Jihwan Lim

Burning and Ignition Characteristics of Single Aluminum and Magnesium Particle

Ignition and burning characteristics of single aluminum and magnesium particles are experimentally investigated. Burning time, ignition delay, flame temperature, and ignition temperature were measured. The single metal particle (30-100 μm in diameter) is uplifted by an electrodynamic levitator, exposed and ignited by a CO2 laser. The thermal radiation intensity was measured using the photomultiplier tube and combustion history was monitored by high-speed cinematography. Two-wavelength pyrometry measured the temperature of the burning particles. The burning time of the Al particle is approximately 5 to 8 times longer than that of the Mg particle. Exponents of D n -law, for the burning rate of the magnesium and aluminum particles of diameters less than 100 μm, were found to be 0.6 and 1.5, respectively. The instant of the aluminum ignition was clearly distinguished with the ignition delay time little less than 10 ms, however the burning history of the magnesium particle exhibited no clear instant of the ignition. The ignition delay time of the magnesium particle (less than 100 μm) might be in the range from 50 to 200 ns. The flame and ignition temperatures of a single Al particle are slightly lower than the boiling and melting point of Al2O 3

Optical Diagnostic Study for Flame Characteristic Analysis in Aluminum Dust Clouds

Corresponding author. E-mail: wsyoon@yonsei.ac.krABSTRACT In this study, In order to develop the measurement method of high energy density metal aluminum dust cloud combustion, flame temperature and emission spectrum was measured using spectrometer. Because of the ultra high ㎛-sized aluminum flame temperature more than 2400 K, it was meas ured by non-contact optical technique which is the modified two wavelength pyrometry with 520, 640 nm and spectrum comparison method. These methods were applied to e xperiment after accurate verification. As a result, we could identify that flame tempera ture is more than 2400 K in bottom of combustor in both methods. And on the emission spectrum analysi s, we could measure AlO radical which is occurred dominantly in aluminum combustion.초 록 본 연구에서는 고에너지 금속 알루미늄 군입자 연소 화염 분석을 위한 측정기법 개발 연구로서 스펙트로메터를 사용하여 화염 온도와 자발광 스펙트럼을 측정하였다. 마이크로 크기의 알루미늄 군입자 연소 반응시 발생하는 화염온도는 약 2400 K 이상의 초고온이므로 비접촉식 광학 계측 방법을 사용하였으며, 측정을 위해 개발된 기법은 520 nm, 640 nm를 사용하는 이색법을 응용한 방법과 광대역 파장 비교법으로서 각각의 방법은 정밀하게 검증 후 실험에 적용되었다. 연소실 하단에서 화염온도 측정결과 두 방법 모두 2400 K 이상의 화염온도를 확인할 수 있었으며 자발광 측정 결과 알루미늄 연소 반응시 가장 지배적으로 발생하는 화학종인 AlO를 확인할 수 있었다.Key Words: High Temperature Measurement(고온측정법), Emission Spectroscopy(방출분광법)Received 14 June 2013 / Revised 11 September 2013 / Accepted 18 September 2013

Design and Analysis of a Second-Throat Exhaust Diffuser for Altitude Simulation

In this paper, as an altitude simulator, a second-throat exhaust diffuser with no induced secondary flow has been studied. To design a startable diffuser, we first summarize a simple theoretical method based on the normal shock theory. Using the diffusers designed from the present design method, we obtain the diffuser characteristic curves from the small-scale cold-gas tests using cold nitrogen gas as a working fluid. All the experimental test cases are numerically reproduced by using a Reynolds-averaged Navier–Stokes solver, and the numerical method is properly validated with the measured pressure distributions along the diffuser wall andthe pressure in the vacuum chamber. We investigate the effects of the essential geometric factors of a second-throat exhaust diffuser, such as subsonic diffuser, second throat area ratio, nozzle expansion ratio, and nozzle contour, on the starting and evacuation performance. Finally, to get a full picture of a second-throat exhaust diffuser operation, evolving diffuser flows during the starting transient and plume blowback at diffuser breakdown are also studied. Nomenclature A � = cross-sectional area of nozzle throat Ad = cross-sectional area of diffuser inlet Ae = cross-sectional area of nozzle exit As = cross-sectional area of the second throat duct Ax = cross-sectional area of diffuser exit D = diameter of diffuser

Parametric Investigation on the Essential Flow Factors Commanding Steady Operations of the Second Throat Exhaust Diffuser

The constant area exhaust diffuser (CAED) demands a higher starting pressure than the second throat exhaust diffuser (STED). In the design process, one dimensional (1D) normal shock theory was explored to obtain the optimum starting pressure of STED. Experiments were conducted with a small scale cold gas simulator using nitrogen gas as injectant. The application of 1D normal shock theory for STED design was examined with 20-25% difference in each accuracy in comparison to numerical and experimental evidences. The relation between evacuation quality and essential geometrical parameters such as diffuser– to–nozzle throat area ratio (Ad/At), diffuser–to–the second throat area ratio (Ad/As), and the nozzle expansion ratio (e) is presented for the optimization of STED. The optimum starting pressure increases in proportion to Ad/At and the optimized Ad/As was predicted in the range of 2.2-2.5. After STED starting, the evacuation quality is the same whether the expansion ratio of the nozzle is large or not. However, the range of the transition regime varied according to the nozzle expansion ratio. Nomenclature d A = area of diffuser inlet s A = area of the second throat t A = area of nozzle throat D = diameter e

Thermo-physical Characteristics of Nickel-coated Aluminum Powder as a Function of Particle Size and Oxidant

Aluminum particles 15–25 μm in size are widely used in fuel propellants and underwater propulsion systems in national defense research. However, these particles are covered with an aluminum oxide film, which has a high melting point, so ignition is difficult. To improve the ignitability of high-energy aluminum powder and to understand the reaction phenomenon as a function of particle size(15–25 μm, 74–105 μm, and 2.38 mm) and oxidizer(air, CO2, and argon), the natural oxide films are chemically removed. The particles are then coated with nickel using an electro-less method. The degree of nickel deposition is confirmed qualitatively and quantitatively through surface analysis using scanning electron microscopy/energy dispersive spectroscopy. To characterize the nickel coatings, elemental analysis is also conducted by using X-ray diffraction. Thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) enable comparisons between the uncoated and coated aluminum, and the reaction process are investigated through fine structural analysis of the particle surfaces and cross sections. There are little difference in reactivity as a function of oxidant type. However, a strong exothermic reaction in the smaller nickel-coated aluminum particles near the melting point of aluminum accelerates the reaction of the smaller particles. Explanation of the reactivity of the nickel-coated aluminum depending on the particle sizes is attempted.

A Steam-Plasma Igniter for Aluminum Powder Combustion

High-temperature ignition is essential for the ignition and combustion of energetic metal fuels, including aluminum and magnesium particles which are protected by their high-melting-temperature oxides. A plasma torch characterized by an ultrahigh-temperature plasma plume fulfills such high-temperature ignition conditions. A new steam plasma igniter is designed and successfully validated by aluminum power ignition and combustion tests. The steam plasma rapidly stabilizes in both plasma and steam jet modes. Parametric investigation of the steam plasma jet is conducted in terms of arc strength. A high-speed camera and an oscilloscope method visualize the discharge characteristics, and optical emission spectroscopy measures the thermochemical properties of the plasma jet. The diatomic molecule OH fitting method, the Boltzmann plot method, and short exposure capturing with an intensified charge coupled device record the axial distributions of the rotational gas temperature, excitation temperature, and OH radical distribution, respectively. The excitation temperature at the nozzle tip is near 5500 K, and the gas temperature is 5400 K.

Fabrication and thermophysical properties of nickel-coated aluminum powder by electroless plating

To improve the ignitability of high energy aluminum powder, in this study, natural oxide films (alumina, Al2O3) were chemically removed and nickel coatings were deposited using an electroless method for nickel plating. The time-dependent degree of nickel deposition was confirmed qualitatively and quantitatively through surface analysis using scanning electron microscopy/energy dispersive spectroscopy. To characterize the nickel coatings, we also conducted elemental analysis by using X-ray diffraction and weight analysis by using inductively coupled plasma optical emission spectrometry. Thermophysical studies were also conducted using thermogravimetric analysis/differential scanning calorimetry in an airoxidized environment. The results of these analyses explain the ignition enhancement mechanism observed in the nickel-coated aluminum powder. A novel plating method for creating a nickel-coated aluminum powder was established and the mechanism for the enhancement of the ignition and combustion of the powder is elucidated.

Measurement of Pressure-coupled Combustion Instability Characteristics : Acoustic Attenuation by Particulate Matter(Al) and Combustion Response of Solid Propellant

ABSTRACT T-Burner tests of an Al/HTPB propellant in conjunction with a Pulsed DB/AB Method were conducted to find an acoustic amplification factor. Aluminum-fr ee and aluminum-heavy propellants were examined. Instant surface ignition was successfully made by the use of a supplementary propellant of fractionally higher reaction rate. With the prese nce of higher aluminum concentration in the propellants, the pressure perturbations were promptly dampe d down and the pressure fluctuations were no longer dispersive. Addition of aluminum particles into the propellant was advantageous for stabilizing pressure-coupled unstable waves.초 록 연소 시, 입자상 물질에 대한 HTPB/AP 계열 고체추진제의 음향특성을 정량화하기 위해서, Pulsed DB/AB T-burner 실험을 수행하였다. 추진제 전면에서 동시 점화를 위해, 대상 고체추진제보다 연소속도가 빠른 다른 고체추진제를 대상 추진제 앞면에 부착하였다. 다량의 알루미늄이 포함된 고체추진제에서는 T-burner 내부에서 만들어진 압력섭동에 의한 음향학적 불안정성이 매우 빠르게 감쇠되었고, 반대로 알루미늄이 포함되지 않은 고체추진제에서는 상대적으로 매우 느리게 감쇠함을 확인하였다. 본 연구에서는 음향학적 특성값들을 정량화하였고, 이를 통해 연소응답 특성을 계산하였다.Key Words: Solid Propellant(고체추진제), Combustion Response(연소응답), T-burner(T-버너), Fast Ignition Disk(점화보조제), Pulsed DB/AB Method(펄스형 DB/AB 방법)Received 2 December 2013 / Revised 1 March 2014 / Accepted 8 Ma rch 2014

Temperature Field and Emission Spectrum Measurement of High Energy Density Steam Plasma Jet for Aluminum Powder Ignition

ABSTRACT In this study, DC (Direct current) type steam plasma igniter is developed for effective ignition of high-energy density metal aluminum and gas temperature is measu red by emission spectrum of OH radical. Because of the ultra-high gas temperature, the DC plas ma jet is measured by Boltzmann plot method which is the non-contact optical technique and spectrum comparison-analysis. And both methods were applied to experiment after accurate verification. As a result, we could identify that plasma jet temperature is 2900 K ~ 5800 K in the 30 mm range fr om the nozzle tip.초 록 본 연구에서 고에너지 금속 알루미늄의 효과적인 점화를 위해 개발한 직류 방식의 스팀 플라즈마 점화기 가스온도를 OH radical의 방출 스펙트럼을 사용하여 측정하였다. 플라즈마 제트온도는 초고온이므로 비접촉식 광학 계측 방법인 볼츠만 기울기법과 스펙트럼 비교 분석법을 이용하여 측정하였으며 각각의 방법은 정밀하게 검증 후 실험에 적용되었다. 플라즈마 점화기의 노즐 팁으로부터 30 mm 범위에서의 제트온도 측정결과 두 방법 모두 알루미늄의 점화온도(≈2400 K) 이상의 2900 K ~ 5800 K 를 확인할 수 있었다.Key Words: Steam Plasma Igniter(스팀 플라즈마 점화기), High Temperature Measurement(고온측정법), Emission Spectroscopy(방출분광법), Aluminum Ignition(알루미늄 점화)Received 2 June 2013 / Revised 3 January 2014 / Accepted 11 Jan uary 2014