Validation of the Fuel Saving Potential of Downsized and Supercharged Hybrid Pneumatic Engines Using Vehicle Emulation Experiments

The pneumatic hybridization of power trains is especially effective when it is combined with strong downsizing and supercharging of spark ignited engines. This paper presents measurement results obtained from such an engine. Specifically, performance measurements for all additional engine modes are shown. The pneumatic motor mode and the pneumatic pump mode are individually optimized over their whole operating range for maximum recuperation efficiency. Jointly with the conventional combustion mode and the pneumatic supercharged mode, they are implemented in one engine control system, thereby enabling the switching between all modes. A dynamometer simulates the longitudinal dynamics of two series production vehicles for the modified engine. This experimental setup, defined as emulation, is used to accurately measure the engine’s fuel consumption in the MVEG-95 and federal test procedure (FTP) drive cycles. Causal and noncausal energy management strategies are presented and used for choosing the engine mode during a drive cycle. Fuel savings of up to 35% are measured when comparing the modified engine to the vehicles’ standard engines with the same rated power. Hybrid pneumatic vehicles (HPVs) may prove to be a viable alternative to hybrid electric vehicles since fuel savings and driveability are comparable, while the added cost is expected to be substantially lower for HPVs.