Preliminary investigation on the influence of hydrogen addition in air/C2H4 premiixed flames

Recent research and development in the area of combustion have been motivated by the commitment of preserving a clean environment and to reduce energy consumption. In this direction, hydrogen-hydrocarbon hybrid fuels have received increasing attention. Blends of hydrogen and hydrocarbons show an improved ignitability and flame stability, especially in the lean burning regimes where stable combustion of hydrocarbons is extremely difficult [1]. The use of hydrogen blended with traditional hydrocarbon fuels, such as natural gas, extends low CO emissions to leaner mixtures in swirl-stabilized flames through its effect on flame chemistry [2]. In fact, changes in fuel composition affect both the chemical and physical processes occurring in flames. Few of these issues are clearly understood and an important research field consists of identification and understanding of the chemical effects of additives, like hydrogen, on soot formation. The influence of hydrogen addition to fuel on temperature and soot formation in co-flow laminar diffusion flames of ethylene, propane, butane and methane has been experimentally studied [3,4]. It was found that while methane exhibits a peculiar behavior [4], in the case of propane and butane flames, hydrogen and helium addition reduces soot by the same amount showing that hydrogen has mainly a dilution effect. On the contrary, in the ethylene flame hydrogen addition reduces soot more than helium, indicating also the presence of a chemical route for soot reduction. More recently, Guo et al. [5], using a computational approach, suggested that the chemically inhibiting effect of hydrogen addition on soot formation can be ascribed both to the H radicals concentration reduction in the surface growth region and to the higher H2 concentration in the lower region of the diffusion flame. In this work an experimental study, concerning temperature and extinction measurements, has been carried out on laminar premixed ethylene/air and ethylene/H2/air fuel-rich flames. The results confirm that the presence of hydrogen in the fuel results in an overall suppression of soot formation. Further studies are needed for a deeper understanding of the possible competitive phenomena involved in the process.