The swirling flow in a lean premixed prevaporized (LPP) combustor model (LPP chamber) is studied, making use of high-speed photography, Laser Doppler Velocimetry (LDV), sound probes, fine-wire thermocouples, and suction probes for chemical gas analysis. The experimental study, which involved parametric changes of Re , S , and { , extends from the combustor primary zone to the premixing chamber and was conducted with and without reaction, burning either gaseous propane or liquid fuel assisted with preheated air at 300 °C. Measurements show that the swirling flow mixture that enters the primary zone of the combustor chamber shows evidence of a PVC structure, for S > 0.5, that embraces the central recirculation zone (CRZ). Furthermore, reaction test results show that increasing the swirl number decreases CO and NO x concentrations at the combustor exit and reduces flame stability limits to levels close to the lean limit because of flashback. In addition, a detailed study of the reacting condition ( S =1.05, { =0.5) was performed; the results indicate that the PVC is still present, embracing the base of the CRZ and staying in the inner shear layer, where the flame should also be stabilized, and contributing particularly to an abnormal radial distribution of W rms . Large gradients of mean temperature andUnburnedHydrocarbons(UHC) concentration were found to be limited to the base of the CRZ.

The injection of green hydrogen and biomethane is currently seen as the next step towards the decarbonization of the gas sector in several countries. However, the introduction of these gases in existent infrastructure has energetic, material and operational implications that should be carefully looked at. With regard to a fully blown green gas grid, transport and distribution will require adaptations. Furthermore, the adequate performance of end-use equipment connected to the grid must be accounted for. In this paper, a technical analysis of the energetic, material and operational aspects of hydrogen and biomethane introduction in natural gas infrastructure is performed. Impacts on gas transmission and distribution are evaluated and an interchangeability analysis, supported by one-dimensional Cantera simulations, is conducted. Existing gas infrastructure seems to be generally fit for the introduction of hydrogen and biomethane. Hydrogen content up to 20% by volume appears to be possible to accommodate in current infrastructure with only minor technical modifications. However, at the Distribution System Operator (DSO) level, the introduction of gas quality tracking systems will be required due to the distributed injection nature of hydrogen and biomethane. The different tolerances for hydrogen blending of consumers, depending on end-use equipment, may be critical during the transition period to a 100% green gas grid as there is a risk of pushing consumers off the grid.