Vehicle driving cycle simulation of a pneumatic hybrid bus based on experimental engine measurements

In the study presented in this paper, a vehicle driving cycle simulation of the pneumatic hybrid has been conducted. 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. During pneumatic hybrid operation the engine can be used as a 2-stroke compressor for generation of compressed air during vehicle deceleration and during vehicle acceleration the engine can be operated as a 2-stroke air-motor driven by the previously stored pressurized air. There is also a possibility to use the stored pressurized air in order to supercharge the engine when there is a need for high torque, like for instance at take off after a standstill or during a overtake maneuver. Previous experimental studies have shown that the pneumatic hybrid is a promising concept with great possibility for fuel consumption reduction during city-driving conditions. Earlier studies have shown a great reduction in fuel consumption whit 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 the pneumatic hybrid regarding reduction in fuel consumption (FC) compared to a traditional internal combustion engine (ICE) powered vehicle. The results show that a reduction in fuel economy of up to about 30% is possible for a pneumatic hybrid bus on the Braunschweig duty cycle. The main part of this reduction comes from the stop/start functionality of the system, while regenerative braking only contributes with 8.4 % to the reduction in FC. The results also show that an amazing 87% of the braking power can be absorbed and converted to compressed air. However, only a small portion of this energy, about 20%, can be converted to positive work.