Marine propellers and propulsion

Modeling of spray jet flame under MILD condition with non-adiabatic FGM and a new conditional droplet injection model

LES of pulverized coal combustion with a multi-regime flamelet model

The selective non-catalytic reduction (SNCR) process used to transform nitrogen monoxide molecules into environmentally friendly gases is reviewed with its numerical modeling. The fundamentals of SNCR in terms of chemistry and flow physics are first discussed, to then examine how they impact on the design and optimization of furnaces and incinerators relying on this technology. The various options in operation today are presented for coal-fired or waste-to-energy power plants, biomass and CO boilers. In complement, specific applications using additive components are discussed along with the amine reclaimer waste approach. The methodology and the challenges of computational fluid dynamics applied to SNCR systems are reviewed, before discussing emerging simulation techniques, as large eddy simulation (LES) of such complex systems. The modeling of the multicomponent evaporation of the liquid reagent injected for transforming NOx, as urea, and the modeling of the chemistry in the gaseous phase, are addressed for the numerical simulation of SNCR. Finally, reduced-order modeling of SNCR is discussed and perspectives are drawn for the control, in situ, of SNCR systems.

Selective Non-catalytic Reduction (SNCR) of Nitrogen Oxide Emissions: A Perspective from Numerical Modeling

Incorporation of high explosives into nano-aluminum based microspheres to improve reactivity

We investigate the multi-flame phenomenon often seen in spray combustion. To do so, simulations are made of two cases from the Delft Spray in Hot Coflow (DSHC) database. These two cases have the same fuel (ethanol) but differ in the type of coflow: room temperature air (case AII) or products of lean premixed combustion (case HII), and they exhibit remarkably different flame structure, respectively with a ‘double flame’ and a ‘single flame’. The two-phase flow was handled with an Eulerian–Lagrangian approach. Large Eddy Simulation (LES) with Flamelet Generated Manifolds (FGM) method was used to account for the turbulence and combustion. Validation was done by using available experimental data as well as information on similar systems reported in literature. Major features of these two cases were correctly reproduced. Simulation results revealed that four spatially separated reaction regions exist in the flame AII and two in the flame HII. These regions are of different types, premixed or non-premixed, and are formed by different species, major fuel (ethanol) or intermediate species, e.g. carbon monoxide. The mechanism underlying the multi-flame structure was investigated and explained in terms of the relative magnitude of different time scales, namely of droplet evaporation, dispersion, convection and reaction. Parametric studies on the effect of spray polydispersity and coflowing air temperature were carried out, demonstrating an even wider range of flame structures. An important observation is that the ‘single flame’ structure usually present in the hot-diluted coflow case (HII), is also generated in a case of room temperature air coflow, provided the injected droplets are small. This is attributed to the fact that representative droplets in all cases with single flame have similar evaporation time scale. Or stated more generally, by matching important time scales, similar flame structure can be created under considerably different conditions.

Numerical study of the multi-flame structure in spray combustion

This paper presents a numerical modeling study of one ethanol spray flame from the Delft Spray-in-Hot-Coflow (DSHC) database, which has been used to study Moderate or Intense Low-oxygen Dilution (MILD) combustion of liquid fuels (Correia Rodrigues et al Combust Flame 162(3), 759–773, 2015) A “Lagrangian-Lagrangian” approach is adopted where both the joint velocity-scalar Probability Density Function (PDF) for the continuous phase and the joint PDF of droplet properties are modeled and solved The evolution of the gas phase composition is described by a Flamelet Generated Manifold (FGM) and the interaction by exchange with the mean (IEM) micro-mixing model Effects of finite conductivity on droplet heating and evaporation are accounted for The inlet boundary conditions starting in the dilute spray region are obtained from the available experimental data together with the results of a calculation of the spray including the dense region using ANSYS Fluent 15 A method is developed to determine a good estimation for the initial droplet temperature The inclusion of the “1/3” rule for droplet evaporation and dispersion models is shown to be very important The current modeling approach is capable of accurately predicting main properties, including mean velocity, droplet mean diameter and number density The gas temperature is under-predicted in the region where the enthalpy loss due to droplet evaporation is important The flame structure analysis reveals the existence of two heat release regions, respectively having the characteristics of a premixed and a diffusion flame The experimental and modeled temperature PDFs are compared, highlighting the capabilities and limitations of the proposed model

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Likun Ma

Papers

Modeling of spray jet flame under MILD condition with non-adiabatic FGM and a new conditional droplet injection model

Numerical study of the multi-flame structure in spray combustion

Transported PDF Modeling of Ethanol Spray in Hot-Diluted Coflow Flame

Ignition and combustion of a single aluminum particle in hot gas flow

Structure of spray in hot-diluted coflow flames under different coflow conditions: A numerical study