• Energy Research

Abstract It is very important for the diesel engine to achieve a cold startup at low environmental temperature especially in the region with the temperature in the range of −40 °C to 0 °C. Thus, the specific cold start characteristics, such as gas leakage, heat loss and clearance volume, should be investigated in detail. In order to investigate the cold start ability, an improved thermodynamic model for thermodynamic parameters is developed. The prediction of ignition temperature is the closest to the experimental values when the adiabatic index is equal to 1.34 for the compressed gas. The thermodynamic results show that the compression pressure is the most sensitive to the gas leakage rate, followed by the heat transfer loss rate and reference clearance volume. The gas leakage, heat loss and clearance volume are employed to investigate the cold start ability for the diesel engine, which provide a better reference for strengthening the cold start capacity research. The small clearance volume and big initial intake air temperature can improve the exergy of diesel engine. In addition, the entropy production increases with the increase of clearance volume. Similarly, the exergy of system will reduce with the increase of entropy production. Finally, the improvement suggestions for cold starting performance enhancement of the diesel engine are proposed.

Abstract It is very important for the diesel engine to achieve a cold startup at low environmental temperature especially in the region with the temperature in the range of −40 °C to 0 °C. Thus, the specific cold start characteristics, such as gas leakage, heat loss and clearance volume, should be investigated in detail. In order to investigate the cold start ability, an improved thermodynamic model for thermodynamic parameters is developed. The prediction of ignition temperature is the closest to the experimental values when the adiabatic index is equal to 1.34 for the compressed gas. The thermodynamic results show that the compression pressure is the most sensitive to the gas leakage rate, followed by the heat transfer loss rate and reference clearance volume. The gas leakage, heat loss and clearance volume are employed to investigate the cold start ability for the diesel engine, which provide a better reference for strengthening the cold start capacity research. The small clearance volume and big initial intake air temperature can improve the exergy of diesel engine. In addition, the entropy production increases with the increase of clearance volume. Similarly, the exergy of system will reduce with the increase of entropy production. Finally, the improvement suggestions for cold starting performance enhancement of the diesel engine are proposed.

Abstract Hydrocarbon fuel and hydrogen are used as fuels for micro power equipment to replace traditional batteries and provide energy for micro-electromechanical systems, which has become a hot research direction. However, due to the reduction in the size of micro power equipment, not only the flame in the micro combustor is affected, but the overall energy conversion efficiency of micro power equipment is also affected by the size effect. Therefore, it is significance to analyze the energy loss and design optimization methods pertinently from the point of energy conversion. In the past ten years, many researchers have done research about the direction, which has been reviewed in this article. For the flame optimization, the influencing parameters of optimization methods such as exhaust gas recirculation, cavity combustor, bluff body combustor, porous media combustion, and hydrocarbon fuels mixed with hydrogen are summarized. For the micro-thermal photoelectric system, the influence parameters of combustion efficiency, radiant efficiency, spectral efficiency, view factor efficiency and photovoltaic cell efficiency are analyzed. In the micro-thermoelectric system, the influence parameters of combustion efficiency, heat conduction efficiency and thermoelectric conversion efficiency are analyzed. For the micro internal combustion engine, the influencing parameters of combustion efficiency and conversion efficiency are analyzed. Finally, the technical limitations and development of each micro power equipment are summarized in this article.

Abstract Hydrocarbon fuel and hydrogen are used as fuels for micro power equipment to replace traditional batteries and provide energy for micro-electromechanical systems, which has become a hot research direction. However, due to the reduction in the size of micro power equipment, not only the flame in the micro combustor is affected, but the overall energy conversion efficiency of micro power equipment is also affected by the size effect. Therefore, it is significance to analyze the energy loss and design optimization methods pertinently from the point of energy conversion. In the past ten years, many researchers have done research about the direction, which has been reviewed in this article. For the flame optimization, the influencing parameters of optimization methods such as exhaust gas recirculation, cavity combustor, bluff body combustor, porous media combustion, and hydrocarbon fuels mixed with hydrogen are summarized. For the micro-thermal photoelectric system, the influence parameters of combustion efficiency, radiant efficiency, spectral efficiency, view factor efficiency and photovoltaic cell efficiency are analyzed. In the micro-thermoelectric system, the influence parameters of combustion efficiency, heat conduction efficiency and thermoelectric conversion efficiency are analyzed. For the micro internal combustion engine, the influencing parameters of combustion efficiency and conversion efficiency are analyzed. Finally, the technical limitations and development of each micro power equipment are summarized in this article.

Abstract An environmental life cycle assessment of a pilot scale microbial electrolysis cell for hydrogen production was performed for the first time in this study. The microbial electrolysis cell system was designed based on the existing pilot plants with urban wastewater flow rate of 65 L·d−1 at wastewater strength of 500 mg COD·L−1. The effect of the performance parameters of the microbial electrolysis cell on life cycle results was analyzed with SimaPro 8.2.3.0. The results showed that the emissions per kg hydrogen-produced from construction phase are the greatest among all phases of the current microbial electrolysis cell system. An increase in cathodic gas recovery and hydrogen production rate resulted in a decrease in emissions per kg hydrogen-produced from the operation and construction of the microbial electrolysis cell. In addition, the total life cycle emissions decreased with increasing of the cathodic gas recovery and electricity transformation efficiency, and increase with increasing applied voltage. The global warming potential from the operation phase was 18.8 kg carbon dioxide-eq/kg hydrogen under the following conditions: applied voltage of 0.5 V, electricity transformation efficiency of 90%, and cathodic gas recovery of 90%. Compared with existing hydrogen production and wastewater treatment technologies, the current microbial electrolysis cell technology for hydrogen production from wastewater can still be improved in terms of environmental benefits and technical maturity. Nevertheless, microbial electrolysis cell technology with optimized operation parameters will hopefully become an important choice of hydrogen production and wastewater treatment technology in the future.

Abstract An environmental life cycle assessment of a pilot scale microbial electrolysis cell for hydrogen production was performed for the first time in this study. The microbial electrolysis cell system was designed based on the existing pilot plants with urban wastewater flow rate of 65 L·d−1 at wastewater strength of 500 mg COD·L−1. The effect of the performance parameters of the microbial electrolysis cell on life cycle results was analyzed with SimaPro 8.2.3.0. The results showed that the emissions per kg hydrogen-produced from construction phase are the greatest among all phases of the current microbial electrolysis cell system. An increase in cathodic gas recovery and hydrogen production rate resulted in a decrease in emissions per kg hydrogen-produced from the operation and construction of the microbial electrolysis cell. In addition, the total life cycle emissions decreased with increasing of the cathodic gas recovery and electricity transformation efficiency, and increase with increasing applied voltage. The global warming potential from the operation phase was 18.8 kg carbon dioxide-eq/kg hydrogen under the following conditions: applied voltage of 0.5 V, electricity transformation efficiency of 90%, and cathodic gas recovery of 90%. Compared with existing hydrogen production and wastewater treatment technologies, the current microbial electrolysis cell technology for hydrogen production from wastewater can still be improved in terms of environmental benefits and technical maturity. Nevertheless, microbial electrolysis cell technology with optimized operation parameters will hopefully become an important choice of hydrogen production and wastewater treatment technology in the future.

Abstract An investigation on non-premixed H2/air combustion in a cylindrical micro combustor has been carried out. The effects of porous media and outer wall thickness on the combustion characteristics, flame location, thermal performance and energy conversion efficiency of the thermo photovoltaic (TPV) system were investigated. For the application of micro TPV system, a high and uniform outer wall temperature distribution is indispensable for the sustaining output, and the high energy efficiency is desirable. The results indicate that the setting of porous media or the increase of outer wall thickness can enhance the heat transfer in micro combustor and affects the flame stability, and the micro combustor with porous media and outer wall thickness b = 0.2 mm obtains the lowest flame location. They are also conducive to the improvement of outer wall temperature and energy efficiency, the outer wall temperature of the micro combustor with a thicker outer wall and porous media is relatively uniform and the energy conversion efficiency of micro TPV system is also improved, the micro combustor with b = 0.6 mm and porous media is more suitable for the application of micro TPV system. Additionally, the external thermal environment also can improve the outer wall temperature profile and the working performance of the micro combustor.

Abstract An investigation on non-premixed H2/air combustion in a cylindrical micro combustor has been carried out. The effects of porous media and outer wall thickness on the combustion characteristics, flame location, thermal performance and energy conversion efficiency of the thermo photovoltaic (TPV) system were investigated. For the application of micro TPV system, a high and uniform outer wall temperature distribution is indispensable for the sustaining output, and the high energy efficiency is desirable. The results indicate that the setting of porous media or the increase of outer wall thickness can enhance the heat transfer in micro combustor and affects the flame stability, and the micro combustor with porous media and outer wall thickness b = 0.2 mm obtains the lowest flame location. They are also conducive to the improvement of outer wall temperature and energy efficiency, the outer wall temperature of the micro combustor with a thicker outer wall and porous media is relatively uniform and the energy conversion efficiency of micro TPV system is also improved, the micro combustor with b = 0.6 mm and porous media is more suitable for the application of micro TPV system. Additionally, the external thermal environment also can improve the outer wall temperature profile and the working performance of the micro combustor.

Abstract In this work, a three-dimensional mathematical model is established to investigate the flow and the heat transfer of the combustion process and the distribution characteristics of temperature field in the wall-flow in porous media of the wall-flow diesel particulate filter (DPF) based on the Field Synergy Theory (FST). The results indicate that there is the smallest temperature uniformity coefficient in wall-flow DPF when the inlet velocity is 36 m/s. And at first, the microwave assisted regeneration temperature increases and then decreases as the exhaust temperature rises which is affected by the exhaust temperature. The data indicate that the inlet pressure can change the angle between velocity vector and temperature gradient, which leads to the change of synergy degree of the velocity field and temperature field. When the inlet pressure is 0.08 MPa, there is an optimal synergy degree with the maximum average temperature.