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The spatial and thermal dispersals of hydroxyl (OH), formaldehyde (CH2O), and other minor species were acquired using various detailed reaction mechanisms in a weak flame of stoichiometric methane and air mixture at ambient pressure. A weak flame was simulated inside a microflow combustor with a prescribed temperature profile that released a very small amount of heat. A wide reaction zone (~ 1 cm) was observed for the methane and air flames compared to the normal/conventional flames. A detailed oxidation analysis was performed based on the normal and weak flame simulations. The computational flame structure was assessed using the experimental results available in the existing literature. Numerical modeling under experimental conditions with various detailed mechanisms predicted a similarly wide reaction zone. However, species production and consumption temperatures varied according to the different mechanisms used in the present study. The GRI mech 3.0 shows a typical two-peak heat release rate profile. The initial breakdown of the fuel is vital for such scattering. The production of OH radicals governs the initial breakdown of fuel at intermediate temperatures. The present investigation is useful for understanding the chemistry of intermediate species in different fuel-air mixtures, especially at intermediate temperatures of 800-1200 K. [ABSTRACT FROM AUTHOR]

The present work reports experimentation and numerical simulations of laminar burning velocity, emission analysis, and flame structure of dimethyl ether-hydrogen mixtures. The volumetric hydrogen addition is considered into the DME fuel for a range of mixture equivalence ratios (0.6< ϕ < 1.7). The initial mixture temperature is raised to 373 K at constant atmospheric pressure of 1.0 bar. The heat flux method is utilized to investigate the laminar burning velocity in laminar premixed planar adiabatic flames. The laminar burning velocity (LBV), along with the flame position and emission measurements, are extracted from these flames. The computations were performed with freely propagating flames (LBV, species, sensitivity, etc. data), and the burner stabilizes flames (flame position and emission analysis) for the same mixture and initial conditions using various detailed mechanisms. An emphasis is paid to a newly developed Shrestha mechanism, which includes a radiation model and NO sub-mechanism. Both experimental data and competition results were validated against the pure DME air mixture data available in the existing literature, and further analysis was carried out. It is observed that planar flames can be stabilized only up to a hydrogen addition of 40%. Adding hydrogen enhanced the flame temperature, heat release rates, and burning velocity while reducing the CO and NO emissions. A slight shift of peak burning velocity on the rich side of the equivalence ratio (from 1.05 to 1.2) is observed with hydrogen addition (0–40%). The mixture temperature also enhances the flame temperature and laminar burning velocity. It is interesting to note that hydrogen-added mixtures show a relatively lower dependency on initial mixture temperature. The variation of dominant species and heat release rates are also discussed in detail. The sensitivity analysis is carried out to get information on dominant reactions participating in the combustion of DME hydrogen mixtures. • Influence of H2 content on the LBV of premixed laminar DME flames was measured. • Influence of H2 content on the NOx Emission and temperature was measured. • Study of the flame structure characterized by the HRR and species profiles. • Experimental data compared with simulation results of 5 reaction mechanisms. [ABSTRACT FROM AUTHOR]

The current work presents computational investigations of biogas-hydrogen blends' combustion characteristics for various thermo-physical conditions relevant for practical combustor applications. The numerical simulations were performed using 0-D SENKIN and 1-D PREMIX codes, whereas chemical kinetics is modelled using the GRI Mech 3.0 mechanism. Biogas composition represented by 60CH 4 /40CO 2 % (v/v) is blended with different H 2 concentration varying from 0 to 50% (v/v) in the fuel. The effect of initial temperature and pressure on ignition delay, laminar flame speed (S u), flame temperature (T ad), species concentrations (C i), and heat release rate profiles is investigated. The results showed that GRI-Mech 3.0 predictions are in good agreement with the available experimental ignition delay data for CH 4 /CO 2 -air mixture for stoichiometric ambient condition (P = 0.1 MPa and φ = 1). For the high-temperature oxidation, GRI-Mech 3.0 has accurately predicted S u available from literature for pure biogas (R H = 0.0) under a wide range of equivalence ratios (φ = 0.7–1.4) for ambient conditions. The computational analysis was then extended for R H ranging from 0.0 to 0.5 over a wide range of equivalence ratio (φ) = 0.7–1.4, initial temperatures (T) = 300–600 K and initial pressures (P) = 0.1–7.0 MPa. These results obtained were used to develop a new analytical correlation for the laminar flame speed (S u = S u o (φ , R H ) T T u α (φ) P P u β (φ , R H ) ) in terms of operating conditions. The results show that hydrogen addition to the biogas improves both the flame speed and ignition delay. The extent of reduction in flame speed due to elevation of initial pressure is a linear function of hydrogen addition to biogas. Furthermore, the sensitivity analysis was studied to assess the influence of hydrogen added to the biogas using laminar flame speed sensitivity coefficient (σ). The understanding of these mixtures' combustion characteristics at given initial conditions leading to feasibility conformity of optimal blends of biogas/hydrogen mixtures for the design improvement of practical combustors is discussed. • New analytical correlation for biogas/H 2 -air S u (= S u o (φ , R H ) ( T T u ) α (φ) ( P P u ) β (φ , R H ) ) for combustor relevant conditions. • 5 to 10 times reduction in ignition delay with 10–50% H 2 addition to biogas (60CH 4 /40CO 2). • 2 to 3 times increase laminar flame speed (S u) with 10–50% H 2 addition to biogas. • 2 to 3 times increase in HRR peak with 50% H 2 addition to biogas (T = 300 & 600 K). • 1.5 to 2 times increase in peak H and OH peak radials with 50% H 2 addition to biogas. [ABSTRACT FROM AUTHOR]

The effect of hydrocarbon addition on tip opening of lean and stoichiometric hydrogen-air flames is studied computationally by performing two-dimensional numerical simulations. The numerical study reveals that the flame tip of the H 2 -air burner stabilized flame is open at lean and stoichiometric mixture conditions. The flame tip closes upon hydrocarbon addition. The tip closing is mainly affected by preferential diffusion of the multi-component mixture and the stretch effects. In the addition of light hydrocarbon (CH 4), the tip closing starts at a higher percentage of hydrocarbon addition in H 2 -air flames. Whereas, upon the addition of heavy hydrocarbons such as propane and butane in H 2 -air flames, tip closing starts with a lesser amount of hydrocarbon addition. Temperature, OH mole fraction and heat release rate have been investigated, focusing on the flame structure at the tip. The tip opening regime diagram for H 2 –CH 4 -air, H 2 –C 3 H 8 -air and H 2 –C 4 H 10 -air mixtures are presented. • Effect of hydrocarbon addition on the tip opening of H 2 -air flames is studied. • Addition of hydrocarbon increases the intensity of burning at the tip. • Tip opening is strongly depended on preferential diffusion for HC-H 2 -air flames. • Tip closing occurs earlier by adding higher hydrocarbons compared to CH 4 addition. • Tip opening regime is presented for lean and stoichiometric HC-H 2 -air flames. [ABSTRACT FROM AUTHOR]

• Detailed physicochemical characterizations of date palm wastes and their blend were measured. • KAS and OFW models were used to estimate pyrolysis kinetic parameters. • Increasing heating rates shifted TG profiles to higher temperature ranges. • Date palm waste pyrolysis was profitable at high heating rates. • This comprehensive study could be useful for future combustion studies of date palm wastes. TGA has been used to evaluate the thermal degradation profiles and kinetic parameters for the pyrolysis of date leaves, date seeds, and leaf stems and their blend at various heating rates (β) in N 2. Using Kissinger–Akahira–Sunose (KAS), and Ozawa-Flynn-Wall (OFW), kinetic parameters like activation energy (E) and frequency factor (A) were estimated. The diffusion, reaction order, and power law models were used to estimate the frequency factors based on the (E) values obtained from the OFW and KAS approaches. Thermal degradation profiles showed two major loss processes: volatilization of cellulose, hemicelluloses, and lignin; and slow oxidation of the residual char. The findings demonstrated that as β increased, the TG profiles shifted to higher temperature ranges. The date palm's decomposition was not favourably reflected by the high (ΔG av) values obtained. The high (ΔS av) values obtained using OFW compared to KAS confirm these materials' high reactivity. The average activation energies (E av) for the different parts of the date palm wastes ranged between 86 and 117 kJ/mole as predicted by the KAS method, while they were between 92 and 120 kJ/mole using the OFW method. The calculated frequency factor (A) values, evaluated by the KAS and the OFW methods, ranged between 0.0 and ∼ 0.8 × 1019 min - 1. The difference in (E av) values between the KAS and OFW techniques is no greater than 8 kJ/mole. For the diffusion models of DSW, DL, and Blend, the best frequency distribution profiles are essentially normal, and the blend exhibits high frequency (A) values in a relatively constrained range of (α). That denotes quick and efficient pyrolysis. The pyrolysis index (CPI) significantly increased as β increased, indicating that pyrolysis was profitable at high heating rates. The volatile release index (D dev) increases significantly with increasing (β) value, showing that volatiles was easier to release at a high heating rate. [ABSTRACT FROM AUTHOR]