Characterization of fuel injector mixing dynamics in an atmospheric jet-stabilized hydrogen combustor using 1 dimensional laser Raman spectroscopy

In this work, a new fuel injection concept for non-premixed jet stabilized hydrogen combustion was analysed and compared to a conventional one in an atmospheric single-nozzle FLOX® combustor. In both cases, the fuel nozzle was installed concentrically inside the air nozzle with flush nozzle exits, so that no premixing takes place before both fluids, fuel and air, enter the combustion chamber. The first fuel nozzle was a metal tube with an inner diameter of ID = 1.5 mm. The second novel fuel injector consisted of a three-armed cross-section with three outlet orifices (ID = 0.5 mm) in each arm. The effective total outlet cross-section of the injectors was kept the same at 1.76 mm 2 . To compare their performances at typical conditions for jet-stabilized combustion systems, the global operating condition was fixed with a bulk air coflow at v exit = 115 m/s preheated to T pre = 573 K, an equivalence ratio of ϕ = 0.66, corresponding to an adiabatic flame temperature of T adiabat = 2100 K and a thermal power of P th = 10.5 kW. The resulting flames were monitored using OH* chemiluminescence imaging, showing a significantly reduced flame lift-off height with the novel fuel injector. Major species concentrations and gas temperature downstream of the nozzle exit were measured using 1 dimensional laser Raman spectroscopy. The reconstructed 2 dimensional distribution of mixture fraction clearly demonstrated an enhanced fuel–air mixing and more distributed combustion with the novel injector. Additional evidence of such enhancement was found at the exhaust, with about 10% reduction in NO x emission using the novel injector.