Propagation of CH4-N2O-N2 Flames in a Closed Spherical Vessel

Abstract

Flammable fuel-N2O mixtures raise safety and environmental protection issues in areas where these mixtures are used (such as: industry, research, internal combustion engines). Therefore, it is important to know their laminar combustion velocities and propagation speeds—important safety parameters for design of active protection devices against gas explosions and corresponding safety recommendations. In this paper, the laminar combustion velocities of N2-diluted CH4-N2O flames, obtained in experiments on outwardly propagating flames, at various initial pressures (within 0.5–2.0 bar) and room temperature, are reported. The experiments were made in a 0.5 L spherical cell with central ignition. The laminar combustion velocities were calculated from the constants of cubic law of flame propagation during the early stage of closed cell explosions and the expansion coefficients of unburned flammable mixtures, using the adiabatic model of the flame propagation. The expansion coefficients were determined from equilibrium calculations on flames propagating under isobaric conditions. The laminar combustion velocities were compared with data reported in the literature. Using the laminar combustion velocities and the expansion coefficients, the propagation speeds of N2-diluted CH4-N2O flames were calculated. Both laminar combustion velocities and propagation speeds decrease with the initial pressure increase.

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

“…A linear increase in the cubic law coefficients was observed when the initial pressure increased. An increase in the cubic law coefficients with the initial pressure increase was already reported in [17,23]. Referring to the example in the Figure 5 and keeping the initial pressure constant (e.g., p0 = 1.00 bar), the values of the cubic law coefficients increase from the time interval 1/4 t to the time interval t. The incipient stage of pressure-time variation during propagation of laminar flames in closed bombs gives important information regarding the formation and development of the flame core trigger off an electric spark.…”

“…A linear increase in the cubic law coefficients was observed when the initial pressure increased. An increase in the cubic law coefficients with the initial pressure increase was already reported in [17,23]. Referring to the example in the Figure 5 and keeping the initial pressure constant (e.g., p 0 = 1.00 bar), the values of the cubic law coefficients increase from the time interval 1/4 t to the time interval t. Taking into account those presented above, the cubic law coefficients were obtained for corresponding shorter time intervals of 1/4 t, 1/2 t, 3/4 t and t by means of a nonlinear regression procedure of p(t) data, assuming the validity of Equation (2).…”

“…Luo et al [22] investigated the effects of the addition of ethane, ethylene, hydrogen and carbon monoxide on the flammability limits and limiting oxygen concentrations of methane under N 2 dilution in a pipeline at atmospheric temperature and pressure. Mitu et al [23] studied the laminar burning velocities of N 2 -diluted CH 4 -N 2 O flames by experiments in a spherical bomb, at various initial pressures and room temperature.…”

Nitrous Oxide: Oxidizer and Promoter of Hydrogen and Hydrocarbon Combustion

“…A similar variation was observed for N 2 -diluted lean and stoichiometric CH 4 –N 2 O mixtures , at ambient initial conditions. Laminar burning velocities for methane–nitrous oxide mixtures were reported also by Pfahl et al and Ross, but the studied mixtures included other flammable constituents such as H 2 and NH 3 .…”

“…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. ,,,,,,,,,,− …”