In this study, a reduced 50 species 373 elementary chemical mechanism is developed for the high-temperature combustion of H2/CO/C1–C4 compounds. The reduced skeletal mechanism, based on the detailed skeletal USC 2.0 mechanism (111 species, 784 reactions), is used to study the ignition and combustion characteristics of the H2/H2–CO and C1–C4 hydrocarbons. It is found that the reduced skeletal mechanism can reproduce the results from the detailed USC 2.0 mechanism with a maximum error of less than 12% in the ignition delay times under a range of operating conditions with P = 1–20 atm, T = 900–2000 K, and ϕ = 0.3–2.0. The applicability of the reduced skeletal mechanism is then demonstrated numerically in an industrial gas swirl burner for a 100% C3H8 + air non-premixed turbulent swirl-stabilized flame. The profiles of radial temperature and mole fraction of CO at various axial distances are validated with existing experimental data and are found to be in good agreement. It is therefore established that the reduced skeletal mechanism can be utilized for rapid implementation in a commercial computational fluid dynamics (CFD) package for combustion analysis. It is found that the central-processing-unit (CPU) time cost of the skeletal mechanism is about one-third of that of the detailed USC Mech 2.0 mechanism for the ignition delay and laminar flame speed simulations and is about half of that of the detailed USC Mech 2.0 for non-premixed CFD simulations using a laminar flamelet approach. The present results demonstrate that the reduced skeletal mechanism can provide better scope for studying the combustion characteristics of C1–C4 hydrocarbons at different pressure conditions and compositions.

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The present work investigates both the autoignition and the combustion characteristics on highly preheated and diluted combustion of laminar premixed stoichiometric CH4/O2/N2 mixture in a cylindrical combustor operating at elevated pressure. The analysis has been carried out for a range of operating parameters such as reactant preheat temperature of 1100-1500 K, combustor pressure of 1-10 atm, and highly diluted mixture, which is achieved by decreasing the oxygen content in the oxidizer from 21 to 3% in volume basis. The simulations have been carried out using the laminar premixed adiabatic PFR (plug flow reactor) model of Ansys Chemkin Pro. Twodimensional pictorial representation is carried out using finite volume-based CFD code Ansys Fluent 19.2. Finite-rate chemistry with detailed chemical mechanism GRI Mech 3.0 is used for combustion analysis. The results show that OH and HCO mole fractions are decreased with increased combustor pressure and N2 dilution (or decreased O2 content) while it increases with the reactant's temperature. Also, it has been found that by reducing the oxygen content in the mixture, the flame gets stabilized far away from the combustor inlet. In contrast, an increase in combustor pressure and reactant temperature stabilize the flame towards the combustor inlet. The flame stabilization characteristics at different locations of the combustor are explained in terms of ignition delay time, which is calculated using the closed homogenous reactor (CHR) model available in the Ansys Chemkin Pro package. The flame peak temperature decreases with an increase in N2 dilution and increases with increasing the reactant temperature. Moreover, the peak temperature varies marginally with increasing the combustor pressure. Finally, a regime diagram is prepared to show the various combustion mode such as HiTAC, MILD combustion, and No ignition region as a function of O2 content and reactant temperature for different operating pressure. The CO and NO emission are reduced with an increase in pressure in the MILD combustion region.

In this present study, computational fluid dynamics and chemical kinetic analysis are conducted to explore the formation of CO and CO2 for a fuel jet comprising C1–C4 hydrocarbon alkanes in a hot co-flow burner under a moderate or intense low-oxygen dilution (MILD) combustion environment. The fuel jet comprises three cases of fuel mixture (case 1: CH4 + H2, case 2: C3H8 + H2, and case 3: C4H10 + H2) having constant mixture density and operating under a fixed jet Reynolds number. The combustion and emission characteristics are analyzed in terms of radial profiles of temperature and mass fraction of OH, CH2O, HCO, CO, CO2, and C2H2 in the MILD combustion region. The formations of CO and CO2 are examined with the help of reacting flow analysis using the computational fluid dynamics (CFD) tool. The formation of CO is reported as maximum for case 3 and minimum for case 1. However, the reverse trend is observed in the case of CO2 formation. The reacting flow analysis from the CFD work suggests that the reaction C2H2 + O = CH2 + CO strongly influences CO formation in all three fuel mixtures cases. In the current study, acetylene is found to be the primary species that affects the CO formation in the adopted fuel mixtures and is mainly responsible for the increased CO concentration in case 3. Likewise, the formation of CO2 is majorly influenced by the reaction CO + OH = CO2 + H. The reacting flow analysis is assisted with the help of a zero-dimensional perfectly stirred reactor (PSR) model to elucidate the underlying chemistry and explore the significant reaction pathways influencing the formation of CO and CO2. The ethylene route in the reaction pathway substantially plays a vital role in the CO formation in all three fuel mixtures.

For the very first time, the present study attempts to address the heat dissipation from an isothermal ribbed sphere under the action of pure natural convection. Semi-circular ribs of different radius are superimposed azimuthally on the outer surface of a sphere. The addition of ribs on the sphere serves a dual purpose in its practical applications; beautification of electronic devices such as spherical light sources and also increase the heat dissipation from the hot surface, which prevents the electronic component from getting overheated. Finite-volume method (FVM) based axisymmetric numerical simulations are performed in the laminar flow regime for the following ranges of non-dimensional parameters: Rayleigh number (102≤=Ra≤=108), inter rib-spacing to sphere diameter (0.191≤=P/D≤=0.785), and rib-radius to sphere diameter (0.03≤=R/D≤=0.083). The main target of this study is to identify the critical parameters for heat transfer enhancement from the ribbed sphere compared to a conventional plane sphere. The results obtained from the present work show that the average Nusselt number increases with an increase in Ra and P/D, whereas it decreases as R/D increases. Effectiveness of the ribs (εrib) and critical Rayleigh numbers (Racr), corresponding to εrib=1, are also calculated. Ribs are more effective in heat dissipation at low Ra and P/D and high R/D. A correlation for the average Nusselt number is also developed in this work, which would help design a better thermal management system.