NOx emission and energy conversion efficiency studies on ammonia-powered micro-combustor with ring-shaped ribs in fuel-rich combustion

Abstract

Ammonia, as an alternative option of conventional hydrocarbon energy source, can achieve carbon free emission. However, the production of NOx is responsible for photochemical pollution and human health. In order to reduce NOx emission at the premise of guaranteeing energy conversion efficiency, three micro-combustors with different ring-shaped ribs in a cross-sectional view of 1) rectangular, 2) Ո-shaped and 3) Ս-shaped are proposed and fuelled by NH3. Extensive numerical comparisons are made with 3D models built by structured mesh. The effects of 1) inlet velocity, 2) equivalence ratio, 3) rib shape and 4) key parameters of these ribs are evaluated. In addition, the normalized sensitivity of NO formation and related reaction pathways are analyzed. It is found that the double-rib structure is more conducive to achieving better thermal performance. Besides, HNO is found to contribute the most of NO, while NH and NH2 are beneficial to the consumption of NO. When the dimensionless distance x between the rib and the combustor inlet is 3/9, comparing the condition of Φ being 1.1 and 1.0, NO emission is reduced by 47.0%, while the radiation efficiency is only decreased by 1.76%. This work has proven that a high energy conversion efficiency and a low NO emission can be achieved at the same time by properly optimizing the internal structure of the combustor in fuel-rich condition.