Study on pneumatic-fuel hybrid system based on waste heat recovery from cooling water of internal combustion engine

The paper proposes a novel pneumatic-fuel hybrid system, which combines a traditional internal combustion engine (ICE) and a pneumatic engine. One important merit of this concept is that the system can recover waste from cooling water of internal combustion engine to optimize the working process of pneumatic engine, and thus to improve the entire efficiency of the hybrid system. Meanwhile, energy-saving effect due to lower cooling fan power can be achieved on ICE by waste heat recovery of pneumatic engine. Based on thermodynamic analysis, an experimental system is designed and established for verification. The experimental results show that the performance of pneumatic engine is improved when the waste heat recovery concept of the hybrid system is applied. Then an application example on a 4-cylinder engine is analyzed and discussed using numerical simulation. The results show that the fan power of the ICE cooling system can be saved up to 50% by applying the hybrid system. Considering the appreciable improvements on the energy efficiency with only limited system modifications when the concept is applied to traditional ICE based power systems, the proposed hybrid concept has the potential to serve as an alternative technology aiming for energy saving and emission reduction.