A Numerical Analysis of Hydrogen Underexpanded Jets Under Real Gas Assumption

Abstract

This work examines the fluid dynamic structure of underexpanded gas jets by using a highperformance computing (HPC) methodology in order to untangle the question of whether it is necessary to include the real gas assumption dealing with hydrogen jets. The answer to this question is needed in order to guarantee accurate numerical simulations of such jets in practical engineering applications, such as direct-injection hydrogen engines. An axial symmetric turbulent flow model, which solves the Favre-averaged Navier-Stokes equations for a multicomponent gas mixture, has been implemented and validated. The flow model has been assessed by comparing spreading and centreline property decay rates of subsonic jets at different Mach numbers with those obtained by both theoretical considerations and experimental measurements. Besides, the Mach disk structure of underexpanded jets has been recovered, thus confirming the suitability and reliability of the computational model. To take into account the effects of real gases, both van der Waals and Redlich-Kwong equations of state have been implemented. The analysis of a highly underexpanded hydrogen jet with total pressure equal to 75 MPa, issuing into nitrogen at 5 MPa, shows that the use of real gas equations of state affects significantly the jet structure in terms of temperature, pressure, and Mach number profiles along the jet centerline and also in terms of jet exit conditions, with differences up to 38%.

Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures

“…It is believed that due to the negative Joule-Thomson coefficient of hydrogen, the temperature profile very close to the nozzle exit may not be predicted accurately by the ideal gas equation of state (EoS) employed here. As it has been presented by some researchers [38,41], for hydrogen jets with extremely high injection pressures (P 0 >>100 bar) using a real gas EoS like Redlich-Kwong, resulted in capturing a higher temperature than that of ambient just after the Mach disk. The specific effect of a real gas EoS for the current flow is under on-going study by the current authors and it will be discussed in a future publication.…”

“…Recently large eddy simulation (LES) was employed to investigate under-expanded methane and nitrogen jets [13,35]. However, very limited experimental and computational studies are available in the literature on under-expanded hydrogen and methane jets and specifically with respect to applications in DI gaseous engines [36][37][38][39][40][41]. Recently, the authors of the present paper used LES to investigate the near-nozzle shock structure and mixing characteristics of highly under-expanded hydrogen and methane jets with NPR=8.5-70 issuing from a circular nozzle into a low ambient pressure (P ∞ ≈1 bar) [14,42].…”

Mixing characterization of highly underexpanded fluid jets with real gas expansion

“…Consequently, considerable efforts have been made in recent years to develop reliable numerical frameworks (e.g., Banholzer et al 2017;Hamzehloo and Aleiferis 2016a;Velikorodny and Kudriakov 2012;Vuorinen et al 2013;Mohamed and Paraschivoiu 2005;Bonelli et al 2013;Khaksarfard et al 2010).…”

Real-Gas Effects and Phase Separation in Underexpanded Jets at Engine-Relevant Conditions

“…The variables a ij and b i in Eq. (8) are calculated using the corresponding state principle and can therefore be evaluated dependent on the EoS, see Tab. elements of a ij the respective critical parameters of the pure components are used, see Tab.…”

“…Challenges resulting from the direct injection of gaseous fuels at high pressure ratios are the gas dynamics of the near-nozzle flow structure, the gaseous jet penetration and the fuel-oxidizer mixing. These fluid dynamic aspects are accompanied by strong pressure and temperature changes leading to non-negligible real-gas effects, see, e.g., Khaksarfard et al [7] and Bonelli et al [8]. In Fig.…”