The Numerical Study of Methane Flame Characteristics in the Ammonia/Air Environment at Sub-Atmospheric Pressure

<div class="section abstract"><div class="htmlview paragraph">The low emission of carbon and minimum level of soot formation in combustion engines and turbines strategy is adopted by many countries to counteract global warming and climate change. The use of ammonia with hydrocarbon fuels can limit the formation of soot and carbon emissions due to non-carbon atoms. The current study explores the use of ammonia with air at coflow flame conditions, which was not tested before. It may give the choice for diesel cycle engines to use the ammonia either with air or fuel. The combustion and emission characteristics of methane coflow flame were studied at low pressure and air polluted by ammonia conditions. The results showed that a significant decline in carbon formation was observed when ammonia was boosted, 5-10%. The impact of sub-atmospheric pressure, 90-70 KPa, on COx development was higher than that of NH<sub>3</sub> addition, 0-5%, thanks to the lower formation of hydroxymethylium, formaldehyde, and aldehyde radical. In the environment of lower pressure, the reaction rates were reduced due to increasing molecules' interaction space. The sub-atmospheric pressure had more impact on the reduction of nitric oxide than that of nitrous oxide, and ammonia impact was greater on the increment of nitric oxide than that of nitrous oxide. The maximum reduction and increment in the profile of nitric oxide were observed ~ 42.1% at 5% NH<sub>3</sub> and 182% at 80 KPa. The acetylene species was more affected by sub-atmospheric pressure rather than cyclopropenyl radical, while ammonia highly reduced acetylene species compared to cyclopropenyl radical. The acetylene species has a lower C-H ratio, which transformed easily with another lower species after reacting with ammonia. The peak reduction was observed by ammonia 19% at 90 KPa, and by sub-atmospheric pressure 13% at 5-10% NH<sub>3</sub> acetylene profiles. The lower formation of acetylene and cyclopropenyl radicals reduced the precursor formation. The peak reduction of 14.4% at 70 KPa was observed in pyrene by ammonia enrichment and of 11.1% at 10% NH<sub>3</sub> in benzene by sub-atmospheric pressure. The impact of ammonia and sub-atmospheric pressure on soot particle number density formation in methane flame was dominant over soot volume fraction because the soot particle reaction rates were more active than that of soot volume. The peak reduction was observed about 35% at 5% NH<sub>3</sub> by pressure impact.</div></div>