A simulation study quantifying the effects of drive cycle characteristics on the performance of a pneumatic hybrid bus

In the study presented in this paper, the effect of different vehicle driving cycles on the pneumatic hybrid has been investigated. The pneumatic hybrid powertrain has been modeled in GT-Power and validated against experimental data. The GT-Power engine model has been linked with a MATLAB/simulink vehicle model. The engine in question is a single-cylinder Scania D12 diesel engine, which has been converted to work as a pneumatic hybrid. The base engine model, provided by Scania, is made in GT-power and it is based on the same engine configuration as the one used in real engine testing. Earlier studies have shown a great reduction in fuel consumption with the pneumatic hybrid compared to conventional vehicles of today. However, most of these studies have been completely of theoretical nature. In this paper, the engine model is based on and verified against experimental data, and therefore more realistic results can be expected. The intent with the vehicle driving cycle simulation is to investigate the potential of a pneumatic hybrid bus regarding reduction in fuel consumption (FC) compared to a traditional internal combustion engine (ICE) powered bus. The results show that the improvement in fuel economy due to pneumatic hybridization varies heavily with choice of drive cycle. The New York bus drive cycle shows a reduction of up to 58 % for the pneumatic hybrid while the FIGE drive cycle only shows a reduction of 8%. What all cycles have in common is that the main part of the fuel consumption reduction comes from the start/stop-functionality, while regenerative braking only account for a modest part of up to about 12% of the fuel consumption. The results also show that the optimal pressure tank volume varies with drive cycles, ranging from 60 to over 500 liters.