D. J. E. M. Roekaerts

Delft University of Technology | TU · Department of Process and Energy (P&E)

Transcritical fuel sprays form an indispensable part of high-pressure energy-conversion systems. Modeling the complex real-fluid effects in the high-pressure multiphase regime of such sprays accurately, especially the hybrid subcritical-to-supercritical mode of evaporation during mixing fuel and oxidizer, is essential and challenging. This paper re...

We present a novel framework for high-fidelity simulations of inert and reacting sprays at transcritical conditions with highly accurate and computationally efficient models for complex real-gas effects in high-pressure environments, especially for the hybrid subcritical/supercritical mode of evaporation during the mixing of fuel and oxidizer. The...

The present work focuses on the large eddy simulation (LES) and the study of turbulent dilute methanol spray flames in vitiated coflow using the secondary-oxidizer Flamelet Generated Model (FGM). The modified FGM model uses an additional secondary oxidizer parameter in addition to the three other parameters previously used for spray flames - progre...

The simple semi-empirical precursor soot model of Brookes and Moss based on the soot number density and soot mass concentration is adopted in a transported probability density function (PDF) method for turbulent diffusion flames. The gas phase chemistry is described by a flamelet generated manifold (FGM) based on the mixture fraction, progress vari...

Accurate simulations of high-pressure transcritical fuel sprays are essential for the design and optimization of next-generation gas turbines, internal combustion engines, and liquid propellant rocket engines. Most important and challenging is the accurate modelling of complex real-gas effects in high-pressure environments, especially the hybrid su...

Oxy-fuel combustion of coal pyrolysis gas has recently been proposed to serve as internal heat source of a vertical low-temperature pyrolysis furnace, in order to make the output pyrolysis gas nearly free of nitrogen and widely useful. To keep the pyrolysis temperature and the heat carrier gas volume unchanged from air combustion to oxy-fuel combus...

The flamelet generated manifold (FGM) model is suitable for moderate or intense low oxygen dilution (MILD) combustion provided the flamelets underlying the manifold include the effects of strong dilution by products of the fuel/oxidizer mixture. Here we propose such an extended model based on the use of non-premixed flamelets diluted at the airside...

This study investigates the potential of a newly released multi-phase solver to simulate atomisation in an air-blast type atomiser. The 'VOF-to-DPM' solver was used to simulate primary and secondary atomisation in an atomiser with a coaxial injector-like geometry. The solver uses a hybrid Eulerian/Eulerian-Lagrangian formulation with geometric tran...

The present work investigates the modeling of turbulent heat transfer in flows where radiative and convective heat transfer are coupled. In high temperature radiatively participating flows, radiation is the most relevant heat transfer mechanism and, due to its non-locality, it causes counter intuitive interactions with the turbulent temperature fie...

A Generalized Langevin Model (GLM) formulation to be used in transported joint velocity-scalar probability density function methods is recalled in order to imply a turbulent scalar-flux model where the pressure-scrambling term is in correspondence with standard Monin's return-to-isotropy term. The proposed non-constant C0 formulation is extended to...

In this paper we report results of a numerical investigation of turbulent natural gas combustion for jet in a coflow of lean combustion products in the Delft-Jet-in-Hot-Coflow (DJHC) burner which emulates MILD (Moderate and Intense Low Oxygen Dilution) combustion behavior. The focus is on assessing the performance of the Eddy Dissipation Concept (E...

Eddy dissipation concept (EDC) model and flamelet generated manifolds (FGM) model are developed separately to study the temperature profiles and extinction limits of non-premixed hydrothermal flames. Predictions by the two models are evaluated comparatively by experimental data in literatures. FGM model shows relatively better prediction of tempera...

Flameless combustion, also called MILD combustion (Moderate or Intense Low Oxygen Dilution), is a technology that reduces NOx emissions and improves combustion efficiency. Appropriate turbulence-chemistry interaction models are needed to address this combustion regime via computational modelling. Following a similar analysis to that used in the Ext...

A probability density function (PDF)-based combustion modeling approach for RANS simulation of a jet issuing into a hot and diluted coflow is performed. A tabulated chemistry-based model, i.e., flamelet-generated manifold (FGM), is adopted in the PDF method. The manifolds are constructed using igniting counterflow diffusion flamelets with different...

From the book preface: "Chapter 12 provides the relevant tools and guidelines to simulate mixed convection and radiation in porous media, within the framework of solar thermal absorbers. First, a general introduction of modelling strategies for mixed convection and radiation is presented. The main challenges will be addressed and the relevant solut...

Counterflow diffusion flames of methanol hydrothermal combustion are investigated to improve the understanding of hydrothermal flames. It is indicated that the thermodynamic properties by the Peng-Robinson equation of state and the modified transport properties can reduce the flame temperature by about 500 K. The Takahashi correlation for mass diff...

The present work investigates gray and non-gray gas turbulence-radiation interactions (TRI) in a turbulent channel flow bounded by two isothermal hot and cold walls. Cases of various optical thicknesses are examined using Direct Numerical Simulations (DNS), coupled with a computationally efficient Monte Carlo radiative transfer solver. Several nove...

In facilities handling combustible dusts, the isolation of propagating deflagrations requires great attention due to the potential catastrophic consequences of secondary dust explosions. While the ability of dust explosions to propagate is widely recognized, some misconceptions still exist. One of the common myths is that a dust explosion cannot pr...

This work reports an experimental study on supercritical water oxidation of quinoline. Moderate preheat temperature (420 °C–510 °C) and initial concentration (1 wt%–10 wt%) are selected to address the possibility of utilizing the heat released during the reaction, in order to realize high conversion rate at relatively low preheat temperature. The e...

Since its discovery, the Flameless Combustion (FC) regime has been seen as a promising alternative combustion technique to reduce pollutant emissions of gas turbine engines. This combustion mode is often characterized by well-distributed reaction zones, which can potentially decrease temperature gradients, acoustic oscillations and, consequently NO...

The increasing amount of renewable energy and emission norms challenge gas turbine power plants to operate at part-load with high efficiency, while reducing NOx and CO emissions. A novel solution to this dilemma is external Flue Gas Recirculation (FGR), in which flue gases are recirculated to the gas turbine inlet, increasing compressor inlet tempe...

The present work consists of an investigation of the turbulence radiation interaction (TRI) in a radiative turbulent channel flow of grey gas bounded by isothermal hot and cold walls. The optical thickness $\unicode[STIX]{x1D70F}$ of the channel is varied from 0.1 to 10 to observe different regimes of TRI. A high-resolution finite volume method for...

Solid oxide fuel cells (SOFCs) operate at high temperatures, leading to stringent requirements for the thin ceramic structures in these devices. Heat transfer models aimed to study the temperature distribution within SOFCs are however often simplified by ignoring radiative heat transfer (RHT). A computational model is developed to study the influen...

Metal dust deflagrations have become increasingly common in recent years. They are also more devastating than deflagrations involving organic materials, owing to metals' higher heat of combustion, rate of pressure rise, explosion pressure and flame temperature. Aluminum finishing operations offer a particularly significant hazard from the very smal...

In the past 25 years high temperature air combustion (HiTAC) technology has been proved and utilized in industry as a promising way to increase thermal efficiency, create a relatively uniform temperature distribution, and reduce emissions of harmful pollutants such as NOX and CO. However, due to the complexity of fuel-oil combustion, to date HiTAC...

Dust explosibility is traditionally described by two parameters, namely the maximum explosion pressure, P$_{max}$, and the deflagration index, K$_{St}$, usually determined through testing in a closed, pressure-resistant spherical vessel, either 20 L or 1 m$^{3}$ in volume. These parameters constitute key variables in the design of explosion protect...

Dust explosibility is traditionally described by two parameters, namely the maximum explosion pressure, Pmax, and the deflagration index, KSt, usually determined through testing in a closed, pressure-resistant spherical vessel, either 20 L or 1 m³ in volume. These parameters constitute key variables in the design of explosion protection systems, su...

Mild combustion in a lab-scale furnace has been experimentally and numerically studied. The furnace was operated with Dutch natural gas (DNG) at 10 kW and at an equivalence ratio of 0.8. OH* chemiluminescence images were taken to characterize the reaction zone. The chemiluminescence intensity is relatively low compared to conventional flames and re...

We report results of a computational study of oxy-fuel spray jet flames. An experimental database on flames of ethanol burning in a coflow of a O2–CO2 mixture, created at CORIA (Rouen, France), is used for model validation (Cléon et al., 2015). Depending on the coflow composition and velocity the flames in these experiments start at nozzle (type A)...

This contribution presents an outline of a new mathematical formulation for Classical Non-Equilibrium Thermodynamics (CNET) based on a contact structure in differential geometry. First a non-equilibrium state space is introduced as the third key element besides the first and second law of thermodynamics. This state space provides the mathematical s...

This work studies the influence of coflow conditions on the structure of the Delft Spray in Hot-diluted Coflow (DSHC) flames, using Large Eddy Simulation (LES) techniques. The developed modeling approach was first applied to three different experimental cases for validation. Major properties such as droplet velocity, SMD, gas phase velocity and tem...

In this paper we present an overview of CFD modeling of spray combustion of liquid biofuels, with focus on the application of Flamelet Generated Manifolds (FGM) on modeling of MILD combustion. Most attention is paid to the case of experimentally well-documented ethanol flames. For each of the model components (atomization, evaporation, dispersion,...

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...

In this paper we investigate and compare two di�erent solar receiver technologies for concentrated solar power plants operating with supercritical CO2. The �rst receiver is based on conventional surface absorbers, while the second receiver is based on an innovative idea to use volumetric receivers where sunlight is transmitted through a transparent...

This paper reports a numerical study on the Delft Spray-in-Hot-Coflow (DSHC) flame with a new OpenFOAM solver developed by the authors, in which the Flamelet Generated Manifolds (FGM) model has been implemented, and used to account for the Turbulence-Chemistry Interaction (TCI). The enthalpy loss effect due to droplet vaporization is considered by...

This chapter deals with radiative transfer in combustion systems, where laminar or turbulent reactive flows are present, and radiation is often an important heat transfer mode. The reactive medium emits, absorbs and, if solid particles are present (e.g., pulverized coal, fly ash), scatters radiation. It is referred to as a participating medium, sin...

A new OpenFOAM solver for modeling spray combustion has been developed by the authors. In this solver, the Flamelet Generated Manifolds (FGM) model has been implemented, and used to account for the Turbulent-Chemistry Interaction (TCI). We report here a numerical study on the Delft Spray-in-Hot-Colfow (DSHC) flame with this new " sprayFGMFoam " sol...

Large quantities of hydrogen can be generated and released into the containment during a severe accident in a PWR. The generated hydrogen, when mixed with air, can lead to hydrogen combustion. The dynamic pressure loads resulting from hydrogen combustion can be detrimental to the structural integrity of the reactor safety systems and the reactor co...

tThe control of hydrogen in the containment is an important safety issue in NPPs during a loss of coolantaccident, because the dynamic pressure loads from hydrogen combustion can be detrimental to thestructural integrity of the reactor safety systems and the reactor containment. In Sathiah et al. (2012b),we presented a computational fluid dynamics...

A methanol spray flame in a combustion chamber of the NIST was simulated using an Eulerian-Lagrangian RANS model. Experimental data and previous numerical investigations by other researchers on this flame were analysed to develop methods for more comprehensive model validation. The inlet boundary conditions of the spray were generated using semi-em...

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...

MILD Combustion, also known as flameless combustion, is attracting wide scientific interest due to its potential of high efficiency and low NOx emission. The Delft Spray-in-Hot-Coflow (DSHC) burner was designed to study the fundamental aspects of flameless oxidation of light oils. The present paper reports a numerical study of an ethanol flame of t...

Flameless combustion technology can provide high effciency with less emissions. Although spray combustion is prevalent in industrial furnaces, little research has been carried out to investigate flameless spray combustion. This article reports on numerical simulation of the Delft Spray-in-Hot-Coow (DSHC) burner, which has been constructed to simula...

Non-premixed turbulent combustion in a laboratory scale flame (Delft III flame) is studied using a statistical description at the one-point one-time joint velocity-scalar composition probability density function (PDF) level. The PDF evolution equation is solved using a stochastic Lagrangian Monte Carlo method. The PDF equation requires a so called...

A laboratory scale experimental setup was built to study ethanol pressure-swirl spray flames in a coflow of either air or hot-diluted oxidant. The latter case resembles conditions similar to those found in practical combustion systems of liquid fuels operating in MILD conditions. First, experiments have been performed to investigate the phenomena a...

Measurements of the flame luminescence, velocity and temperature were conducted in four flames with different natural-gas/hydrogen fuel mixtures (at similar jet Reynolds numbers) in a jet-in-hot-coflow burner that mimics conditions found in real flameless combustion burners. The results show major changes in the flame stabilization mechanism when t...

This chapter gives a basic introduction to the theoretical modeling of heat and mass transfer. The general principles are illustrated with specific examples concerning evaporation of ethanol droplets and devolatilization of wood particles. The chapter discusses the transport terms in the governing equations. Heat transfer systems can be classified...

The structure of a turbulent non-premixed flame of a biogas fuel in a hot and diluted coflow mimicking moderate and intense low dilution (MILD) combustion is studied numerically. Biogas fuel is obtained by dilution of Dutch natural gas (DNG) with CO2. The results of biogas combustion are compared with those of DNG combustion in the Delft Jet-in-Hot...

MILD Combustion, also known as flameless combustion, is attracting wide scientific interest due to its potential of high efficiency and low NOx emission. This paper focuses on the numerical modeling of one of the ethanol spray flame cases from the Delft Spray-in-Hot-Coflow (DSHC) burner, which has been used to study MILD oxidation of liquid fuels....

In the present paper autoignition is studied as the main stabilization mechanism in turbulent lifted H2/N2 jet flames issuing into a vitiated hot coflow. The numerical study is performed using the joint scalar PDF approach with detailed chemistry in a two dimensional axisymmetric domain. The SSG Reynolds stress model is used as a turbulence model i...

The flameless combustion is a promising approach to increase the combustion efficiency and decrease the pollutant emission. In contrast with the wide range of investigations of its gaseous counterpart, the flameless combustion of liquid fuel is still in its infant stage. Numerical simulation provides an efficient way for the understanding of the fl...

In the present work the stabilization mechanism and structure of a turbulent non-premixed flame in a biogas mixture in a hot and diluted coflow mimicking the MILD combustion are studied experimentally and numerically. Biogas-like fuel is obtained by dilution of Dutch natural gas (DNG) with CO2. The results of biogas combustion are compared with tho...

The potential of the Levenberg–Marquardt method combined with an explicit Runge–Kutta method for non-stiff systems, and, an implicit Rosenbrock method for stiff systems to investigate burning velocities using explosion bombs was explored. The implementation of this combination of methods was verified on three benchmark test problems, and, by the ap...

The conditional velocity field of the Delft jet-in-hot-coflow flames is studied by the simultaneous application of planar laser-induced fluorescence of the OH radical (OH-PLIF) and particle image velocimetry (PIV). The goal of this study is to assess the role of turbulence on chemical processes in the Delft jet-in-hot-coflow flames and similar setu...

We report the characteristics of heat transfer and emissions in natural gas fired flameless oxidation conditions created using multiple semi-industrial regenerative burners. Burner positions and firing modes (parallel and staggered) are varied, and their effects on efficiency, emissions (NO, CO) and temperature uniformity are studied. Also the exce...

A simple semi-empirical soot model based on the soot number density and soot mass concentration is adopted in a transported PDF method for turbulent diffusion fl ames. The gas phase chemistry is reduced by a flamelet generated manifold (FGM) based on the mixture fraction, progress variable and enthalpy loss. To account for the radiative heat transf...

An experimental setup was designed to study spray flames in an hot-diluted coflow resembling conditions arising in flameless oxidation furnaces. Simultaneous droplet size and velocity measurements were made by Phase Doppler Anemometry for two ethanol and one acetone spray flame. Coflow entrainment and also momentum exchange between gas and droplets...

The stabilization region of four natural gas jet flames in hot coflow with increasing hydrogen addition from zero to 25% (by volume) was experimentally studied using recordings of the flame luminescence and Particle Image Velocimetry (PIV). The effects of hydrogen are substantial. Hydrogen addition results in shifting upstream the stabilization reg...

A CFD study was made of combustion in a 30 kW natural gas fired furnace. The results are compared to measurements in the furnace and to other results from literature. A specific objective was to compare the heat transfer for two different burner configurations, providing operation in the flameless and the conventional combustion regimes, with 10% a...

In this study, several conditions in a 9 MW heavy fuel-oil boiler were numerically studied in order to get a better understanding of the application of HiTAC in such a boiler. Simulations were done with an Euler-Lagrange approach. The Eddy Dissipation model was used for combustion. Simulation results showed that by recycling various ratios of flue...

An experiment was performed to study ethanol spray flames in conditions similar to those arising in industrial flameless oxidation devices. Special emphasis was placed on creating a wide and homogeneous hot-diluted co-flow so that numerical simulations complexity is minimized. The studied ethanol spray flames are weakly luminescent, transparent and...

A transported probability density function (PDF) method is developed for pulverized coal combustion. Two separate PDF transport equations, one for the gas phase (joint velocity-composition PDF) and one for the coal particle phase, are solved by means of stochastic Lagrangian methods. The gas composition is described by two mixture fractions (one th...

A transported probability density function (PDF) method is developed for pulverized coal combustion. Two separate PDF transport equations, one for the gas phase (joint velocity-composition PDF) and one for the coal particle phase, are solved by means of stochastic Lagrangian methods. The gas composition is described by two mixture fractions (one th...

A four dimensional look-up table is constructed in the context of transported probability density function (PDF) methods for modeling the flameless combustion in the Delft Jet-in-Hot-Coflow(DJHC) burner. The tabulated chemistry model is based on the Flamelet Generated Manifold (FGM) to include finite rate chemistry effects. The table that describes...

The control of hydrogen in the containment is an important safety issue in NPPs during a loss of coolant accident, because the dynamic pressure loads from hydrogen combustion can be detrimental to the structural integrity of the reactor safety systems and the reactor containment. In Sathiah et al. (2012b), we presented a computational fluid dynamic...

An experiment was performed to study ethanol spray flames in conditions similar to those arising in industrial flameless oxidation devices. Special emphasis was placed on creating a wide and homogeneous hot-diluted co-flow so that numerical simulations complexity is minimized. The studied ethanol spray flames are weakly luminescent, transparent and...

The potential consequences of hydrogen release and combustion during a severe accident in a Light Water Reactor (LWR) have received considerable attention after the Fukushima accident. The pressure loads resulting from hydrogen combustion can be detrimental to the structural integrity of the nuclear reactor safety systems and the reactor containmen...

Explosive evaporation of a superheated liquid is a relevant hazard in the process industry. A vessel rupture during storage, transport or handling may lead to devastating blast effects. In order to assess the risk associated with this hazard or to design protective measures, an accurate prediction model for the blast generated after vessel rupture...

The ignition of impulsively started jets of natural gas in a hot coflow has been studied, with the aim of gaining insight into the processes that occur in a furnace equipped with regenerative burners. The development of the velocity field was measured in a time resolved manner with Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV)...

A transported probability density function (PDF) method is used for modeling the flameless combustion in the Delft-Jet-in-Hot-Coflow (DJHC) burner. The DJHC burner creates a turbulent diffusion flame of natural gas fuel in a hot coflow of lean combustion products. The main advantage of the PDF method is that complex finite-rate chemistry is treated...