Effects of wall heat loss on emission characteristics of liquid ammonia spray combustion using a swirling burner

Liquid ammonia (LNH3) spray combustion is considered to achieve zero carbon emissions without the need for a pre-vaporization system, thereby reducing costs. It enables rapid power adjustment to cope with the intermittency of renewable energy sources. However, LNH3 evaporation absorbs energy, lowering the reaction temperature during fuel/air mixing. Low-temperature NH3 reaction has been shown to produce deleterious substances, such as N2O. Therefore, this study investigates the effects of wall heat loss (low-temperature region) on emissions during LNH3 spray combustion in a swirling burner and compares the results to those from gaseous ammonia combustion. A liner with a cooling air jacket was designed to control the low temperature region by adjusting the air flowrate passing through the cooling cavity. As wall-cooling rose from 0 to 0.8 kW (approximately 0 % to 10 % of the total enthalpy input), overall emissions analyses showed increased unburned NH3 and N2O, alongside a reduction in NO emissions on the fuel-lean side, likely due to flame quenching near the wall and decreased flame temperature. To mitigate the production of harmful emissions under increased heat loss, two-stage combustion was applied. This approach significantly reduced unburned NH3; however, N2O and NO emissions remained comparable to those from single-stage combustion. Moreover, we compared the emissions at the wall and center under fuel-lean conditions, revealing higher NO emissions and near-zero unburned NH3 and N2O emissions at the center under increased cooling air flow, highlighting the influence of wall cooling on overall emissions characteristics.