Experimental, Kinetic Modeling and Morphologic Study of the Premixed Combustion of Hydrogen/Methane Mixtures

Abstract

In this work, an experimental study and kinetic characterization of the combustion process and a morphologic study of hydrogen/methane–air mixtures are presented. The experimental study was performed in an optical access cylindrical constant-volume combustion bomb. This bomb is equipped to register the instantaneous pressure during combustion and records the combustion images using the high-speed Schlieren optical technique. This provides straightforward information to compute the flame propagation speed and direct evidence of the apparition of cellularity on the flame front. Through the images of the combustion process, it is possible to conduct a morphological study of the process using a flame monitoring model. Simultaneously, by means of a two-zone thermodynamical model, with the temporal evolution of pressure as the main intake, significant parameters are determined during the combustion process of different fuels under premixed conditions: burning velocity, rate of combustion, burned and unburned temperature, burned mass fraction, and rate of heat release, among others. Experimental results are compared with kinetic modeling results obtained with the Cantera package using the Gri-Mech 3.0 kinetic mechanism. Results show that a greater percentage of hydrogen in the fuel mixture increases the burning velocity and the cellularity of the flame front surface. At the same time, leaner mixtures and higher equivalence ratios enhance the apparition of the cellularity onset in the flames. Burning velocity increases with the increase in the initial temperature and the fuel/air mixture equivalence ratio. All the results obtained were validated with other data from the literature.

The Laminar Burning Velocities of Stoichiometric Methane–Air Mixture from Closed Vessels Measurements

“…On the other hand, data computed with the Warnatz mechanism are higher than those computed with the GRI 3.0 mechanism which may be due to the fact that, in the present work, the runs with the INSFLA package were performed without taking into account the radiative energy losses. Excepting the data reported by Reyes et al [39], the computed laminar burning velocities obtained using the GRI Mech 3.0 agree well with literature data computed with the same kinetic mechanism, as it results from Table 3 where data referring to the stoichiometric mixture of methane-air at ambient initial conditions are given.…”

“…Our results ranging from 35.3 cm/s (data from spherical vessel S obtained using the burnt mass fraction) to 37.5 cm/s (data from cylindrical vessel C1 obtained using the cubic law) are within the interval of confidence described in above mentioned papers. Therefore, we can consider these values to be reliable even if, as was pointed out in [39], the method of registration of pressure-time evolution does not allow the direct observation of the flame front, and therefore, it is more difficult to analyze the dependence of the laminar burning velocity on the stretch rate, or the examination of the cellular structure of a flame at a given pressure and temperature.…”

“…Bunsen Burner 36.3 [20] Constant-volume Cylindrical vessel 34.6 [34] 37.0 [21] 39.8 [35] 36.0 [22] 44.5 [36] Heat flux 38.0 [23] 35.5 [37] 37.2 [24] 35.5 [39] 36.6 [25] Spherical vessel 36.6 [40] 35.7 [26] 36.8 [41] 36.7 [27] 37.0 [42] 36.5 [28] 34.9 [43] 35.5 [29] 33.0 [44] Counter-flow twin flames 35.0 [30] 37.6 [46] 40.0 [31] Cubic chamber 34.5 [47] 36.8 [32] 39.4 [48] All experimental methods used to determine the laminar burning velocities of methaneair mixtures have advantages and disadvantages. The Bunsen method is a simple method, but the flames are affected by curvature, instability, stretch, and heat loss [49,50].…”

“…In addition to experimental results, the laminar burning velocities of methane-air mixtures were predicted using various detailed kinetic mechanisms such as USC Mech II [4], Konnov Mech [53], Gri Mech 3.0 [7,22,33,39,54], Aramco [39] or San Diego Mech [54].…”

“…The laminar burning velocities of methane-air mixtures were measured using both constant-pressure methods (experiments using Bunsen flames [20][21][22], flat flames [23][24][25][26][27][28][29], counter-flow twin flames [30][31][32]), or constant-volume methods (experiments using cylindrical vessels [33][34][35][36][37][38][39], spherical vessels [7,33,[40][41][42][43][44][45][46], or cubic chambers [47,48]). The measurements were conducted for various equivalence ratios between 0.6 and 1.7 at various initial pressures (up to 70 atm [41]) and temperatures (up to 650 K [33]).…”