Burning velocity measurements of nitrogen-containing compounds

Burning velocity measurements of nitrogen-containing compounds, i.e., ammonia (NH₃), methylamine (CH₃NH₂), ethylamine (C₂H₅NH₂), and propylamine (C₃H₇NH₂), were carried out to assess the flammability of potential natural refrigerants. The spherical-vessel (SV) method was used to measure the burning velocity over a wide range of sample and air concentrations. In addition, flame propagation was directly observed by the schlieren photography method, which showed that the spherical flame model was applicable to flames with a burning velocity higher than approximately 5 cm s⁻¹. For CH₃NH₂, the nozzle burner method was also used to confirm the validity of the results obtained by closed vessel methods. We obtained maximum burning velocities (S_u0,max) of 7.2, 24.7, 26.9, and 28.3 cm s⁻¹ for NH₃, CH₃NH₂, C₂H₅NH₂, and C₃H₇NH₂, respectively. It was noted that the burning velocities of NH₃ and CH₃NH₂ were as high as those of the typical hydrofluorocarbon refrigerants difluoromethane (HFC-32, S_u0,max = 6.7 cm s⁻¹) and 1,1-difluoroethane (HFC-152a, S_u0,max = 23.6 cm s⁻¹), respectively. The burning velocities were compared with those of the parent alkanes, and it was found that introducing an NH₂ group into hydrocarbon molecules decreases their burning velocity.