Byungil Choi

Correlation between Hypermixer and Fuel Injection Locations

An experiment was conducted to understand the relation between a wall-mounted alternating-ramp-wedge type hyper mixer and transverse injectors with two different injection locations in a supersonic flow. Three experimental techniques, such as a schlieren visualization, a gas-sampling method, and a stereoscopic particle image velocimetry, were employed to study flowfield having velocity components and vortex structures induced by the interaction between the hyper mixer and the transverse injections, and also to compare the difference of mixing performance of the hyper mixer driven by the different injection location. For normal 1 injection case, an injection hole is located under the compression wedge, so injected helium is immediately impinged on the wedge and widely spread downstream, leading to enhancing mixing performance and holding helium in the mixing layer. On the other hand, for normal 2 injection case, helium is injected downstream of the hyper mixer, thus two flow structures created from the hyper mixer and the transverse injection interact with each other; as momentum flux ratio is increased, the flow structure from the transverse injection plays a significant role on the mixing region, and plenty of helium is penetrated into the supersonic flow.

Flowfield Characteristics of a Hypermixer Interacting with Transverse Injection in Supersonic Flow

Nonreacting experiments were conducted at Mach 2 to understand the relationship between a wall-mounted alternating-ramp-wedge-type hypermixer and transverse injection compared with a step mixer. Experimental techniques such as schlieren visualization and stereoscopic particle image velocimetry were employed to study the three-dimensional flowfield with vortex structures induced by the interaction between the mixer and transverse injection.Without injection, the hypermixer creates a region that contains vortical motions.When a transverse jet is injected in the vortical region, flowparameters onmixing performance, such as the penetration height, vorticity, and turbulent stress, are improved. Three turbulent-stress components show relatively distinct distributions, and strong turbulent stresses are observed at the upper side of the jet plume. Turbulent-stress distributions are significantly associated with strain rate, which peaks along the sonic line of the jet plume.

Effect of a Vent Slot Mixer with a Plasma Jet Torch in Unheated Supersonic Flow

Mixing and combustion experiments were conducted in a supersonic wind-tunnel of Mach number 2. In the current work, a new idea for dual-mode scramjet engine was simply introduced, and a new mixer, vent slot mixer, was developed to perform the supersonic combustion. The new idea of flight vehicle is based on forced ignition in cold supersonic inflow condition. Thus, an igniter such as a plasma jet torch was used to ignite fuel-air mixture in the combustor. The vent slot mixer shows high mixing efficiency, which is significantly sensitive to fuel injection locations. The mixing in the recirculation region is enhanced by the interaction between the fuel injectant and inflow air through the vent slot. The plasma jet torch ignites the fuel-air mixture within the plasma jet plume (hot gas zone), and its combustion region is mainly distributed on the lower wall. Thus, the combustion shows good performance when the fuel injectant is distributed around the plasma jet plume on the lower wall. In cold inflow condition, thermal choking in the combustor occurs for low equivalence ratio without a diffuser. Although the thermal choking occurs in the combustor, the combustion region on the lower wall cannot intrude into the main flow in the cold inflow condition.

Development of a New Supersonic Mixier for Dual-Mode Scramjet Engine Combustor

The Mach 2 hydrogen–air supersonic combustor model without diffuser was designed and tested in atmospheric inflow condition. A new supersonic mixer, which was vent slot mixer (VSM), was developed and confirmed its performance as a mixing device. At low enthalpy inflow condition, plasma jet torch was used as the igniter and the flame-holder. The VSM showed that the interaction between the fuel and the air through the vent spread the fuel to the spanwise direction in the recirculation region. The shock train structure generally depends on the combustion pressure, and the combustor condition becomes the unstart condition with combustion pressure increase. Although the mixer loses its mixing efficiency under the shock train, the VSM shows that it stabilizes the combustion around the vent. Therefore, the VSM has distinct characteristics for the mixing efficiency and the combustion stabilization.

Characteristic Study on Effect of the Vent Mixer to Supersonic Fuel-Air Mixing with Stereoscopic-PIV Method

․ Byungil Choi*** ․ Toshinori Kouchi*** ․ Goro Masuya***ABSTRACT Vent mixer can provide main flow directly into a recirculatio n region downstream of the mixer to enhance fuel-air mixing efficiency. Based on experimental results of three-dimensional velocity, vorticity and turbulent kinetic energy obtained by a stereoscopic PIV met hod, the performance of the vent mixer was compared with that of the step mixer which was used as a basic model. Thick shear layers of the vent mixer induced the increase of the penetration heigh t. The turbulent kinetic energy mainly distributed along a boundary layer between the main flow and th e jet plume. This turbulent field activates mass transfer in a mixing region, leading to the mixi ng enhancement.초 록 벤트 혼합기는 혼합기 후류에 존재하는 재순환 영역으로 공기를 유입시켜 연료-공기 혼합을 증대시키는 혼합기이다. Stereoscopic PIV기법을 통해 얻은 3차원 속도, 와류, 난류운동에너지를 토대로 계단형 혼합기를 기본 모델로 하여 벤트 혼합기의 성능을 분석하였다. 벤트 혼합기는 두터운 전단층으로 인해 높은 침투거리를 보였으며, 난류운동에너지는 주로 주유동과 제트유동의 경계면을 따라 분포하였다. 이 난류 영역은 혼합영역 내에서 활발히 물질전달을 일으키며, 혼합 증대를 가져온다. Key Words: Vent Mixer(벤트 혼합기), Stereoscopic PIV(3차원 PIV), Vorticity Field(와류장), Counter- rotating Vortex Pair(한 쌍의 회전하는 와류), Turbulent Kinetic Energy(난류운동 에너지)

Effect of Fuel Injection Locations with a Hyper Mixer in Supersonic Combustion

A reacting-experiment was conducted to understand the relation between a wallmounted alternating-ramp-wedge type hyper mixer and various injection locations in unheated supersonic flow. The hydrogen gas and a plasma jet torch were used as the fuel and the igniter, respectively. The parallel injection method shows the maximum combustion efficiency for the forced ignition. This is because the fuel-air mixture can be ignited in the heat source (plasma jet) and providing the fuel-air mixture to the plasma jet, i.e ., the parallel injection, is very effective to enhance the combustion efficiency. In the cold main flow, the combustion region is restrained and affected by the location of the plasma jet.