Effects of hydrogen addition and turbulence on ignition and meso-scale flames of propane mixtures

Abstract

This study has investigated experimentally the effects of hydrogen addition and turbulence on the ignition and the flame-kernel development characteristics in isotropic and homogeneous turbulence for propane mixtures. In this study, the lean-and rich-fueled hydrogen added propane mixtures with different equivalence ratios (=0.5~1.4) and hydrogen additional rates ( H =0.0~1.0) are prepared, while maintaining the laminar burning velocity (S L0 =25 or 15 cm/s). First, in order to investigate the ignition and flame-kernel development in quiescence, the minimum ignition energy Ei min and the relationship between the flame radius and the burning velocity of meso-scale laminar flames in the range of flame radii r f approximately from 1 to 5 mm are examined quantitatively by using sequential schlieren photography in a constant volume vessel. Then, the experiments in isotropic and homogeneous turbulence are carried out for two turbulence level with the turbulence intensity u' being approximately 0.35 and 1.76 m/s. Ei min for each mixture is also defined experimentally at each u'. It is found that the effects of hydrogen addition and turbulence on the ignition and the burning velocity of meso-scale flame characteristics are much different between the lean and the rich hydrogen added propane mixtures. It also becomes clear that there is a good relationship between Ei min characteristics in turbulence and Lewis number or the Markstein number. Additionally, the transition region of the minimum ignition energy could be summarized regardless of ,  H and u'/S L0 by using the proposed turbulent Karlovitz number based on the burning velocity of the meso-scale flame in quiescence.