Analysis of diesel combustion in four-stroke marine engines : an integrated CFD and reduced chemical kinetics approach

The present thesis aims at characterising and understanding flow and combustion processes in four-stroke marine engines by means of detailed Computational Fluid Dynamics (CFD) modelling. In particular, two dual-fuel engines operating in the diesel mode are considered: Lister LV1 and Wärtilä 50DF. A systematic approach is followed, consisting in: (a) Characterising the spray dynamics in a constant volume chamber, and adapting the Cascade Atomisation Breakup (CAB) spray model, for conditions relevant to operation of the engines considered in the present study. (b) Adapting a tool developed by means of coupling the chemical kinetics CHEMKIN-II code with the KIVA-3vr2 CFD code, thus enabling CFD simulations with reliable chemistry. (c) Performing CFD simulations of flow and combustion in the two engines for operation in the 80% load for Lister LV1, and in the full load range for Wärtilä 50DF, and comparing results against one-step chemistry simulations, as well as against respective experimental data. Thus, to author’s knowledge, the present thesis reports the first CFD studies in marine engines operating in the diesel mode, including realistic combustion chemistry. The computational results demonstrate that the spray breakup corresponds to the catastrophic regime. Adaptation of the CAB model has yielded values of model constants in a range that does not considerably deviate from relevant literature studies. Two validated reduced-order chemical kinetic mechanisms of n-heptane combustion have been implemented in the course of the present CFD studies: (i) Patel et al. (2004), with 29 species and 52 elementary reactions, and (ii) Ra and Reitz (2008), with 45 species and 142 elementary reactions. The two mechanisms have been supplemented with a NOx sub mechanism. The main findings of the present study can be summarised as follows: - Ignition delay times are in good agreement with chemical kinetics simulations using realistic chemistry. - For simulations with reduced order chemistry, fuel disintegration nearly terminates at the end of injection, in contrast to results of the one-step approach. On the other hand, similarities in Rate of Heat Release Rates are attained for the two approaches. - The evolution of important species can differ considerably between the two reduced mechanisms. - The distribution of main pollutants bears similarities between the two reduced mechanisms, and may differ significantly from the one-step approach. While the present study demonstrates that using reduced order chemistry is essential for characterising engine aerothermochemistry albeit at a significant increase in computational cost, the one-step approach is shown to still be valid as an engineering tool, providing a basic characterisation of flow and combustion, which can be useful in the frame of marine engine development.The present thesis aims at characterising and understanding flow and combustion processes in four-stroke marine engines by means of detailed Computational Fluid Dynamics (CFD) modelling. In particular, two dual-fuel engines operating in the diesel mode are considered: Lister LV1 and Wärtilä 50DF. A systematic approach is followed, consisting in: (a) Characterising the spray dynamics in a constant volume chamber, and adapting the Cascade Atomisation Breakup (CAB) spray model, for conditions relevant to operation of the engines considered in the present study. (b) Adapting a tool developed by means of coupling the chemical kinetics CHEMKIN-II code with the KIVA-3vr2 CFD code, thus enabling CFD simulations with reliable chemistry. (c) Performing CFD simulations of flow and combustion in the two engines for operation in the 80% load for Lister LV1, and in the full load range for Wärtilä 50DF, and comparing results against one-step chemistry simulations, as well as against respective experimental data. Thus, to author’s knowledge, the present thesis reports the first CFD studies in marine engines operating in the diesel mode, including realistic combustion chemistry. The computational results demonstrate that the spray breakup corresponds to the catastrophic regime. Adaptation of the CAB model has yielded values of model constants in a range that does not considerably deviate from relevant literature studies. Two validated reduced-order chemical kinetic mechanisms of n-heptane combustion have been implemented in the course of the present CFD studies: (i) Patel et al. (2004), with 29 species and 52 elementary reactions, and (ii) Ra and Reitz (2008), with 45 species and 142 elementary reactions. The two mechanisms have been supplemented with a NOx sub mechanism. The main findings of the present study can be summarised as follows: - Ignition delay times are in good agreement with chemical kinetics simulations using realistic chemistry. - For simulations with reduced order chemistry, fuel disintegration nearly terminates at the end of injection, in contrast to results of the one-step approach. On the other hand, similarities in Rate of Heat Release Rates are attained for the two approaches. - The evolution of important species can differ considerably between the two reduced mechanisms. - The distribution of main pollutants bears similarities between the two reduced mechanisms, and may differ significantly from the one-step approach. While the present study demonstrates that using reduced order chemistry is essential for characterising engine aerothermochemistry albeit at a significant increase in computational cost, the one-step approach is shown to still be valid as an engineering tool, providing a basic characterisation of flow and combustion, which can be useful in the frame of marine engine development

Experimental Validation of Combustion Models for Diesel Engines Based on Tabulated Kinetics in a Wide Range of Operating Conditions

Computational fluid dynamics represents a useful tool to support the design and development of Heavy Duty Engines, making possible to test the effects of injection strategies and combustion chamber design for a wide range of operating conditions. Predictive models are required to ensure accurate estimations of heat release and the main pollutant emissions within a limited amount of time. For this reason, both detailed chemistry and turbulence chemistry interaction need to be included. In this work, the authors intend to apply combustion models based on tabulated kinetics for the prediction of Diesel combustion in Heavy Duty Engines. Four different approaches were considered: well-mixed model, presumed PDF, representative interactive flamelets and flamelet progress variable. Tabulated kinetics was also used for the estimation of NOxemissions. The proposed numerical methodology was implemented into the Lib-ICE code, based on the OpenFOAM®technology, and validated against experimental data from a light-duty FPT engine. Ten points were considered at different loads and speeds where the engine operates under both conventional Diesel combustion and PCCI mode. A detailed comparison between computed and experimental data was performed in terms of in-cylinder pressure and NOxemissions

Modeling Non-Premixed Combustion Using Tabulated Kinetics and Different Fame Structure Assumptions

Nowadays, detailed kinetics is necessary for a proper estimation of both flame structure and pollutant formation in compression ignition engines. However, large mechanisms and the need to include turbulence/chemistry interaction introduce significant computational overheads. For this reason, tabulated kinetics is employed as a possible solution to reduce the CPU time even if table discretization is generally limited by memory occupation. In this work the authors applied tabulated homogeneous reactors (HR) in combination with different turbulent-chemistry interaction approaches to model non-premixed turbulent combustion. The proposed methodologies represent good compromises between accuracy, required memory and computational time. The experimental validation was carried out by considering both constant-volume vessel and Diesel engine experiments. First, the ECN Spray A configuration was simulated at different operating conditions and results from different flame structures are compared with experimental data of ignition delay, flame lift-off, heat release rates, radicals and soot distributions. Afterwards, engine simulations were carried out and computed data are validated by cylinder pressure and heat release rate profiles

Thermo-kinetic multi-zone modelling of low temperature combustion engines

Many researchers believe multi-zone (MZ), chemical kinetics–based models are proven, essential toolchains for development of low-temperature combustion (LTC) engines. However, such models are specific to the research groups that developed them and are not widely available on a commercial nor open-source basis. Consequently, their governing assumptions vary, resulting in differences in autonomy, accuracy and simulation speed, all of which affect their applicability. Knowledge of the models´ individual characteristics is scattered over the research groups´ publications, making it extremely difficult to see the bigger picture. This combination of disparities and dispersed information hinders the engine research community that wants to harness the capability of multi-zone modelling. This work aims to overcome these hurdles. It is a comprehensive review of over 120 works directly related to MZ modelling of LTC extended with an insight to primary sources covering individual submodels. It covers 16 distinctive modelling approaches, three different combustion concepts and over 60 different fuel/kinetic mechanism combination. Over 38 identified applications ranging from fundamental-level studies to control development. The work aims to provide sufficient detail of individual model design choices to facilitate creation of improved, more open multi-zone toolchains and inspire new applications. It also provides a high-level vision of how multi-zone models can evolve. The review identifies a state-of-the-art multi-zone model as an onion-skin model with 10–15 zones; phenomenological heat and mass transfer submodels with predictive in-cylinder turbulence; and semi-detailed reaction kinetics encapsulating 53-199 species. Together with submodels for heat loss, fuel injection and gas exchange, this modelling approach predicts in-cylinder pressure within cycle-to-cycle variation for a handful of combustion concepts, from homogeneous/premixed charge to reactivity-controlled compression ignition (HCCI, PCCI, RCCI). Single-core simulation time is around 30 minutes for implementations focused on accuracy: there are direct time-reduction strategies for control applications. Major tasks include a fast and predictive means to determine in-cylinder fuel stratification, and extending applicability and predictivity by coupling with commercial one-dimensional engine-modelling toolchains. There is also significant room for simulation speed-up by incorporating techniques such as tabulated chemistry and employing new solving algorithms that reduce cost of jacobian construction.© 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).fi=vertaisarvioitu|en=peerReviewed

A numerical study of the effect of nozzle diameter on diesel combustion ignition and flame stabilization

This is the author's version of a work that was accepted for publication in International Journal of Engine Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published as https://doi.org/10.1177/1468087419864203.[EN] The role of nozzle diameter on diesel combustion is studied by performing computational fluid dynamics calculations of Spray A and Spray D from the Engine Combustion Network. These are well-characterized single-hole sprays in a quiescent environment chamber with thermodynamic conditions representative of modern diesel engines. First, the inert spray evolution is described with the inclusion of the concept of mixing trajectories and local residence time into the analysis. Such concepts enable the quantification of the mixing rate, showing that it decreases with the increase in nozzle diameter. In a second step, the reacting spray evolution is studied focusing on the local heat release rate distribution during the auto-ignition sequence and the quasi-steady state. The capability of a well-mixed-based and a flamelet-based combustion model to predict diesel combustion is also assessed. On one hand, results show that turbulence-chemistry interaction has a profound effect on the description of the reacting spray evolution. On the other hand, the mixing rate, characterized in terms of the local residence time, drives the main changes introduced by the increase of the nozzle diameter when comparing Spray A and Spray D.The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: The work was partially funded by the Government of Spain through the CHEST Project (TRA2017-89139-C2-1-R) and by Universitat Politecnica de Valencia through the Programa de Ayudas de Investigaciony Desarrollo (PAID-01-16).Desantes Fernández, JM.; García-Oliver, JM.; Novella Rosa, R.; Pachano-Prieto, LM. (2020). A numerical study of the effect of nozzle diameter on diesel combustion ignition and flame stabilization. International Journal of Engine Research. 21(1):101-121. https://doi.org/10.1177/1468087419864203S101121211Pickett, L. M., & Siebers, D. L. (2002). An investigation of diesel soot formation processes using micro-orifices. Proceedings of the Combustion Institute, 29(1), 655-662. doi:10.1016/s1540-7489(02)80084-0Pickett, L. M., & Siebers, D. L. (2005). Orifice Diameter Effects on Diesel Fuel Jet Flame Structure. Journal of Engineering for Gas Turbines and Power, 127(1), 187-196. doi:10.1115/1.1760525Du, C., Andersson, S., & Andersson, M. (2018). Two-dimensional measurements of soot in a turbulent diffusion diesel flame: the effects of injection pressure, nozzle orifice diameter, and gas density. Combustion Science and Technology, 190(9), 1659-1688. doi:10.1080/00102202.2018.1461850Ishibashi, R., & Tsuru, D. (2016). An optical investigation of combustion process of a direct high-pressure injection of natural gas. Journal of Marine Science and Technology, 22(3), 447-458. doi:10.1007/s00773-016-0422-xPang, K. M., Jangi, M., Bai, X.-S., Schramm, J., & Walther, J. H. (2017). Effects of Nozzle Diameter on Diesel Spray Flames: A numerical study using an Eulerian Stochastic Field Method. Energy Procedia, 142, 1028-1033. doi:10.1016/j.egypro.2017.12.350Pickett, L. M., Manin, J., Genzale, C. L., Siebers, D. L., Musculus, M. P. B., & Idicheria, C. A. (2011). Relationship Between Diesel Fuel Spray Vapor Penetration/Dispersion and Local Fuel Mixture Fraction. SAE International Journal of Engines, 4(1), 764-799. doi:10.4271/2011-01-0686García-Oliver, J. M., Malbec, L.-M., Toda, H. B., & Bruneaux, G. (2017). A study on the interaction between local flow and flame structure for mixing-controlled Diesel sprays. Combustion and Flame, 179, 157-171. doi:10.1016/j.combustflame.2017.01.023Dahms, R. N., Paczko, G. A., Skeen, S. A., & Pickett, L. M. (2017). Understanding the ignition mechanism of high-pressure spray flames. Proceedings of the Combustion Institute, 36(2), 2615-2623. doi:10.1016/j.proci.2016.08.023Gimeno, J., Martí-Aldaraví, P., Carreres, M., & Peraza, J. E. (2018). Effect of the nozzle holder on injected fuel temperature for experimental test rigs and its influence on diesel sprays. International Journal of Engine Research, 19(3), 374-389. doi:10.1177/1468087417751531Matusik, K. E., Duke, D. J., Kastengren, A. L., Sovis, N., Swantek, A. B., & Powell, C. F. (2017). High-resolution X-ray tomography of Engine Combustion Network diesel injectors. International Journal of Engine Research, 19(9), 963-976. doi:10.1177/1468087417736985Pandurangi, S. S., Bolla, M., Wright, Y. M., Boulouchos, K., Skeen, S. A., Manin, J., & Pickett, L. M. (2016). Onset and progression of soot in high-pressure n-dodecane sprays under diesel engine conditions. International Journal of Engine Research, 18(5-6), 436-452. doi:10.1177/1468087416661041Aubagnac-Karkar, D., Michel, J.-B., Colin, O., & Darabiha, N. (2017). Combustion and soot modelling of a high-pressure and high-temperature Dodecane spray. International Journal of Engine Research, 19(4), 434-448. doi:10.1177/1468087417714351Ihme, M., Ma, P. C., & Bravo, L. (2018). Large eddy simulations of diesel-fuel injection and auto-ignition at transcritical conditions. International Journal of Engine Research, 20(1), 58-68. doi:10.1177/1468087418819546Yue, Z., & Reitz, R. D. (2017). An equilibrium phase spray model for high-pressure fuel injection and engine combustion simulations. International Journal of Engine Research, 20(2), 203-215. doi:10.1177/1468087417744144Bhattacharjee, S., & Haworth, D. C. (2013). Simulations of transient n-heptane and n-dodecane spray flames under engine-relevant conditions using a transported PDF method. Combustion and Flame, 160(10), 2083-2102. doi:10.1016/j.combustflame.2013.05.003Pei, Y., Hawkes, E. R., & Kook, S. (2013). Transported probability density function modelling of the vapour phase of an n-heptane jet at diesel engine conditions. Proceedings of the Combustion Institute, 34(2), 3039-3047. doi:10.1016/j.proci.2012.07.033Pang, K. M., Jangi, M., Bai, X.-S., Schramm, J., & Walther, J. H. (2018). Modelling of diesel spray flames under engine-like conditions using an accelerated Eulerian Stochastic Field method. Combustion and Flame, 193, 363-383. doi:10.1016/j.combustflame.2018.03.030D’Errico, G., Lucchini, T., Contino, F., Jangi, M., & Bai, X.-S. (2014). Comparison of well-mixed and multiple representative interactive flamelet approaches for diesel spray combustion modelling. Combustion Theory and Modelling, 18(1), 65-88. doi:10.1080/13647830.2013.860238Kösters, A., Karlsson, A., Oevermann, M., D’Errico, G., & Lucchini, T. (2015). RANS predictions of turbulent diffusion flames: comparison of a reactor and a flamelet combustion model to the well stirred approach. Combustion Theory and Modelling, 19(1), 81-106. doi:10.1080/13647830.2014.982342Lucchini, T., D’Errico, G., Onorati, A., Frassoldati, A., Stagni, A., & Hardy, G. (2017). Modeling Non-Premixed Combustion Using Tabulated Kinetics and Different Fame Structure Assumptions. SAE International Journal of Engines, 10(2), 593-607. doi:10.4271/2017-01-0556Pal, P., Keum, S., & Im, H. G. (2015). Assessment of flamelet versus multi-zone combustion modeling approaches for stratified-charge compression ignition engines. International Journal of Engine Research, 17(3), 280-290. doi:10.1177/1468087415571006Pope, S. B. (1978). An explanation of the turbulent round-jet/plane-jet anomaly. AIAA Journal, 16(3), 279-281. doi:10.2514/3.7521Novella, R., García, A., Pastor, J. M., & Domenech, V. (2011). The role of detailed chemical kinetics on CFD diesel spray ignition and combustion modelling. Mathematical and Computer Modelling, 54(7-8), 1706-1719. doi:10.1016/j.mcm.2010.12.048CONVERGE manual. Madison, WI: Convergent Science, 2016.Yao, T., Pei, Y., Zhong, B.-J., Som, S., Lu, T., & Luo, K. H. (2017). A compact skeletal mechanism for n-dodecane with optimized semi-global low-temperature chemistry for diesel engine simulations. Fuel, 191, 339-349. doi:10.1016/j.fuel.2016.11.083Perez E. Application of a flamelet-based combustion model to diesel-like reacting sprays. Unpublished PhD Thesis, Universitat Politècnica de València, Valencia, 2019.Peters, N. (2000). Turbulent Combustion. doi:10.1017/cbo9780511612701Naud, B., Novella, R., Pastor, J. M., & Winklinger, J. F. (2015). RANS modelling of a lifted H2/N2 flame using an unsteady flamelet progress variable approach with presumed PDF. Combustion and Flame, 162(4), 893-906. doi:10.1016/j.combustflame.2014.09.014Payri, R., García-Oliver, J. M., Xuan, T., & Bardi, M. (2015). A study on diesel spray tip penetration and radial expansion under reacting conditions. 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A conceptual model of the flame stabilization mechanisms for a lifted Diesel-type flame based on direct numerical simulation and experiments. Combustion and Flame, 201, 65-77. doi:10.1016/j.combustflame.2018.12.00

Turbulent Spray Combustion Modeling Using Direct Integration Of Chemistry And Flamelet Generated Manifolds

Turbulent spray combustion of n-dodecane was modeled at engine relevant conditions using various combustion models (Direct Integration of Chemistry and Flamelet Generated Manifolds) and turbulence models (Dynamic Structure Large Eddy Simulation and RNG Reynolds-Averaged Naiver-Stokes). A recently developed n-dodecane mechanism was utilized and the turbulent spray was simulated at various combustion chamber initial gas temperature and pressure conditions. Mesh with size of 31 microns was utilized to resolve small eddies around the spray. The pressure-based ignition delay, flame lift-off length, and spray and jet penetrations were studied and compared with experimental measurements. The Direct Integration of Chemistry and Flamelet Generated Manifolds using various turbulence models are in agreement with measured data

Chemical kinetics and CFD analysis of supercharged micro-pilot ignited dual-fuel engine combustion of syngas

A comprehensive chemical kinetics and computational fluid-dynamics (CFD) analysis were performed to evaluate the combustion of syngas derived from biomass and coke-oven solid feedstock in a micro-pilot ignited supercharged dual-fuel engine under lean conditions. The developed syngas chemical kinetics mechanism was validated by comparing ignition delay, in-cylinder pressure, temperature and laminar flame speed predictions against corresponding experimental and simulated data obtained by using the most commonly used chemical kinetics mechanisms developed by other authors. Sensitivity analysis showed that reactivity of syngas mixtures was found to be governed by H2 and CO chemistry for hydrogen concentrations lower than 50% and mostly by H2 chemistry for hydrogen concentrations higher than 50%. In the mechanism validation, particular emphasis is placed on predicting the combustion under high pressure conditions. For high hydrogen concentration in syngas under high pressure, the reactions HO2 + HO2 = H2O2 + O2 and H2O2 + H = H2 + HO2 were found to play important role in in-cylinder combustion and heat production. The rate constants for H2O2 + H = H2 + HO2 reaction showed strong sensitivity to high-pressure ignition times and has considerable uncertainty. Developed mechanism was used in CFD analysis to predict in-cylinder combustion of syngas and results were compared with experimental data. Crank angle-resolved spatial distribution of in-cylinder spray and combustion temperature was obtained. The constructed mechanism showed the closest prediction of combustion for both biomass and coke-oven syngas in a micro-pilot ignited supercharged dual-fuel engine

Characterisation of the autoignition delay behaviour of n-heptane in the IQT combustion bomb using CFD modelling

Word processed copy.Includes bibliographical references.When n-heptane was tested in the IQT device over a range of temperatures and pressures, the measured autoignition delay did not correlate with the chemical autoignition delay associated with a stoichiometric, homogenous mixture as predicted by detailed chemical kinetic models. ... This project involved an investigation to study and reconcile this discrepancy, using computational fluid dynamic (CFD) techniques to explore the physical conditions prevailing in the IQT device. Specifically, CFD was used to model fuel injection into the IQT, this allowed a more accurate description of the fuel/air ratio and temperature history of the fuel inside the IQT combustion chamber than an assumption of global values. An empirical description of autoignition delay, developed by Yates et al. (2004), was then coupled to the CFD code: enabling the model to determine the progress of the fuel/air mixture to autoignition

Numerical Studies of Methanol PPC Engines and Diesel Sprays

The global environment suffers from utilizing fossil fuels to powering internal combustion engines (ICE), due to the massive amounts of released CO2. Besides the global impact, the local environments experience high concentrations of harmful pollutants such as NOx, CO, soot and particulate matter (PM). The automotive industry is continuously striving to find new solutions to decrease fuel consumption and also to develop cleaner and more advanced combustion systems, i.e., low-temperature combustion (LTC) engines.The goal of this thesis is to employ computational fluid dynamics (CFD) simulations to investigate methanol under the partially premixed combustion (PPC) regime, which is one of the advanced LTC concepts alongside HCCI and RCCI. The benefit of PPC engines is the reduced average combustion temperature, which results in optimized emission rates of UHC/CO and NOx, maintaining high thermal efficiency. Interesting properties of methanol, such as a low stoichiometric air to fuel ratio and high latent heat of vaporization as well as non-sooting combustion, may enable further improvement of the PPC concept. Studies have been carried out by employing RANS and LES models to simulate mixing and ignition processes. It was found that methanol PPC can be achieved at relatively later injection timings (similar to those in diesel engines), in comparison to gasoline. Late injection timings can ease injection targeting into the piston bowl and utilize strong wall-spray interaction to help control the in-cylinder flow and therefore reduce the wall heat losses. The well-stirred-reactor (WSR) approach fails to predict pressure traces at highly stratified mixture compositions, such as $0.3 2$) can be accumulated in the near-wall region until the impingement vortices are developed, which then accelerates the mixing rate. Both wall jets resulted in more entrained air after the end of injection, which is considered to be the main reason for the faster oxidation of soot, with comparison to the free jet, which is in agreement with experimental measurements of the optical soot thickness KL