Addressing NOX formation mechanisms of NH3/H2 dual-fuel flame under DBD plasma-assisted combustion resolved by intermediate radicals analysis

Abstract

In order to attain carbon-neutrality, the implementation of zero-carbon fuel containing ammonia (NH3)/hydrogen (H2) has become more and more practically popular. This work focuses on addressing the combustion performance and nitrogen oxide (NOX) formation mechanisms of dielectric barrier discharge (DBD) plasma-assisted NH3/H2 dual-fuel flames at varied plasma voltages (VAC) and hydrogen ratios (ZH2), which were resolved by PLIF and chemiluminescence techniques concurrently. The analytical results obtained show that VAC had positive effectiveness on contributing to NOX emissions with a threshold of VAC = 11 kV found for triggering NOX formation. With VAC increased from 11 kV to 12.5 kV constantly, NOX grew dramatically by 8.3%–12.3% (ZH2 elevated from 0.2 to 0.3). This phenomenon was mainly because of the growing propagation of OH radicals being faster than that of NH2 radicals. Besides, three NOX formation regions, including low-formation region, medium-formation region and high-formation region were determined, which essentially reflected that hydrogen ratio predominated over discharge voltage on forming NOx. Moreover, the inter-relationship between flame surface density (FSD, revealing combustion intensity) and NOX has been comprehensively explored. And high DBD-VAC (with low hydrogen blending ratio) was found to significantly promote the FSD resulting in better combustion intensity, but caused inappreciable NOX formation. In upcoming future application, high voltage of DBD plasma could be utilized for replacing high hydrogen blending ratio in ammonia/hydrogen combustion, to obtain promotional combustion intensity with effective NOX control.