Browse Publications Technical Papers 08-07-01-0001

On WTW and TTW Specific Energy Consumption and CO 2 Emissions of Conventional, Series Hybrid and Fully Electric Buses 08-07-01-0001

This also appears in SAE International Journal of Alternative Powertrains-V127-8EJ

Making use of a specifically designed dynamical vehicle model, the authors here presented the results of an activity for the evaluation of energy consumption and CO2 emissions of buses for urban applications.
Both conventional and innovative (series hybrid, and fully electric) vehicles were considered to obtain interesting comparative conclusions. The derived tool was used to simulate the dynamical behaviour of these vehicles on a number of kinematic profiles measured during real buses operation in different contexts, varying from really congested city centre routes to fast-lane operated services.
It was so possible to evaluate the energetic performances of those buses on a Tank-to-Wheel (TTW) basis. Results were also extended to a Well-To-Wheel (WTW) basis making use of numerical and experimental results about Well-to-Tank (WTT) energy consumption by the JRC (Joint Research Centre) of the European Union, to take into account the use of different energy vectors (gasoil vs electricity).
Sensitiveness of energy consumption with the main influencing parameters was evaluated and, in coherence with the CorInAIR program (defined within the UE and already applied to conventional means), the coefficients of the required interpolating curves describing TTW energy consumption dependence on bus payload, road slope and mean service speed were calculated and made available for the scientific community, for the three bus categories already identified within the CorInAIR program (8 m, 12 m and 18 m long buses) and for an additional 6 m reference small bus representing those means specifically conceived for urban application in UE historical city centres.
Calculated data clearly showed that, both in terms of TTW and WTW specific energy consumption, as well as in terms of specific CO2 emissions, BEV buses are normally the optimal solution, with some limited exception regarding some operative conditions of the small 6 m long buses.
Instead, the convenience between conventional a series hybrid configurations showed to be strongly dependent on vehicle size and on its specific operation conditions.


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