TY - GEN A1 - Wadekar, Sandip A1 - Oevermann, Michael A1 - Lipatnikov, Andrei T1 - Large Eddy Simulation of Stratified Combustion in Spray-guided Direct Injection Spark-ignition Engine T2 - SAE Technical Papers N2 - Stratified combustion in gasoline engines constitutes a promising means of achieving higher thermal efficiency for low to medium engine loads than that achieved with combustion under standard homogeneous conditions. However, creating a charge that leads to a stable efficient low-emission stratified combustion process remains challenging. Combustion through a stratified charge depends strongly on the dynamics of the turbulent fuel-air mixing process and the flame propagation. Predictive simulation tools are required to elucidate this complex mixing and combustion process under stratified conditions. For the simulation of mixing processes, combustion models based on large-eddy turbulence modeling have typically outperformed the standard Reynolds averaged Navier-Stokes methods. Therefore, we investigated spray-guided stratified combustion in a single cylinder engine using large-eddy turbulence modeling with a variant of the flame speed closure (FSC) model for premixed turbulent combustion. This model reveals the influence of the mixture composition on the flame speed. The effect of fluctuations in the composition were accounted for by using a presumed probability density function (PDF) approach for the mixture fraction. The fuel injection process was modeled with a standard Lagrangian spray model. More importantly, the measured in-cylinder pressure traces for three different loading cases with varying injection and ignition timings (leading to different levels of stratification) were accurately reproduced by the simulation. High-speed video images were used to evaluate the ability of the model to accurately simulate flame propagation under stratified conditions. The influence of mixture fluctuations on flame propagation was also investigated. KW - Single cylinder engines KW - Ignition timing KW - Combustion and combustion processes KW - Fuel injection Y1 - 2018 U6 - https://doi.org/10.4271/2018-01-1420 SN - 2688-3627 SN - 0148-7191 ER - TY - GEN A1 - Fistler, Marco A1 - Kerstein, Alan R. A1 - Wunsch, Scott A1 - Oevermann, Michael T1 - Turbulence modulation in particle-laden stationary homogeneous shear turbulence using one-dimensional turbulence T2 - Physical Review Fluids N2 - Turbulence modulation in particle-laden stationary homogeneous shear turbulence (HST) is investigated using one-dimensional turbulence (ODT), a low-dimensional stochastic flow simulation model. For this purpose, an ODT formulation previously used to study turbulence modulation in forced homogeneous isotropic turbulence (HIT) is extended, so that the model emulates the anisotropic character of HST and, potentially, anisotropic turbulence in general. This is done by limiting the kinetic-energy redistribution during an eddy event to an exchange involving two velocity components, where the three possible choices of the omitted component define three eddy types whose relative likelihoods control the anisotropy. Comparisons of ODT and direct-numerical-simulation results with reference to signatures of turbulence modulation are the basis of a broader ODT parameter study that is reported. Owing to the reduced dimensionality of ODT, it is found that the fidelity of the model for single-phase HST does not extend to particle effects on flow anisotropy, but for quantities averaged over components, parametric trends are captured. The consistent approach to case comparisons that was introduced in the HIT study to evaluate sensitivities to particle-phase parameters in a given flow configuration is extended here to a cross-comparison of HST and HIT model results, and its efficacy is again confirmed. The results provide an overall characterization of the potential for ODT to support the incorporation of particle-induced turbulence modulation into subgrid-scale closures of large-eddy simulations. Y1 - 2020 U6 - https://doi.org/10.1103/PhysRevFluids.5.124303 SN - 2469-990X VL - 5 IS - 12 ER - TY - GEN A1 - Wadekar, Sandip A1 - Yamaguchi, Akichika A1 - Oevermann, Michael T1 - Large-Eddy Simulation on the Effects of Fuel Injection Pressure on the Gasoline Spray Characteristics T2 - SAE Technical Papers N2 - Increasing the injection pressure in gasoline direct injection engines has a substantial potential to reduce emissions while maintaining a high efficiency in spark ignition engines. Present gasoline injectors are operating in the range of 20 MPa to 25 MPa. Now there is an interest in higher fuel injection pressures, for instance, around 40 MPa, 60 MPa and even higher pressures, because of its potential for further emission reduction and fuel efficiency improvements. In order to fully utilize the high-pressure fuel injection technology, a fundamental understanding of gasoline spray characteristics is vital to gain insight into spray behavior under such high injection pressures. The understanding achieved may also be beneficial to improve further model development and facilitate the integration of such advanced injection systems into future gasoline engines. In the present study, a gasoline fuel spray has been investigated over a range of fuel injection pressures from 40 to 150 MPa through a numerical simulation study. The numerical calculations have been performed in a constant volume chamber under non-vaporizing conditions to best match the experimental setup. The numerical model utilized a large-eddy simulation (LES) approach for the gas flow and a standard Lagrangian spray model for the liquid phase. The spray atomization has been modeled using the Kelvin Helmholtz - Rayleigh Taylor (KH-RT) atomization model with a droplet size distribution from the injector assumed to follow a Rosin-Rammler distribution function. Simulation results for the spray liquid penetration length are validated with experimental findings under different fuel injection pressures. Afterwards, an arithmetic mean droplet diameter (D10) and a Sauter mean droplet diameter (D32) as a function of pressure are compared against the measured droplet diameters. Simulated drop size distributions are presented and compared with measured droplet sizes. The results indicate that a high fuel injection pressure increases the liquid penetration length and significantly reduces droplet sizes. The results also exhibit that the SMD decreases from 13.4 μm to 7.5 μm, when injection pressure changes from 40 MPa to 150 MPa and that probability of finding the 5-9 μm droplet diameter decreases from 72% to 40% for the injection pressure drops from 150 MPa to 40 MPa. KW - Spark ignition engines KW - Fuel injection KW - Fuel economy KW - Energy conservation Y1 - 2019 U6 - https://doi.org/10.4271/2019-01-0060 SN - 2688-3627 SN - 0148-7191 ER - TY - GEN A1 - Somhorst, Joop A1 - Oevermann, Michael A1 - Bovo, Mirko A1 - Denbratt, Ingemar T1 - A Method to Evaluate the Compression Ratio in IC Engines with Porous Thermal Barrier Coatings T2 - SAE Technical Papers N2 - The compression ratio is an important engine design parameter. It determines to a large extend engine properties like the achievable efficiency, the heat losses from the combustion chamber and the exhaust losses. The same properties are affected by insulation of the combustion chamber. It is therefore especially important to know the compression ratio when doing experiments with thermal barrier coatings (TBC). In case of porous TBCs, the standard methods to measure the compression ratio can give wrong results. When measuring the compression ratio by volume, using a liquid, it is uncertain if the liquid fills the total porous volume of the coating. And for a thermodynamic compression ratio estimation, a model for the heat losses is needed, which is not available when doing experiments with insulation. The subject of this paper is the evaluation of an alternative method to assess the compression ratio. It is based on motored cylinder pressure data like other thermodynamic methods but does not need a model for the heat losses. The validation and application of the method is done with data from experiments involving two types of porous TBCs, performed on a light duty single cylinder diesel engine. The results indicate that the proposed method accurately predicts the compression ratio for porous thermal barrier coatings. KW - Combustion chambers KW - Combustion and combustion processes KW - Coatings, colorants, and finishes KW - Insulation Y1 - 2018 U6 - https://doi.org/10.4271/2018-01-1778 SN - 2688-3627 SN - 0148-7191 ER - TY - GEN A1 - Wadekar, Sandip A1 - Oevermann, Michael T1 - Large-Eddy Simulation Study of Ultra-High Fuel Injection Pressure on Gasoline Sprays T2 - Flow, Turbulence and Combustion N2 - The development of gasoline spray at ultra-high injection pressures was analyzed using Large-Eddy simulation (LES). Two different nozzle hole geometries, divergent and convergent shape, were considered to inject the fuel at injection pressures ranging from 200 to 1500 bar inside a constant volume spray chamber maintained at atmospheric conditions. The discrete droplet phase was treated using a Lagrangian formulation together with the standard spray sub-models. The numerical results were calibrated by reproducing experimentally observed liquid penetration length and efforts were made to understand the influence of ultra-high injection pressures on the spray development. The calibrated model was then used to investigate the impact of ultra-high injection pressures on mean droplet size and droplet size distribution. In addition, the spray-induced large-scale eddies and entrainment rate were evaluated at different ultra-high injection pressures. Overall, simulation results showed a good agreement with available measurement data. At ultra-high injection pressures mean droplet sizes were significantly reduced and comprised very high velocities. Integral length scales of spray-induced turbulence and air entrainment rate into the spray were larger at higher injection pressure compared to lower ones. KW - Sprayinduced turbulence KW - Ultra-high injection pressure KW - Large-Eddy simulation KW - Air-entrainment KW - Gasoline spray Y1 - 2020 U6 - https://doi.org/10.1007/s10494-020-00231-0 SN - 1573-1987 SN - 1386-6184 VL - 107 (2021) IS - 1 SP - 149 EP - 174 ER - TY - GEN A1 - Pütz, Michele A1 - Movaghar, Amirreza A1 - Oevermann, Michael T1 - Numerical simulation of a gasoline spray using one-dimensional turbulence for primary atomization T2 - ICLASS 2018 - 14th International Conference on Liquid Atomization and Spray Systems N2 - Predictive and reliable simulations have the potential to constitute a valuable tool for the optimization of spray systems if accurate submodels are developed for the entire range of the governing processes. The primary breakup of the turbulent liquid jet is one the most important mechanisms in sprays, yet the least developed in terms of numerical modeling. The most accurate method to simulate primary breakup is the proper resolution of liquid-gas interfaces and turbulent flow structures. However, a wide range of relevant length and time scales implicate grid requirements that are often prohibitive for real engineering applications. The most widely used method in practice is still the representation of both the continuous liquid core and the dispersed phase by means of discrete Lagrangian particles evolving in and interacting with the Eulerian gas phase. The available models for primary breakup are mainly phenomenological and involve a number of empirical constants. The one-dimensional turbulence (ODT) model is an alternative stochastic approach to model turbulence in flows with a dominant direction of property gradients. The stochastic representation of turbulent eddies on a one-dimensional domain enables high resolution at moderate computational costs. Applications of ODT to atomization revealed a great potential in recent studies. The objective of the present study is to combine ODT as a primary breakup model with a conventional Eulerian-Lagrangian method for the further spray evolution in order to asses ODT as a submodel in full spray models. Our numerical investigations were conducted on the ECN spray G, a gasoline-like, evaporating spray. The results in terms of spray penetration are encouraging, though the applicability of ODT to the transient injection phase and effects on additional spray characteristics require further investigation. KW - Breakup KW - Numericsl simulation KW - ECN Spray G KW - ODT KW - One-dimensional turbulence modeling KW - Gasoline Y1 - 2018 UR - https://research.chalmers.se/publication/519110 ER - TY - GEN A1 - Fistler, Marco A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - A new LES subgrid-scale approach for turbulence modulation by droplets T2 - ICLASS 14th Triennial International Conference on Liquid Atomization and Spray Systems Chicago, USA, 2018-07-21 - 2018-07-26 N2 - We present a new modelling approach for turbulence modulation by droplets on the subgrid-scale (SGS) level of Large-Eddy-Simulations (LES). Many SGS models exist for the effect of gas phase SGS on the droplet phase, but very few for the mechanisms vice versa on the turbulent intensity of the gas phase. The reasons are a lack of physical understanding and limited computational resources for extensive DNS studies. To address both problems a dimension-reduced and consequently less costly model, namely One-Dimensional- Turbulence (ODT), is used to gather information about this specific flow phenomena. ODT is a stochastic tool simulating turbulent flows along a notional 1D line of sights. For modeling the turbulent advection instantaneous maps are applied to the line which represent the effect of individual eddies on property fields and the dispersed phase. After validating the general test case of a droplet-laden shear flow against DNS data, a concept is presented on how to gather turbulence modulation for several parameter ranges in a data base and how to make them accessible on the flight for LES. The three most significant parameters, the unladen flow Reynolds number, the droplet loading and the particle momentum number, are chosen to construct an efficient data base. KW - Turbulence modulation KW - ODT KW - One-Dimensional-Turbulence KW - Particle-laden Y1 - 2018 UR - https://research.chalmers.se/en/publication/519108 ER - TY - CHAP A1 - Movaghar, Amirreza A1 - Chiodi, Robert A1 - Desjardins, Olivier A1 - Oevermann, Michael A1 - Kerstein, Alan R. T1 - A Subgrid-Scale Model for Large-Eddy Simulation of Liquid/Gas Interfaces Based on One-Dimensional Turbulence T2 - Turbulent Cascades II N2 - The interface/turbulence interaction between two fluids in a turbulent environment has an important role in many technical processes, e.g. primary liquid atomization in combustion devices. Primary atomization has a significant role in spray formation and its characteristics. The resulting dynamics typically span 4–6 orders of magnitude in length scales, making detailed numerical simulations exceedingly expensive. This motivates the need for modeling approaches based on spatial filtering such as large-eddy simulation (LES). In this paper, a new approach based on One-Dimensional turbulence (ODT) is presented to describe the subgrid interface dynamics. ODT is a stochastic model simulating turbulent flow evolution along a notional one-dimensional line of sight by applying instantaneous maps that represent the effects of individual turbulent eddies on property fields. It provides affordable high resolution of interface creation and property gradients within each phase, which are key for capturing the local behavior as well as overall trends. ODT has previously been shown to reproduce the main features of an experimentally determined regime diagram for primary jet breakup. Here a new approach called VODT is presented which produces a size-conditioned as well as a total time rate of generation of droplets for given flow conditions at an interface. At the LES level, the total droplet generation from VODT is interpreted as a rate of mass conversion of LES-resolved liquid into unresolved droplets. Preliminary results of applying VODT to a cell with a planar-shear-layer are discussed at the end of the paper. KW - combustion KW - Large eddy simulation KW - scalar dissipation Y1 - 2019 SN - 978-3-030-12547-9 SN - 978-3-030-12546-2 U6 - https://doi.org/10.1007/978-3-030-12547-9_10 SP - 83 EP - 91 PB - Springer Nature Switzerland AG CY - Schweiz ER - TY - GEN A1 - Somhorst, Joop A1 - Oevermann, Michael T1 - Effects of thermal barrier coating porosity on combustion and heat losses in a light duty diesel engine T2 - International Journal of Engine Research N2 - Plasma sprayed thermal barrier coatings (TBCs), applied in internal combustion engines, can have a profound impact on the apparent rate of heat release. Upon fuel jet contact with the piston wall, the heat loss seems to increase compared to an uncoated piston and combustion appears delayed. Permeable porosity of plasma sprayed TBCs is identified as one of the possible causes for this unwanted effect. In this article the impact of open porosity and sealing of the TBC surface are investigated with single cylinder engine experiments and with simulations. Based on the results, a mechanism is presented to explain the observations. KW - Thermal barrier coating KW - Porosity KW - Insulation KW - Combustion engine KW - Crevice effect KW - Heat transfer KW - Fuel entrainment Y1 - 2024 U6 - https://doi.org/10.1177/14680874231215526 SN - 1468-0874 VL - 25 (2024) IS - 5 SP - 940 EP - 958 ER - TY - GEN A1 - Medina Méndez, Juan Ali A1 - Fistler, Marco A1 - Oevermann, Michael A1 - Schmidt, Heiko A1 - Riebel, Ulrich T1 - Economical map-based turbulence models: Developments and perspectives for the numerical analysis of electrostatic precipitation T2 - Book of Abstracts PARTEC International Congress on Particle Technology, September 26-28, 2023, Nürnberg Y1 - 2023 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Medina_2023_Extended Abstract_Template_PARTEC_ODT.pdf SP - 634 EP - 638 PB - VDI Verlag GmbH CY - Düsseldorf ER - TY - GEN A1 - Menon, Abhilash A1 - Kerstein, Alan A1 - Oevermann, Michael T1 - Assessing the multi-regime capability of the Super-Grid Linear Eddy Model (SG-LEM) using the Darmstadt multi-regime burner T2 - Flow, Turbulence and Combustion N2 - AbstractRecent advances in combustion modelling for Large Eddy Simulation (LES) have increasingly utilised lower-dimensional manifolds, such as Flamelet Generated Manifolds and Flamelet/Progress Variable methods, due to their computational efficiency. These methods typically rely on one-dimensional representations of flame structures, often assuming premixed or non-premixed configurations. However, practical combustion devices frequently operate under partially-premixed conditions and present challenges due to mixture inhomogeneities and complex flow features. The Linear Eddy Model (LEM) offers an alternative by directly simulating turbulence-chemistry interactions without presuming specific flame structures. However, traditional LES-LEM approaches are computationally quite expensive due to the need for resolved LEM domains to be embedded in every LES cell.The authors developed the Super-Grid LEM (SG-LEM) method (Comb. Theor. Model.  28, 2024) to address these computational challenges by coarse-graining the LES mesh and embedding individual LEM domains within clusters of LES cells. This study evaluates SG-LEM in the context of the Multi-Regime Burner (MRB) introduced by Butz et al. (Combust. Flame, 210, 2019), which features both premixed and non-premixed flame characteristics. SG-LEM simulations of the MRB case demonstrate the method’s sensitivity to clustering parameters, with flow-aligned clusters significantly improving flame stability. LEM domains on the super-grid were able to represent the MRB flame topology while LES radial profiles including velocity, mixture fraction, temperature, and $${\textrm{CO}}$$ CO mass fraction, were validated against experimental data and also reference simulations using standard combustion closures. The work also investigates discrepancies in CO profiles using conditional statistics and stand-alone LEM simulations. Finally, the work identifies areas of improvement for the SG-LEM framework, in particular relating to cluster generation, and (advective and diffusive) mass exchange between neighbouring LEM domains, as well as possible solutions for future SG-LEM implementations which could improve the model’s predictive capability. Y1 - 2024 U6 - https://doi.org/10.1007/s10494-024-00602-x SN - 1386-6184 VL - 2024 PB - Springer Science and Business Media LLC ER - TY - GEN A1 - Klein, Rupert A1 - Nadolski, Maikel A1 - Zenker, Christian A1 - Oevermann, Michael A1 - Paschereit, Christian Oliver T1 - Pressure gain combustion for gas turbines : analysis of a fully coupled engine model T2 - Journal of Engineering for Gas Turbines and Power N2 - The “Shockless Explosion Combustion” (SEC) concept for gas turbine combustors, introduced in 2014, approximates constant volume combustion (CVC) by harnessing acoustic confinement of auto-igniting gas packets. The resulting pressure waves simultaneously transmit combustion energy to a turbine plenum and facilitate the combustor's recharging against an average pressure gain. Challenges in actualizing an SEC-driven gas turbine include (i) the creation of charge stratifications for nearly homogeneous auto-ignition, (ii) protecting the turbocomponents from combustion-induced pressure fluctuations, (iii) providing evidence that efficiency gains comparable to those of CVC over deflagrative combustion can be realized, and (iv) designing an effective one-way intake valve. This work addresses challenges (i)–(iii) utilizing computational engine models incorporating a quasi-one-dimensional combustor, zero- and two-dimensional (2D) compressor and turbine plena, and quasi-stationary turbocomponents. Two SEC operational modes are identified which fire at roughly one and two times the combustors' acoustic frequencies. Results for SEC-driven gas turbines with compressor pressure ratios of 6:1 and 20:1 reveal 1.5-fold mean pressure gains across the combustors. Assuming ideally efficient compressors and turbines, efficiency gains over engines with deflagration-based combustors of 30% and 18% are realized, respectively. With absolute values of 52% and 66%, the obtained efficiencies are close to the theoretical Humphrey cycle efficiencies of 54% and 65% for the mentioned precompression ratios. Detailed thermodynamic cycle analyses for individual gas parcels suggest that there is room for further efficiency gains through optimized plenum and combustor designs. Y1 - 2024 U6 - https://doi.org/10.1115/1.4066348 SN - 0742-4795 VL - 147 IS - 2 PB - ASME International ER - TY - GEN A1 - Movaghar, Amirreza A1 - Chiodi, Robert A1 - Oevermann, Michael A1 - Desjardins, Olivier A1 - Kerstein, Alan T1 - Assessment of a multiphase formulation of one-dimensional turbulence using direct numerical simulation of a decaying turbulent interfacial flow T2 - Physical Review Fluids N2 - The interaction between turbulence and surface tension is studied numerically using the one-dimensional-turbulence (ODT) model. ODT is a stochastic model simulating turbulent flow evolution along a notional one-dimensional line of sight by applying instantaneous maps that represent the effects of individual turbulent eddies on property fields. It provides affordable high resolution of interface creation and property gradients within each phase, which are key for capturing the local behavior as well as overall trends, and has been shown to reproduce the main features of an experimentally determined regime diagram for primary jet breakup. Here ODT is used to investigate the interaction of turbulence with an initially planar interface. The notional flat interface is inserted into a periodic box of decaying homogeneous isotropic turbulence, simulated for a variety of turbulent Reynolds and Weber numbers. Unity density and viscosity ratios serve to focus solely on the interaction between fluid inertia and the surface-tension force. Statistical measures of interface surface density and spatial structure along the direction normal to the initial surface are compared to corresponding direct-numerical-simulation (DNS) data. Allowing the origin of the lateral coordinate system to follow the location of the median interface element improves the agreement between ODT and DNS, reflecting the absence of lateral nonvortical displacements in ODT. Beyond the DNS-accessible regime, ODT is shown to obey the predicted parameter dependencies of the Kolmogorov critical scale in both the inertial and dissipative turbulent-cascade subranges. Notably, the probability density function of local fluctuations of the critical scale is found to collapse to a universal curve across both subranges. Published by the American Physical Society 2024 Y1 - 2024 U6 - https://doi.org/10.1103/PhysRevFluids.9.104003 SN - 2469-990X VL - 9 IS - 10 PB - American Physical Society (APS) ER - TY - GEN A1 - Menon, Abhilash M. A1 - Oevermann, Michael A1 - Kerstein, Alan R. T1 - A super-grid approach for LES combustion closure using the linear eddy model T2 - Combustion Theory and Modelling N2 - LES–LEM is a simulation approach for turbulent combustion in which the stochastic Linear Eddy Model (LEM) is used for sub-grid mixing and combustion closure in Large-Eddy Simulation (LES). LEM resolves, along a one-dimensional line, all spatial and temporal scales, provides on-the-fly local turbulent flame statistics, captures finite rate chemistry effects and directly incorporates turbulence-chemistry interaction. However, the approach is computationally expensive as it requires advancing an LEM-line in each LES cell. This paper introduces a novel turbulent combustion closure model for LES using LEM to address this issue. It involves coarse-graining the LES mesh to generate a coarse- level ‘super-grid’ comprised of cell-clusters. Each cell-cluster, instead of each LES cell, then contains a single LEM domain. This domain advances the combined advection–reaction–diffusion solution and also provides suitably conditioned statistics for thermochemical scalars such as species mass fractions. Local LES-filtered thermochemical states are then obtained by probability-density-function (PDF) weighted integration of binned conditionally averaged scalars, akin to standard presumed PDF approaches for reactive LES but with physics-based determination of the full thermochemical state for particular values of the conditioning variables. The proposed method is termed ‘super-grid LEM’ or ‘SG-LEM’. The paper describes LEM reaction–diffusion advancement, the LEM representation of turbulent advection, a novel splicing algorithm (a key feature of LES–LEM) formulated for the super-grid approach, a wall treatment, and a thermochemical LES closure procedure. To validate the proposed model, a pressure-based solver was developed using the OpenFOAM library and tested on a premixed ethylene flame stabilised over a backward facing step, a setup for which some DNS data is available. SG-LEM provides high resolution flame structures, temperature and mass fractions suitable for LES thermochemical closure. Additionally, it provides reaction-rate data at the coarse level, a unique feature compared to other mapping-type closure methods. Quantitative comparisons are made between the proposed model and time-averaged DNS data, focussing on velocity, temperature and species mass fraction. Results show good agreement downstream of the step. Furthermore, comparison with an equivalent Partially-Stirred Reactor (PaSR) simulation demonstrates the superior predictive capability of SG-LEM. Additionally, the paper briefly examines the sensitivity of the model to coarse-graining parameters and finally, explores computational efficiency highlighting the substantial speedup achieved when compared to the standard LES–LEM approach with potentially significant speedup relative to PaSR closure for the intensely turbulent regimes of principal interest. KW - LES KW - LEM KW - Combustion closure KW - Presumed PDFs KW - Splicing Y1 - 2023 U6 - https://doi.org/10.1080/13647830.2023.2260351 SN - 1364-7830 VL - 28 IS - 1 SP - 99 EP - 126 PB - Informa UK Limited ER - TY - JOUR A1 - Doubiani, Nidal A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - A pressure-coupled Representative Interactive Linear Eddy Model (RILEM) for engine simulations JF - Fuel N2 - The Representative Linear Eddy Model (RILEM) was introduced by Lackmann et al. (2018) as an alternative modeling approach to simulate turbulent non-premixed combustion in engines. The model utilizes a RANS approach for turbulence and the Linear Eddy Model (LEM) with a presumed probability density function (PDF) approach for combustion closure. A distinct feature of RILEM is its potential to handle arbitrary combustion regimes and the consideration of complex physical phenomena such as differential diffusion effects. The original version of RILEM implemented a volume-based coupling between LEM and the flow solver. This work presents a new variant of RILEM, i.e., Multiple Representative Interactive Linear Eddy Model (MRILEM) based on a pressure-based coupling, to overcome some deficiencies of the original RILEM, namely statistical fidelity. Due to the introduced pressure coupling, the effects of heat losses (wall heat fluxes, latent heat of evaporation) on combustion are intrinsically included via the pressure trace. Furthermore, we introduce a new step function PDF for the progress variable defined by its mean value only. Issues with an incomplete solution space for mixture fraction and progress variable due to the stochastic nature of LEM are remedied with a PDF scaling technique, aided by a novel parameterization of the progress-variable PDF The new variant of RILEM is evaluated using part- and full-load cases of a heavy-duty metal engine. The impact of utilizing multiple LEM lines on the completeness of the solution space and its influence on the distribution of scalar values in the CFD domain was demonstrated. Results for pressure trace, flame structure, and CO emissions are analyzed and compared with simulations using the Multi-Zone Well-Mixed Model (MZWM) model and experiments. While pressure traces agree well among the different models and experiments, noteworthy differences are observed between the models regarding CO emissions and temperature. Effects of turbulence chemistry interaction were noticed when comparing MRILEM to the results of the MZWM simulation, namely flame brush and species mass fraction distribution. KW - Linear Eddy Model KW - Turbulence-chemistry interaction KW - Presumed PDF approach KW - Pollutant formation KW - Pressure coupling KW - Engine combustion Y1 - 2024 U6 - https://doi.org/10.1016/j.fuel.2023.129423 SN - 0016-2361 VL - 355 (2024) SP - 1 EP - 15 PB - Elsevier BV ER - TY - GEN A1 - Doubiani, Nidal A1 - Oevermann, Michael T1 - Multiple representative interactive linear eddy model: Investigation of turbulence chemistry interaction and evaluation of progress variable definition and PDFs T2 - Fuel N2 - Improving the predictions of unsteady effects in combustion processes requires novel combustion models that include turbulence chemistry interaction effects. The Multiple Representative Interactive Linear Eddy Model (MRILEM) is an improved version of the previous RILEM variant. MRILEM utilizes a pressure coupling instead of a volume constraint to intrinsically include heat effects into the LEM line with no supplementary modeling. In addition, it advances multiple LEM lines in parallel to improve statistical fidelity. The pressure coupling of MRILEM generates a coupling effect between the LEM lines that assists in communicating the combustion process between the lines. The ”Spray-B” engine of the Engine Combustion Network (ECN) was simulated using MRILEM. While the original RILEM variation employs a straightforward Dirac δ-peak for the progress variable, a realistic PDF requires this function to extend over the entire space. The introduced MRILEM compares the utilization of two progress variable PDFs, namely a step function defined based on the mean and a β-PDF generated from the progress variable mean and variance. The progress variable variance was calculated based on the Pierce and Moin formulation with a RANS adaptation based on the integral length scale. In addition, two definitions of the progress variable are investigated, namely O2 and h298. A tabulation method is introduced for RILEM to reduce the computational time by advancing pre-generated LEM solution matrices constructed in mixture fraction Z and progress variable c spaces. The different variants of the model, i.e., MRILEM-βZ-Stepc, MRILEM-βZ-βc, TRILEM-β-Stepc, and TRILEM-βZ-βc were compared against experiments based on heat release rate, ignition delay, flame lift-off, and computational time. KW - Linear eddy model KW - Turbulence chemistry interaction KW - Probability density function KW - Tabulation Y1 - 2025 U6 - https://doi.org/10.1016/j.fuel.2024.133445 SN - 0016-2361 VL - 381 SP - 1 EP - 15 PB - Elsevier BV ER - TY - GEN A1 - Doubiani, Nidal A1 - Oevermann, Michael A1 - Lucchini, Tommaso A1 - Zhou, Qiyan T1 - Numerical investigation of ducted fuel injection using Multiple Representative Interactive Linear Eddy Model T2 - International Journal of Engine Research N2 - Fuel-air mixing in non-premixed and partially premixed combustion has a major influence on soot emissions. Improving the mixing quality of the premixed region in non-premixed combustion upstream of the auto-ignition zone aids substantially in reducing soot emissions. The Ducted Fuel Injection (DFI) concept is based on injecting fuel inside a metal cylinder inside the combustion chamber at a certain distance from the injection nozzle exit hole. Although the concept is straightforward, recent studies have shown that implementing DFI in compression ignition combustion chambers dramatically affects soot mitigation. DFI improves air entrainment by a suction effect when fuel travels inside the duct, which increases the turbulence level at the inlet and enhances the fuel-air mixing quality. Additionally, DFI delays ignition by preventing the formation of stoichiometric regions at the spray cone’s outer region. This work utilizes a recently presented combustion model titled the Multiple Representative Interactive Linear Eddy Model (MRILEM) to simulate DFI in a high-pressure, high-temperature constant volume chamber. Several simulations are realized for two different ambient temperatures using an n-dodecane mechanism, where several parameters, such as ignition delay, lift-off length, and flame structure, are assessed. Simulation results are compared to experimental data from the literature and simulation results obtained with the Multi-Zone Well Mixed (MZWM) model simulation results. Results show that by enforcing the duct on the LEM line and modifying the turbulence implementation strategy, MRILEM shows overall realistic predictions for DFI cases and reasonable quantitative results for lift-off length and ignition delay compared to the MZWM model. Y1 - 2024 U6 - https://doi.org/10.1177/14680874241298046 SN - 1468-0874 VL - 2025 PB - SAGE Publications ER - TY - GEN A1 - Özgünoğlu, Mehmet A1 - Mouokue, Gerard A1 - Oevermann, Michael A1 - Bensow, Rickard E. T1 - Numerical investigation of cavitation erosion in high-pressure fuel injector in the presence of surface deviations T2 - Fuel N2 - This study investigates cavitation-induced erosion in high-pressure fuel injectors using numerical simulations, focusing on the effects of surface deviations, turbulence modeling, and a refined approach for the erosion assessment. The proposed erosion model combines advanced erosion indicators to enhance predictive accuracy while addressing limitations in existing methodologies. Cavitation dynamics are simulated with the modified Zwart–Gerber–Belamri model, employing Reynolds-averaged Navier–Stokes (RANS) and Large Eddy Simulation (LES) approaches. Numerical results for a high-lift needle position are validated against experimental data, providing insights into erosion behavior in industrial heavy-duty injectors. Both Computer-Aided Design (CAD) and Tomography Scan (TS) models are used to evaluate the impact of surface deviations on erosion patterns. Results reveal that incorporating surface deviations reduces the vapor volume and alters the erosion patterns. LES simulations exhibit enhanced sensitivity to the surface deviations, capturing finer turbulence structures and local pressure fluctuations, whereas RANS provides reasonable accuracy with lower computational cost. KW - Fuel injector KW - CFD KW - Cavitation erosion KW - Surface deviations Y1 - 2025 U6 - https://doi.org/10.1016/j.fuel.2024.134174 SN - 0016-2361 VL - 386 SP - 1 EP - 21 PB - Elsevier BV ER - TY - GEN A1 - Menon, Abhilash M. A1 - Kerstein, Alan A1 - Oevermann, Michael T1 - Investigation of coarse-graining parameters for super-grid LEM closure applied to LES of practical bluff-body flames T2 - Combustion Theory and Modelling N2 - Large Eddy Simulation (LES) coupled with the Linear Eddy Model (LEM) provides a robust method for studying turbulent combustion, but it is computationally expensive due to the need for highly resolved sub-grid LEM domains. These domains simulate sub-grid stirring through stochastic rearrangements of scalar fields, while large-scale transport is modelled using a Lagrangian ‘splicing’ scheme. To address the computational cost of LES-LEM, a super-grid (SG) framework for LEM closure was developed by the authors (Comb. Theor. Model. 28, 2024), which uses coarse-graining, on-the-fly chemistry tabulation and a presumed PDF approach to reconstruct thermochemical fields at LES resolution. This study applies SG-LEM to a challenging setup, Case 1 of the Volvo Validation Rig, which involves a bluff-body-stabilised turbulent premixed propane-air flame, as a stress test to identify limitations that were not revealed by the previous application, in particular that of the coarse-graining parameters used to generate the super-grid. The intent is to yield a more realistically constrained assessment of the current capabilities of the method, and insight into possible ways for improving it. Four simulations were conducted using three SG cluster sizes. The finest resolution was tested with a global 2-step mechanism, showing good agreement with experimental data for temperature and velocity, particularly near the bluff body. The two larger cluster sizes used a 66-step skeletal mechanism for more detailed chemical closure but led to unphysical quenching due to splicing inaccuracies. To mitigate these issues, two novel additions were introduced: an intra-cluster-stirring routine and a method to control SG cluster shapes to reduce numerical dissipation. These methods improved flame stability with coarser SG clusters and more detailed mechanisms. Comparison with experiments showed good agreement for temperature and velocity, though elevated CO levels were observed in the recirculation region. Potential methods for further improving SG-LEM's capabilities are discussed. KW - LES-LEM KW - Premixed flames KW - Stabilised flames KW - Turbulence modelling KW - Subgrid-scale closure Y1 - 2024 U6 - https://doi.org/10.1080/13647830.2024.2428156 SN - 1364-7830 VL - 2024 SP - 1 EP - 22 PB - Taylor&Francis ER -