Pneumatic hybridization of internal combustion engines may prove to be a viable and cost-efficient alternative to electric hybridization. This paper evaluates the effects of pneumatic hybridization of various engine concepts using the criteria of fuel efficiency, driveability, emissions, and cost efficiency.
The most promising engine concept is found to be the pneumatic hybridization combined with downsizing and supercharging spark-ignited engines. With this concept, a fuel consumption reduction of over 30% compared to a standard engine with the same rated power can be achieved. The poor driveability usually associated with heavily downsized and supercharged engines is completely overcome by injecting additional air during transients.
The most important design issues for this new concept are discussed and several possible solutions are presented. Following these considerations, the first fully functional hybrid pneumatic engine was realized.
Experimental results for all additional engine modes are shown, i.e., conventional combustion, supercharged mode, pneumatic motor mode, and pneumatic pump mode. Transient mode switches, beginning with pneumatic engine start, are also tested successfully. Up to now, the experimental results fully confirm the promising simulation results for all engine modes.