@article{DoubianiKersteinOevermann, author = {Doubiani, Nidal and Kerstein, Alan R. and Oevermann, Michael}, title = {A pressure-coupled Representative Interactive Linear Eddy Model (RILEM) for engine simulations}, series = {Fuel}, volume = {355 (2024)}, journal = {Fuel}, publisher = {Elsevier BV}, issn = {0016-2361}, doi = {10.1016/j.fuel.2023.129423}, pages = {1 -- 15}, abstract = {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.}, language = {en} } @misc{DoubianiOevermann, author = {Doubiani, Nidal and Oevermann, Michael}, title = {Multiple representative interactive linear eddy model: Investigation of turbulence chemistry interaction and evaluation of progress variable definition and PDFs}, series = {Fuel}, volume = {381}, journal = {Fuel}, publisher = {Elsevier BV}, issn = {0016-2361}, doi = {10.1016/j.fuel.2024.133445}, pages = {1 -- 15}, abstract = {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.}, language = {en} } @misc{DoubianiOevermannLucchinietal., author = {Doubiani, Nidal and Oevermann, Michael and Lucchini, Tommaso and Zhou, Qiyan}, title = {Numerical investigation of ducted fuel injection using Multiple Representative Interactive Linear Eddy Model}, series = {International Journal of Engine Research}, volume = {2025}, journal = {International Journal of Engine Research}, publisher = {SAGE Publications}, issn = {1468-0874}, doi = {10.1177/14680874241298046}, abstract = {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.}, language = {en} }