Emissions analyses of humidified cracked ammonia swirling flames
J. Davies, Syed Mashruk, Daisuke Sato, Luca Mazzotta, D. Pugh, Agustín Valera-Medina
Abstract
Using renewably produced ammonia as a zero-carbon fuel is gaining momentum due to its ease of transportation and storage as a hydrogen vector. This is particularly true for partially cracking ammonia immediately prior to use, injecting a blend of NH 3 , H 2 and N 2 . Challenges with this fuel combination relate to the emissions of NOx and unburned NH 3 , as well as understanding flame stability for practical applications. In this study, a 20 % (vol.) cracked ammonia blend was investigated using a fully premixed swirl burner, operating at a thermal power of 10 kW with steam injection of 30 % (vol.) of the fuel and preheating inlet temperatures of up to 390 K, for a range of equivalence ratios from lean to rich. Emissions of NO, NO 2 , N 2 O, NH 3 , H 2 , O 2 and H 2 O were recorded, along with OH*, NH* and NH 2 * chemiluminescence. Additionally, a numerical investigation was conducted using CHEMKIN-PRO to elucidate the main reactions responsible for reducing emissions by providing a rate of production analysis. The 20 % (vol.) cracked ammonia blend was found to reduce NO, NO 2 and N 2 O significantly, with an increase in NH 3 emissions at rich conditions and instabilities at both lean and rich extremes, compared to the widely investigated 70/30 (vol %) ammonia/hydrogen blend. Humidification reduced NO and NO 2 emissions due to a reduction in HNO production via OH and NH but caused an increase in N 2 O by reducing the flame temperature and unburned NH 3 emissions at rich, low power conditions due to combustion instabilities. Unburned H 2 emissions however were reduced, likely relating to a reduction in exhaust temperature thermally cracking less unburned NH 3 into H 2 and N 2 .