exergy analysis under different operating conditions, one of the systems is directly fueled by hydrogen (direct hydrogen system), and another by methane (natural gas) with steam methane reforming (reformed hydrogen system). The results indicate that for both systems, a higher fuel cell operating temperature tends to increase the efficiency and power output of the system. However, higher inlet air relative humidity and operating pressure has insignificant influence on improving the quality of both systems. Fuel cell stack is the place where exergy loss is the highest, which means more efforts should be focused on improving the energy exchange efficiency and decreasing the irreversibility of fuel cell to increase the system efficiency.

AbstractA pore-scale contamination model is developed to resolve the physicochemical processes in the anode catalyst layer for a deeper insight into the hydrogen sulfide (H2S) contamination mechanism. The present model is based on lattice Boltzmann method (LBM) and a novel iteration algorithm is coupled to overcome the time-scale issue in LBM which can extend its application. The microstructure of CL is stochastically reconstructed considering the presence of carbon, Pt, ionomer, and pores. The proposed model is validated by comparing the experimental data and can accurately predict the effect of H2S contamination on performance with time. The results show that the fuel cell performance is not sensitive to the anode Pt loading under the clean fuel condition as the hydrogen oxidation reaction is easy to activate. However, higher Pt loading can effectively prolong the operation time under the H2S contamination by providing a larger buffer reactive area and a lower H2S concentration condition. Furthermore, the H2S contamination in the fuel gas should be strictly restricted as it directly affects the poisoning rate and significantly affects the operation time. Graphical abstract Physicochemical processes in the ACL with reactant transport through micro porous layer (MPL) to active Pt sites

AbstractA pore-scale contamination model is developed to resolve the physicochemical processes in the anode catalyst layer for a deeper insight into the hydrogen sulfide (H2S) contamination mechanism. The present model is based on lattice Boltzmann method (LBM) and a novel iteration algorithm is coupled to overcome the time-scale issue in LBM which can extend its application. The microstructure of CL is stochastically reconstructed considering the presence of carbon, Pt, ionomer, and pores. The proposed model is validated by comparing the experimental data and can accurately predict the effect of H2S contamination on performance with time. The results show that the fuel cell performance is not sensitive to the anode Pt loading under the clean fuel condition as the hydrogen oxidation reaction is easy to activate. However, higher Pt loading can effectively prolong the operation time under the H2S contamination by providing a larger buffer reactive area and a lower H2S concentration condition. Furthermore, the H2S contamination in the fuel gas should be strictly restricted as it directly affects the poisoning rate and significantly affects the operation time. Graphical abstract Physicochemical processes in the ACL with reactant transport through micro porous layer (MPL) to active Pt sites

Abstract This paper presents a comprehensive study of the effects of n-heptane low temperature reforming (LTR) products on n-heptane/LTR products ignition characteristics by two-dimensional direct numerical simulation (2-D DNS) and zero-dimensional (0-D) reactor under advanced compression ignition engine-like conditions. N-heptane/LTR products reactivity controlled compression ignition is a concept based on “single-fuel” reactivity controlled compression ignition. Two reforming gas compositions are obtained through a reforming-cooling combined process, and the parent fuel (n-heptane) conversion rates are 66.0% and 85.6%, respectively. LTR products are found to retard or promote the ignition depending on the initial mixture composition and temperature in both 2-D DNS and 0-D reactor. Particularly, 0-D results show that LTR products will suppress the ignition event at low initial temperature, while with more n-heptane addition, LTR products will help to shorten the ignition delay time. Moreover, the Negative Temperature Coefficient (NTC) behavior is weakened with LTR products, and this phenomenon is more obvious with higher degree LTR products. Finally, based on the chemical reaction pathway analysis, it is found that the onset of low temperature ignition is advanced in the presence of LTR products, but it may delay the high temperature ignition (HTI). The basic reason of LTR products effect on HTI attributes to heat accumulation in the early phase. This heat accumulation depends on not only the production of active radicals before the crossover temperature around 1000 K, but also the competition of active radicals between LTR products and n-heptane.