Self-Regulating System for Natural Gas Cooling in a Bimodal Internal Combustion Engine

Natural gas is an attractive option for transportation applications in the United States due to its abundant availability and potential for reduced emissions. The scarcity of refueling resources imposes a barrier to widespread use of natural gas in internal combustion engines. The development of a novel bi-modal engine capable of operating in a compressor mode provides refueling capabilities without any supplemental devices and attempts to overcome this infrastructure limited barrier. Heat generated in the compression process however results in undesirable effects such as increased work input for compression, pre-heating of natural gas stored in the fuel tank, and thermal loads in the components used in the modified cylinder head. In order to make the system self-contained, heat exchangers that utilize engine coolant as a heat sink are included in the system design to maintain natural gas temperatures at an acceptable level in between compression stages. This is planned to be done in a novel fashion so as to make the system self-regulating permitting the cooling of natural gas while maintaining the coolant temperature in the cylinder head at acceptable levels to maintain combustion efficiency. To this end, an EES model of the system that incorporates elements of the original vehicle coolant system and modifications made to incorporate the heat exchangers is developed and analyzed to ensure satisfactory performance. Parametric studies of system performance as a function of varying heat loads are used to determine the best strategy to maintain acceptable natural gas temperatures without causing a drop in engine performance.