Numerical Study on Flammability Limit and Performance of Compression-Ignition Argon Power Cycle Engine with Fuel of Hydrogen

2021 ◽  
Author(s):  
Kaien Xie ◽  
Jun Deng ◽  
Shaoye Jin ◽  
Liguang Li
Keyword(s):  
Numerical Study ◽  
Compression Ignition ◽  
Flammability Limit ◽  
Power Cycle ◽  
And Performance

scholarly journals Numerical Modeling and Performance Evaluation of Standing Wave Thermoacoustic Refrigerators with a Multi-Layered Stack

Energies ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 4360
Author(s):  
Umar Nawaz Bhatti ◽  
Salem Bashmal ◽  
Sikandar Khan ◽  
Rached Ben-Mansour
Keyword(s):  
Standing Wave ◽  
Numerical Study ◽  
Temperature Drop ◽  
Acoustic Power ◽  
Heat Energy ◽  
Coefficient Of Performance ◽  
Material Layer ◽  
And Performance ◽  
Stacked Material ◽  
Thermoacoustic Refrigerators

Thermoacoustic refrigerators have huge potential to replace conventional refrigeration systems as an alternative clean refrigeration technology. These devices utilize conversion of acoustic power and heat energy to generate the desired cooling. The stack plays a pivotal role in the performance of Standing Wave Thermoacoustic Refrigerators (SWTARs), as the heat transfer takes place across it. Performance of stacks can be significantly improved by making an arrangement of different materials inside the stack, resulting in anisotropic thermal properties along the length. In the present numerical study, the effect of multi-layered stack on the refrigeration performance of a SWTAR has been evaluated in terms of temperature drop across the stack, acoustic power consumed and device Coefficient of Performance (COP). Two different aspects of multi-layered stack, namely, different material combinations and different lengths of stacked layers, have been investigated. The combinations of four stack materials and length ratios have been investigated. The numerical results showed that multi-layered stacks produce lower refrigeration temperatures, consume less energy and have higher COP value than their homogeneous counterparts. Among all the material combinations of multi-layered stack investigated, stacks composed of a material layer with low thermal conductivity at the ends, i.e., RVC, produced the best performance with an increase of 26.14% in temperature drop value, reduction in the acoustic power consumption by 4.55% and COP enhancement of 5.12%. The results also showed that, for a constant overall length, an increase in length of side stacked material layer results in an increase in values of both temperature drop and COP.

Wind tunnel and numerical study of a straight-bladed Vertical Axis Wind Turbine in three-dimensional analysis (Part II: For predicting flow field and performance)

Energy ◽  
2016 ◽  
Vol 104 ◽  
pp. 295-307 ◽  
Author(s):  
Qing'an Li ◽  
Takao Maeda ◽  
Yasunari Kamada ◽  
Junsuke Murata ◽  
Toshiaki Kawabata ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Flow Field ◽  
Wind Turbine ◽  
Dimensional Analysis ◽  
Numerical Study ◽  
Three Dimensional ◽  
Vertical Axis ◽  
Vertical Axis Wind Turbine ◽  
And Performance

Numerical Study of Deterministic Fluxes in Compressor Passages

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Feng Wang ◽  
Mauro Carnevale ◽  
Luca di Mare
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Navier Stokes ◽  
Design Stage ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Radial Profiles ◽  
And Performance ◽  
Stage Matching ◽  
Unsteady Effects

Computational fluid dynamics (CFD) has been widely adopted in the compressor design process, but it remains a challenge to predict the flow details, performance, and stage matching for multistage, high-speed machines accurately. The Reynolds Averaged Navier-Stokes (RANS) simulation with mixing plane for bladerow coupling is still the workhorse in the industry and the unsteady bladerow interaction is discarded. This paper examines these discarded unsteady effects via deterministic fluxes using semi-analytical and unsteady RANS (URANS) calculations. The study starts from a planar duct under periodic perturbations. The study shows that under large perturbations, the mixing plane produces dubious values of flow quantities (e.g., whirl angle). The performance of the mixing plane can be considerably improved by including deterministic fluxes into the mixing plane formulation. This demonstrates the effect of deterministic fluxes at the bladerow interface. Furthermore, the front stages of a 19-blade row compressor are investigated and URANS solutions are compared with RANS mixing plane solutions. The magnitudes of divergence of Reynolds stresses (RS) and deterministic stresses (DS) are compared. The effect of deterministic fluxes is demonstrated on whirl angle and radial profiles of total pressure and so on. The enhanced spanwise mixing due to deterministic fluxes is also observed. The effect of deterministic fluxes is confirmed via the nonlinear harmonic (NLH) method which includes the deterministic fluxes in the mean flow, and the study of multistage compressor shows that unsteady effects, which are quantified by deterministic fluxes, are indispensable to have credible predictions of the flow details and performance of compressor even at its design stage.

Operation and Control of a Supercritical CO2 Compressor

2021 ◽  
Author(s):  
Joshua D. Neveu ◽  
Stefan D. Cich ◽  
J. Jeffrey Moore ◽  
Jason Mortzheim
Keyword(s):  
Steady State ◽  
Critical Point ◽  
Operating Conditions ◽  
State Control ◽  
Power Cycle ◽  
Low Head ◽  
And Performance ◽  
Steady State Control ◽  
And Control ◽  
Thermal Sources

Abstract Among the list of advanced technologies required to support the energy industry’s novel Supercritical Carbon Dioxide (sCO2) power cycle is the need for a robust and responsive control system. Recent testing has been performed on a 2.5 MWe sCO2 compressor operating near the critical temperature (31C) and critical pressure (73.8 bar), developed with funding from the US DOE Apollo program and industry partners. While sCO2 compression has been performed before, operating near the critical point has many key benefits for power generation with its low head requirements and smaller physical footprint. However, with these benefits come unique challenges, namely controlling this system to steady-state operating conditions. Operating just above the critical point (35°C [95°F] and 8.5 MPa [1,233 psi]) there can be large and rapid swings in density produced by subtle changes in temperature, leading to increased difficulty in maintaining adequate control of the compressor system. This means that proper functionality of the entire compressor system, and its usefulness to a closed loop recompression Brayton power cycle, is largely dependent on variables such as thermal sources, precision and response time of the instrumentation, proper heat soaking, and strategic filling and venting sequences. While other papers have discussed the science behind and performance of sCO2 compressors, this paper will discuss the challenges associated with steady-state control of the compressor at or near operating conditions, how the fill process was executed for optimal startup, and changes that occurred while idling during trip events.

Effects of Circumferential Nonuniform Tip Clearance on Flow Field and Performance of a Transonic Turbine

2020 ◽  
Author(s):  
Yun Zheng ◽  
Xiubo Jin ◽  
Hui Yang ◽  
Qingzhe Gao ◽  
Kang Xu
Keyword(s):  
Flow Field ◽  
Numerical Study ◽  
Circumferential Direction ◽  
Tip Clearance ◽  
Computational Domain ◽  
Aerodynamic Efficiency ◽  
Aerodynamic Loss ◽  
The Difference ◽  
And Performance ◽  
Downstream Flow

Abstract The numerical study is performed by means of an in-house CFD code to investigate the effect of circumferential nonuniform tip clearance due to the casing ovalization on flow field and performance of a turbine stage. A method called fast-moving mesh is used to synchronize the non-circular computational domain with the rotation of the rotor row. Four different layouts of the circumferential nonuniform clearance are calculated and evaluated in this paper. The results show that, the circumferential nonuniform clearance could reduce the aerodynamic performance of the turbine. When the circumferential nonuniformity δ reaches 0.4, the aerodynamic efficiency decreases by 0.58 percentage points. Through the analysis of the flow field, it is found that the casing ovalization leads to the difference of the size of the tip clearance in the circumferential direction, and the aerodynamic loss of the position of large tip clearance is greater than that of small tip clearance, which is related to the scale of leakage vortex. In addition, the flow field will become nonuniform in the circumferential direction, especially at the rotor exit, which will adversely affect the downstream flow field.

Numerical study on combustion characteristics of six-stroke-cycle gasoline compression ignition engine with continuously variable valve duration valve technology

2019 ◽  
Vol 22 (1) ◽  
pp. 165-183 ◽  
Author(s):  
Oudumbar Rajput ◽  
Youngchul Ra ◽  
Kyoung-Pyo Ha ◽  
You-Sang Son
Keyword(s):  
Numerical Study ◽  
Power Stroke ◽  
Compression Ignition ◽  
Ignition Timing ◽  
Compression Ignition Engine ◽  
Engine Operation ◽  
Wide Range ◽  
Negative Valve Overlap ◽  
Variable Valve ◽  
Valve Overlap

Engine performance and emissions of a six-stroke gasoline compression ignition engine with a wide range of continuously variable valve duration control were numerically investigated at low engine load conditions. For the simulations, an in-house three-dimensional computational fluid dynamics code with high-fidelity physical sub-models was used, and the combustion and emission kinetics were computed using a reduced kinetics mechanism for a 14-component gasoline surrogate fuel. Variation of valve timing and duration was considered under both positive valve overlap and negative valve overlap including the rebreathing of intake valves via continuously variable valve duration control. Close attention was paid to understand the effects of two additional strokes of the engine cycle on the thermal and chemical conditions of charge mixtures that alter ignition, combustion and energy recovery processes. Double injections were found to be necessary to effectively utilize the additional two strokes for the combustion of overly mixed lean charge mixtures during the second power stroke. It was found that combustion phasing in both power strokes is effectively controlled by the intake valve closure timing. Engine operation under negative valve overlap condition tends to advance the ignition timing of the first power stroke but has minimal effect on the ignition timing of second power stroke. Re-breathing was found to be an effective way to control the ignition timing in second power stroke at a slight expense of the combustion efficiency. The operation of a six-stroke gasoline compression ignition engine could be successfully simulated. In addition, the operability range of the six-stroke gasoline compression ignition engine could be substantially extended by employing the continuously variable valve duration technique.

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