Development and operation of a self-refueling compressed natural gas vehicle

A dual-mode engine has been developed where in one mode all engine cylinders fire normally, providing locomotion for the vehicle. In the other mode, one cylinder of the engine is used to compress low pressure residential natural gas (NG), in multiple stages, to a standard U.S. compressed natural gas (CNG) vehicle storage tank pressure of 248 bar [3600 psig]. This allows a natural gas vehicle (NGV) to be refueled anywhere there is access to the natural gas distribution network. Experimental studies were conducted on this prototype engine and are reported here. Knowledge gained from applying numerical models combined with empirical results led to the realization of a self-refueling natural gas vehicle. On the test stand, air (a surrogate for NG) was compressed by the engine to over 138 bar [2000 psig] filling an 11.8 GGE [140 L] tank in 150 min. On the vehicle platform, the integral compressor had an approximate refueling efficiency of 70%, with an electrical-equivalent parasitic load of 12.6%. Idling of non-compression cylinders and the distance between the compressor and the three-way valves used to control the compression staging were noteworthy sources of inefficiency within the system. At the conclusion of the project the vehicle powered by the dual mode engine was driven over 161 km [100 miles] using self-compressed natural gas which originated from the local utility.