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

Numeričko modeliranje procesa izgaranja pomoću tabeliranih podataka propagacije plamena i modela izgaranja koherentnih plamenova

In recent times, combustion modelling employing computational fluid dynamics (CFD) in combination with experiment has become an irreplaceable tool in the design process of the diesel engines. Combustion process as a phenomenon of exceptional complexity can be numerically solved with detailed chemical kinetics or with the utilisation of approximated combustion models. Detailed chemical kinetics provides a comprehensive insight into the chemical aspect of the combustion process, while combustion models are described with approximated chemical kinetics in order to reduce the computational demand. An appropriate modelling approach to overcome these challenges is the Flamelet generated manifold (FGM) combustion modelling approach, which computes the chemistry kinetics in preprocessing and stores the result data in a look-up table that is interpolated during the CFD simulations. One of the combustion models, which has proven an ability to simulate the combustion process in internal combustion engines is Three-zones extended coherent flame model (ECFM-3Z+). In this thesis, ECFM-3Z+ and FGM approaches were employed for the calculation of combustion process in a diesel engine. The primary aim of the thesis is to analyse and validate numerical results obtained with FGM and ECFM-3Z+ models against experimental data. Numerical simulations are performed using commercial CFD software AVL FIRE TM, where the calculated results such as mean in-cylinder pressure, mean temperature, rate of heat release and NO emissions are calculated for single and multi-injection strategies. The NO emission trend observed in the experiment is well reproduced with both combustion models, while the computational time for CFD simulations with FGM is reduced by half. The results obtained with both combustion modelling approaches are found to be in a good agreement with the experimental data. Thus it is conducted, that both ECFM-3Z+ and FGM combustion modelling approaches are capable of predicting the combustion process in the real industrial diesel engines.Korištenje računalne dinamike fluida (RDF) u kombinaciji s eksperimentalnim istraživanjima je postao nezaobilazan pristup u razvoju dizel motora. Proces izgaranja je vrlo kompleksan fenomen, a numerički se može opisati pomoću dva pristupa: detaljne kemijske kinetike i modela izgaranja. Detaljna kemijska kinetika pruža opsežan uvid u kemijske aspekte procesa izgaranja, dok su modeli izgaranja opisani s aproksimiranom kemijskom kinetikom s ciljem smanjenja potrebe za računalnim resursima. Pristup u modeliranju izgaranja koji omogućava efikasno numeričko rješavanje procesa izgaranja bez ograničenja na složenost kemijske kinetike ili dostupnih računalnih resursa je metoda tabeliranja kemijskih vrsta u predprocesoru (engl. Flamelet generated manifold, FGM). Ovim pristupom detaljna kemijska kinetika se izračunava u predprocesoru, a rezultati se spremaju u tablicu koja se interpolira tijekom RDF procedura. Jedan od konvencionalnih modela izgaranja u motorima s unutarnjim izgaranjem je model koherentnih plamenova (engl. Three-zones extended coherent flame model, ECFM-3Z+). U ovom radu za modeliranje procesa izgaranja u dizel motoru korišten je FGM pristup i ECFM-3Z+ model. Cilj ovog rada je analizirati i validirati rezultate numeričkih simulacija s eksperimentalnim podacima. Numeričke simulacije izvršene su korištenjem komercijalnog programskog paketa AVL FIRE TM. Rezultati poput tlaka, temperature, brzine oslobađanja topline i NO emisija izračunati su za radne točke motora s jednim i s tri ubrizgavanja goriva u cilindar. Trend emisija NO-a izmjeren u eksperimentu dobro je reproduciran s oba modela. Budući da se rezultati oba korištena pristupa u modeliranju izgaranja dobro poklapaju s eksperimentalnim podacima, zaključeno je da su i ECFM-3Z+ model i FGM pristup valjani za opisivanje procesa izgaranja u industrijskim dizel motorima

Unstable recurrent patterns in Kuramoto-Sivashinsky dynamics

We undertake a systematic exploration of recurrent patterns in a 1-dimensional Kuramoto-Sivashinsky system. For a small, but already rather turbulent system, the long-time dynamics takes place on a low-dimensional invariant manifold. A set of equilibria offers a coarse geometrical partition of this manifold. A variational method enables us to determine numerically a large number of unstable spatiotemporally periodic solutions. The attracting set appears surprisingly thin - its backbone are several Smale horseshoe repellers, well approximated by intrinsic local 1-dimensional return maps, each with an approximate symbolic dynamics. The dynamics appears decomposable into chaotic dynamics within such local repellers, interspersed by rapid jumps between them.Comment: 11 pages, 11 figure

Synergetic Application of Zero-, One-, and Three-Dimensional Computational Fluid Dynamics Approaches for Hydrogen-Fuelled Spark Ignition Engine Simulation

Nowadays hydrogen, especially if derived from biomass or produced by renewable power, is rising as a key energy solution to shift the mobility of the future toward a low-emission scenario. It is well known that hydrogen can be used with both internal combustion engines (ICEs) and fuel cells (FCs); however, hydrogen-fuelled ICE represents a robust and cost-efficient option to be quickly implemented under the current production infrastructure. In this framework, this article focuses on the conversion of a state-of-the-art 3.0L diesel engine in a hydrogen-fuelled Spark Ignition (SI) one. To preliminarily evaluate the potential of the converted ICE, a proper simulation methodology was defined combining zero-, one-, and three-dimensional (0D/1D/3D) Computational Fluid Dynamics (CFD) approaches. First of all, a detailed kinetic scheme was selected for both hydrogen combustion and Nitrogen Oxides (NOx) emission predictions in a 3D-CFD environment. Afterward, to bring the analysis to a system-level approach, a 1D-CFD predictive combustion model was firstly optimized by implementing a specific laminar flame speed correlation and, secondly, calibrated against the 3D-CFD combustion results. The combustion model was then integrated into a complete engine model to assess the potential benefit derived from the wide range of flammability and the high flame speed of hydrogen on a complete engine map, considering NOx formation and knock avoidance as priority parameters to control. Without a specific modification of turbocharger and combustion systems, a power density of 34 kW/L and a maximum brake thermal efficiency (BTE) of about 42% were achieved, thus paving the way for further hardware optimization (e.g., compression ratio reduction, turbocharger optimization, direct injection [DI]) to fully exploit the advantages enabled by hydrogen combustion

High-Speed Infrared Measurement of Injector Tip Temperature during Diesel Engine Operation

[EN] Pre-catalyst engine emissions and detrimental injector deposits have been widely associated with the near-nozzle fluid dynamics during and after the injection events. Although the heating and evaporation of fuel films on the nozzle surface directly affects some of these processes, there are no experimental data for the transient evolution of nozzle surface temperature during typical engine conditions. In order to address this gap in knowledge, we present a non-intrusive approach for the full-cycle time resolved measurement of the surface temperature of production nozzles in an optical engine. A mid-wave infrared high-speed camera was calibrated against controlled conditions, both out of engine and in-engine to account for non-ideal in surface emissivity and optical transmissivity. A custom-modified injector with a thermocouple embedded below the nozzle surface was used to validate the approach under running engine conditions. Calibrated infrared thermography was then applied to characterise the nozzle temperature at 1200 frames per second, during motored and fired engine operation, thus revealing for the first time the effect of transient operating conditions on the temperature of the injector nozzle's surface.This work was supported by the UK's Engineering and Physical Science Research Council (EPSRC grant EP/S513751/1) and BP International Ltd. Raul Payri was hosted at the University of Brighton under the Salvador de Madariaga programme (reference PRX18/00243) from Ministerio de Ciencia, Innovacion y universidades from the Spanish Government.Gander, A.; Sykes, D.; Payri, R.; De Sercey, G.; Kennaird, D.; Gold, M.; Pearson, RJ.... (2021). High-Speed Infrared Measurement of Injector Tip Temperature during Diesel Engine Operation. Energies. 14(15):1-19. https://doi.org/10.3390/en14154584119141

Advanced Technologies for the Optimization of Internal Combustion Engines

This Special Issue puts together recent findings in advanced technologies for the optimization of internal combustion engines in order to help the scientific community address the efforts towards the development of higher-power engines with lower fuel consumption and pollutant emissions