Experimental validation of accuracy of dynamic hydrogen-compressed natural gas mixing system using a single cylinder spark ignition engine

Natural gas is considered as one of the best alternate fuels because of its lower emissions and highest H/C ratio amongst hydrocarbons. Its usage requires minimum modifications in the existing engine hardware. Addition of hydrogen to the compressed natural gas (CNG) improves its combustion, performance and emission characteristics. In the present study, a compression ignition (CI) engine was modified to operate on hydrogen enriched compressed natural gas (HCNG) mixtures using port fuel injection in spark ignition (SI) mode. HCNG engine technology is not widespread and HCNG is not available commercially hence there is need of developing an online HCNG mixing system, which can deliver desired HCNG compositions dynamically on demand so that a wide range of experiments can be carried out to determine the optimum mixture composition. Very few researchers have made efforts to develop such a system and because of lack of such a system, majority of HCNG investigations are confined to 3-4 premixed HCNG mixtures. In this study, a dynamic HCNG mixing system was developed for producing different HCNG mixtures. The working of this dynamic mixing system was validated on a single cylinder SI engine for its performance and accuracy in delivering desired HCNG compositions. Experiments were performed for comparing combustion, performance and emission characteristics of dynamic HCNG mixtures with premixed blends, prepared using conventional method, employing Dalton's law of partial pressures. Results showed satisfactory performance of the dynamic mixing system at all engine loads. The HCNG mixture quality was the best at higher engine loads.