Large-eddy simulation of highly underexpanded transient gas jets

Vuorinen, Ville; Yu, Jingzhou; Tirunagari, Santosh; Kaario, Ossi; Larmi, Martti; Duwig, Christophe; Boersma, Bendiks Jan

doi:10.1063/1.4772192

Cited by 154 publications

(174 citation statements)

References 45 publications

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“…For instance, Ashkenas and Sherman [11], Velikorodny and Kudriakov [12] and Vuorinen et al [13] suggested C H values of 0.67, 0.63 and 0.62, respectively. The authors of the current work found that for hydrogen jets with values of NPR up to 10, C H had a value of ~0.65 [14].…”

Section: Mach Disk Dimensionsmentioning

confidence: 99%

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

Hamzehloo

Aleiferis

2016

International Journal of Hydrogen Energy

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The current study used large eddy simulations to investigate the sonic and mixing characteristics of turbulent under-expanded hydrogen and methane jets with various nozzle pressure ratios issued into various ambient pressures including elevated conditions relevant to applications in direct injection gaseous-fuelled internal combustion engines. Due to the relatively low density of most gaseous fuels such as hydrogen and methane, DI requires high injection pressures to achieve suitable mass flow rates for fast in-cylinder fuel delivery and rapid fuel-air mixing. Such pressures typically form an under-expanded fuel jet past the nozzle exit. Test cases of hydrogen injection with nozzle pressure ratio (NPR) of 10 issued into quiescent air with pressure P ∞ ≈1, 5 and 10 bar were simulated. Direct comparison between hydrogen and methane jets with NPR=8.5 and P ∞ ≈1 was also made. The effect of ambient pressure on features of transient development of the nearnozzle shock structure and tip vortices (vortex ring) was investigated. It was observed that at constant NPR, higher ambient pressure resulted in slightly faster formation of the Mach reflection and shorter Mach disk settlement time. Different mechanisms were observed between hydrogen and methane with regards to transient formation of their initial tip vortex rings. It was found that the initial transient tip vortices of hydrogen jets may also contribute to the flow instabilities at the boundary of the intercepting shock and, unlike for methane, promote fuel-air mixing before the Mach reflection. It was also shown that the nearnozzle shock structure was only affected by NPR regardless of the ambient pressure. Furthermore, no flow recirculation zone was found just downstream of the Mach disk, a finding comparable to all previous experimental investigations. Also, it was observed that a locally richer mixture was created for jets with higher NPR or with higher ambient pressure at constant NPR. Based on the results of the current study, correlations were proposed for the shock cell spacing and jet tip penetration of highly under-expanded jets issued from millimetre-size circular nozzles.

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Section: Mach Disk Dimensionsmentioning

confidence: 99%

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

Hamzehloo

Aleiferis

2016

International Journal of Hydrogen Energy

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“…However, the respective constant C w is highly dependent on the pressure ratio. For nitrogen, the value of C w increases for higher pressure ratios; for instance, when the pressure ratio increased from 4 to 8, C w was calculated to vary from 0.15 to 0.7 in [39]. Assuming hydrogen as an ideal gas and with similar Mach disk characteristics to nitrogen, Equation (1) may be used to estimate the width of the Mach disk W disk for under-expanded hydrogen jets.…”

Section: Straight and Stepped Nozzlesmentioning

confidence: 99%

“…The height of the Mach disk (H disk ) can be calculated using the empirical relation in Equation (1). The value of the constant C has been suggested to be 0.67 for pressure ratios higher than 10 and 0.55 for smaller pressure ratios [35,39]. For the pressure ratio of ~67 of Test Case 7 in Figure 10, using C=0.67, the height of the Mach disk H disk is calculated to be ~5.5 times greater than the nozzle diameter (D=0.2 mm).…”

Section: Reference Test Casementioning

confidence: 99%

“…The authors specifically concluded that the resolution that they employed was not adequate to resolve these details. Under-expanded jets have been studied for air and gaseous fuels (primarily natural gas), experimentally [31][32][33][34][35] and by LES [36][37][38][39]. In a recent publication on under-expanded jets, Scarcelli et al [40] validated RANS predictions of a sonic argon jet, injected at a flow rate corresponding to 100 bar nominal injection pressure into atmospheric environment, against experimental data obtained by means of X-ray radiography.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Computational Study of Hydrogen Direct Injection for Internal Combustion Engines

Hamzehloo¹,

Aleiferis²

2013

SAE Technical Paper Series

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Hydrogen has been largely proposed as a possible fuel for internal combustion engines. The main advantage of burning hydrogen is the absence of carbon-based tailpipe emissions. Hydrogen's wide flammability also offers the advantage of very lean combustion and higher engine efficiency than conventional carbon-based fuels. In order to avoid abnormal combustion modes like pre-ignition and backfiring, as well as air displacement from hydrogen's large injected volume per cycle, direct injection of hydrogen after intake valve closure is the preferred mixture preparation method for hydrogen engines. The current work focused on computational studies of hydrogen injection and mixture formation for direct-injection spark-ignition engines. Hydrogen conditions at the injector's nozzle exit are typically sonic. Initially the characteristics of under-expanded sonic hydrogen jets were investigated in a quiescent environment using both Reynolds-Averaged NavierStokes (RANS) and Large-Eddy Simulation (LES) techniques. Various injection conditions were studied, including a reference case from the literature. Different nozzle geometries were investigated, including a straight nozzle with fixed cross section and a stepped nozzle design. LES captured details of the expansion shocks better than RANS and demonstrated several aspects of hydrogen's injection and mixing. Incylinder simulations were also performed with a side 6-hole injector using 70 and 100 bar injection pressure. Injection timing was set to just after inlet valve closure with duration of 6 μs and 8 μs, leading to global air-to-fuel equivalence ratios  typically in the region of 0.2-0.4. The engine intake air pressure was set to 1.5 bar absolute to mimic boosted operation. It was observed that hydrogen jet wall impingement was always prominent. Comparison with non-fuelled engine conditions demonstrated the degree of momentum exchange between in-cylinder hydrogen injection and air motion. LES highlighted details of hydrogen's spatial distribution throughout the injection duration and up to ignition timing. Higher peak velocities were predicted by LES, especially on the tumble plane. With the employed injection strategy, the areas closer to the cylinder wall were richer in fuel than the centre of the chamber close to the end of compression.

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“…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).…”

Section: 44 Page 2 Of 10mentioning

confidence: 99%

Mixing characterization of highly underexpanded fluid jets with real gas expansion

et al. 2018

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We report a comprehensive speed of sound database for multi-component mixing of underexpanded fuel jets with real gas expansion. The paper presents several reference test cases with well-defined experimental conditions providing quantitative data for validation of computational simulations. Two injectant fluids, fundamentally different with respect to their critical properties, are brought to supercritical state and discharged into cold nitrogen at different pressures. The database features a wide range of nozzle pressure ratios covering the regimes that are generally classified as highly and extremely highly underexpanded jets. Further variation is introduced by investigating different injection temperatures. Measurements are obtained along the centerline at different axial positions. In addition, an adiabatic mixing model based on non-ideal thermodynamic mixture properties is used to extract mixture compositions from the experimental speed of sound data. The concentration data obtained are complemented by existing experimental data and represented by an empirical fit.

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Large-eddy simulation of highly underexpanded transient gas jets

Cited by 154 publications

References 45 publications

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

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

Computational Study of Hydrogen Direct Injection for Internal Combustion Engines

Mixing characterization of highly underexpanded fluid jets with real gas expansion

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