Effects of Fuel Preinjection on Mixing in Mach 1.6 Airflow

Abstract

The effects of injection behind a pylon upstream of a supersonic combustion chamber were evaluated for liquid JP-10 and gaseous ethylene. A generic, rearward-facing, rectangular step was used as the primary ameholding mechanism. A pilot-hydrogen ame injected from the base of the step provided ignition. The fuel was injected from a 1.5-mm-diam wall ori ce behind a thin triangular cross section pylon placed in the isolator at 10 step heights upstream of the step. The role of the pylon is to facilitate the penetration and the spreading of the liquid jet. Tests were performed under connected-pipe conditions in a Mach 1.6 air ow channel and air stagnation temperatures to 900 K, corresponding to the beginning of the hypersonic ight regime. The hydrogen, ethylene, and JP-10 ow rates were modulated during the tests and wall pressures and temperatures were measured along the duct and in the recirculation region. Shadowgraph imaging indicated the effect of injection on the isolator shock train and the combustion chamber mixing. Combustion without upstream ashback has been observed with isolator JP-10 equivalence ratios to 0.5. Nomenclature D= diameter, cm H = height of rearward-facing step, 12 mm h = jet penetration height, cm P = pressure, KPa, MPa q = dynamic pressure ratio T = temperature, K X = axial location, cm Y = transverse location parallel to contoured sides of nozzle, cm Z = transverse location perpendicular to contoured sides of nozzle, cm g = ef ciency U = equivalence ratio Subscripts air = air property C2H4 = ethylene property fuel = fuel property H2 = hydrogen property inj = injector property JP-10 = JP-10 property jet/air = ratio of jet/air property mix = mixing 0 = stagnation property 32 = sauter mean diameter = freestream property

Performance of Pylons Upstream of a Cavity-Based Flameholder in Non-Reacting Supersonic Flow (Postprint)

“…The pylons' optimal heights, widths and distances from the injection port are determined from previous computational methods 6 and correlated to sizes used in prior experimentation. 7,8 Designs are determined from the top two configurations which show enhancement of fuel penetration. A schematic of the pylon and injector port design used in this research is given in Figure 1 below.…”

“…Pylon designs were based on the two best geometries determined from a computational study, 6 and correlated with sizes used in separate experimental work. 7,8 The research showed that pylons improved penetration and mixing potential over a baseline transverse injection case without a pylon. However, due to the techniques used, information on aerodynamic losses could not be obtained.…”

Experimental Studies of Pylon-Aided Fuel Injection into a Supersonic Crossflow

“…If a flammable mixture of fuel and air resides in the boundary layer, it is possible that combustion could occur well upstream of the combustor, resulting in potentially catastrophic consequences. Results from these studies [11][12][13] suggested that pylon-aided fuel injection could enhance the fuel jet penetration into the supersonic flow, compared with simple wall injection without a pylon. Results also suggested that little, if any, fuel remained in the near-wall region.…”

“…Pylon-aided fuel injection has been investigated as a method for introducing liquid or gaseous fuel into the supersonic airstream in the inlet duct well upstream of the combustor [11][12][13]. In this approach, a small aerodynamically shaped fin (called a pylon) is positioned just upstream of a fuel injector.…”

“…1; the details of each of the three configurations employed in this study are provided in Table 1. These pylons were designed based on earlier results [11][12][13]. Figure 2 contains a schematic of a typical pylon-injector configuration as installed into the flowpath.…”