Deflagration Characteristics of N2-Diluted CH4-N2O Mixtures in the Course of the Incipient Stage of Flame Propagation

Abstract

In this study, experimental measurements in a spherical combustion bomb were performed in order to investigate the flame propagation in N2-diluted CH4-N2O mixtures with stoichiometric equivalence ratio, at several initial pressures (0.5–1.75 bar) and ambient initial temperatures. Methane was chosen as a test-fuel, since it is the main component of natural gas, a fuel often used as a substitute to gasoline in engines with internal combustion and industrial plants. The method approached in this study is based on a simple examination of the cubic law of pressure rise during the early (incipient) period of flame propagation. The incipient stage defined by a pressure rise equal or smaller than the initial pressure, was divided into short time intervals. The burnt mass fractions (obtained using three different Equations) and flame radii at various moments of the flame propagation in the course of the incipient stage were calculated. The cubic law coefficients and corresponding laminar burning velocities at considered time intervals were also reported.

Nitrous Oxide: Oxidizer and Promoter of Hydrogen and Hydrocarbon Combustion

“…The same was reported by Parker and Wolfhard for C 2 H 2 /N 2 O flames at low initial pressures, by Wang and Zhang for C 2 H 4 /N 2 O flames in the range 0.5 to 2.0 atm, and by Naumann et al for C 2 H 4 /N 2 O flames in the range 1.0 to 10.0 bar . For lean and stoichiometric CH 4 –N 2 O–N 2 mixtures, the laminar burning velocities dependence on pressure was well described by an empirical equation: ,, where S u,0 is the reference value of LBVs, at the reference pressure p 0,ref (usually, 1 bar), and β is the baric coefficient of LBVs. The baric coefficients of CH 4 –N 2 O–N 2 stoichiometric mixtures ([N 2 ] = 40, 50, and 60 vol %) varied within 0.08 and 0.15 under the pressure range 0.5–2.0 bar. , …”

“…Numerous studies examined the combustion rate of various fuels with N 2 O, delivering a large body of measured and computed burning velocities at ambient initial conditions or under different operating conditions. Experimental data were obtained by using stationary flames anchored on burners, as either conical flames ,,,− or flat flames. ,− Nonstationary flames were examined in closed vessel experiments, by making synchronous records of the pressure and flame radius. ,,,,,,,,,,− …”

“…For lean and stoichiometric CH 4 –N 2 O–N 2 mixtures, the laminar burning velocities dependence on pressure was well described by an empirical equation: ,, where S u,0 is the reference value of LBVs, at the reference pressure p 0,ref (usually, 1 bar), and β is the baric coefficient of LBVs. The baric coefficients of CH 4 –N 2 O–N 2 stoichiometric mixtures ([N 2 ] = 40, 50, and 60 vol %) varied within 0.08 and 0.15 under the pressure range 0.5–2.0 bar. , …”

“…119 The same was reported by Parker and Wolfhard 130 for C 2 H 2 /N 2 O flames at low initial pressures, by Wang and Zhang for C 2 H 4 / N 2 O flames in the range 0.5 to 2.0 atm, 163 and by Naumann et al for C 2 H 4 /N 2 O flames in the range 1.0 to 10.0 bar. 63 For lean and stoichiometric CH 4 −N 2 O−N 2 mixtures, the laminar burning velocities dependence on pressure was well described by an empirical equation: 162,165,166…”

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

“…Methane (SIAD-Italy), 99.9% was used without further purification. Other details can be found in our previous works [7,9,56]. The experiments were carried out in the following way: (1) the methane-air mixture was prepared by partial pressure method at a total pressure of 5 bar, stored in a 10 L metallic bottle, and left for 48 h to become homogenous prior use; (2) before every test, the explosion vessel was flushed with dry air and then evacuated down to 0.1 mbar in order to avoid the traces of the burned gas which may influence the mixture composition; (3) the methane-air mixture was then introduced, at the desired pressure, and it was allowed to become quiescent to avoid the turbulence due to a fast admission; (4) the explosion was initiated by inductive-capacitive sparks whose energy was adjusted to a minimum value (≤5 mJ) to avoid any disturbing turbulence at initiation; (5) the signals of the acquisition system and ionization probes were captured, stored, and then evaluated.…”