Thermodynamic Analysis of CNG Fast Filling Process of Composite Cylinder Type IV

Abstract

Due to ecological and economic advantages, natural gas is used as an alternative fuel in the transportation sector in the form of compressed natural gas (CNG) and liquefied natural gas (LNG). Development of infrastructure is necessary to popularize vehicles that use alternative fuels. Selected positive factors from EU countries supporting the development of the CNG market were discussed. The process of natural gas vehicle (NGV) fast filling is related to thermodynamic phenomena occurring in a tank. In this study, the first law of thermodynamics and continuity equations were applied to develop a theoretical model to investigate the effects of natural gas composition on the filling process and the final in-cylinder conditions of NGV on-board composite cylinder (type IV). Peng–Robinson equation of state (P-R EOS) was applied, and a lightweight composite tank (type IV) was considered as an adiabatic system. The authors have devised a model to determine the influence of natural gas composition on the selected thermodynamic parameters during fast filling: Joule–Thomson (J-T) coefficient, in-cylinder gas temperature, mass flow rate profiles, in-cylinder mass increase, natural gas density change, ambient temperature on the final natural gas temperature, influence of an ambient temperature on the amount of refueled natural gas mass. Results emphasize the importance of natural gas composition as an important parameter for the filling process of the NGV on-board composite tank (type IV).

Effects of Hydrogen, Methane, and Their Blends on Rapid-Filling Process of High-Pressure Composite Tank

“…The temperature of methane, which has the positive values of the µ J−T coefficient, decreases during expansion, whereas hydrogen, with a negative µ J−T coefficient, heats up. The temperature change in relation to pressure is directly correlated to the value of the Joule-Thomson coefficient µ J−T ; thus, it is recommended to ascertain this coefficient during the filling process of the composite tank [24,29,30].…”

“…The analysis results indicate a decrease in the temperature of methane (Sample 1) in the composite tank, whereas, for pure hydrogen (Sample 4), the temperature rises rapidly at the onset of the refueling process. The initial decline in methane temperature (Sample 1) at the outset of composite tank filling is ascribed to the Joule-Thomson effect, which takes place during the isenthalpic expansion at the orifice, from the reservoir tank's inlet pressure of 35.5 MPa to the initial low pressure within the composite tank exceeding 0.101325 MPa [24,29,50]. During the rapid-filling process, the injected gas mixes with the gas initially present in the tank, compressing it.…”

“…It was assumed that the type IV composite tank maintains a constant volume and possesses only one entry point (inlet). A full description of the thermodynamic analysis of the composite tank fast-filling process is presented in our previous work [24].…”

“…The present chapter clarifies the methodologies used for calculating these properties. Detailed procedures for computing most of the thermodynamic parameters of gases can be found in [24,26,27,42,43].…”

“…Galassi et al performed CFD simulations for hydrogen fast filling (up to 70 MPa) to evaluate the hydrogen temperature inside the tank during this process [18]. Although there is a focus on modeling the process of filling cylinders with hydrogen [19][20][21][22][23], some studies have also explored the thermodynamic parameters involved in the rapid filling of cylinders with compressed natural gas (types III and IV) [24][25][26][27][28][29][30][31]. This research, therefore, serves to critically analyze, compare, and provide new insights into the operational intricacies of hydrogen and CNG filling processes, contributing towards more efficient, safer, and cost-effective strategies for high-pressure gas storage in composite cylinders.…”