An evaluation of future energy conversion systems including fuel cell

Transcription

1 An evaluation of future energy conversion systems including fuel cell T. S. Saitoh, A. Yoshimura 2 & N. Yamada Graduate School of Environmental Studies, Tohoku University, Sendai, Japan 2 Yanmar Co. Ltd., Japan Abstract This paper presents a comparison among various vehicles when using fossil fuels and renewable energy. In the case of using fossil fuel, we compared 5 key factors among the fuel cell electric vehicle (), internal combustion engine (ICE) vehicle (gasoline or diesel), battery-powered and hybrid vehicles. Comparison factors are cruising range, carbon dioxide (CO 2 ) emissions, waste heat rejection, air pollutants and noise. According to this comparison, hybrid, battery-powered and fuel cell electric vehicle have better potentials than ICE vehicles. In the case of utilizing renewable energy, will become the mainstream among various vehicles. In addition, will play an important role until that age. Moreover, we designed a high efficiency from the viewpoint of fuel effective utilization. This vehicle not only has fuel cell, but also various energy utilization and storage systems, for example, battery, flywheel and PV cell. This vehicle has excellent fuel economy more than km/liter. The proposed will be very promising to mitigate urban and global warming, and to conserve fossil fuel consumption. Further, the effect of the introduction of the above environment compatible vehicles into urban area will be discussed by 3-D heat island simulations. Introduction Urban environment in mega-cities like Tokyo is getting worse and worse. For example, the concentration of NO 2 is still increasing and has risen gradually above the regulated level in the Tokyo metropolitan area. The cause of aggravation in the urban environment can be mainly attributed to the increase of 24 WIT Press, ISBN

2 68 Urban Transport X automobiles in this area. Another serious environmental issue is "urban warming (i.e. heat island )", which is caused by concentrated consumption of energy in the urban area. In order to resolve the problems, new energy conversion systems should be established. This paper presents a comparison among various vehicles when using fossil fuels and renewable energy. In case of using fossil fuel, we compared 5 key factors among the fuel cell electric vehicle (), internal combustion engine (ICE) vehicle (gasoline or diesel), battery-powered and hybrid vehicles. Comparison factors are cruising range, carbon dioxide (CO 2 ) emissions, waste heat rejection, air pollutants and running noise. According to this comparison, hybrid, battery-powered and fuel cell electric vehicle have better potentials than ICE vehicles. On the other hand, in case of utilizing renewable energy, will become the mainstream among vehicles. will play an important role until that age. Moreover, we designed a high efficiency in order to use fuel more effectively. This vehicle has not only fuel cell, but also various energy utilization and energy storage systems, for example, battery, flywheel and PV cell. This vehicle has excellent fuel economy more than 9km/liter. The proposed will be very promising to mitigate urban and global warming, and to conserve fossil fuel consumption. Further, the effect of the introduction of environmentally compatible vehicles will be shown by 3-D heat island simulations. 2 Comparison in case of using fossil fuels 2. Cruising range and CO 2 emissions We compared the fuel cell electric vehicle () with internal combustion engine (ICE) vehicle (gasoline or diesel), battery-powered and hybrid vehicles. Figure (a) shows the comparison among these vehicles for a cruising range under Japanese 5 schedule. Assumed that these vehicles have same energy storage capacity (corresponds to 3 liters of gasoline) and same parameter excluding engine and energy storage mass. The fuel of is selected from hydrogen-storing alloy, liquid hydrogen, high-pressure hydrogen and methanol. In this case, liquid hydrogen run the longest range than the other vehicles. s run longer range than the ICE vehicles and battery-powered, because has higher efficiency than ICE. Next, Figure (b) shows a comparison of CO 2 emissions including CO 2 emitted in the fuel production process. Hydrogen-storing alloy has the lowest CO 2 emissions, because hydrogen emits no CO 2 in running in the urban area. Methanol has higher emissions than hydrogen, because methanol fuel needs reforming for producing hydrogen and then CO 2 is emitted. But all has about half CO 2 emissions compared with ICE vehicles. 24 WIT Press, ISBN

3 Urban Transport X Battery- Powered Battery- Powered Cruising range,km (a) Carbon emissions,kg-c/km (b) Figure : Comparison of (a) cruising range and (b) Carbon dioxide emissions among various vehicles, ; Fuel cell electric vehicle with hydrogen-storing alloy; 2; Fuel cell electric vehicle with liquid hydrogen; 3; Fuel cell electric vehicle with high-pressure hydrogen; 4; Fuel cell electric vehicle with methanol. 2.2 emissions and NOx emissions In Fig.2(a), we will show a comparison of waste heat emissions among various vehicles. In the ICE vehicles, the thermal efficiency is much less than the Carnot efficiency. The thermal efficiency of the hybrid vehicle (HV) is better than that of ICE vehicles. The running energy of is 2.7 times larger than that of ICE vehicle. However, the waste heat emissions emitted when the vehicles run in the urban area becomes a subject of discussion. When running in the urban area, the thermal efficiency of electric vehicle () is the best since no waste heat is emitted. Figure 2(b) shows a comparison of NOx emissions per unit distance among various vehicles. In this comparison, NOx emitted in fuel production process is also included. Hydrogen and emits no NOx and air pollutant matters when it running. Methanol emits a very small mount of NOx(/35 of gasoline vehicle), which is emitted in the reforming process. (hydrogen) (methanol) Battery- Powered emissions,mj/km (a) (hydrogen) (methanol) Battery- Powered NOx emissions,g-nox/km (b) Figure 2: Comparison of (a) waste heat emissions and (b) NOx emissions per unit distance among various vehicles. 24 WIT Press, ISBN

4 6 Urban Transport X 2.3 Table shows a contribution of noise source of ordinary vehicles for two running conditions. In acceleration, engine, tire and exhaust contribute largely to making noise. In constant-speed, tire noise occupies 8 % among the whole noise. Figure 3 shows a comparison of noise fraction in acceleration among various vehicles. levels of gasoline and vehicles are set to be unity. and are much quieter than the HV and ICE vehicles. Table : Contribution of noise source for two running conditions. source Tire Engine Traction Cooling sys. Suction Exhaust Others Acceleration % Constant-speed % Batterypowered fraction Figure 3: Comparison of noise fraction among various vehicles. Cruising 走行距離 range Cruising range 走行距離 Cruising range 走行距離 騒音.5.5 CO2 2 騒音 CO C O 2 騒音.5 CO CO2 2 Cruising 走行距離 range Cruising range 走行距離 Cruising range 走行距離.5 騒音 CO 2 騒音.5 CO CO2 2 騒音.5 CO2 2 Battery-powered (methanol) (liq.hydrogen) Figure 4: Pentagon comparison among gasoline,, hybrid, batterypowered, (methanol), and (hydrogen). 24 WIT Press, ISBN

5 Urban Transport X Pentagon comparison among various vehicles Figure 4 shows a pentagon comparison among various vehicles. The area enclosed by pentagonal diagram indicates a total performance for environment. The larger area means the better performance. HV, and battery-powered have advantage over the ICE vehicles for 5-key factors. These vehicles will be promising to mitigate urban and global environment. 3 Comparison when using renewable energy In the future, if fossil fuels run out eventually, we have to utilize renewable energies including solar, wind, hydroelectric, and biomass etc. as energy source of vehicles. In this case, battery-powered and are available for the future vehicle, which can use electric power produced from renewable energy. Battery-powered Solar energy % PV Battery conversion charging 5% 95% Total efficiency : 2.8% Motor efficiency 9% PV conversion 5% Electrolytic conversion 5% Fuel cell 4% Motor efficiency 9% Total efficiency : 2.7% Figure 5: Comparison of total efficiency between battery-powered and fuel cell if electricity were produced originally from renewable energy. The change of fossil fuel Utilization of renewable energy about solar, wind, water and biomass Battery-powered 2 year 2~22 Figure 6: Transition of fossil fuel to renewable energy. 24 WIT Press, ISBN

6 62 Urban Transport X Figure 5 shows a comparison of total efficiency between battery-powered and if electricity were produced originally from solar energy. Total efficiency of battery-powered is superior to that of because needs electrolytic conversion, while can directly use electricity from photovoltaic (PV) conversion. Figure 6 shows predicted transition of fossil fuel to renewable energy. Fossil fuels will be run out and in the long run, the renewable energies will be only energy source in the future (for ex. at end of the 2st century). In case of utilizing renewable energy, will become the mainstream among vehicles. In addition, will play an important role until that age. 4 Optimal design of fuel cell electric vehicle According to the comparison mentioned above, is promising in the near future. However, fuel cell has no energy storage system in itself. In this section, we will evaluate optimal specifications of a high efficiency equipped with battery, flywheel and PV cell. We call this as the hybrid. Table 2 shows principal specifications for the hybrid. Li-ion battery has the highest energy density among chemical batteries. On the other hand, the energy density of the flywheel made of CFRP is three times as high as Pb battery, which has been frequently used for the automobiles. The most noticeable feature of the flywheel (Bitterly []) is that it has a very fast charging rate compared with the conventional chemical batteries. It can restore more than 7 % of the total kinetic energy, while the other batteries can restore only about %. If the flywheel were employed in the hybrid, it is expected that the weight of the battery can be reduced considerably [3]. Berndt et al. [2] have already described a flywheel energy storage system, with 93% energy storage efficiency, developed for passenger transit vehicles by which over 3% fuel savings can be achieved on urban driving cycles. Table 2: Principal specifications for hybrid. Curb weight kg 822 Drag coefficient.2 Frontal projected area m Coefficient of rolling resistance. Motor efficiency % 9 PV cell Area m 2.8 Module efficiency % 5 Energy density Wh/kg 36 Fuel cell 35 kw Output density W/kg 35.5 Auxiliary equipment % 7 Type Li-ion Battery (Li-ion) 5 kw Energy density Wh/kg 3 Output density W/kg 2 Regeneration and energy storage device Flywheel kg 2 24 WIT Press, ISBN

7 Urban Transport X 63 PV cells are placed on the roof of the vehicle as shown in Fig. 7. Whenever the vehicle is parked, the area of PV module can be extended to collect as much energy as possible. PV cell Fly wheel Fuel cell system Li-ion battery Controller In-wheel motor Figure 7: Imaginary sketch of the hybrid. Table 3: Fuel consumption rate ( 5 mode), running cost, and transport cost for gasoline, pure, with Li-ion battery, with Li-ion battery + Flywheel, and with Li-ion battery + Flywheel + PV cell. Fleet Fuel consumption rate km/liter Running cost Yen/km Transport cost kj/(km kg) (5cc) Hydrogen Pure Methanol Daytime 2.2 electricity 4 +Battery (Li-ion) Nighttime.8 electricity 5 Daytime 2. +Battery electricity (Li-on)+Flywheel + Battery (Li-ion) +Flywheel + PV cell (Community-drive mode) Nighttime electricity Table 3 shows a result of running simulation of the hybrid. In order to validate the effectiveness of the flywheel and PV cell, the running simulations for daily use of the were performed by using the community-drive 24 WIT Press, ISBN

8 64 Urban Transport X mode [4]. This mode has been developed for testing an actual running mode in the urban area and includes deceleration, acceleration, and braking patterns. Two driving periods are scheduled at the worker s commuter time in the morning and evening hours. During daytime, it is assumed that the is parked at a sunny place and charged by the PV panel. The hybrid has an excellent fuel consumption rate more than km/liter, running cost and transport cost. The proposed hybrid will be very promising to mitigate urban and global warming, and to conserve fossil fuel consumption. 5 Effect of reduction of CO 2 emissions In the previous section, the hybrid was designed to reduce urban warming and air pollution including CO 2 emissions in the urban area. In the future, if the concept of the hybrid were accepted to almost all the vehicle, the urban atmospheric environment will be improved significantly. In this section, the effect of reduction of CO 2 emissions in the urban area by the 3-D computer simulations will be shown. 5. CO emissions in Tokyo metro area 2 In the Tokyo metro area, it was reported that the annual mean concentration of CO 2 in 997 reached 39 ppmv, and its maximum value took about 6 ppmv. These values are higher than the global background concentration (about 37 ppmv). Namely, it is seen that the greenhouse effect is more evident in the urban atmosphere than the global one. In Chiyoda, Chuo and Minato wards which occupy the central area of Tokyo, it was estimated that the annual CO 2 emissions per square meter is larger than the other wards, and average annual CO 2 emissions by the gasoline consumption is 2.83 kg/m 2 in the Tokyo metro area. 5.2 Simulation results and discussion In order to evaluate CO 2 emissions due to the gasoline consumption, the authors carried out two 3-D simulations. One is for the present Tokyo corresponding to the gasoline consumption, and another is for the present Tokyo without gasoline consumption. In this simulation, the equation of radiant heating balance by CO 2 was solved to evaluate the greenhouse effect. For further details of the simulation model including governing equation, see the literature by Saitoh et al. [6][7][8][9]. Figure 8 shows the horizontal and vertical contours of the reduced fraction (ppmv) of CO 2 concentration at z=.5 m and y=8.9 km. At the heart of Tokyo where the gasoline consumption is very high, the reduced fraction is more than 3 ppmv. It is seen that the reduced fraction over the urban area is relatively 24 WIT Press, ISBN

9 Urban Transport X 65 higher than that over the rural areas. It is evident that the heat island plume formed over the urban area causes this phenomenon. TOKYO (Summer, 8:) z=.5 m N 3 2 TOKYO BAY Reduced fraction of CO 2 concentration, ppmv 3 2 TOKYO (Summer, 8:) y=8.9 km 3 2 Reduced fraction of CO 2 concentration, ppmv x, km Figure 8: x, km Reduced fraction (ppmv) of CO 2 concentration in Tokyo metro area when CO 2 emissions due to gasoline consumption are reduced. TOKYO (Summer, 8:) z=.5 m N 3 2 TOKYO BAY x, km Figure 9: Decrease of ambient temp., ºC TOKYO (Summer, 8:) 3 2 y=8.9 km x, km Temperature decrease in Tokyo metro area when CO 2 emissions due to gasoline consumption are reduced Decrease of ambient temp., ºC Figures 9 show the decrease temperature in the same case. Maximum temperature decrease during the period of the simulation is about.2 o C at z=.5m. This temperature decrease is prominent in the urban area where the ground surface temperature is also high. In particular, temperature decrease over the urban area is comparatively high. This phenomenon corresponds to the contours of reduced fraction of CO 2 concentration shown in Fig Conclusion In this article, a comparison among various vehicles was conducted for the future vehicles. Comparison factors are cruising range, carbon dioxide (CO 2 ) emissions, waste heat emissions, air pollutants and running noise. Further, the new environmentally compatible vehicle (hybrid ) was designed and proposed 24 WIT Press, ISBN

10 66 Urban Transport X to reduce urban warming, air pollution and CO 2 emissions in the urban area. Principal specifications of the hybrid were clarified. The following conclusions may be drawn from the present study. () According to the present comparison, hybrid, battery-powered and fuel cell electric vehicle have better potentials than gasoline and diesel vehicles. In case of utilizing renewable energy, will become the mainstream among vehicles. In addition, will play an important role until that age. (2) We designed an ideal hybrid for the purpose of fuel effective utilization. This vehicle has not only fuel cell, but also various energy utilization and storage systems, for example, battery, flywheel and PV cell. This vehicle has excellent fuel economy more than km/liter. (3) The proposed hybrid will be very promising to mitigate urban warming, global warming, and to conserve fossil fuel consumption. (4) The 3-D simulation results indicate that if the proposed concept of the hybrid were accepted in almost the all gasoline powered vehicle in the urban area, the reduction of CO 2 emissions can significantly mitigate air pollution and urban warming as well as global warming. References [] Bitterly, J.G., Flywheel Technology Past, Present, and 2st Century Projections, Proc. of IECEC, pp , 997. [2] Berndt, J., Jänig, N., Jefferson, C., Lohner, A. and Thoolen, F., Brake Energy Recovery in Urban Transport, Proc. of Urban Transport and the Environment VII, pp64-65, 22. [3] Jefferson, C.M. and Ackerman, M., A Flywheel Variator Energy Storage System, Energy Conversion and Management, 37(), pp.48-49, 996. [4] Saitoh, T.S., Hoshi, A., Yamada, N., Yoshimura, A. and Ando, D., A Grand Design of Future Advanced Electric Vehicle Powered by Fuel Cell, Battery, Flywheel and Photovoltaic Cell., Proc. of Urban Transport and the Environment VII, pp , 22. [5] Timony, C.M, Ultralight Vehicles : Principles and Design, Proc. of S-3 Session 5A, 996. [6] Saitoh, T.S. and Yamada N., 3-D Simulation of Urban Warming in Tokyo and Proposal of Air-cooled City Project, Proc. of ASME-JSME Joint Thermal Engineering Conference, CD-ROM, 999. [7] Saitoh, T.S., Urban Warming and Energy Consumption in Metropolitan Tokyo. Proc. of Urban Metabolism, Kobe, pp.-8, 993. [8] Saitoh, T.S., Shimada, T. and Hoshi, H., Modeling and Simulation of the Tokyo Urban Heat Island. Atmospheric Environment 3(2), pp , 996. [9] Saitoh, T.S. and Yamada, N., Evaluation of Effective Temperature Scale under Heat Island Formation, Int. J. JSME, Series B, 44(), pp.-8, WIT Press, ISBN