M. Owens

Effects of Mixing Schemes on Kerosene Combustion in a Supersonic Airstream

A study of kerosene combustion in a supersonic vitiated aire ow at Mach 4.75 e ight enthalpy was conducted in direct-connect tests at Mach 1.8 at a stagnation temperature of 1000 K. The effects of shockand vortex-enhanced mixing mechanisms on the combustion efe ciency were evaluated. Also included in this study were the effects of fuel heating and jet penetration. The experimental conditions corresponded to the low end of the hypersonic e ight regime. The following geometric cone gurations were employed: 1) a generic, rearward-facing step, 2 ) a modie ed rearward-facing step with beveled edges to facilitate vortex-enhanced mixing, and 3 ) a rearward-facing wedge (15 or 30 deg) placed downstream of the rearward-facing step to induce shock-enhanced mixing. In all cone gurations, a gaseous hydrogen ‐ pilot jet was injected parallel to the main e ow from the base of the rearward-facing step and the liquid kerosene was injected normal to the main e ow at three or e ve step heights downstream of the step (the step height was 10 mm). Stable kerosene combustion was obtained for a maximum injected kerosene equivalence ratio of 0.86. For efe ciency evaluation, the pilot ‐ hydrogen equivalence ratio was selected between 0.02 ‐ 0.04, while the kerosene equivalence ratio was maintained at 0.325. In all experiments, locally rich stratie ed kerosene combustion took place in a layer close to the injection wall. The wedge e ameholder contributed to an increased kerosene combustion efe ciency by the generation of shock ‐ jet interactions. The beveled-edge step improved far-e eld mixing, thereby reducing the local kerosene equivalence ratio, resulting in the highest kerosene combustion efe ciency among all cone gurations tested. Fuel heating below levels required for e ash vaporization (one-third of the e ash vaporization energy, in this case ) did not contribute to increased combustion efe ciency. On the contrary, this level of heating reduced the fuel density with adverse effects on penetration and mixing.

Effects of fuel pre-injection on mixing in a Mach 1.6 airflow

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 flameholding mechanism. A pilot-hydrogen flame injected from the base of the step provided ign.ition. The fuel was injected from a 1.5-mm diameter wall orifice behind a thin triangular cross section pylon placed in the isolator at IO 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 airflow channel and air stagnation temperatures to 900 K, corresponding to the beginning of the hypersonic flight regime. The hydrogen, ethylene and JP-10 flow 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. Stable combustion without upstream flashback has been observed with isolator JP-10 equivalence ratios to 0.5. Y Transverse location parallel’ cm to contoured sides of nozzle Z Transverse location cm perpendicular to contoured