An Experimental Study on High Pressure Pulsed Jets for DI Gas Engine Using Planar Laser-Induced Fluorescence

Yu, Jingzhou; Vuorinen, Ville; Hillamo, Harri; Sarjovaara, Teemu; Kaario, Ossi; Larmi, Martti

doi:10.4271/2012-01-1655

Cited by 32 publications

(22 citation statements)

References 29 publications

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“…The near-nozzle shock structure and the strong compression effects were taken into account by using a bulk viscosity model in conjunction with a second-order filter that was activated at the location of the strong shocks. Vourinen et al [51] also showed that the Mach disk dimensions and shock structure were in very good agreement with the experimental observations of Yu et al [37,52] that included PLIF visualisation. Important mixing characteristics, e.g.…”

Section: Les Modellingsupporting

confidence: 77%

“…Fluorescence (PLIF) in order to measure the mixing parameters and visualise the near-field shock structure of under-expanded air/nitrogen jets [23,25,26,29,[34][35][36][37]. Computational studies of under-expanded jets have been performed using compressible Euler equations [38][39][40][41], Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) methodologies [41][42][43][44][45][46][47][48][49][50][51][52], mainly for air jets or by assuming the injection of a passive scalar.…”

Section: Literature Surveymentioning

confidence: 99%

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Large eddy simulation of highly turbulent under-expanded hydrogen and methane jets for gaseous-fuelled internal combustion engines

Hamzehloo¹,

Aleiferis²

2014

International Journal of Hydrogen Energy

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Burning hydrogen in conventional internal combustion (IC) engines is associated with zero carbon-based tailpipe exhaust emissions. In order to obtain high volumetric efficiency and eliminate abnormal combustion modes such as preignition and backfire, in-cylinder direct injection (DI) of hydrogen is considered preferable for a future generation of hydrogen IC engines. However, hydrogen's low density requires high injection pressures for fast hydrogen penetration and sufficient in-cylinder mixing. Such pressures lead to chocked flow conditions during the injection process which result in the formation of turbulent under-expanded hydrogen jets. In this context, fundamental understanding of the under-expansion process and turbulent mixing just after the nozzle exit is necessary for the successful design of an efficient hydrogen injection system and associated injection strategies. The current study used large-eddy simulation (LES) to investigate the characteristics of hydrogen under-expanded jets with different nozzle pressure ratios (NPR), namely 8.5, 10, 30 and 70. A test case of methane injection with NPR=8.5 was also simulated for direct comparison with the hydrogen jetting under the same NPR. The near-nozzle shock structure, the geometry of the Mach disk and reflected shock angle, as well as the turbulent shear layer were all captured in very good agreement with data available in the literature. Direct comparison between hydrogen and methane fuelling showed that the ratio of the specific heats had a noticeable effect on the near-nozzle shock structure and dimensions of the Mach disk. It was observed that with methane, mixing did not occur before the Mach disk, whereas with hydrogen high levels of momentum exchange and mixing appeared at the boundary of the jet. This was believed to be the effect of the high turbulence fluctuations at the nozzle exit of the hydrogen jet which triggered Gortler vortices. Generally, the primary mixing was observed to occur after the location of the Mach disk and particularly close to the jet boundaries where large-scale turbulence played a dominant role. It was also found that NPR had significant effect on the mixture's local fuel richness. Finally, it was noted that applying higher injection pressure did not essentially increase the penetration length of the hydrogen jets and that there could be an optimum NPR that would introduce more enhanced mixing whilst delivering sufficient fuel in less time. Such an optimum NPR could be in the region of 100 based on the geometry and observations of the current study.3

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Section: Les Modellingsupporting

confidence: 77%

Section: Literature Surveymentioning

confidence: 99%

Large eddy simulation of highly turbulent under-expanded hydrogen and methane jets for gaseous-fuelled internal combustion engines

Hamzehloo¹,

Aleiferis²

2014

International Journal of Hydrogen Energy

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“…4 The fuel injection nozzles and jet engine exhaust lie somewhere in between the two extreme cases. 13,14 Also the nozzle operating conditions, nozzle pressure ratio (NPR), depend on the application.…”

Section: Introductionmentioning

confidence: 99%

Large-eddy simulation of highly underexpanded transient gas jets

Vuorinen¹,

Yu²,

Tirunagari³

et al. 2013

Physics of Fluids

157

142

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Large-eddy simulations (LES) based on scale-selective implicit filtering are carried out in order to study the effect of nozzle pressure ratios on the characteristics of highly underexpanded jets. Pressure ratios ranging from 4.5 to 8.5 with Reynolds numbers of the order 75 000-140 000 are considered. The studied configuration agrees well with the classical picture of the structure of highly underexpanded jets. Similarities and differences between simulation and experiments are discussed by comparing the concentration field structures from LES and planar laser induced fluorescence data. The transient stages, leading eventually to the highly underexpanded state, are visualized and investigated in terms of a phase diagram revealing the shock speeds and duration of the transient stages. For the studied nozzle pressure ratio range, the Mach disk dimensions are found to be in good agreement with literature data and experimental observations. It is observed how the nozzle pressure ratio influences the Mach disk width, and thereby the slip line separation, which leads to co-annular jets with inner and outer shear layers at higher pressure ratios. The improved mixing with increasing pressure ratio is demonstrated by the probability density functions of the concentration. The coherent structures downstream of the Mach disk are identified using proper orthogonal decomposition (POD). The structures indicate a helical mode originating from the shear layers of the jet. Despite the relatively low energy content of the dominant POD modes, the frequencies of the POD time coefficients explain the dominant frequencies in the pressure fluctuation spectra. C

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“…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%

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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An Experimental Study on High Pressure Pulsed Jets for DI Gas Engine Using Planar Laser-Induced Fluorescence

Cited by 32 publications

References 29 publications

Large eddy simulation of highly turbulent under-expanded hydrogen and methane jets for gaseous-fuelled internal combustion engines

Large eddy simulation of highly turbulent under-expanded hydrogen and methane jets for gaseous-fuelled internal combustion engines

Large-eddy simulation of highly underexpanded transient gas jets

Computational Study of Hydrogen Direct Injection for Internal Combustion Engines

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