Experimental investigation of the combustion of natural gas/hydrogen mixtures in a novel laboratory combustor

Silva, Marco; Pacheco, Gonçalo; Mendes, Miguel; Coelho, Pedro

Key information

Authors:

Silva, Marco; Pacheco, Gonçalo (Gonçalo de Sousa Pina Pernicha Pacheco); Mendes, Miguel (Miguel Abreu de Almeida Mendes); Coelho, Pedro (Pedro Jorge Martins Coelho)

Published in

June 2025

Abstract

The combustion of natural gas/hydrogen mixtures is experimentally investigated in a laboratory-scale combustor. A distinctive feature of this combustor is the injection of secondary air through holes in a plenum located at the top of the combustor in a direction opposite to the fuel jet, which is supplied along with the primary air through a swirl burner operating at a constant thermal power of 5 kW. The influence of the fuel composition (0% - 100% vol. H2 in the mixture), excess air coefficient (=1.3-1.7) and primary air percentage (=50%-100%) on the temperature and flue gas composition was investigated. The experiments were performed using thermocouples and gas analysers. The results show that the increase of the hydrogen in the mixture, for fixed excess air and primary air percentage, has a relatively small influence on the temperature when the hydrogen content in the fuel ranges from 0 to 80% (vol.) but a greater impact when pure hydrogen is burnt. At λ=1.3, CO emissions are excessively high when secondary air is used, indicating incomplete combustion, but decrease with higher excess air, reduced secondary air, or hydrogen content above 20%. At λ=1.3, NOx emissions increase with hydrogen content, decrease slightly as α rises from 50 to 66.7%, but increase for =100%, reaching a peak for pure hydrogen At higher excess air coefficients, NOx emissions vary weakly up to 80% hydrogen but rise for pure hydrogen, staying below 50 ppm. Secondary air reduces NOx emissions but increases CO emissions, making it effective only if the excess air keeps CO emissions within acceptable limits.