Side-wall quenching (SWQ) is one of the generic configurations for flame-wall interaction and has been widely investigated through simulations using detailed and reduced chemical kinetics. In all previous related studies using manifold-based reduced kinetic models, the reduced model equations are solved in thermokinetic coordinates. This study, by contrast, will for the first time conduct SWQ simulations based on reduced model equations in generalised coordinates. The implementation has been validated by comparison to both simulation results using detailed kinetics and experimental data. Comparing the results of computations solving reduced model equations in generalised coordinates to those in thermokinetic coordinates, it is found that there are only slight differences when the manifold is perfectly invariant, while large discrepancies appear if the manifold is not exactly invariant. Under the latter condition, only reduced model equations in generalised coordinates yield correct results. Within the combined framework of reduced model equations in generalised coordinates and the so-called reaction–diffusion manifold for tabulation, the sensitivity with respect to the gradient estimation is investigated to find out what degree of simplification is reasonable for SWQ simulations.

The localised forced ignition and subsequent flame propagation have been analysed for stoichiometric mixtures with different spatial distributions and mean levels of dilution (i.e. mole fraction of in blend) for different flow conditions (e.g. quiescent laminar condition and different turbulence intensities) using three-dimensional Direct Numerical Simulations. The mixture is taken to represent biogas, as and are its two principal constituents. A two-step chemical mechanism, which has been demonstrated to capture the effects of dilution on the laminar burning velocity with sufficient accuracy, has been used for the purpose of a parametric analysis in terms of the mean value, standard deviation and integral length scale of the initial spatial Gaussian distributions of dilution in the unburned gas. An increase of mean dilution level was found to reduce the maximum values of temperature and the reaction rate magnitude of . Moreover, an increase of mean dilution acts to reduce the probability of finding large reaction rate magnitudes of , which also leads to a decreasing trend of burned gas volume irrespective of flow conditions. Furthermore, an increase in turbulence intensity acts to reduce the burned gas volume irrespective of mixture composition due to the enhancement of heat transfer from the hot gas kernel. However, the initial values of integral length scale and standard deviation of dilution variation (i.e. and ) have been found not to have significant influences on the burned gas volume for the parameter range considered here. Although a small value of promotes high rates of mixing of within the unburned gas, the overwhelming probability of finding dilution close to its mean value eclipses the effects of and even under laminar conditions, and this trend strengthens further under high turbulence intensities due to enhanced mixing.

Numerical methods for predicting the primary breakup length, the ligament and droplet diameter of fuels are a suitable substitute for experimental work. Mazut, diesel, biodiesel and water fluids are selected for the study. A linear instability model has been applied for the analysis of various liquid sprays. The effects of velocity (axial and swirl), viscosity and temperature on the atomisation of fuels annular jets are investigated. The parameters of wave growth value, length of jet breakup, drops and ligaments diameter are obtained by solving the governing equation of the flow spray. The results show that by decreasing the viscosity and increasing the axial and swirl velocity, the rate of disturbance growth increases and causes the faster atomisation of the liquids spray. Also, by increasing the maximum amount of disturbance growth rate and the number of wave that depends on it, the breakup length, diameter of ligament and droplet of fuel are reduced. In general, the atomisation parameters decrease as a power function with increasing wave number. Mazut 40, Mazut 80 and diesel are sprayed experimentally. The breakup lengths obtained from the experimental results are compared with the numerical results. Uncertainty analysis is done for the temperature, mass flow rate and velocity. The experimental results are in good agreement with the numerical results. Finally, the breakup length, drop diameter and ligament diameter are plotted in terms of Reynolds, Ohnesorge, Weber numbers and Temperature. The Ohnesorge number is directly related to Weber number and inversely related to Reynolds number. , and decrease exponentially and , L b, d L and d D decrease linearly with increasing temperature. Experimental and numerical analyses of various and applied fluids in order to gasify and compare the atomisation characteristics among applied fluids give a better understanding of how they behave.

Large Eddy Simulation (LES) of the lab-scale methane fire plumes investigated experimentally by McCaffrey is performed using the steady laminar flamelet/presumed beta filtered density function model on grids of different resolution ranging from the Taylor length scale to about six times the Kolmogorov length scale. This work focuses on investigating existing subgrid (SGS) mixing models for mixture fraction variance prediction. Three different models based on the local equilibrium assumption, the variance transport equation (VTE) and the second moment transport equation (STE) are assessed. In the non-equilibrium modelling (VTE and STE), the scalar dissipation rate is modelled with an algebraic expression involving an SGS mixing time-scale. The comparison of the solutions is based on the convergence properties of LES statistics for mixture fraction, temperature and axial velocity with respect to the filter width. The simulations show that the equilibrium algebraic model is not suitable for purely buoyant flows. On the other hand, simulations performed with the transport models show that grids coarser than 1 cm cannot resolve adequately the natural laminar instability near the edge of the plume that governs the formation of large-scale vortex and, therefore, underestimate the mixing process, especially in the lower part of the continuous flame. For grid resolutions finer than 1 cm, the STE model is less sensitive to grid refinement than the VTE formulation and differences between the two models are reduced with grid refinement. The STE model predicts also a stronger mixing, resulting in a slightly larger lateral expansion of the fire plume. Predicted solutions by the two models are in quantitative agreement with the experimental data in terms of axial temperature, velocity and temperature fluctuations.

This paper presents numerical and asymptotic analytical solutions for the current–voltage characteristic of a flame using a one-dimensional ion transport model with boundary conditions that include detailed treatment of sheath formation. Non-dimensional conservation equations are presented for the free electron, the hydronium ion, and the electrical potential in a one-dimensional flow field with uniform velocity, electrical mobility, and diffusivity, but allowances are made for non-equilibrium electron temperature. In this study, the size and location of the ion formation region and the electric Reynolds numbers are changed, and their impacts are studied. The model predicts the formation of charged sheaths at both ends of the domain, which are responsible for saturation events that are reliably observed in experiments. A new saturation regime can be made to appear in the model, but its absence from the experiment is argued to have implications on transport near absorbing surfaces in the experiment. For example, the Reynolds numbers at which the current–voltage characteristic converges to the shape and magnitude observed in the experiment implies that the sheaths form in the low-velocity region in the real flow that reduces the apparent Reynolds number.

Shuttle kilns are widely used in the sanitary ware industry. A key parameter to reduce energy consumption and increase their overall performance is temperature uniformity. Therefore, in this paper a systematic and statistical study of the effect of the position of burners and their interactions on the temperature uniformity of a shuttle kiln is performed. CFD simulations and a 4k factorial analysis were used to determine, quantitatively and qualitatively, the best burner configuration in hterms of kiln temperature uniformity. It was found that the proximity of the burners has a negative impact on the temperature distribution of the kiln. These proximities caused collisions of the burners streams which deflected the flow in the Y-axis direction. This may increase the outlet velocity of the combustion gases, diminishing the heat exchange between gases and the ceramic pieces, producing a heterogeneous distribution of temperature. The standard deviation varied from 2.29 to 3.78 depending of the configuration of the burners used. To avoid these negative effects, collisions between the streams of the burners should be avoided. Also, the distance between the furniture carts of the kiln could be varied to maximise the heat exchange inside. The results obtained are useful in the design of ceramic shuttle kilns, as it allows one to determine the quantitative and qualitative effect of the position of the burners at different sections of the kiln.

A reduced order kinetic model for NO (nitric oxide) prediction, based on the virtual chemistry methodology [M. Cailler, N. Darabiha, and B. Fiorina, Development of a virtual optimized chemistry method. Application to hydrocarbon/air combustion, Combust. Flame 211 (2020), pp. 281–302], is developed and applied. Virtual chemistry aims to optimise thermochemical properties and kinetic rate parameters of a network of virtual species and reactions. A virtual main chemical mechanism is dedicated to temperature and heat release prediction and is coupled with the flow governing equations, whereas satellite sub-mechanisms are designed to predict pollutants formation. Two virtual chemistry mechanisms are here employed: a main mechanism for calculating the temperature and heat release rate and a second mechanism dedicated to NO prediction. To recover the chemical structure of multi-mode combustion, both premixed and non-premixed flamelets are included in the learning database used to optimise the virtual NO mechanism. A multi-zone optimisation procedure is developed to accurately capture both fast and slow NO chemistry that include prompt, thermal and reburning pathways. The proposed NO sub-mechanism and optimisation methodology are applied to CH/air combustion. Laminar 1-D premixed and non-premixed flamelet configurations are first tested. The approach is then further assessed in 2-D CFD laminar flame simulations, by providing a direct comparison against detailed chemistry. 2-D premixed, non-premixed and partially premixed flame configurations are numerically investigated. For all cases, the virtual mechanism fairly captures temperature and chemistry with only 12 virtual species and 8 virtual reactions with a drastic CPU time reduction compared to detailed chemistry.

A novel combustion modelling approach is proposed here to study the transient effects of diesel spray. Conditional Source-term Estimation (CSE) is a combustion model which invokes the Conditional Moment Closure (CMC) hypothesis to provide an approximation of the mean chemical source term in an averaged transport equation. Unlike CMC, where transport equations are solved for conditional moments, CSE recovers these conditional moments through the solution of an inverse problem. Integral equations are inverted for the conditional moments, by assuming spatial homogeneity in the conditional averages where Tikhonov regularisation is applied. Previous CSE studies have shown that the model is able to predict the flame characteristics successfully for both premixed and non-premixed combustion modes. However, most of these investigations were based on methane flames. This study will be the first successful application of CSE to a complex hydrocarbon fuel, n-dodecane, under the Engine Combustion Network's (ECN) ‘Spray A’ conditions. Detailed chemistry is included in tabulated form using the Flamelet Generated Manifold (FGM) methodology. The predictions of this study include both the Favre averaged conditional mass fraction of reactive species and temperature. The results are compared with available experimental data and previous numerical results. Both RANS and LES simulations are performed under the same condition. The objectives of the paper are (i) assessment of the application of CSE on igniting diesel spray (ii) comparison of the CSE numerical results with available experimental results and previous numerical simulations. Overall, the combination of a chemical mechanism that has been tuned to predict ‘Spray A’ conditions with the CSE-FGM model is able to successfully predict autoignition delay time and lift-off length of n-dodecane spray within the scatter of the experimental data. CSE-FGM offers a feasible tool for detailed combustion analysis of diesel spray flames. Both RANS and LES can give reasonably good global predictions of the flame.

State-to-state rotational relaxation processes play a critical role in predicting rotational nonequilibrium, which can significantly affect total laser power and spectral distribution. In this paper, the state-to-state rotational relaxation rate coefficients for the pumping reaction of F + H2, the rotational energy transfer processes of HF(υ, j = 0–10) + HF(υ′, j′ = 0–10) and HF(υ, j = 0–10) + H2 are calculated. Subsequently, a detailed state-to-state chemical kinetic mechanism is constructed including 61 species and 124,482 elementary reactions for HF chemical lasers. All of these rotational relaxation rate coefficients have been expressed with Arrhenius-like formulas. A comparison of the Boltzmann distribution model with the detailed state-to-state chemical mechanism has been analysed and discussed. These results show that rotational nonequilibrium processes can significantly affect the distribution of ro-vibrational excited HF molecules. The rotational distributions of HF(υ = 0–2, j) are far from equilibrium distribution. Conversely, the distributions of HF(υ = 3, 4, j) seem to be a Boltzmann distribution. These results indicate that numerical models must include the rotational nonequilibrium processes and numerical models using a Boltzmann distribution for the rotational populations cannot predict performance of real HF chemical lasers.

ABSTRACT In this paper, we present a systematic roadmap for developing a robust and parallel multi-material reactive hydrodynamic solver that integrates historically stable algorithms with new and current modern methods to solve explosive system design problems. The Ghost Fluid Method and Riemann solvers were used to enforce appropriate interface boundary conditions. Improved performance in terms of computational work and convergence properties was achieved by modifying a local node sorting strategy that decouples ghost nodes, allowing us to set material boundary conditions via an explicit procedure, removing the need to solve a coupled system of equations numerically. The locality and explicit nature of the node sorting concept allows for greater levels of parallelism and lower computational cost when populating ghost nodes. Non-linear numerical issues endemic to the use of real Equations of State in hydro-codes were resolved by using more thermodynamically consistent forms allowing us to accurately resolve large density gradients associated with high energy detonation problems at material interfaces. Pre-computed volume tables were implemented adding to the robustness of the solver base.