Developmental Status of Internal Combustion-Hydrostatic Storage Power Systems for City Bus Lines

Various regenerative power systems have been hypothesized for vehicle use; the most promising are the internal combustion engine-flywheel and the internal combustion-hydrostatic storage designs. The paper reviews the latter.

Hydrostatic storage encompasses compression of gas~usually nitrogen~during periods of energy storage, powered either by the primary combustion circuit or recouped from braking processes. Low losses provide high conversion efficiency (e.g., 99% for energy storage) although energy storage per weight ratios are lower than those of flywheel systems. Automatic controls facilitate regulation of energy conversion processes; the paper correlates these processes with different driving operations.

Passenger bus frames are well suited for the system's spatial requirements. A trial bus completed 4500 km of suburban operations. Fuel savings amounted to 20%; since fuel costs represent 5% of a conventional bus's total costs, the additional equipment costs were not offset. Increase of energy storage concentration values is considered crucial for economic feasibility