An improved formulation of the Bray-Moss-Libby (BML) model for SI engine combustion modelling

In this paper an improved version of the BML model has been developed so that it could be applied to wall-bounded combustion modelling, eliminating the wall flame acceleration problem. Based on the Kolmogorov-Petrovski-Piskunov (KPP) analysis and fractal theory, a new dynamic formulation has been proposed to evaluate the mean flame wrinkling scale making necessary allowance for spatial inhomogeneity of turbulence. A novel empirical correlation has been derived based on experimentally estimated flame image data to quantify the quenching rates near solid boundaries. The proposed modifications were then applied to simulate premixed combustion in two spark ignition engines with different operating conditions. Results show that the present improvements have been successful in eliminating the wall flame acceleration problem found with the original BML model, while accurately predicting the in-cylinder pressure rise, mass burn rates and heat release rates

Development of a user-friendly, low-cost home energy monitoring and recording system

This paper reports research undertaken to develop a user-friendly home energy monitoring system which is capable of collecting, processing and displaying detailed usage data. The system allows users to monitor power usage and switch their electronic appliances remotely, using any web enabled device, including computers, phones and tablets. The system aims to raise awareness of consumer energy use by gathering data about usage habits, and displaying this information to support consumers when selecting energy tariffs or new appliances. To achieve these aims, bespoke electrical hardware, or ‘nodes’, have been designed and built to monitor power usage, switch devices on and off, and communicate via a Wi-Fi connection, with bespoke software, the ‘server’. The server hosts a webpage which allows users to see a real-time overview of how power is being used in the home as well as allowing scheduled tasks and triggered tasks (which respond to events) to be programmed. The system takes advantage of well standardised networking specifications, such as Wi-Fi and TCP, allowing access from within the home, or remotely through the internet. The server runs under Debian Linux on a Raspberry Pi computer and is written in Python, HTML and JavaScript. The server includes advanced functionality, such as device recognition which allows users to individually monitor several devices that share a single node. The openPicus Flyport is used to provide Wi-Fi connectivity and programmable logic control to nodes. The Flyport is programmed with code compiled from C

Eulerian particle flamelet modelling of a bluff-body CH4/H2 flame

In this paper an axisymmetric RANS simulation of a bluff-body stabilized flame has been attempted using steady and unsteady flamelet models. The unsteady effects are considered in a postprocessing manner through the Eulerian particle flamelet model (EPFM). In this model the transient history of scalar dissipation rate, conditioned by stoichiometric mixture fraction, is required to generate unsteady flamelets and is obtained by tracing Eulerian particles. In this approach unsteady convective–diffusive transport equations are solved to consider the transport of Eulerian particles in the domain. Comparisons of the results of steady and unsteady calculations show that transient effects do not have much influence on major species, including OH, and the structure of the flame therefore can be successfully predicted by steady or unsteady approaches. However, it appears that slow processes such as NO formation can only be captured accurately if unsteady effects are taken into account, while steady simulations tend to overpredict NO. In this work turbulence has been modeled using the Reynolds stress model. Predictions of velocity, velocity rms, mean mixture fraction, and its rms show very good agreement with experiments. Performance of three detailed chemical mechanisms, the GRI Mech 2.11, the San Diego mechanism, and the GRI Mech 3.0, has also been evaluated in this study. All three mechanisms performed well with both steady and unsteady approaches and produced almost identical results for major species and OH. However, the difference between mechanisms and flamelet models becomes clearly apparent in the NO predictions. The unsteady model incorporating the GRI Mech 2.11 provided better predictions of NO than steady calculations and showed close agreement with experiments. The other two mechanisms showed overpredictions of NO with both unsteady and steady models. The level of overprediction is severe with the steady approach. GRI Mech 3.0 appears to overpredict NO by a factor of 2 compared to GRI Mech 2.11. The NO predictions by the San Diego mechanism fall between those of the two GRI mechanisms. The present study demonstrates the success of the EPFM model and when used with the GRI 2.11 mechanism predicts all flame properties and major and minor species very well, and most importantly the correct NO levels

Numerical study of bluff-body non-premixed flame structures using laminar flamelet model

A laminar flamelet model is applied for bluff-body stabilized flames to study the flow field, mixing pattern, and the flame structure at two different velocities. The k 1 turbulence model is applied for accounting the turbulence fluctuations. It is found that the recirculation zone dominates the near field, while the far field structure is similar to the jet flow. The intermediate neck zone is the intense mixing region. The computation shows that the fuel jet velocity has significant effect on the structure of the flow field, which in turn has significant effect on the combustion characteristics. The laminar flamelet model is found to be adequate for simulating the temperature and the flame composition inside the recirculation zone. The flamelet model has, however, failed to account for the local extinction in the neck zone. Possible limitation of the laminar flamelet model to predict the local extinction is discussed

Simulation of premixed combustion and near wall flame quenching in spark ignition engines with an improved formulation of the Bray-Moss-Libby model

Theoretical and experimental based modifications have been investigated, such that the BML model can be applied to wall-bounded combustion modelling eliminating the wall flame acceleration problem. Estimation of integral length scale of turbulence has been made dynamic so that allowance for spatial inhomogeneity of turbulence is made. A new dynamic formulation has been proposed based on the Kolmogorov- Petrovski-Piskunov analysis and fractal geometry to evaluate the mean flame wrinkling scale. In addition, a novel empirical correlation to quantify the quenching rates in the influenced zone of the quenching region near solid boundaries has been derived based on experimentally estimated flame image data. The proposed model was then applied to simulate the premixed combustion in spark ignition engines. Full cycle combustion in a Ricardo E6 engine for different operating conditions was simulated. Results show that the present improvements have been successful in eliminating the wall flame acceleration problem, while accurately predicting the in-cylinder pressure rise

Effects of radiation on predicted flame temperature and combustion products of a burning liquid fuel spray

The effects of radiative heat transfer calculations on the predicted temperature rise in a burning liquid-fuel spray, are studied. The adiabatic temperature rise resulting from a comprehensive spray combustion model is adjusted for heat transfer to the chamber cooling water by incorporating a radiation model using the Discrete Transfer Technique. The spray combustion model used is of the ‘mixed-is-burnt’ type where combustion is treated as a post process event. The data needed for the combustion post-processor are obtained from an effective property Locally Homogeneous CFD flow model, incorporating a droplet evaporation model to account for the liquid phase. The combustion model itself is based on the minimisation of Gibbs free energy and incorporates kinetic sub-modules for soot formation and oxidation. The results from the combustion model are fed into a radiation sub model for calculating cell emmisivities. These are used to calculate corrective terms for incorporation within the energy balance employed by the combustion model resulting in corresponding temperature (and, subsequently, composition) corrections. The convergence of this iterative process yields results of product concentrations and of temperature throughout the combustion chamber. The predicted results are compared with existing experimental result in a case study. The results are also compared with those obtained from the combustion model with no radiation correction and also with ones obtained with empirical corrections

Simulation of engine combustion with ethanol as a renewable fuel

Ethanol as a fuel is an important bio-fuel for future energy needs. In this work the combustion process of gasoline-ethanol blends in spark ignition engines was investigated using computational fluid dynamics and turbulent combustion modeling. A modified flame surface density approach developed for gasoline engine combustion was adapted to calculate fuel-burning rate of the blend. The rise in in-cylinder peak pressure and temperature for blends up to E20 was found relatively small compared to E00. A significant reduction of CO and an increment of NOx were observed for optimized combustion with adjusted ignition timing

Comparison of discrete transfer and Monte-Carlo methods for radiative heat transfer in three-dimensional non-homogeneous scattering media

Modified formulations of the discrete transfer and Monte Carlo methods are presented for the prediction of radiative heat transfer in three-dimensional nonhomogeneous participating media. Numerical solutions found with both algorithms are in good agreement with published benchmark results, which used contemporary methods to determine the radiative transport in a unit cube. New solutions in an arbitrary L-shaped geometry using a nonorthogonal body-fitted mesh are also presented. The average deviation between the two methods is less than 1.2% for both the boundary surface flux and the divergence of radiative flux or gas emissive power within the enclosed, isotropically scattering media

Validation of unsteady flamelet / progress variable methodology for non-premixed turbulent partially premixed flames

This paper highlights the modeling capabilities of UFPV approach for the modeling of turbulent partially premixed lifted flames to capture the extinction and re-ignition phenomena. Large eddy simulation (LES) with the probability density function (PDF) approach provides the turbulence-chemistry interaction. All scalars are represented as a function of mean mixture fraction, mixture fraction variance, mean progress variable and scalar dissipation rate. Mixture fraction is assumed to follow a β-PDF distribution. Progress variable and scalar dissipation rate distributions are assumed to be a δ-PDF. Results are compared with experimental data of a vitiated co-flow burner with fuels like CH4/Air and H2/N2. Results of radial plots for temperature, mixture fraction and scattered data of temperature with mixture fraction at various axial locations are compared. Lift-off height for a CH4/Air flame appears to be over-predicted while the predicted lift-off height for a H2/N2 flame shows an under-prediction

Transient computational fluid dynamics modelling of the melting process in thermal bonding of porous fibrous media

A continuum model of the melting process in porous fibrous media is introduced. The fluid flow, heat transfer and phase change within the porous nonwoven web is numerically solved using computational fluid dynamics. Boundary conditions from an experimentally validated whole system model of a typical industrial machine, producing fibrous webs are incorporated. The presented model shows the capability to investigate the phase change during heating of the thermoplastic fibres during nonwoven web formation. Moreover, the fibres' geometrical information and constitutive equations, describing the material behaviour are included. The approach considers the fibre thickness, sheath fraction, and thermophysical properties like melting temperature, latent heat of fusion and the liquid fraction, enabling the assessment of different fibre types and to determine the properties of the fabric. The model results reveal that the web porosity has the most significant effect on the melting process among the considered parameters. Thermal gradients that occur inside the web are due to the combined convection and latent heat of fusion effect, which stores heat to melt the fibres. The model is applicable to a wide variety of systems ranging from textiles, fibrous beds, ceramics, membranes and porous composite materials. © IMechE 2012 Reprints and permissions: sagepub.co.uk/ journalsPermissions.nav