Comparative lifecycle assessment of diesel, hydrogen and electric buses in real driving cycles in Tehran

This study uses real driving cycles of a city bus and a standard driving cycle “WLTP” to implement a full comparison for energy demand and fuel consumption for different propulsion systems (i.e., Diesel ICE, Fuel cell and Electric engines). These results were obtained by simulating each propulsion system in MATLAB, SIMULINK and EES. To better understand the comparison, a life cycle assessment is conducted using “GREET” and “GHGenius” software, which represents a clear demonstration of side effects and emissions of each engine on the environment. The results show that for “WLTP” cycle the bus needs 2423kJ energy for traveling each kilometer while the averaged amount of energy for traveling one kilometer of real driving cycle reaches to 1708kJ, the difference is due to speed range difference and number of stop/start points. In both cycles inertia force consumes the most used energy portion of the bus. By computing total energy use of an electric bus we conclude, electric buses use almost 58% of electric energy for driving and the rest is lost. Then fuel cell and internal combustion engine buses have energy efficiency of 36% and 24% respectively. Concerning LCA analysis, it becomes apparent that unlike efficiency, electric buses are not environmentally benign as fuel cell buses. LCA analysis showed that fuel cell buses that use steam reforming hydrogen production process are a cleaner option than electric buses, for instance a fuel cell bus emit 90 (g/100km) CO, 140 (g/100km) SOx and 67 (g/100km) NOx while an electric bus emit 110 (g/100km), 220 (g/100km) and 99 (g/100km) respectively which in all cases the fuel cell bus is more environment friendly than the electric bus. Finally, since diesel buses produce the most emission, especially CO2, and consume the most energy in the total life cycle, they have no advantage for public transportation fleet.