Internal Combustion Engine Simulations Research Articles

Dynamic mesh analysis by numerical simulation of internal combustion engines

Dynamic mesh analysis by numerical simulation of internal combustion engines

Modeling study of the ignition characteristics of directly injected 1,3-Cyclohexadiene in surrogate Gasoline/Air under RCCI combustion conditions

In this work a validated chemical kinetic model of the combustion of multicomponent gasoline surrogate fuels containing 680 reactions of 152 species has been used to simulate conditions reminiscent of those of Reactivity Controlled Compression Ignition (RCCI) in order to evaluate 1,3-cyclohexadiene (CYC6H8) as the high reactivity directly injected fuel and a gasoline surrogate fuel as the low reactivity premixed fuel. A single-zone modeling approach was adopted using a modified Cantera example describing the simulation of a gaseous Diesel-type internal combustion engine. The adaptable chemical structure of CYC6H8 to cis-1,3,5-hexatriene (lC6H8), load, start of injection and premixed fuel mass fraction were varied in order to analyze the potential of CYC6H8 as an ignition enhancer. Results have been compared to n-heptane and show that CYC6H8 and its isomer lC6H8 have the potential to be used as the high reactivity directly injected fuel in dual-fuel RCCI combustion, especially at high load conditions. For increased load, the ignition promoting effect is more pronounced at lower premixed fuel mass fractions and less affected by a delayed start of injection. The ignition promoting effect of lC6H8 is more pronounced than CYC6H8 for a decreasing premixed fuel mass fraction. Results from the kinetic analysis indicate that at increased concentrations of lC6H8, the thermal effects are becoming more significant.

Numerical investigation on the use of Dimethyl Ether (DME) as an alternative fuel for compression-ignition engines

Dimethyl Ether (DME) is an oxygenated fuel that could favour the transition of the heavy-duty transportation sector to carbon neutrality thanks to its similarities in terms of thermophysical properties with diesel fuel, which will facilitate the retrofitting of existing architectures, and the possibility to achieve good trade-offs between NOx emissions, soot formation and overall combustion efficiency. The possibility of producing it from a multitude of carbon–neutral sources and the low hydrogen-to-carbon ratio would allow for an overall lower CO2 output, making an attractive option in limiting the global warming impact of the heavy-duty transportation sector. In the present work, a numerical analysis of the combustion process of DME is carried out. First, the numerical setup is validated against experimental data available for a constant volume vessel with an initial density of 14.8 kg/m3, discussing the capabilities of a chemistry-based combustion model using tabulated kinetics of homogeneous reactors: the Tabulated Well Mixed (TWM) model. Ignition delay times (IDT) are compared for a wide range of temperatures, from 750 K to 1100 K, and oxygen concentrations, from 15% to 21%. The same setup is then applied in the simulation of a heavy-duty internal combustion engine (ICE). A first validation was done to assess the performance of the numerical methodology in a traditional Mixing Controlled Compression Ignition (MCCI) scenario. Then, two other points were simulated: an MCCI condition with 35% of EGR and a Late-Premixed Charge Compression Ignition (L-PCCI) one, with 35% of EGR and an SOIe of 4 CAD aTDC. Local temperature distributions were compared, analyzing the effect of these technologies in NOx emission mitigation and their impact on gross indicated efficiency (ηg), showing the advantages that using DME can have on a real-world application.

Combustion Chamber Development to Maximize the Performance of the Hydrogen Combustion Engine for the T1 Ultimate Category of the Dakar Rally Competition

<div class="section abstract"><div class="htmlview paragraph">As the world strives toward the common goal of carbon neutrality by 2050, motorsport cannot be allowed to stand alone as an exception. A gradual energy transition is clearly underway in the automotive industry but has already begun in motorsport as well. Among other initiatives, the Dakar Rally and the FIA have created the T1 ultimate category for prototypes powered by low-carbon fuels, including hydrogen. The Dakar is the pinnacle of off-road endurance rally competitions. It offers a great opportunity to ORECA Magny-Cours and FEV to expose their jointly developed internal combustion engine (ICE), fuelled with hydrogen only, to extreme conditions. In addition, the racing environment imposes a unique pace of development which can serve as a catalyst for spurring the H<sub>2</sub>-ICE technology. Moreover, a hydrogen powered engine is an interesting fit for motorsports because it combines high power output, a relatively long driving range and driving pleasure with an excellent carbon footprint.</div><div class="htmlview paragraph">This article outlines how ORECA Magny-Cours and FEV are currently converting a gasoline racing engine to hydrogen direct injection to meet the numerous challenges of the Dakar Rally. In several development steps, a combustion chamber was newly developed that is tailored to gaseous hydrogen combustion. A high level of charge motion and optimized mixture formation have ultimately been realized using FEV’s dedicated H<sub>2</sub>-ICE simulation tool chain. Design changes resulting from the simulation results are incorporated into the engine. Further thermodynamic investigations on an engine test bench will be undertaken by ORECA Magny-Cours to maximize performance while ensuring knock free operation and best engine efficiency. Although there are still development hurdles to overcome, the combined ORECA/FEV experience will bring a viable carbon neutral powertrain solution to compete in the future Dakar Rally.</div></div>

Acquiring reliable boundary conditions for three-dimensional simulation of internal combustion engines by means of one-dimensional simulation: an insight on pre chamber design

Acquiring reliable boundary conditions for three-dimensional simulation of internal combustion engines by means of one-dimensional simulation: an insight on pre chamber design

Computational simulation of IC engine cooling using different materials for different shapes of fins: a comparative study

Internal combustion (IC) engines are always exposed to extreme temperatures and thermal stresses. So, cooling the internal combustion (IC) engine is necessary to operate. The fins are used in engines to disperse the heat produced by the engine, especially in 4-stroke bike engines. The main focus of this research is to analyse and compare the thermal properties of the IC engine, such as temperature and total heat flux, by varying the shape and materials of four-stroke bike engine fins. In this study, Beryllium oxide (BeO) was proposed as an engine fin besides a few traditional metals. To obtain various temperatures and maximum total heat flux results, a four-stroke 125cc HERO GLAMOUR BS 6 motorcycle engine for various fin shapes such as circular, parabolic, wavy and slotted fins and different materials such as Aluminium 6061, Aluminium 2014, Beryllium oxide (BeO) and Silicon Carbide-Aluminium 2124 (SiC-Al 2124 25%) alloys used in this study. The best performance in case of maximum heat flux was found 8.417% more for Beryllium oxide (BeO) compared to Aluminium 6061 in circular fins.

Three-Dimensional Computational Fluid Dynamics Simulation and Mesh Size Effect of the Conversion of a Heavy-Duty Diesel Engine to Spark-Ignition Natural Gas Engine

Abstract With developing in computer technology, three-dimensional (3D) computational fluid dynamics (CFD) internal combustion (IC) engine simulations, which generally use reduced chemical kinetic mechanisms and simplified combustion models, can provide more accurate results along with less initial investment and calculation costs compared to experimental setup. In this study, a heavy-duty diesel engine effects on performance, combustion, and emission characteristics by spraying natural gas from the intake port and transforming it into a spark-ignition engine were investigated through 3D ansysfortecfd program. The spark time was accepted as 0.5 °CA before top dead center (bTDC), which was the start of injection time for the diesel injector. Analyzes were carried out at 2300 rpm, full load, 17.5: 1 of high compression ratio, constant air/fuel ratio. Six different global mesh sizes were used in the converted engine model. Performance, in-cylinder combustion, and emission values were examined for these six different global mesh sizes and the most suitable one was tried to be found. As a result of the global mesh size study, it was concluded that the most suitable size was 2.25 mm. In terms of performance, when the data obtained with usage of natural gas were compared to that of diesel fuel, the gross indicated power (GIP), indicated mean effective pressure (IMEP), and indicated thermal efficiency (ITE) values were increased by 12.02%, 8.93%, and 8.7%, respectively, while the gross indicated specific fuel consumption (GISFC) value was decreased by 9.78%. When the emission values were examined, it was seen that the engine met the stage IIIB norms without usage of selective catalytic reduction (SCR), diesel particulate filter (DPF), and diesel oxidation catalyst (DOC) under the conditions.

Validation and Enhancement of a Supermesh Strategy for the CFD Simulation of Four-Stroke Internal Combustion Engines

The present paper describes and validates an efficient CFD implementation to replicate the working fluid-dynamics of a real four-stroke internal combustion engine. To do this, experimental data obtained on a single-cylinder engine are used to validate the proposed computational approach. The engine domain is divided into regions according to each moving zone, and these are coupled using a pseudo-supermesh interface presented in a previous work by the authors. In this work, the original pseudo-supermesh strategy is enhanced by introducing the dual-boundary concept to model the valve opening/closing events to increase the accuracy and simplicity of the simulation procedure. The results produced by the proposed software tool show a good correlation to the experimental measurements of the complete engine cycle. Macroscopic quantities of the in-cylinder flow are accurately replicated as well as the instantaneous evolution of the in-cylinder and intake manifold pressure. Furthermore, the present work shows that the computational efficiency and scalability of the enhanced pseudo-supermesh approach are preserved even when applied to more complex real problems. In this sense, this work contributes to a new engineering tool promoting the enhanced pseudo-supermeshes as an effective tool for the design, development, and optimization of internal combustion engines.

Development of a reduced n-heptane/toluene/unsaturated furans-PAH reaction mechanism for dual-fuel engine applications

Furan, 2-methylfuran (MF) and 2,5-dimethylfuran (DMF) have gathered much attention in the research community. However, the reaction chemistry of the three unsaturated furans for the internal combustion engine (ICE) simulations remains scarce. Therefore, a reduced five-component reaction mechanism contains furan, MF, DMF, n-heptane and toluene was proposed for dual-fuel engine applications in present research. First, a detailed reaction mechanism for furanic fuels was reduced under a wide range of enginelike conditions by using combined reduction methods. Second, the reduced mechanism of furanic fuels was combined with an existing n-heptane/toluene mechanism containing the formation of polycyclic aromatic hydrocarbon (PAH) up to C16 to construct a combined mechanism. Third, the combined mechanism were optimized by adjusting the reaction rate constants of some significant reactions and the newly proposed reduced n-heptane/toluene/unsaturated furans-PAH mechanism comprising 98 species taking part in 253 reactions. Subsequently, the proposed mechanism was compared and evaluated with experimental measurements of ignition delay times and species mole fractions acquired from published papers. Meanwhile, new dual-fuel engine experiments were performed in a single-cylinder diesel engine, the experimental results were also used to validate the proposed mechanism. Overall, the predicted results obtained by this proposed n-heptane/toluene/unsaturated furans-PAH mechanism are in reasonable agreement with the available experimental data.

Complex Phenomena Unified Simulation Framework "CUBE" and Automotive Internal Combustion Engine Simulation

Complex Phenomena Unified Simulation Framework "CUBE" and Automotive Internal Combustion Engine Simulation

Analysis and Interpretation of Data-Driven Closure Models for Large Eddy Simulation of Internal Combustion Engine

<div class="section abstract"><div class="htmlview paragraph">We present an automatic data-driven machine learning (ML) approach for the development, evaluation and interpretation of deep neural networks (DNNs) for turbulence closures and demonstrate their usage in the context of cold-flow large-eddy simulation (LES) of the four-stroke Darmstadt engine using an open-source compressible multi-dimensional CFD solver OFICE, in a hybrid PDE-ML framework. Rather than explicitly using canonical formulations of closure terms, these DNNs robustly discover the functional relationships between the large-scale features of the resolved flow (cell Re, strain and rotation rate tensors etc.) obtained by solving the Navier Stokes to the small-scale unresolved terms. Experimentally validated high-fidelity LES solutions of the engine at different crank angles are utilized as the ground truth to train the DNN based closure models. Since optimizing these DNNs can be a laborious process for scientific datasets, and often require specialized expertise, we propose a Bayesian optimization framework that automatically determines the best set of network parameters, including the architecture and training hyperparameters - batch size, regularization etc. for optimum performance. We compare and contrast various networks for their effectiveness in an <i>a-priori</i> testing setting. Finally, the best ‘learnt’ network is integrated with the open-source CFD solver (OFICE), and solutions are obtained over several injection cycles. These experiments reveal that the DNN models temporally track resolved scalar variance with a good accuracy. Additionally, we interpret the artificial neural networks with sensitivity analysis to determine the relevant large-scale features for the learning process.</div></div>

Unified strategy of supermesh generation for planar, cylindrical, and spherical non-conformal interfaces by using 2-D intersection algorithm

Aimed at decreasing the complexity of calculating the intersection of a pair of overlapped interfaces, this paper presents an efficient unified strategy to generate a supermesh for planar, cylindrical, and spherical non-conformal interfaces uniquely, which retains the computational efficiency of a 2-D intersection algorithm. The coordinate transformations for both the cylindrical and spherical interfaces are considered because the nodes of both types of interfaces can be described by two variable coordinates and a constant coordinate. The coordinate transformation of the spherical interfaces is performed by combining the Gnomonic projection and notion of rigid rotation. This task is incorporated in the local-supermeshing approach to generate the supermesh, which is employed as an auxiliary mesh to realize one-to-one addressing between the cells on both sides of the interfaces. Tests are performed to determine the pure geometric error of the supermeshing approach, and the results show the method does not induce additional geometric error. Besides, the accuracy and conservation of the fluxes when applying the supermeshing approach in a particular solver are studied. The results of the full-cycle unsteady simulation of internal combustion engine indicate the feasibility to applying the proposed method to realistic numerical problems.

Development of a Computationally Efficient Tabulated Chemistry Solver for Internal Combustion Engine Optimization Using Stochastic Reactor Models

The use of chemical kinetic mechanisms in computer aided engineering tools for internal combustion engine simulations is of high importance for studying and predicting pollutant formation of conventional and alternative fuels. However, usage of complex reaction schemes is accompanied by high computational cost in 0-D, 1-D and 3-D computational fluid dynamics frameworks. The present work aims to address this challenge and allow broader deployment of detailed chemistry-based simulations, such as in multi-objective engine optimization campaigns. A fast-running tabulated chemistry solver coupled to a 0-D probability density function-based approach for the modelling of compression and spark ignition engine combustion is proposed. A stochastic reactor engine model has been extended with a progress variable-based framework, allowing the use of pre-calculated auto-ignition tables instead of solving the chemical reactions on-the-fly. As a first validation step, the tabulated chemistry-based solver is assessed against the online chemistry solver under constant pressure reactor conditions. Secondly, performance and accuracy targets of the progress variable-based solver are verified using stochastic reactor models under compression and spark ignition engine conditions. Detailed multicomponent mechanisms comprising up to 475 species are employed in both the tabulated and online chemistry simulation campaigns. The proposed progress variable-based solver proved to be in good agreement with the detailed online chemistry one in terms of combustion performance as well as engine-out emission predictions (CO, CO2, NO and unburned hydrocarbons). Concerning computational performances, the newly proposed solver delivers remarkable speed-ups (up to four orders of magnitude) when compared to the online chemistry simulations. In turn, the new solver allows the stochastic reactor model to be computationally competitive with much lower order modeling approaches (i.e., Vibe-based models). It also makes the stochastic reactor model a feasible computer aided engineering framework of choice for multi-objective engine optimization campaigns.

Effect of engine compression ratio on thermodynamic behavior using alternative hydrogen-LPG fuel

ABSTRACT Combustion modeling plays an important role in an internal combustion engine (IC) simulation to predict in-cylinder flow behavior development. Therefore, this work presents a predictive thermodynamic model of an IC engine fueled with gasoline, LPG, and LPG-hydrogen blend, using zero-dimensional modeling. The effects of the compression ratio combining hydrogen enrichment on thermodynamic process are numerically evaluated on gasoline engine fueled alternative hydrogen-LPG fuel. Moreover, hydrogen volumetric fractions of 0%, 5%, 10%, 15%, and 20% were used in the simulation prediction. The main finding in this study was that the compression end temperature in-cylinder pressure, the thermal efficiency, and the supplied power prove that a compression ratio between 9 and 10 is the most reliable. Hence, comparisons with experimental results justify the choice of the compression ratio.

Internal Combustion Engine Modeling Framework in Simulink: Gas Dynamics Modeling

With advancements in computer-aided design, simulation of internal combustion engines has become a vital tool for product development and design innovation. Among the simulation software packages currently available, MATLAB/Simulink is widely used for automotive system simulations, but does not contain a comprehensive engine modeling toolbox. To leverage MATLAB/Simulink’s capabilities, a Simulink-based 1D flow engine modeling framework has been developed. The framework allows engine component blocks to be connected in a physically representative manner in the Simulink environment, reducing model build time. Each component block, derived from physical laws, interacts with other blocks according to block connection. In this Part 1 of series papers, a comprehensive gas dynamics model is presented and integrated in the engine modeling framework based on MATLAB/Simulink. Then, the gas dynamics model is validated with commercial engine simulation software by conducting a simple 1D flow simulation.

Application of a zonal hybrid URANS/LES turbulence model to high and low-resolution grids for engine simulation

A zonal hybrid unsteady Reynolds-averaged Navier–Stokes/large eddy simulation (URANS-LES) Zonal detached-eddy simulation (ZDES) model is applied to internal combustion engine (ICE) simulation and comparisons of predicted flow morphology and variability are carried out against on the transparent combustion chamber (TCC-III) particle image velocimetry (PIV) data set for motored conditions. To this aim, a previously developed model derived from a standard seamless-detached eddy simulation (DES) formulation is adopted for two different grid resolutions. In particular, two zonalization choices are evaluated based on previous single-grid results, in order to assess the model outcomes based on the joint turbulence treatment/grid density: the seamless-DES mode is applied (1) only to the cylinder (TCC-Z1) and (2) to the cylinder and intake port (TCC-Z2). Multi-cycle simulations (50 samples) are carried out and the results are compared to experimental data in terms of PIV images using multiple quality indices on multiple planes ( Y = 0 and X = 0). Finally, comparison of predicted mean flow fields is extended to standard URANS mode. Results show that the use of a cylinder-only seamless-DES treatment on a relatively coarse grid results in a quantitative agreement between simulated and measured (PIV) flow fields, both in terms of average morphology and flow variability, whereas the extension of the DES mode to the intake port does not introduce relevant variations. Quality indicators seem to be moderately sensitive to the grid resolution, thus confirming the adaptive potential of a ZDES–like model and promoting the use of DES–type turbulence modelling even on relatively low-resolution grids. The analysis of average fields compared to URANS simulations highlights the benefit for both grids of a scale-resolving ZDES modelling when the same underlying turbulence model ( k-ε RNG) is used. This study reinforces the recommendation in the use of hybrid URANS-LES models to simulate ICE flows. The adopted ZDES formulation based on the two-equation k-ε RNG model shows that high-quality results can be obtained even on engineering-grade grids, both in terms of average and cycle-to-cycle variation. The numerical results obtained using the two grids with variable resolution are consistent, and this further promotes a wider adoption of this class of models to simulate engine flows in industrial applications.

A machine learning methodology for improving the accuracy of laminar flame simulations with reduced chemical kinetics mechanisms

The focus of the present work is to investigate a new methodology for the rapid generation of laminar flame speed lookup tables, to be used replacing correlation laws in internal combustion engine simulations. Current production engines run mostly under the thickened wrinkled flame combustion regime, which allows the application of a flamelet modelling approach, which requires the a-priori evaluation of the laminar flame speed and thickness. The use of correlation laws, derived from experimental data, has the advantage to be extremely fast to compute, but displays a lack of precision in conditions far from the experimental reference, as it usually happens for ICE applications. On the other hand, the detailed chemical simulation of a freely propagating adiabatic flame, performed for a sufficiently refined grid of reference points, to be interpolated during runtime, might require hundreds of hours of computing. The use of a reduced chemical mechanism can potentially cut by orders of magnitude the required time, but on the other hand it will decrease accuracy. In the present work, the potential of integrating machine learning algorithms and neural networks in the workflow with different approaches was valuated, leveraging the potential of new and optimized software libraries, to reduce simulation times while maintaining a high level of accuracy, with respect to the results obtained with the complete scheme.

Large eddy simulation analysis of the turbulent flow in an optically accessible internal combustion engine using the overset mesh technique

Computational fluid dynamics has become a fundamental tool for the design and development of internal combustion engines. The meshing strategy plays a central role in the computational efficiency, in the management of the moving components of the engine and in the accuracy of results. The overset mesh approach, usually referred to also as chimera grid or composite grid, was rarely applied to the simulation of internal combustion engines, mainly because of the difficulty in adapting the technique to the specific complexities of internal combustion engine flows. The article demonstrates the feasibility and the effectiveness of the overset mesh technique application to internal combustion engines, thanks to a purposely designed meshing approach. In particular, the technique is used to analyze the cycle-to-cycle variability of internal combustion engine flows using large eddy simulation. Fifty large eddy simulation cycles are performed on the well-known TCC-III engine in motored condition. Results are analyzed in terms of tumble center trajectory and using proper orthogonal decomposition to objectively characterize the spatial and temporal evolution of turbulent flow field in internal combustion engines. In particular, an original decomposition method previously applied by the authors to the TCC-III measured flow fields is here extended to computational fluid dynamics results.

Effect of Piston Crevices on the Numerical Simulation of a Heavy-Duty Diesel Engine Retrofitted to Natural-Gas Spark-Ignition Operation

Three-dimensional computational fluid dynamics internal combustion engine simulations that use a simplified combustion model based on the flamelet concept provide acceptable results with minimum computational costs and reasonable running times. Moreover, the simulation can neglect small combustion chamber details such as valve crevices, valve recesses, and piston crevices volume. The missing volumes are usually compensated by changes in the squish volume (i.e., by increasing the clearance height of the model compared to the real engine). This paper documents some of the effects that such an approach would have on the simulated results of the combustion phenomena inside a conventional heavy-duty direct injection compression-ignition engine, which was converted to port fuel injection spark ignition operation. Numerical engine simulations with or without crevice volumes were run using the G-equation combustion model. A proper parameter choice ensured that the numerical results agreed well with the experimental pressure trace and the heat release rate. The results show that including the crevice volume affected the mass of a unburned mixture inside the squish region, which in turn influenced the flame behavior and heat release during late-combustion stages.

Development of a compact and robust Polyoxymethylene Dimethyl Ether 3 reaction mechanism for internal combustion engines

With high oxygen content, Polyoxymethylene Dimethyl Ether 3 (PODE3) is a potential fuel additive to reduce soot emissions. However, reaction mechanisms to describe PODE3 combustion are not yet compact enough for 3-D numerical simulations. Therefore, the current work aims to develop a small yet reliable PODE3 reaction mechanism. Based on sensitivity analysis, the major reaction pathway is identified to construct the PODE3 sub-mechanism. Thereafter, it is integrated with a primary reference fuel (PRF) mechanism to create a PRF-PODE3 mechanism containing 61 species and 190 reactions. The major reaction pathway of the PODE3 sub-mechanism consists of only 11 species and 17 reactions. Furthermore, the new mechanism has been well validated with experimental results in terms of ignition delay times (rapid compression machine at pressures = 1.0 MPa and 1.5 MPa, equivalence ratios = 0.5, 1.0 and 1.5), laminar flame speeds (Pin = 1 atm, Tin = 408 K), flame species concentrations (pressure = 33.3 mbar, equivalence ratio = 1) and homogeneous charge compression ignition (HCCI) combustion (equivalence ratios = 0.18 and 0.34). Overall, this highly compact yet robust PRF-PODE3 mechanism is demonstrated to be suitable for internal combustion engine simulations. In addition, with good agreement in terms of fundamental combustion validations, the proposed PRF-PODE3 mechanism can reasonably be applied to other practical applications such as simulations in jet engines, pulse detonation engines, boilers and furnaces.