Combustion Characteristics of Bi-Liquid Swirl Coaxial Injectors with Respect to a Recess

Abstract

Uni-element combustion tests were conducted employing double swirl coaxial injectors fed by liquid oxygen and kerosene. In this study, two major experimental parameters have been considered: the recess length and fuel swirl chamber shape. It was revealed that combustion efficiency depends mainly on the mixing mechanism for the present swirl coaxial injectors, and acoustic intensities become reduced with a decrease of the recess length. Low-frequency pressure oscillations around 200 Hz have been observed for all injectors. Dynamic behavior examined by the measurements of pressure fluctuations considerably differs for external and internal mixing based on the recess length. Internal mixing induces a mixture ratio and a total mass flow rate that vary with strong bias at a single frequency, resulting in highamplitude pressure fluctuations generated by combustion of pulsating coherent flow structures. However, the results for external mixing show that the fuel and oxidizer mixture flow carries more dispersed, multiple-wave characteristics due to the broad mixing region as well as disintegration and merging phenomena of propellant sheets before mixing.

Effects of Injector Recess and Chamber Pressure on Combustion Characteristics of Liquid–Liquid Swirl Coaxial Injectors

“…As the recess number increases above 1.0, the LOx film impinges against the kerosene film inside the fuel nozzle (internal mixing). The present injector configurations are the same as those in the previous researches (Kim et al, 2005;Seo et al, 2010a). The calculated film thickness and the swirl angle for LOx and kerosene are 0.84 and 0.40 mm and 65 and 122 , respectively.…”

“…The design momentum flux ratio of LOx to kerosene is 6.12. Typical images of water flow tests for the injectors used in the present study can be seen in Seo et al (2010a). From the water flow test, the individual spray cone angles are measured as 64 and 119 for LOx and kerosene, respectively.…”

“…The larger recess number caused time-averaged combustion chamber pressure and characteristic velocity to improve at almost constant mass flow rate and oxidizer-to-fuel ratio (Kim et al, 2005). Seo et al (2010a) indicated that the intensities of pressure oscillations generally increased with an increase in recess length. This is contrary to the result from the shear coaxial injector (Lux and Haidn, 2009).…”

“…This is contrary to the result from the shear coaxial injector (Lux and Haidn, 2009). Some researchers have observed low-frequency oscillations in liquid sheets and chamber pressure while using swirl injectors (Kim, 2007;Marchione et al, 2007;Seo et al, 2010a). In a fuel-rich gas generator composed of swirl coaxial injectors using LOx and kerosene, low-frequency pressure pulsations attenuated along with an increase of chamber pressure (Seo et al, 2010b).…”

“…The effects of the oxidizer post recess in unielement combustors with various swirl coaxial injectors were examined by Kim et al (2005) and Seo et al (2010a). The larger recess number caused time-averaged combustion chamber pressure and characteristic velocity to improve at almost constant mass flow rate and oxidizer-to-fuel ratio (Kim et al, 2005).…”