Effect of Port Water Injection on the Knock and Combustion Characteristics for an Argon Power Cycle Hydrogen Engine

Argon power cycle hydrogen engine is an internal combustion engine that employs argon instead of nitrogen of air as the working fluid, oxygen as the oxidizer, and hydrogen as the fuel. Since argon has a higher specific heat ratio than air, argon power cycle hydrogen engines have theoretically higher indicated thermal efficiencies according to the Otto cycle efficiency formula. However, argon makes the end mixture more susceptible to spontaneous combustion and thus is accompanied by a stronger knock at a lower compression ratio, thus limiting the improvement of thermal efficiency in engine operation. In order to suppress the limitation of knock on the thermal efficiency, this paper adopts a combination of experimental and simulation methods to investigate the effects of port water injection on the knock suppression and combustion characteristics of an argon power cycle hydrogen engine. The results show that the port water injection can effectively reduce the knock intensity of the argon power cycle hydrogen engine and optimize the combustion process, thus achieving the improvement of the indicated thermal efficiency and the indicated mean effective pressure. A maximum indicated thermal efficiency of 50.8% was achieved in the test at -5 °CA ATDC ignition time and 2ms per cycle water injection pulse width(15.83mg). However, excessive water injection rather deteriorates the combustion process with a loss of indicated thermal efficiency. Further simulation analysis based on the GT-Power model showed that the indicated thermal efficiency was improved to a maximum value 52.4%, when the water injection was reduced to 13 mg and the ignition time was -6 °CA ATDC.