This review examines the potential of hydrogen,ammonia,and biodiesel as alternative fuels,focusing on spray dynamics,droplet evaporation,combustion,and emissions.Hydrogen offers superior combustion characteristics but...This review examines the potential of hydrogen,ammonia,and biodiesel as alternative fuels,focusing on spray dynamics,droplet evaporation,combustion,and emissions.Hydrogen offers superior combustion characteristics but faces challenges in NO_(x)emissions.Strategies like nonpremixed direct injection,increased intake boost pressure,and low-pressure EGR are suggested for robust hydrogen combustion in compression-ignition engines.Control of hydrogen start of injection(SOI)and water injection(WI)are identified as effective techniques for reducing NO_(x)emissions.Ammonia shows inferior combustion and higher NO_(x)and unburned NH_(3)emissions in the same conditions as conventional fuels with conventional engines.Understanding ammonia spray and evaporation conditions is significant for optimizing an ammonia-air mixture and minimizing wall impingement and ammonia trap in the crevice,thereby improving combustion and emission reduction.Increasing intake pressure,injection pressure,and EGR rate,employing a turbulent jet,and preheating ammonia improve efficiency and reduce NO_(x)emissions.Utilizing ammonia combustion requires the implementation of after-treatment systems such as NH_(3)adsorber and De NO_(x)catalysts to mitigate unburned NH_(3)and NO_(x)emissions.Biodiesel affects the fuel supply system,combustion,and emission characteristics according to its viscosity and density.Increasing injection pressure and blending with volatile fuels enhance spray and combustion.Optimum biodiesel preheating temperatures for the injection pump and injector are crucial for achieving the best pump capacity and spray formation.By utilizing biodiesel-PODE blends and investigating low-temperature biodiesel combustions,there is potential to improve thermal efficiency and PMNO_(x)trade-off.Therefore,carbon-neutral fuel adoption should be accelerated to mitigate CO_(2)emissions,highlighting the importance of combustion techniques and emissions reduction strategies.展开更多
Vehicle evaporation is an essential source of VOCs in cities but is not well understood in China.Reported emission factors from previous studies are not enough for understanding the atmospheric chemical process of veh...Vehicle evaporation is an essential source of VOCs in cities but is not well understood in China.Reported emission factors from previous studies are not enough for understanding the atmospheric chemical process of vehicular evaporative VOCs.In this work,a serious of detailed VOCs speciation profiles are developed based on test processes and emission processes.A mass balance method was used to divide different emission processes during diurnal tests.The results show that headspace vapor of gasoline cannot represent the real-world vehicle evaporation because of the significant differences in VOCs speciation profiles,especially for aromatics.To further distinguish emissions from evaporation and exhaust,only the ratios of MTBE/benzene and MTBE/toluene can serve as indicators when considering species from all evaporative processes.Besides,emissions from different sources change significantly with the seasons.To solve these problems,we developed a monthly comprehensive evaporation speciation profile.The individual profiles at the emission processes are weighted by the emission of the in-use vehicle fleet in Beijing to derive the comprehensive speciation profile of evaporative VOCs.Ozone formation potential(OFP)and secondary organic aerosol potential(SOAP)were used to evaluate the environmental impact.For SOAP,100 g evaporative emissions are equal to 6.05-12.71 g toluene in different months,much higher than that given using headspace vapors,especially in winter(7.2 times higher in December).These findings would improve our understanding of the evaporative VOCs emissions in China and their environmental impacts(e.g.,O3 and SOA formation).展开更多
基金supported by the Laboratory of Space Utilization and D-Drive Project,Hokkaido University,Japan。
文摘This review examines the potential of hydrogen,ammonia,and biodiesel as alternative fuels,focusing on spray dynamics,droplet evaporation,combustion,and emissions.Hydrogen offers superior combustion characteristics but faces challenges in NO_(x)emissions.Strategies like nonpremixed direct injection,increased intake boost pressure,and low-pressure EGR are suggested for robust hydrogen combustion in compression-ignition engines.Control of hydrogen start of injection(SOI)and water injection(WI)are identified as effective techniques for reducing NO_(x)emissions.Ammonia shows inferior combustion and higher NO_(x)and unburned NH_(3)emissions in the same conditions as conventional fuels with conventional engines.Understanding ammonia spray and evaporation conditions is significant for optimizing an ammonia-air mixture and minimizing wall impingement and ammonia trap in the crevice,thereby improving combustion and emission reduction.Increasing intake pressure,injection pressure,and EGR rate,employing a turbulent jet,and preheating ammonia improve efficiency and reduce NO_(x)emissions.Utilizing ammonia combustion requires the implementation of after-treatment systems such as NH_(3)adsorber and De NO_(x)catalysts to mitigate unburned NH_(3)and NO_(x)emissions.Biodiesel affects the fuel supply system,combustion,and emission characteristics according to its viscosity and density.Increasing injection pressure and blending with volatile fuels enhance spray and combustion.Optimum biodiesel preheating temperatures for the injection pump and injector are crucial for achieving the best pump capacity and spray formation.By utilizing biodiesel-PODE blends and investigating low-temperature biodiesel combustions,there is potential to improve thermal efficiency and PMNO_(x)trade-off.Therefore,carbon-neutral fuel adoption should be accelerated to mitigate CO_(2)emissions,highlighting the importance of combustion techniques and emissions reduction strategies.
基金supported by the National Key R&D Program(2016YFC0201504)the National Natural Science Foundation of China(Nos.41822505 and 41571447)+2 种基金National Research Program for Key Issues in Air Pollution Control(DQGG0201&0207)Beijing Nova Program(Z181100006218077)SEE Foundation.
文摘Vehicle evaporation is an essential source of VOCs in cities but is not well understood in China.Reported emission factors from previous studies are not enough for understanding the atmospheric chemical process of vehicular evaporative VOCs.In this work,a serious of detailed VOCs speciation profiles are developed based on test processes and emission processes.A mass balance method was used to divide different emission processes during diurnal tests.The results show that headspace vapor of gasoline cannot represent the real-world vehicle evaporation because of the significant differences in VOCs speciation profiles,especially for aromatics.To further distinguish emissions from evaporation and exhaust,only the ratios of MTBE/benzene and MTBE/toluene can serve as indicators when considering species from all evaporative processes.Besides,emissions from different sources change significantly with the seasons.To solve these problems,we developed a monthly comprehensive evaporation speciation profile.The individual profiles at the emission processes are weighted by the emission of the in-use vehicle fleet in Beijing to derive the comprehensive speciation profile of evaporative VOCs.Ozone formation potential(OFP)and secondary organic aerosol potential(SOAP)were used to evaluate the environmental impact.For SOAP,100 g evaporative emissions are equal to 6.05-12.71 g toluene in different months,much higher than that given using headspace vapors,especially in winter(7.2 times higher in December).These findings would improve our understanding of the evaporative VOCs emissions in China and their environmental impacts(e.g.,O3 and SOA formation).
