Experimental Study of NH3-Simulated LPG Combustion Characteristics in a Crossflow Slot Burner

Among pathways toward carbon neutrality, substituting hydrocarbons with hydrogen-carrier fuels such as ammonia presents significant potential for carbon emission reduction. This study examines the combustion characteristics of ammonia (NH3) and simulated LPG consisting of 70% propane (C3H8) and 30% butane (C4H10) by volume blends under non-premixed conditions using a crossflow slot burner. Flame appearance, OH* chemiluminescence, flame temperature, and CO and NOx emissions were evaluated at equivalence ratios (Φ) of 0.4, 0.7, and 1.0, with ammonia fractions ranging from 0% to 70%. Increasing ammonia content decreased OH* chemiluminescence intensity, indicating a reduced radical pool and lower reaction intensity, particularly under lean conditions. Nevertheless, stable combustion was achieved at Φ = 1.0 due to improved mixing and heat recirculation. Flame temperature declined by only 9.3%, even at 70% ammonia, confirming good thermal stability. NOx emissions exhibited non-monotonic behavior, increasing at moderate ammonia fractions due to fuel-bound nitrogen and thermal mechanisms, and then decreasing at higher ammonia levels as flame temperature and radical activity diminished, while CO emissions remained low up to 50% ammonia near stoichiometric conditions but increased under ultra-lean operation because of limited oxidation kinetics. These results highlight the feasibility of simulated LPG–NH3 blends as transitional low-carbon fuels in practical combustion systems.