CSP-inspired adaptive chemistry reduction for combustion simulations without tabulation

Delft-Jet-in-Hot-Coflow burner can operate Moderate and intense low oxygen dilution (MILD) combustion which yields high thermal efficiency and low fuel consumption along with less pollutant’s emission. This study includes a numerical CFD simulation investigation of non-premixed turbulent combustion for a jet of Dutch natural gas with a lean combustion hot and dilutes co-flow that products in the Delft-Jet-in-Hot-Coflow (DJHC) burner and to mimic Moderate and Intense Low Oxygen Dilution (MILD) characteristics. The simulation has been conducted to measure lift-off height, velocity and temperature of Dutch natural gas (DNG) combustion in the Delft Jet-in-Hot-Coflow (DJHC) burner for two different fuel jet Reynolds numbers (i.e., Re=4100 and Re=8800). The CFD numerical simulations are performed through solving Reynolds-averaged Navier-Stokes equations (RANS) equations where standard k-epsilon (SKE) model has been used as a turbulent model in combustion along with two different turbulent-chemistry interaction models of Eddy Dissipation Concept (EDC) and transported probability density function (PDF). The two-step global kinetic mechanism of methane and air (methane-air 2 step mechanism) is applied as chemical kinetics with the EDC model and on other hand Flamelet Generated Manifold (FGM) is applied in the Probability Density Function (PDF). The simulations results are associated with existing experimental data for understanding better CFD performance to simulation turbulent combustion. The simulation results for both models also yield similar prediction with experimental observation in trend of decrease in lift-off height with higher Reynolds jet.

A Multi-environment probability density function (MEPDF) approach coupled with a tabulated chemistry has been developed to numerically investigate the flame structure under Moderate and intense low oxygen dilution (MILD) combustion with strong flow reversal. The tabulated chemistry is represented by Flamelet generated manifolds (FGM). To realistically represent the highly recirculated flameless combustion, we employed the chemistry database using laminar premixed flamelets rather than laminar diffusion flamelets. Moreover, the present FGM-based MEPDF realistically accounts for the heat loss effects caused by convective heat transfer at the wall. Numerical results in this study were validated against experimental data. Based on numerical results, detailed discussions were made for the essential features of the highly recirculated flameless combustion.

Analysis of the Eddy Dissipation Concept formulation for MILD combustion modelling

Recently large attention is paid to Moderate and Intense Low Oxygen Dilution (MILD) combustion [1], also denoted as flameless combustion, as it allows limiting pollutants formation, in particular that of CO and NOx. MILD combustion is generally achieved through a massive recirculation of exhaust gases in the reaction region, which ensures dilution of reactants before reaction can occur. In this manner oxidation takes place across a relatively large volume rather than restricted to a flame front, thus reducing temperature peaks and NO formation via thermal mechanism. A requirement to obtain a stable combustion is that reactants are heated up above their self-ignition temperature. MILD combustion has been exploited for industrial processes that require a high and homogeneous temperature distribution within the combustion chamber, as in the glass and ceramic industry, as well as in steel thermal treatments. Moreover MILD combustion is receiving increasing interest because it allows fuel flexibility, it being suited also for low-calorific value fuels, highcalorific industrial wastes and industrial byproducts (.e.g coke oven gas) [2]. The modeling of MILD combustion systems generally requires an accurate description of the gas-phase oxidation. However to what extent a kinetic scheme can be reduced is under debate. To this purpose the comparison of predicted and measured CO emissions is crucial. The present paper summarizes and discusses the modeling of CO and NO emissions in terms of kinetic schemes and pollutant formation routes, comparing predictions to measurements taken in three different MILD combustion devices: a self-recuperative burner, a lab-scale burner and a micro-CHP system. All systems are fed with methane and methane/hydrogen mixtures, but with different H2 concentrations and air excess. In this manner a wide range of operating conditions and burner geometries is covered. The level of confidence and the error budget associated to the computations, to better discriminate the limits and potential of the proposed CFD model are evaluated following the Verification and Validation methodology [3].

Moderate and intense low-oxygen dilution (MILD) combustion is regarded as a new clean combustion mode, which can simultaneously improve combustion efficiency and decease NOx emission. The computati...

Chemical Explosive Mode Analysis for a Jet-in-Hot-Coflow burner operating in MILD combustion

In the field of energy production, cogeneration systems based on micro gas turbine cycles appear particularly suitable to reach the goals of improving efficiency and reducing pollutants. Moderate and Intense Low-Oxygen Dilution (MILD) combustion represents a promising technology to increase efficiency and to further reduce the emissions of those systems. The present work aims at describing the behavior of a combustion chamber for a micro gas turbine operating in MILD regime. The performances of the combustion chamber are discussed for two cases: methane and biogas combustion. The combustor performed very well in terms of emissions, especially CO and NO x , for various air inlet temperatures and air-to-fuel ratios, proving the benefits of MILD combustion. The chamber proved to be fuel flexible, since both ignition and stable combustion could be achieved by also burning biogas. Finally, the numerical model used to design the combustor was validated against the experimental data collected. The model performs quite well both for methane and biogas. In particular, for methane the Partially Stirred Reactor (PaSR) combustion model proved to be the best choice to predict both minor species, such as CO, more accurately and cases with lower reactivity that were not possible to model using the Eddy Dissipation Concept (EDC). For the biogas, the most appropriate kinetic mechanism to properly model the behavior of the chamber was selected.

Extension of the Eddy Dissipation Concept for turbulence/chemistry interactions to MILD combustion

Effect of fuel mixture on moderate and intense low oxygen dilution combustion

Effect of fuel mixture on moderate and intense low oxygen dilution combustion

Modeling turbulent reacting jets issuing into a hot and diluted coflow

Assessment of the potential benefits and constraints of a hybrid solar receiver and combustor operated in the MILD combustion regime

The future of today's society is greatly depending on the energy development. Due to the depletion of fossil fuel and the gradual development of energy generation from renewable sources, energy security becomes an important intergovernmental issue. This paper discusses the energy needs and the new combustion technology that will aid in achieving lean and clean combustion. In 2001, British Petroleum estimated the total natural gas reserves to be 187.5 trillion cubic meters, which can supply up to 7×10^15 MJ of energy. The total petroleum reserves can supply up to 1,383 billion barrels which amounts to 8.4×10^15 MJ of energy. Due to the increasing population and economic development, these fuel reserves will not last long. Energy efficiency and greenhouse gas emissions are two important and critical issues. The new combustion technology, moderate and intense low oxygen dilution (MILD) combustion provides a feasible solution. MILD, also known as flameless oxidation (FLOX) and high temperature air combustion (HiTAC) was discovered by Wünning in 1989. The thermal efficiency of combustion can be increased by about 30% and NOx emission reduced by 50%. MILD also can be achieved using different types of fuel such as gas fuel, liquid fuel and industrial waste fuel (saw dust). MILD combustion will be an important future combustion technology due to it producing higher efficiency and very low emissions.

Numerical study of CO and CO2 formation in CH4/H2 blended flame under MILD condition

Evaluation of ignition process and NOx reduction of coal under moderate and intensive low-oxygen dilution combustion by implementing fuel-rich/lean technology