Reaction Mechanism Reduction for Ozone-Enhanced CH4/Air Combustion by a Combination of Directed Relation Graph with Error Propagation, Sensitivity Analysis and Quasi-Steady State Assumption

In this study, an 18-steps, 22-species reduced global mechanism for ozone-enhanced CH4/air combustion processes was derived by coupling GRI-Mech 3.0 and a sub-mechanism for ozone decomposition. Three methods, namely, direct relation graphics with error propagation, (DRGRP), sensitivity analysis (SA), and quasi-steady-state assumption (QSSA), were used to downsize the detailed mechanism to the global mechanism. The verification of the accuracy of the skeletal mechanism in predicting the laminar flame speeds and distribution of the critical components showed that that the major species and the laminar flame speeds are well predicted by the skeletal mechanism. However, the pollutant NO was predicated inaccurately due to the precursors for generating NO were removed as redundant components. The laminar flame speeds calculated by the global mechanism fit the experimental data well. The comparisons of simulated results between the detailed mechanism and global mechanism were investigated and showed that the global mechanism could accurately predict the major and intermediate species and significantly reduced the time cost by 72%Peer reviewe

Verification and Validation of a Low-Mach-Number Large-Eddy Simulation Code against Manufactured Solutions and Experimental Results

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).To investigate turbulent reacting flows, a low-Mach number large-eddy simulation (LES) code called ‘LESsCoal’ has been developed in our group. This code employs the Germano dynamic sub-grid scale (SGS) model and the steady flamelet/progress variable approach (SFPVA) on a stagger-structured grid, in both time and space. The method of manufactured solutions (MMS) is used to investigate the convergence and the order of accuracy of the code when no model is used. Finally, a Sandia non-reacting propane jet and Sandia Flame D are simulated to inspect the performance of the code under experimental setups. The results show that MMS is a promising tool for code verification and that the low-Mach-number LES code can accurately predict the non-reacting and reacting turbulent flows. The validated LES code can be used in numerical investigations on the turbulent combustion characteristics of new fuel gases in the future.Peer reviewedFinal Published versio

Single-longitudinal-mode Fiber Ring Lasers With Taper-coupled Double-microsphere-cavities

This letter proposes and demonstrates a fiber ring laser using taper-coupled double-microsphere-cavities (DMC) to achieve single-longitudinal-mode operation. Whispering-gallery-mode (WGM) intensity distributions and transmission spectra of the DMC with different microsphere diameters are investigated both theoretically and experimentally. Due to the Vernier effect, the DMC can produce WGM spectra with a higher extinction ratio, a higher side-mode-suppression ratio (SMSR), a larger FSR and a narrower bandwidth, as compared to a single-microsphere cavity. A single-longitudinal-mode fiber ring laser operating near 1.5 μm with a bandwidth of < 0.01 nm and a signal-to-background ratio of about 60 dB is demonstrated using the taper-coupled DMC as an all-fiber mode selector

Characteristics of alkali species release from a burning coal/biomass blend

© 2018 Elsevier Ltd Solvent fractionation, Laser induced breakdown spectroscopy (LIBS), X-ray Diffraction (XRD) and chemical analysis were applied to binary fuel mixtures of Zhundong coal and cornstalk agricultural class to investigate the release characteristics of alkali species during co-firing of coal and biomass. As the biomass proportion increases, the water-soluble, NH 4 Ac-soluble and HCl-soluble alkali species interconvert; the extent of the conversion depends on the composition of the blend. From LIBS measurements, it was found that adding the biomass accelerates combustion and outgassing processes. The higher the proportion of the biomass in the blend, the earlier the peak concentrations of alkali appear, and the magnitude of peak concentrations of sodium and potassium decrease and increase, respectively. Furthermore, the interaction between coal and biomass can generate crystals causing the eutectic melting phenomenon (similar to feldspar in XRD results), which results in a sharp decline of the ash fusion temperatures (AFTs). The results not only provide the information of fundamental transformation but also guide industrial co-firing applications of lignite and agricultural class biomass to reduce the risk of ash deposition

In Situ Measurements of the Release Characteristics and Catalytic Effects of Different Chemical Forms of Sodium during Combustion of Zhundong Coal

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Energy Fuels, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acs.energyfuels.8b00773.This work studies the temporal release characteristics of different chemical forms of sodium during the combustion of Zhundong coal and the catalytic effects of sodium on the combustion process via target-sodium removal and enrichment approaches. The target-sodium removal approach extracts specific forms of sodium from the raw coal via a chemical method to produce coal samples with designated characteristics. In the target-sodium enrichment approach, three kinds of H2O-soluble sodium compounds, including NaCl, NaOH and Na2SO4, are manually added into the raw coal. The experimental measurement is conducted using a multi-point Laser-Induced Breakdown Spectroscopy (LIBS) system. The system quantitatively measures the temporal release flux of sodium during the combustion process, and performs the in-situ measurement of surface temperature and diameter of a burning coal pellet. It is found that H2O-soluble sodium is the major chemical form of sodium released during the combustion and exhibits the highest volatility. All the three forms of enriched H2O-soluble sodium compounds show a catalytic effect on the coal combustion (burnout time decreased by more than 5.7%) and the catalytic activity of NaOH is found to be the strongest (burnout time decreased by 36.8%)

Simulation of char-pellet combustion and sodium release inside porous char using lattice Boltzmann method

Char-pellet combustion is studied with the lattice Boltzmann method (LBM) including sodium release and the ash inhibition effect on oxygen diffusion in the porous char. The sodium release and the shrinking of the char pellet are simulated by accounting for the reactions occurring both in the solid and gas phases. The combustion of a single char pellet is considered first, and the results are compared against measurements. The simulation of the pellet mass, pellet temperature and sodium release agreed well with in-house optical measurements. The validated lattice Boltzmann approach is then extended to investigate the combustion of porous char and sodium release inside the porous medium. The pore-structure evolution and the flow path variation are simulated as combustion proceeds. The simulations reproduce the expected different behaviors between the combustion products (CO and CO2) and the released volatile, here the sodium vapor. The combustion products are mostly generated at the flame front and then transported by the flow and molecular diffusion inside the complex porous char structure. However, the volatile sodium vapor forms in the entire porous char and tends to accumulate in regions where the flow motion stays weak, as in internal flow microchannels, or blocked, as in closed pores. These results confirm the potential of the LBM formalism to tackle char-pellet combustion accounting for the topology of the porous medium.National Natural Science Foundation of China; China Postdoctoral Science Foundation; Royal Society and the Engineering and Physical Sciences Research Council (EPSRC) (UK

Measurement of atomic sodium release during pyrolysis and combustion of sodium-enriched Zhundong coal pellet

National Natural Science Foundation of China; Ph.D. Programs Foundation of Ministry of Education of Chin

On the robustness and accuracy of large-eddy simulation in predicting complex internal flow of a gas-turbine combustor

The objective of this study is to evaluate the effects of numerical and model setups on the large-eddy simulation (LES) predictive capability for the internal flow of a propulsion-relevant configuration. The specific focus is placed on assessing the LES technique with lower mesh resolutions, which is of technological relevance to practical industrial design. A set of Riemann flux formulations and commonly used subgrid-scale models are considered in this work to produce a hierarchy of LES setups with different dissipation effects (both numerically and physically). The LES results obtained from different setups are compared qualitatively in terms of the key flow characteristics and evaluated quantitatively against the experimental measurements. The error landscape is generated to reveal the predictive qualities of different LES setups. The study shows that the choice of numerical flux formulation plays a prominent role in governing the general flow patterns, while the effect of subgrid-scale model is mainly manifested in transient flow characteristics, such as vortex breakdown and swirl-induced vortical structures. Based on the error analysis, it is found that lower dissipative LES setup is not always beneficial to the LES accuracy. This is in contrast to the commonly accepted understanding in literature for the LES, which was established solely with canonical flow configurations