Thin Flame Research Articles

A localized thickened flame model for simulations of flame propagation and autoignition under elevated pressure conditions

The present study proposes a localized thickened flame (LTF) model for the accurate prediction of flame propagation and autoignition timing. The unresolved-scale terms appeared in spatially-filtered governing equations due to thin flame structures are constructed under a physical constraint in which laminar flame speed is maintained. A high-order derivative is introduced to dynamically localize the effects of the LTF in the regions of unresolved propagating flame. The model is also designed such that the thickened flame is resolved by the same number of grid points for any grid size used. Therefore, a user-specified constant in the model does not need to be adjusted depending on the employed grid size. Laminar flame propagation problems are used to validate the performance of the proposed LTF model and determine the appropriate value of the user-specified constant. The results using a one-dimensional constant-volume reactor demonstrate that the LTF successfully captures the accurate flame propagation behaviors under elevated pressure conditions, while not affecting the end-gas autoignition timing, even on relatively coarse grid resolutions. The high-order derivative in the LTF serves as a dynamic parameter for detecting the thinning flame under elevated pressure conditions.

3D tomography integrating view registration and its application in highly turbulent flames

Recently, reconstruction integrating view registration (RIVR) has been demonstrated as an improved method to significantly enhance the accuracy of three-dimensional (3D) measurements in nonreactive flows. This work extended the RIVR method to 3D measurements of highly turbulent reactive flows with two specific goals. The first goal was to examine if the RIVR method can be effectively applied to highly turbulent flame structures, which display distinctively different spatial features from nonreactive flows. This examination of RIVR was performed specifically using two performance metrics, accuracy and spatial resolution. The second goal was to quantify the end benefits the RIVR can bring about on key flame properties involved in turbulence-chemistry interaction, such as flame surface density. The results demonstrated that the RIVR method can effectively enhance reconstruction accuracy of the thin flame front marked by CH radicals in 3D distribution. Compared to past methods, the RIVR method reduced the reconstruction errors by ~48% on average and improved the spatial resolution by ~26% on average. Such accuracy enhancement ultimately led to a ~15% improved accuracy on the determination of the 3D flame surface density as an indicator of the total burning rate.

Flame structure of supercritical ethanol/water combustion in a co-flow air stream characterized by Raman chemical analysis

The thermochemical properties of the ethanol hydrothermal flame (30%-v ethanol-water solution), established in air co-flow under supercritical water conditions, are measured by a quantitative Raman diagnostic technique. The unique spectroscopic features of the chemical compounds are revealed to aid understanding of the fuel decomposition and oxidation process in supercritical phase. A point-wise fiber-optic probe is designed to resolve the needle-like thin flame and identify the spatial profiles – across the flame thickness and over the height of the visible flame – of the combustion species at different fuel/air ratios and airflow rates. An attempt is made to analyze the steep thermal gradients in the primary reaction zone near the fuel nozzle by estimating thermodynamic temperatures from the measured fluid density. The test cell was held at conditions above the critical point of water, at a nominal pressure of 25 MPa and a nominal temperature of 723 K (450 °C). The flames were over ventilated with an excess air:fuel ratio between two and five times stoichiometric. Depending upon the air:fuel ratio non-sooting blue flames or yellow sooting flames are observed. The results of the Raman diagnostic provide temperature and species profiles that will prove useful for validating numerical models using an idealized laboratory hydrothermal flame. The Raman diagnostic results are augmented with imaging from two orthogonal camera views: a backlit shadow-graphic image of the co-flow jet and a color image of the flame.

Influence of gas radiative property models on Large Eddy Simulation of 1 m methanol pool fires

The main objective of this work is to analyze the effects of gas radiative property models on the radiative outputs and flame structure in a 1 m diameter methanol pool fire. Large Eddy Simulation (LES) are run with the non-adiabatic steady laminar flamelet (SLF)/presumed filtered density function (FDF) model to close subgrid-scale (SGS) turbulence-chemistry and turbulence-radiation emission interactions. The radiative transfer equation (RTE) is solved using the Finite Volume Method (FVM) with different angular meshes, including uniform angular dicretizations comprising 16 (polar angle) × 24 (azimuthal angle) and 48 × 96 control angles and the FTn scheme with n up to 48. Four gas radiative property models, namely the Rank Correlated Full Spectrum k-distribution (RCFSK), the non-grey Weighted-Sum-of-Grey-Gases (WSGG), and two versions of the grey WSGG based on different evaluations of the mean path length are assessed. Model predictions with the RCFSK reproduce with fidelity the available experimental data in terms of flame structure and radiative loss to the surrounding. The radiative heat transfer within the flame, where radiation is isotropic, is adequately resolved with the FT12 angular resolution whereas finer angular meshes with at least 32 segments to discretize the polar angle are required to predict accurately the vertical distributions of radiative flux outside the flame. The grey models fail to reproduce the radiative structure of the flame, predicting an optically thin flame instead of an optically intermediate medium. In an opposite way, although the non-grey WSGG overestimates both emission and absorption, it provides predictions in overall reasonable agreement with the RCSFK.

Instability of free interfaces in premixed flame propagation

<p style="text-indent:20px;">In this survey, we are interested in the instability of flame fronts regarded as free interfaces. We successively consider a classical Arrhenius kinetics (<em>thin flame</em>) and a stepwise ignition-temperature kinetics (<em>thick flame</em>) with two free interfaces. A general method initially developed for thin flame problems subject to interface jump conditions is proving to be an effective strategy for smoother thick flame systems. It relies on the elimination of the free interface(s) and reduction to a fully nonlinear parabolic problem. The theory of analytic semigroups is a key tool to study the linearized operators.

The entropy wave generation in a heated one-dimensional duct

This paper presents a theoretical analysis on entropy wave generation in a heated one-dimensional duct, which is a simple thermoacoustic model of a combustor. Following a new observation that an entropy wave is caused by the fluctuations of heat/flow power ratio, the entropy transport equation is analytically solved for a heat input uniformly distributed over an acoustically compact zone. Investigating transfer functions from heat and acoustic fluctuations to the entropy wave, we obtain a deeper understanding on the low-pass filtering property of entropy waves with a closed-form expression of the entropic cutoff frequency. A theoretical explanation on why a thinner flame generally results in a stronger entropy wave is also given. These findings are extended to a general flame distribution from a temporal-spatial filtering interpretation of the entropy transport equation. Furthermore, the thin flame limits of our entropy wave models are compared with a popular entropy model based on the thin flame assumption and jump conditions. A numerical example supporting our theoretical findings is also presented.

Large eddy simulation of hydrogen piloted CH4/air premixed combustion with CO2 dilution

Large eddy simulation (LES) of constant adiabatic temperature, hydrogen-piloted, turbulent lean premixed methane/air jet flames with varying amounts of CO2 addition are reported. Constant adiabatic temperature is achieved by increasing the fuel flow rate slightly to account for the higher specific heat of CO2 compared to N2. Such flames are relevant to low NOx gas turbines with high hydrogen content fuels and Exhaust Gas Recirculation (EGR). A newly designed burner called Piloted Axisymmetric Reactor Assisted Turbulent (PARAT) flame burner was utilized. The operating conditions in the experiment were selected to highlight the kinetic effects of CO2 addition by matching the Reynolds numbers, Lewis numbers and adiabatic flame temperatures. The LES simulations utilize a finite rate chemistry solver with DRM19 combustion mechanism with adaptive zoning and a dynamic structure turbulence model. A five-level adaptive mesh refinement (AMR) improves the velocity and temperature gradient resolution. The LES predicts the experimentally observed increase in flame length with CO2 levels caused by a decrease in the turbulent flame speed. The computational results also capture the experimentally observed departure from the thin flame limit and a collapse of the root mean square (RMS) versus mean temperature profiles for the three levels of CO2. The flame structure analysis showed super-equilibrium CO concentrations because of non-equilibrium chemistry effects caused by the external addition of CO2.

Effects of turbulence-chemistry interactions on auto-ignition and flame structure for n-dodecane spray combustion

The Engine Combustion Network (ECN) spray A under diesel engine conditions is investigated with a non-adiabatic 5D Flamelet Generated Manifolds (FGM) model with the consideration of detailed chemical kinetic mechanisms. The enthalpy deficit due to droplet vapourisation is considered by employing an additional controlling parameter in the FGM library. In this FGM model, β-PDF is used for the PDF integration over the control variable space. Validation results in non-reacting conditions indicate relatively good agreement between the predicted and experimental data in terms of liquid and vapour penetrations and mixture fraction spatial distribution. In reacting conditions, the effects of variance of mixture fraction and progress variable were examined. The ignition delay time and the quasi-steady flame structure are both affected by the variances. The variance of mixture fraction delays the ignition process and the variance of progress variable accelerates it. For mixture fraction, the ignition process is quicker at any stage in the case of neglecting variance. While things are more complex for progress variable, the ignition process is advanced in the case of neglecting variance at early times, but surpassed by the case of β-PDF later and until auto-ignition. When variance of mixture fraction is considered, the OH mass fraction shows a wide spatial distribution. While if not, a very thin flame is observed with a higher peak in OH, and a very large lift-off length. The variance of progress variable has little impact on the global flame structure, but makes the flame lift-off length much shorter. This study confirms the general observation, that the variance of mixture fraction is of higher importance in high temperature non-premixed combustion, however, we found that the variance of progress variable is far from negligible.

Counterflow and wall stagnation flow with three-dimensional strain

Three-dimensional (3D) viscous counterflows and wall stagnation flows are analyzed with differing normal strain rates in each of the three directions. Reduction of the equations to a similar form is obtained allowing for variations in density due to temperature and composition, heat conduction, and, for the counterflow, mass diffusion and the presence of a flame. Solutions to the Navier-Stokes equations are obtained without the boundary-layer approximation. For the steady and unsteady incompressible counterflows, analytical solutions are obtained for the flow field and the scalar fields subject to heat and mass transfer. In steady, variable-density configurations, a set of ordinary differential equations (ODEs) governs the two transverse velocity and the axial velocity profiles as well as the scalar-field variables. Diffusion rates for mass, momentum, and energy depend on the two normal strain rates parallel to the counterflow interface or the wall and thereby not merely on the sum of those two strain rates. For thin diffusion flames, the location, burning rate, and peak temperature are readily obtained. Solutions for planar flows and axisymmetric flows are obtained as limits here. Results for the velocity and scalar fields are found for a full range of the distribution of normal strain rates between the two transverse directions, various Prandtl number values, and various ambient (or wall) temperatures. For counterflows with flames and stagnation layers with hot walls, velocity overshoots are seen in the viscous layer, yielding an important correction of theories based on a constant-density assumption.

Dynamic Simulation on Deflagration of LNG Spill

The deflagration characteristics of premixed LNG vapour-air mixtures with different mixing ratios were quantitatively and qualitatively investigated by using CFD (computational fluid dynamics) method. The CFD model was initially established based on theoretical analysis and then validated by a lab-scale deflagration experiment. The flame propagation behaviour, pressure-time history, and flame speed were compared with the experimental data, upon which a good agreement was achieved. A large-scale deflagration fire during LNG bunkering process was conducted using the model to investigate the flame development and overpressure effects. Mesh independence and time scale were tested in order to obtain the suitable grid resolution and time step. Deflagration cases with two different LNG vapour volume fractions, i.e., 10.4% and 15.0%, were simulated and compared. The one with a volume fraction of 10.4% which was around stoichiometric mixing ratio had the highest flame propagating speed. High flame velocity observed in the simulation was coupled with the thin flame front where overpressure occurred. The CFD model could capture the main features of deflagration combustion and account for LNG fire hazard which could provide an in-depth insight when dealing with complicated cases.

Experimental and thermodynamic study of aerosol explosions in a 36 L apparatus

Explosions involving vapor-liquid mixtures have a tragic history in the chemical industry. Numerous incidents such as the Buncefield explosion and the Flixborough disaster have demonstrated the importance of investigating the mechanism and consequence of aerosol explosions. ASTM D3065-01 presents two standard test methods, the flame projection and closed drum tests, for the flammability of aerosol products. The flame projection method involves the spraying of aerosol directly into an open flame to measure whether the aerosol can be ignited. The closed drum test requires the spraying of aerosol directly into a closed drum containing an open flame. The flame projection and closed drum tests in this ASTM standard, are not adopted widely due to the lack of quantification. Motivated by this consideration, this study proposes a test method to quantitatively investigate the flammable hazard and consequence assessment of aerosol explosions. The proposed method has the potential to surpass the existing go/no-go standard test method through an approach quantifying the aerosol hazard. The first stage of the procedure was to characterize the aerosol cloud properties, such as droplet size distribution and concentration. The second stage was to ignite the aerosol cloud in a closed vessel to measure the maximum explosion pressure (Pmax) and the explosibility characteristics (Ka). These parameters can be considered a thermodynamic and kinetic assessment of the explosion, respectively and are critical when designing a venting system. In this experimental study, Pmax and Ka were determined for a range of equivalence ratios for n-octane and n-dodecane. The experimental results were compared to a thermodynamic model, which estimates Pmax, revealing evaporation was the controlling step during the aerosol combustion process. A thin flame and three-zone model were investigated to model the rate of pressure rise during the aerosol explosion. In addition, this study of n-octane and n-dodecane has demonstrated that liquids can be ignited below their flashpoint when they are in aerosol form. It also shows that the aerosol lower flammable limits (LFL) are lower than the corresponding gas vapors.

Impact of sub-grid scale models on resolving mixing and thermal shear layers in large eddy simulation of JHC flames

Predictive performance of sub-grid scale (SGS) models is investigated in Large Eddy Simulation (LES) of a methane/hydrogen jet-in-hot coflow (JHC) flame using a conceptual analysis proposed for the mean values of major combustion products. It is shown that mean values of major combustion products consist of valuable information on several characteristics of JHC flames such as flame thickness, flame volume and reaction intensity. In particular, sudden change of CO2 and H2O mass fractions from coflow contents to higher values, predicted by static SGS models, demonstrated a thin flame constricted around the center line. However, uniform ascending manner of CO2 and H2O contents in the coflow region predicted by dynamic SGS models revealed their ability on capturing characteristics of a distributed volumetric flame. For the temperature fluctuations in shear layers, the dynamic Smagorinsky model is also shown to provide better predictions than the constant-coefficient Smagorinsky model, the latter exhibiting significant over-predictions. It is also observed that the dynamic kinetic energy SGS model with its unique assumption of non-equilibrium turbulence is the best fitted SGS model for the JHC flames as it provides improved accuracy on developing mixing and thermal shear layers by solving an extra transport equation for turbulent kinetic energy.

Flame speed characteristics of turbulent expanding flames in a rectangular channel

We present results from studies of freely expanding flames in a unique small-scale convective facility for different free-stream initial conditions, characterized by Taylor-Reynolds numbers in the range of Reλg=179−395 (using the streamwise RMS velocity component and the lateral Taylor-microscale) and an inertial subrange over two decades of wavenumbers. The isotropic, decaying turbulence is generated by an active vane grid. Adding natural gas far upstream, the premixed flow is ignited using Laser Induced Breakdown (LIB) ignition. The evolution of the resulting spherically expanding flames is investigated using qualitative OH-Planar Laser Induced Fluorescence (PLIF). It is shown that trends of flame speeds derived from mean flame radius growth agree well with results from different experimental setups, using a recently developed scaling based on a spectral closure of a thin flame model (Chaudhuri et al., Phys. Rev. E (2011)). Reliable computation of the flame surface density and turbulent flame brush thickness is enabled by the large number of ensembles that can be collected in this type of facility. Trends of these instantaneous statistical quantities are presented and used to further assess the results of time-dependent mean quantities.

Characterization of six clustered methane-air diffusion microflames through spectroscopic and tomographic analysis of CH* and C2* chemiluminescence

The current study presents an emission spectroscopic investigation of clustered microflames established on a burner consisting of six micro fuel nozzles surrounding a center air nozzle which has been designed for flame synthesis and characterization of microflames. We conducted spectrally resolved measurements of the chemiluminescence of C2* and CH* and compared these results to a tomographic method applied to filtered emission measurements of CH* emission which can yield spatially resolved three dimensional mapping of the flame front. The analysis of the spatial distribution of the integrated band emission of C2* and CH* showed that the emission of both species is generated in the same locations in the flame which are the thin flame sheets shown in the tomography results of CH*. The ratio of the C2* and the CH* emission from the emission spectroscopy measurements was used to determine a corresponding local equivalence ratio through empirically derived correlations for premixed flames reported in literature. The resulting equivalence ratio equals one when the flame zone established at the boundary between fuel and air, indicating that diffusion dominated flame zones are established. Under certain nozzle pitch and flow rate conditions, the equivalence ratio above the center air nozzle inside the merged flame became significantly greater than one, which indicates a local fuel rich premixed type flame zone being established.To determine distributions of rotational and vibrational temperatures throughout the entire flame, we used the spectrally resolved emission from C2* and CH*. The temperature associated with vibrational excitation was different for both species but remained constant throughout the entire flame region and was found no representation of the flame temperature but an artifact of the combustion reactions producing the chemiluminescence. The rotational temperature of di-atomic molecules, however, equilibrates rather quickly with the translational temperature and can accurately represent the gas-dynamic temperature of the flame. The temperature distributions found from the two species agreed qualitatively, the CH* temperature was consistently higher than the C2* temperature by about 200 K. Spatial resolution was assigned to the results from the spectroscopic measurements through a comparison with the tomographically analyzed images of the CH* chemiluminescence.

Effect of Lewis number on premixed laminar lean-limit flames stabilized on a bluff body

In this paper, we present a study on the effect of Lewis number, Le, on the stabilization and blow-off of laminar lean limit premixed flames stabilized on a cylindrical bluff body. Numerical simulations and experiments are conducted for propane, methane and two blends of hydrogen with methane as fuel gases, containing 20% and 40% of hydrogen by volume, respectively. It is found that the Le > 1 flame blows-off via convection from the base of the flame (without formation of a neck) when the conditions for flame anchoring are not fulfilled. Le ≤ 1 flames exhibit a necking phenomenon just before lean blow-off. This necking of the flame front is a result of the local reduction in mass burning rates causing flame merging and quenching of the thin flame tube formed. The structure of these flames at the necking location is found to be similar to tubular flames. It is found that extinction stretch rates for tubular flames closely match values at the neck location of bluff-body flames of corresponding mixtures, suggesting that excessive flame stretch is directly responsible for blow-off of the studied Le ≤ 1 flames. After quenching of the neck, the upstream part forms a steady and stable residual flame in the wake of the bluff body while the downstream part is convected away.

Gas phase combustion in the vicinity of a biomass particle during devolatilization – Model development and experimental verification

A numerical and experimental study on the devolatilization of a large biomass particle is carried out to quantify the effect of homogeneous volatile combustion on the conversion of the particle and on the temperature and species distribution at the particle vicinity. A global chemical kinetic mechanism and a detailed reaction mechanism are considered in a one dimensional numerical model that takes into account preferential diffusivity and a detailed composition of tar species. An adaptive moving mesh is employed to capture the changes in the domain due to particle shrinkage. The effect of gas phase reactions on pyrolysis time, temperature and species distribution close to the particle is studied and compared to experiments. Online in situ measurements of average H2O mole fraction and gas temperature above a softwood pellet are conducted in a reactor using tunable diode laser absorption spectroscopy (TDLAS) while recording the particle mass loss. The results show that the volatile combustion plays an important role in the prediction of biomass conversion during the devolatilization stage. It is shown that the global reaction mechanism predicts a thin flame front in the vicinity of the particle deviating from the measured temperature and H2O distribution over different heights above the particle. A better agreement between numerical and experimental results is obtained using the detailed reaction mechanism, which predicts a wider reaction zone.

Large Eddy Simulation of a Pressurized, Partially Premixed Swirling Flame With Finite-Rate Chemistry

Finite-rate chemical effects at gas turbine conditions lead to incomplete combustion and well-known emissions issues. Although a thin flame front is preserved on an average, the instantaneous flame location can vary in thickness and location due to heat losses or imperfect mixing. Postflame phenomena (slow CO oxidation or thermal NO production) can be expected to be significantly influenced by turbulent eddy structures. Since typical gas turbine combustor calculations require insight into flame stabilization as well as pollutant formation, combustion models are required to be sensitive to the instantaneous and local flow conditions. Unfortunately, few models that adequately describe turbulence–chemistry interactions are tractable in the industrial context. A widely used model capable of employing finite-rate chemistry is the eddy dissipation concept (EDC) model of Magnussen. Its application in large eddy simulations (LES) is problematic mainly due to a strong sensitivity to the model constants, which were based on an isotropic cascade analysis in the Reynolds-averaged Navier–Stokes (RANS) context. The objectives of this paper are: (i) to formulate the EDC cascade idea in the context of LES; and (ii) to validate the model using experimental data consisting of velocity (particle image velocimetry (PIV) measurements) and major species (1D Raman measurements), at four axial locations in the near-burner region of a Siemens SGT-100 industrial gas turbine combustor.

Flammability limit of thin flame retardant materials in microgravity environments

The flammability limits of thin flame retardant materials in an opposed flow under microgravity condition have been discussed by scale analysis. The predicted trends of flammability were verified by parabolic flight experiments. As the samples, meta- and para-aramid fabrics (NOMEX and Kevlar), polyimide film (Kapton) and polycarbonate (PC) were investigated. In order to predict the limiting curve accurately, blow-off tests in high forced flow were conducted and the results were used to obtain proper pre-exponential factor, A, and activation energy, E, for blow-off phenomena. The blow-off tests revealed that the material with high pyrolysis temperature, such as Kevlar and Kapton, had its minimum limiting oxygen concentration (MLOC) at higher opposed velocity region. For such materials, it was predicted that the limiting oxygen concentration in microgravity environments was higher than that in normal gravity, and the prediction was consistent with the result of parabolic flight experiment. For NOMEX and PC, the limiting oxygen concentration increased monotonically with increase of opposed flow velocity. The developed model predicted that such materials could have their MLOC in microgravity environments. Actually, the MLOCs of NOMEX and PC were observed under microgravity condition and they were 2% and 0.5% lower than their limiting oxygen concentrations in normal gravity (LOC1g), respectively. The developed model with blow-off test data could predict the difference between the MLOC and LOC1g quantitatively, and it was found that the model was a good tool to discuss the flammability of the flame retardant materials in microgravity environments.

Autoignited lifted flames of dimethyl ether in heated coflow air

Autoignited lifted flames of dimethyl ether (DME) in laminar nonpremixed jets with high-temperature coflow air have been studied experimentally. When the initial temperature was elevated to over 860 K, an autoignition occurred without requiring an external ignition source. A planar laser-induced fluorescence (PLIF) technique for formaldehyde (CH2O) visualized qualitatively the zone of low temperature kinetics in a premixed flame. Two flame configurations were investigated; (1) autoignited lifted flames with tribrachial edge having three distinct branches of a lean and a rich premixed flame wings with a trailing diffusion flame and (2) autoignited lifted flames with mild combustion when the fuel was highly diluted. For the autoignited tribrachial edge flames at critical autoignition conditions, exhibiting repetitive extinction and re-ignition phenomena near a blowout condition, the characteristic flow time (liftoff height scaled with jet velocity) was correlated with the square of the ignition delay time of the stoichiometric mixture. The liftoff heights were also correlated as a function of jet velocity times the square of ignition delay time. Formaldehydes were observed between the fuel nozzle and the lifted flame edge, emphasizing a low-temperature kinetics for autoignited lifted flames, while for a non-autoignited lifted flame, formaldehydes were observed near a thin luminous flame zone.For the autoignited lifted flames with mild combustion, especially at a high temperature, a unique non-monotonic liftoff height behavior was observed; decreasing and then increasing liftoff height with jet velocity. This behavior was similar to the binary mixture fuels of CH4/H2 and CO/H2 observed previously. A transient homogeneous autoignition analysis suggested that such decreasing behavior with jet velocity can be attributed to partial oxidation characteristics of DME in producing appreciable amounts of CH4/CO/H2 ahead of the edge flame region.

Thermodynamic efficiency assessment of gasoline spark ignition and compression ignition operating strategies using a new multi-mode combustion model for engine system simulations

Advanced combustion strategies for gasoline engines employing highly dilute and low-temperature combustion modes, such as homogeneous charge compression ignition and spark-assisted compression ignition, promise significant improvements in efficiency and emissions. This article presents a novel, reduced-order, physics-based model to capture advanced multi-mode combustion involving spark ignition, homogeneous charge compression ignition and spark-assisted compression ignition operating strategies. The purpose of such a model, which until now was unavailable, was to enhance existing capabilities of engine system simulations and facilitate large-scale parametric studies related to these advanced combustion modes. The model assumes two distinct thermodynamic zones divided by an infinitely thin flame interface, where turbulent flame propagation is captured using a new zero-dimensional formulation of the coherent flame model, and end-gas auto-ignition is simulated using a hybrid approach employing chemical kinetics and a semi-empirical burn rate model. The integrated model was calibrated using three distinct experimental data sets for spark ignition, homogeneous charge compression ignition and spark-assisted compression ignition combustion. The results demonstrated overall good trend-wise agreement with the experimental data, including the ability to replicate heat release characteristics related to flame propagation and auto-ignition during spark-assisted compression ignition combustion. The calibrated model was assessed using a large parametric study, where the predicted homogeneous charge compression ignition and spark-assisted compression ignition operating regions at naturally aspirated conditions were representative of those determined during engine testing. Practical advanced combustion strategies were assessed relative to idealized engine simulations, which showed that efficiency improvements up to 30% compared with conventional spark-ignition operation are possible. The study revealed that poor combustion efficiency and pumping work are the primary mechanisms for efficiency losses for the advanced combustion strategies evaluated.