Reduced Reaction Mechanism Research Articles

Autonomous hybrid optimization of a SiO2 plasma etching mechanism

Computational modeling of plasma etching processes at the feature scale relevant to the fabrication of nanometer semiconductor devices is critically dependent on the reaction mechanism representing the physical processes occurring between plasma produced reactant fluxes and the surface, reaction probabilities, yields, rate coefficients, and threshold energies that characterize these processes. The increasing complexity of the structures being fabricated, new materials, and novel gas mixtures increase the complexity of the reaction mechanism used in feature scale models and increase the difficulty in developing the fundamental data required for the mechanism. This challenge is further exacerbated by the fact that acquiring these fundamental data through more complex computational models or experiments is often limited by cost, technical complexity, or inadequate models. In this paper, we discuss a method to automate the selection of fundamental data in a reduced reaction mechanism for feature scale plasma etching of SiO2 using a fluorocarbon gas mixture by matching predictions of etch profiles to experimental data using a gradient descent (GD)/Nelder–Mead (NM) method hybrid optimization scheme. These methods produce a reaction mechanism that replicates the experimental training data as well as experimental data using related but different etch processes.

Development of a reduced mechanism for methane combustion in OpenFOAM: A computational approach for efficient and accurate simulations

The primary aim of this study is to develop a more efficient reaction mechanism for accurately simulating methane combustion, with a specific focus on ignition delay, laminar flame speed, and 2-D simulated flames, while also reducing computational time. Ten reduced reaction mechanisms for methane combustion were evaluated, with only one, "SK30," meeting the required accuracy standards. However, SK30 proved to be computationally intensive when simulating a 2-D premixed flame at a microscale. To address this challenge, a two-step reduction process was implemented. Firstly, an automated algorithm utilized direct relation graphs and sensitivity analysis with ignition delays as a reference to streamline the mechanism while maintaining accuracy. Subsequently, the second step involved identifying key reactions that had a more significant impact on flame speed than ignition delay through sensitivity analysis. Any missing reactions were then added judiciously, prioritizing the retrieval of the missing but important reactions to overall accuracy while minimizing computational cost. This process resulted in a novel mechanism comprising 25 species and 132 reactions for methane-air combustion. The validity of this mechanism was confirmed through comparison with a benchmark model, demonstrating satisfactory agreement in 1-D flame speed and 2-D premixed flame modeling. Most notably, the new mechanism substantially reduced processing time, achieving a 50 % speedup compared to SK30.

A numerical analysis of hydrotreated vegetable oil and dimethoxymethane (OME1) blends combustion and pollutant formation through the development of a reduced reaction mechanism

The solution to the dilemma of carbon footprint of internal combustion engines and pollutant emissions is necessary for the survival of this technology. In this context, alternative fuels have shown great potential in terms of achieving cleaner combustion and compliance with ever increasing pollutant emissions regulations. This work is focused on the study of two promising alternative fuels as Hydrotreated vegetable oil (HVO), which is a biofuel and Dimethoxymethane also termed as OME1, which is an e-fuel. A comprehensive numerical approach has been followed to study these fuels. Primarily a compact reaction mechanism having 121 species and 678 reactions has been developed which can be utilized to perform 3D CFD simulations of blends of these fuels. Secondly, a detailed numerical investigation including combustion and emissions analysis has been carried out. Results show that the developed mechanism is able to offer predictions, which match the experimental behavior observed in various combustion parameters and thus can be utilized for compression ignition engine applications involving these promising fuels. In addition, the numerical analysis also highlights that a reduction of 50% and 37% in terms soot and NOx emissions respectively can be achieved by addition of 30% OME1 in the blend containing HVO, suggesting that these blends can be utilized in unmodified CI engines to break the soot-NOx tradeoff without significantly penalizing the energy loss.

A Generalised Series Model for the LES of Premixed and Non-Premixed Turbulent Combustion

In this study, the generality and prediction accuracy of a generalised series model for the large eddy simulation of premixed and non-premixed turbulent combustion is explored. The model is based on the Taylor series expansion of the chemical source term in scalar space and implemented into OpenFOAM. The mathematical model does not depend on combustion regimes and has the correct limiting behaviour. The numerical error sources are also outlined and analysed. The model is first applied to a piloted methane/air non-premixed jet flame (Sandia Flame D). The statistical (time-averaged and RMS) results agree well with the experimental measurements, particularly with regard to the mixture fraction, velocity, temperature, and concentrations of major species CH4, CO2, H2O, and O2. However, the concentrations of the intermediates CO and H2 are over-predicted, due to the limitations of the reduced reaction mechanism employed. Then, a Bunsen-piloted flame is simulated. Most of the statistical properties of both the reactive species and progress variables are well reproduced. The only major discrepancy evident is in the temperature, which is probably attributed to the experimental uncertainties of temperature fields in the pilot stream. These findings demonstrate the model’s generality for both a premixed and non-premixed combustion simulation, as well as the accuracy of prediction of reactive species distribution.

Analysis of spontaneous ignition of hydrogen-enriched methane in a rectangular tube

This study investigates the spontaneous ignition of high-pressure hydrogen-enriched methane in air within a rectangular tube. A computationally efficient approach has been adopted, utilizing a reduced reaction mechanism and ignition delay model within a 3D Large Eddy Simulation (LES) framework. This approach overcomes the limitations of traditional 1D and 2D simulations with detailed chemistry models, which are unable to accurately reproduce the complex 3D shock wave structures within the tube. The simulated shock wave behavior during 9 MPa hydrogen leakage (case 1) and 11 MPa 90 vol% hydrogen/10 vol% methane mixture leakage (case 2) are found to agree well with experimental observations. In case 2, the hot spots generated by reflected shock waves and Mach reflections ignite the hydrogen/methane-air mixture, resulting in three sequential spontaneous ignitions. The flame is observed to primarily propagate along the tube corners and wall centers, with the central ignition spreading across the entire cross-section. For the 25 MPa 24 vol% hydrogen/76 vol% methane mixture leakage (case 6), the shock intensity is significantly reduced due to the increased methane proportion, leading to spontaneous ignition only at the tube corners when the hemispherical shock wave reflects from the wall. The flame predominantly forms downstream along the tube corner, gradually spreading along the tube wall. It is indicated that while the probability of spontaneous ignition decreases with increasing methane content, the risk remains significant under sufficiently high pressures. To the best our knowledge, this study represents the first 3D large eddy simulation of spontaneous ignition for high-pressure hydrogen-enriched methane leakage into air, providing valuable insights into the underlying physical phenomena.

A Review on Compression-Ignition Engine Performance And Emissions With Hydrogen-Diesel Mixtures: Effect Of Operational Parameters

The combustion of conventional fuel in Compression-Ignition (CI) engines is generally understood as a primary cause of hydrocarbon exhaust emissions. Alternative fuels and hydrocarbon fuels can be mixed to lower pollution emissions while enhancing engine efficiency. Here, the various variables which impact emissions and engine efficiency are fully illustrated. Numerical work on the engine was done to examine the working and outflow patterns of a dual-fuel CI engine at various fuel combination ratios. In the test setup, diesel is used as main fuel and hydrogen and air as the controlling fuel. In order to formulate this special CI engine numerically, three-dimensional computer based analytical tools were used. For this method, n-heptane was chosen as reaction fuel and a reduced-reaction mechanism was taken into account. To investigate the soot formation rate inside the cylinder, the model by Hiroyasu-Nagel was developed. Here, a study looks into the performance effects on the variations of secondary fuel and its emissions. Presence of good amount of hydrogen during combustion results in better thermal efficiency and better performance. As the hydrogen rate increased, ignition timing was delayed as a result of a time lag in the OH component’s evolution. Meanwhile, Exhaust Gas Recirculation (EGR) and timing of the diesel incorporation strategies are also taken as important performance parameter.

Flame Structure at Elevated Pressure Values and Reduced Reaction Mechanisms for the Combustion of CH4/H2 Mixtures

Understanding and controlling the combustion of clean and efficient fuel blends, like methane + hydrogen, is essential for optimizing energy production processes and minimizing environmental impacts. To extend the available experimental database on CH4 + H2 flame speciation, this paper reports novel measurement data on the chemical structure of laminar premixed burner-stabilized CH4/H2/O2/Ar flames. The experiments cover various equivalence ratios (φ = 0.8 and φ = 1.2), hydrogen content amounts in the CH4/H2 blend (XH2 = 25%, 50% and 75%), and different pressures (1, 3 and 5 atm). The flame-sampling molecular-beam mass spectrometry (MBMS) technique was used to detect reactants, major products, and several combustion intermediates, including major flame radicals. Starting with the detailed model AramcoMech 2.0, two reduced kinetic mechanisms with different levels of detail for the combustion of CH4/H2 blends are reported: RMech1 (30 species and 70 reactions) and RMech2 (21 species and 31 reactions). Validated against the literature data for laminar burning velocity and ignition delays, these mechanisms were demonstrated to reasonably predict the effect of pressure and hydrogen content in the mixture on the peak mole fractions of intermediates and adequately describe the new data for the structure of fuel-lean flames, which are relevant to gas turbine conditions.

Reduced Reaction Mechanisms for Sustainable Aviation Fuel (SAF): Isoparaffinic Alcohol-to-Jet Synthetic Paraffinic Kerosene (AtJ-SPK) and Its Blends with Jet A

Reduced Reaction Mechanisms for Sustainable Aviation Fuel (SAF): Isoparaffinic Alcohol-to-Jet Synthetic Paraffinic Kerosene (AtJ-SPK) and Its Blends with Jet A

Hydrogen concentration effects on a swirl-stabilized non-premixed burner using ammonia

In the present paper, it was aimed to consume pure NH3 by using an existing non-premixed burner with H2 blending strategy, and to examine the temperature and NO emission profiles emerged in a model combustor for NH3/H2 and pure NH3 fuel compositions. The Mixture Fraction/PDF combustion model with a reduced reaction mechanism was used for the numerical modelling. During the experimental studies, a stable NH3/air flame was able to achieve by introducing H2 into the burner since NH3/air mixture has a low reactivity and needs a high ignition energy. However, any flashback or lift-off tendency was not observed for NH3/H2/air or NH3/air flames. The numerical and experimental results showed that H2 addition into NH3/air mixture provided higher temperature values both in the flame region and in the entire combustor. As the concentration of H2 in the mixture was raised, the flame approached towards to the burner outlet with increment effect in burning velocity. However, H2 addition into NH3/air mixture led to more NO emissions formation in the combustor. This can be attributed with that H2 addition promoted both thermal and fuel-NO mechanisms because H2 addition induced to increase the decomposition rate of NH3 and flame temperature of NH3/air mixture. This finding was validated with the prediction of the concentrations of O and HNO radicals for all fuel compositions. Consequently, H2 introduction contributed to the flame stability of NH3/air mixture even if more NO formation was observed.

A Novel Surrogate Fuel Approach for the Numerical Simulation of Renewable Fuels for the Transport Sector

The use of fuels made from renewable resources can be beneficial in reducing the CO2 emission balance of the existing vehicle fleet. These fuels should be drop-in-capable, i.e., their properties should correspond as far as possible to those of fossil fuels. In addition, they should be able to be blended with conventional fuels. In order to determine the full potential of new renewable drop-in fuels, numerical investigations can make a significant contribution.A novel Surrogate Fuel Approach (SFA) was proposed to perform the numerical simulations for blends of paraffinic diesel fuel and alcohols. A set of modeling and mixing rules were used to estimate and extrapolate the required thermo-physical and physicochemical properties of renewable fuels. The detailed chemical mechanisms for n-dodecane and n-octanol were merged. A systematic reduction of the detailed chemical mechanisms was performed using the Directed Relation Graph with Error Propagation (DRGEP) method. For the selected target species, the reduced mechanism from the DRGEP and lumping method contains ∼31% species and ∼40% reactions as of the merged reaction mechanism. The blended fuel properties and the reduced reaction mechanism were incorporated into the numerical simulations. The surrogate fuel approach was validated for steady-state as well as transient operating conditions using the experimental results obtained from the optical high-pressure chamber (HPC) and a heavy-duty single-cylinder engine (HD-SCE). The HD-SCE testing shows that the 60% B0-Di/40% RF blend increases ITE by ∼2% in absolute values and lower ISCO2, ISCO, ISHC and smoke emissions as compared to Diesel fuel. This is due to the paraffinic fuel structure, the fuel-borne oxygen, the high calorific value, and the high cetane number. The calibrated 3D-CFD spray models show an excellent agreement with experimental data from the optical investigations of different spray characteristic values — Liquid and Gaseous penetration Length, Lift of Length and ignition delay for the 60% B0-Di/40% RF fuel. Further, the pressure traces, heat release rates, and nitrogen oxides (NOX) emissions from the numerical 3D-CFD simulations showed a good agreement with the results from the HD-SCE experiments. Overall, these results support the suitability of the proposed novel surrogate fuel approach for simulating different blends of renewable drop-in fuels.

Emission characteristics of turbulent premixed propane/air/carbon dioxide and propane/air/ammonia swirl flames through a rich‐lean combustor

AbstractThis study is dedicated to understanding the combustion characteristics of turbulent premixed C3H8‐Air‐CO2 and C3H8‐Air‐NH3 swirl flames in a rich‐lean combustor at atmospheric pressure. In this study, the emission characteristics of both flames were obtained through two‐dimensional numerical simulations based on the RANS approach with Realizable k‐ϵ turbulence model for turbulence closure, and the P1 radiation model for the flame radiation inside the combustor. The turbulence‐chemistry interaction was modeled using the Finite‐Rate Eddy Dissipation Model (FR/EDM) model with a reduced reaction mechanism (Jones‐Lindstedt). The study was conducted for five volumetric fractions of CO2 or NH3, XCO2/NH3 = 0,4%, 8%, 12%, 16%, two swirl numbers (Sn = 0.6 and 1.05), and four equivalence ratios, ϕ = 0.4 (with dilution), 0.5, 0.8, and 1. The results show that the addition of NH3 to C3H8‐Air flames promotes the production of CO, whereas the minimum NOx emission (0.14 ppm) was obtained for a dilution rate of 16% at ϕ = 0.8 and Sn = 0.6 corresponding to an outlet temperature of Tout = 1652 K.

A Novel Reduced Reaction Mechanism for Diesel/2,5-Dimethylfuran Engine Application

The application of 2,5-dimethylfuran (DMF) as an alternative fuel for internal combustion engines has been gaining popularity. However, it has rarely been studied in previous research on the chemical kinetics of DMF for engine combustion simulations. In the present study, a reduced n-heptane/toluene/DMF-polycyclic aromatic hydrocarbon (PAH) reaction mechanism containing only 78 species amongst 190 reactions was proposed and applied to predict the combustion and emissions of a diesel engine using diesel/DMF blend fuel. First, a detailed reaction mechanism for DMF from the literature was chosen and reduced using combined mechanism reduction methods under engine-relevant conditions. Second, the reduced mechanism of DMF was incorporated into an existing reduced n-heptane/toluene-PAH mechanism to establish a three-component chemistry mechanism. Third, the predictive capability of the combined mechanism was improved by adjusting the rate constants of selected gas-phase reactions. Subsequently, the proposed three-component mechanism was compared and validated with experimental measurements of shock tube ignition delay times and premixed flame species profiles acquired from published papers. Moreover, new experimental data from a conventional diesel engine were used to evaluate the developed mechanism. Overall, the predicted results obtained by this proposed reduced n-heptane/toluene/DMF-PAH mechanism are in reasonable agreement with the available experiments.

Experimental and kinetic modeling study on the oxidation and laminar combustion characteristics of natural gas

The oxidation process in the flow tube reactor and the laminar combustion process in the constant volume combustion bomb of natural gas (0.9 methane/0.07 ethane/0.03 propane, mole fraction) were experimental tested. Furthermore, a reduced reaction mechanism (including 40 species and 189 reactions) of natural gas was developed based on the Aramco 2.0 mechanism by combining the path sensitivity analysis, rate of production analysis, reaction path analysis and the decoupling method. The results show that, in the oxidation process of natural gas, with the equivalence ratio increasing, the starting and ending temperatures for oxidation reaction of natural gas are increased, the reaction temperatures corresponding to CO generation and consumption are higher, and the amount of NO production is decreased. In the the laminar combustion process of natural gas, with the initial temperature and oxygen content increasing or the initial pressure, CO2 and H2O contents decreasing, the laminar flame speed is increased. Through comparing with the calculated results by the Aramco 2.0 mechanism and the corresponding test data, the reduced reaction mechanism can well predict the oxidation, ignition delay and laminar combustion characteristics of natural gas under various conditions.

Assessment of dynamic adaptive chemistry with tabulated reactions for the simulation of unsteady multiregime combustion phenomena

Solving chemistry is an integral part of reacting flow simulations, usually dominating the computational cost. Among the different strategies to accelerate the solution of chemistry and to achieve realizable simulations, the use of Dynamic Adaptive Chemistry (DAC) stands out among other methods. DAC methods are based on the use of reduced mechanisms generated from local conditions. The reduction process is computationally expensive and strategies for reducing the frequency of reduction and the re-utilization of the generated reduced mechanisms are key in making DAC methods computationally affordable. In this study, a new method hereby referred as Tabulated Reactions for Adaptive Chemistry (TRAC) is proposed to correlate chemical states with their reduced mechanisms in order to reduce both the frequency of reduction and to allow for re-utilization of reduced chemical schemes. TRAC introduces a mechanism tabulation strategy based on the use of a low-dimensional space that defines the thermo-chemical conditions for which specific reduced reaction mechanisms are stored. Chemistry reduction is achieved by the use of Path Flux Analysis (PFA) with a reaction rate-sensitivity method to achieve further reduction in the reaction mechanisms. The new TRAC proposal is applied to various canonical transient problems and the results are compared with reference solutions obtained from detailed chemistry calculations. A speedup of about 4x was achieved with TRAC while maintaining an error under 3% in the prediction of the major and minor species, flame structure, and flame propagation.

Numerical and Experimental Investigations of CH4/H2 Mixtures: Ignition Delay Times, Laminar Burning Velocity and Extinction Limits

In this work, the influence of H2 addition on the auto-ignition and combustion properties of CH4 is investigated experimentally and numerically. Experimental ignition delay times (IDT) are compared with simulations and laminar burning velocities (LBVs), and extinction limits/extinction strain rates (ESRs) are compared with data from the literature. A wide variety of literature data are collected and reviewed, and experimental data points are extracted for IDT, LBV and ESR. The results are used for the validation of existing reaction mechanisms. The reaction mechanisms and models used are able to reproduce the influence of H2 addition to CH4 (e.g., shortening IDTs, increasing ESRs and increasing LBVs). IDTs are investigated in a range from 6 to 15 bar and temperatures from 929 to 1165 K with H2 addition from 10 to 100 mol%. We show that LBV and ESR are predicted in a wide range by the numerical simulations. Moreover, the numerical simulations using detailed Aramco Mech 3.0 (581 species) are compared with the derived reduced reaction mechanism UCB Chen (49 species). The results show that the reduced chemistry obtained by considering only the IDT is also valid for LBV and ESR.

Reaction mechanism reduction for ethylene-fueled supersonic combustion CFD

CHEMKIN-Pro was used to build a custom-made reduced reaction mechanism for a 3D simulation of C2H4/Air reaction in a supersonic combustion ramjet (scramjet) combustor for the JAXA S-520-RD1 flight test performed on 24 July 2022. It was also attempted to reproduce the effect of unavoidable H2O vitiation in the facility (ground) test on combustion characteristics. USC Mech II (a 111-species mechanism) was applied as the master mechanism. First, 1D simulation was conducted by applying a plug flow reactor model; 34-, 23-, 20-, 18-, and 19-species mechanisms were suggested as candidates for reduced mechanism. Then, 0D ignition delay simulation by applying a perfectly stirred reactor model by CHEMKIN-Pro, 2D reacting flow simulation by CRUNCH CFD, and 3D reacting flow simulation by RANS were performed to select the most suitable reduced mechanism. The 20-species (96-elementary-reactions) mechanism consisted of H2, O2, N2, H2O, CO2, CO, H, O, OH, HO2, CH2, CH2*, CH3, HCO, CH2O, CH3O, C2H2, C2H3, C2H4, and CH2CHO and was selected as the best-reduced reaction mechanism for C2H4-fueled 3D simulation under the flight and facility conditions corresponding to the RD1 flight test.

A Reduced Reaction Mechanism for Diesel/2-Methyltetrahydrofuran Dual-Fuel Engine Application

2-methyltetrahydrofuran (MTHF2) has been recently regarded as a promising alternative engine fuel. However, the chemical reaction mechanism for MTHF2 combustion in the engine has not been reported to date. In this study, a reduced diesel/MTHF2 reaction mechanism with only 78 species among 233 reactions was constructed for diesel/MTHF2 dual-fuel engine simulations. Firstly, a diesel surrogate mechanism involving the sub-mechanisms of n-decane, iso-octane, methylcyclohexane (MCH), toluene, a reduced mechanism of C2-C3 species and a detailed mechanism of H2/CO/C1 was selected. Secondly, a skeletal MTHF2 mechanism containing 54 species and 294 reactions was formulated under engine-relevant conditions using combined mechanism reduction methods. Thirdly, a reduced sub-mechanism of MTHF2 oxidation with 11 species and 13 reactions was extracted and combined with the four-component diesel surrogate fuel mechanism. Subsequently, the reduced diesel/MTHF2 mechanism was obtained by improving the combined five-component mechanism based on sensitivity analysis. Finally, the proposed mechanism was validated with selected experimental data of ignition delay times, flame species concentrations and laminar flame speeds. In addition, the new measurements from diesel/MTHF2 dual-fuel engine combustion were obtained and then utilized to further assess the developed mechanism. Overall, the developed diesel/MTHF2 mechanism can be used for diesel and MTHF2 dual-fuel engine combustion simulation.

A new dual matrix burner for one-dimensional investigation of aerosol flames

In spray-flame synthesis of nanoparticles, a precise understanding of the reaction processes is necessary to find optimal process parameters for the formation of the desired products. Coupling the chemistries of flame, solvent, and gas-phase species initially formed from the particle precursor in combination with the complex flow geometry of the spray flame means a special challenge for the modeling of the reaction processes. A new burner has been developed that is capable to observe the reaction of precursor solutions frequently used in spray-flame synthesis. The burner provides an almost flat, laminar, and steady flame with homogeneous addition of a fine aerosol and thus enables detailed investigation and modeling of the coupled reactions independent of spray formation and turbulent mixing. With its two separate supply channel matrices, the burner also enables the use of reactants that would otherwise react with each other already before reaching the flame. These features enable the investigation of a wide range of flame-based synthesis methods for nanoparticles and, due to the flat-flame geometry, kinetics models for these processes can be developed and validated. This work describes the matrix burner development and its gas flow optimization by simulation. Droplet-size distributions generated by ultrasonic nebulization and their interaction with the burner structure are investigated by phase-Doppler anemometry. As an example for nanoparticle-forming flames from solutions, iron-oxide nanoparticle-generating flames using iron(III) nitrate nonahydrate dissolved in 1-butanol were investigated. This effort includes measurements of two-dimensional maps of the flame temperature by a thermocouple and height-dependent concentration profiles of the main species by time-of-flight mass spectrometry. Experimental data are compared with 1D simulations using a reduced reaction mechanism. The results show that the new burner is well suited for the development of reaction models for precursors supplied in the liquid phase usually applied in spray-flame synthesis configurations.

A new reduced reaction mechanism of the surrogate fuel for RP-3 kerosene

By combining the reaction class-based global sensitivity analysis (RC-GSA) methodology, species sensitivity analysis (SSA) methodology, decoupling method and genetic algorithm (GA), a reduced reaction mechanism of the surrogate fuel (10% n-dodecane/14% n-decane/30% isohexadecane/36% methylcyclohexane/10% toluene, in mole fraction) for RP-3 kerosene was constructed. As an example, the detailed construction process of skeleton mechanism of methylcyclohexane (MCH) was presented, and the skeleton mechanism constructions of other components in the surrogate fuel were similar to that of MCH. First, the dominant reaction classes in the fuel-relevant mechanism of MCH were recognized by the RC-GSA, the representative species in each retained reaction classes were selected by the SSA, and the skeleton fuel-relevant mechanism of MCH was developed. Second, through combining the skeleton fuel-relevant mechanism of MCH with the reduced reaction mechanism of C0-C3 by the decoupling method, the initial skeleton mechanism of MCH was obtained. Third, based on the GA, the rate constants of fuel-relevant reactions in the initial skeleton mechanism of MCH were optimized to enhance the prediction performance. Finally, by coupling the skeleton reaction mechanisms of n-dodecane, n-decane, toluene, isohexadecane, MCH, and the reduced reaction mechanism of C0-C3, a reduced mechanism (containing 121 species and 469 reactions) of the surrogate fuel for RP-3 kerosene was formed. The predicted main species concentrations during the oxidation process in the jet-stirred reactor, the ignition delay times in the shock tube and laminar flame speeds in the constant volume bomb by this reduced mechanism are in good agreement with the corresponding experimental data of RP-3 kerosene.

Numerical Investigation on the Performance of a 4-Stroke Engine with Different Passive Pre-Chamber Geometries Using a Detailed Chemistry Solver

Pre-chamber turbulent jet ignition represents one of the most promising techniques to improve spark ignition engines efficiency and reduce pollutant emissions. This technique consists of igniting the air-fuel mixture in the main combustion chamber by means of several hot turbulent flame jets exiting a pre-chamber. In the present study, the combustion process of a 4-stroke, gasoline SI, PFI engine equipped with a passive pre-chamber has been investigated through three-dimensional CFD (Computational Fluid Dynamics) analysis. A detailed chemistry solver with a reduced reaction mechanism was employed to investigate ignition and flame propagation phenomena. Firstly, the combustion model was validated against experimental data for the baseline engine configuration (i.e., without pre-chamber). Eventually, the validated numerical model allowed for predictive simulations of the pre-chamber-equipped engine. By varying the shape of the pre-chamber body and the size of pre-chamber orifices, different pre-chamber configurations were studied. The influence of the geometrical features on the duration of the combustion process and the pressure trends inside both the pre-chamber and main chamber was assessed and discussed. Since the use of a pre-chamber can extend the air-fuel mixture ignition limits, an additional sensitivity on the air-fuel ratio was carried out, in order to investigate engine performance at lean conditions.