Soonho Song

Suspended GaN nanowires as NO2 sensor for high temperature applications

We propose a gas sensor operable over a wide temperature range and using suspended GaN nanowires functionalized with Pt-Pd. The sensor is batch-fabricated by directly integrating the GaN nanowires onto batch-processed silicon microelectrodes in parallel. The high thermal stability of the sensor originates from a large band gap of GaN nanowires that enables the detection of NO2 gas at an elevated temperature of up to 350 °C without a decrease in responsiveness. Exposed to NO2 at 100-1000 ppm at 350 °C, the sensor shows a linear increment in relative response with respect to the change in gas concentration. The sensor results in a two- to four-fold increase in responsiveness to NO2 at 100 ppm compared to NH3 at 100 ppm and CO2 at 1000 ppm. The nanowires suspended over a substrate provide increased surface area that could interact with gas molecules for enhanced responsiveness, and prevent any unnecessary interactions between the nanowires and the substrate.

Formation of NOx from Air and N2/O2 Mixtures Using a Nonthermal Microwave Plasma System

We present an experimental study of NOx (NO and NO2) formation from air and N2/O2/NOx mixtures using a nonthermal microwave plasma device. The tests were performed considering the energy consumed to generate plasma gas and the flow rate of air. The results demonstrated that NOx production was proportional to input power and the inverse of air flow rate. In the experiments that used N2 and O2 mixtures instead of air, the maximum NOx concentration produced at equilibrium was 16.02 ×1016 molecules/J (0.66 ×1016 NO molecules/J and 15.36 ×1016 NO2 molecules/J). Under the condition of the source gases consisting of NO and NO2 of 970 ppm in the N2 and O2 mixture with a ratio of 79/21, the concentrations of NOx generated were 5,571 and 5,320 ppm.

Measuring Methanol Concentrations in a Vapor-Fed Direct Methanol Fuel Cell Using Laser Absorption Spectroscopy

Gas-phase absorption spectroscopy using a 3.39 μm He-Ne laser enables the concentration of methanol vapor in a vapor-fed direct methanol fuel cell (DMFC) to be measured in real-time and in situ once high noise levels of the laser are corrected. The changes that methanol vapor concentrations bring to cell performance can be measured under various galvanostatic and potentiostatic conditions and analyzed with regard to methanol crossover and methanol transport capability. The absorption coefficient of +methanol vapor, 0.005336 cm -1 Torr -1 , is nearly constant under the DMFC operating conditions at a wavelength of 3.39 μm.

Conversion of NO to NO2 in air by a micro electric NOx converter based on a corona discharge process

A micro-electric-NO(x)-converter based on volume treatment is proposed for the evaluation of NO(x) concentrations in air. It can electrically convert NO(x) mixture from variable mixing rates into a fixed-mixing rate of 25% NO(2) and 75% NO using the corona discharge process with stable conversion efficiency and high throughput (space velocity = 6.3 x 10(4) h(-1)). The micro-electric-NO(x)-converter is based on a volume process. Applying high voltage to the electrodes of the micro-electric-NO(x)-converter generates a corona discharge. This discharge creates high-energy electrons, which collide with gas molecules. After these collisions, NO and O(2) are broken into single atoms, and they are re-combined as a balanced form, NO(2) in this case. The fabricated micro-electric-NO(x)-converter converted NO into NO(2) at conversion efficiency of 25.63%, when 5.5 kV (the applied corona power = 0.196 W) was applied to the micro-electric-NO(x)-converter.

Development of a Real-Time, In-Situ Particle Sizing Technique: Real-Time Light Transmission Spectroscopy (RTLTS)

We developed an improved particle measurement spectroscopic technique, real-time laser transmission spectroscopy (RTLTS), to detect the number-weighted distribution of particles in real time. The measurement system used a deuterium–tungsten lamp for the light source and a spectrometer as the detector. The operating wavelength range was 300–810 nm. To obtain a physically reasonable number concentration from the experimental results, a sequential regularization method was used during the calculations. To verify the feasibility and reliability of RTLTS, the number-weighted distribution of polystyrene particle suspensions was determined over diameters ranging from 0.005 to 2.000 μm in 0.005-μm increments. The measured concentration error was 0.67–32.67%. A mean diameter of the smallest particle we had detected was 0.09 μm, with a 16% oversizing. The measurable concentration range was ∼108 #/cc to ∼1011 #/cc for 0.895-μm-diameter particles. The measurable concentration range could be adjusted simply by changing the system configuration. This technique is available for both waterborne and airborne particles. Copyright 2013 American Association for Aerosol Research

A highly sensitive micro-thermal sensor for hydrogen detection

This paper reports a new MEMS-based chemical sensor for hydrogen gas detection, using a highly sensitive micro-thermal sensor. The proposed micro-thermal sensor detects the reaction heat between novel metal catalyst and hydrogen by measuring dc voltage from Cr-Bi thermopile. The proposed micro-thermal sensor, which consists of reference and sensing thermopile, was fabricated on a high thermal resistivity layer for reducing parasitic heat transfer. A metal catalyst was deposited on only the sensing thermopile. And then, In order to remove noises such as external change of temperature, gas flow and electrical noise, a difference between output signals of reference and sensing thermopile was measured by using differential amplifier. To verify its feasibility of the sensor for hydrogen gas detection, various concentrations (0.1, 0.5, 1%) of hydrogen gas were measured. The result of the measurement shows that output voltages of the sensor increases linearly according to the gas concentrations.

Evaluate the Effect of the Intake Manifold Geometry on Cylinder-to-cylinder Variation Using 1D-3D Coupling Analysis

CNG engine has been used as a transportation because of higher thermal efficiency and lower CO2 and particulate matter. However its out put power is decreased due to cylinder-to-cylinder variation during the supply of air-fuel mixture to the each cylinder. It also causes noise and vibration. So in this study, 1D engine simulation model was validated by comparison with experiment data and 3D CFD simulation was conducted to steady-state flow analysis about each manifold geometry. Then, the effects of various intake manifold geometries on variation were evaluated by using 1D-3D coupling analysis at engine speed of 2100 rpm range in 12 L CNG engine. As a result, variation was improved about 4 % though 3D CFD analysis and there was a variation within 3 % using 1D-3D coupling analysis.

Numerical study on effect of intake valve timing on characteristics of combustion and emission of Natural gas-Diesel engine

In this study, diesel/natural gas dual-fuel engine was studied numerically using DoE method. The engine is CI engine for power generation and modelled by 1-D simulation GT-power. The combustion and emission characteristics were analyzed as a function of IVO, IVC and the ratio of natural gas to total fuel enegy. As the proportion of natural gas increases, the BSFC(Brake specific fuel consumption) is increased and BSNOx(Brake specific NOx) is decreased. If specific valve timing to improve the BSFC is applied to the engine, the BSFC is decreased by 1% and simultaneously BSNOx is decreased by 36%.

A Effects of Natural Gas-Diesel/Hi-sene Dual Fuel Operation on Performance of a Heavy-Duty Diesel engine for Power Generation

Abstract - This study is a numerical study using commercial simulation program GT-Power on 1.5MW diesel engine for power generation. Performance comparison has done for diesel operation with dual fuel operation for different engine load(50%, 75%, 100%) using the target engine model with additional gas injection system. Effect of using Hi-sene, which is actually being used in island area, instead of diesel was also studied. As a result, under 60% natural gas with diesel condition, BSFC was increased by 32% without modifying system. There was almost no change for natural gas/Hi-sene condition compared with natural gas/diesel condition. Decrease of burned fuel fraction was the main reason of these phenomena. After optimizing system, BSFC was improved by 2% Key words : Diesel, Hi-sene, Dual fuel, Engine, Natural gas, Numerical Analysis † To whom corresponding should be addressed.Dept. of Mechanical engineering, Yonsei UniversityTel : 02-2123-2811 E-mail : soonhosong@yonsei.ac.kr 에너지공학, 제25권 제1호(2016)

The Effect of Y at Ni-YSZ Catalysts for the Application to the Process of Methane Chemical-Looping Reforming

>> Nickel based oxygen transfer materials supported on two different YSZs were tested to evaluate their performance in methane chemical-looping reforming. The oxygen transfer materials of YSZs were selected with different amount of the doped yittrium in the ZrO2 structure. The yittrium of 8 mol% stabilized the zirconia oxide to a cubic structure compare to the 3 mol% doping, which is known to be a good for oxygen transfer. Various nickel amounts (16wt.%, 32wt.%, 48wt.%) were loaded on the selected supports. The nickel amount of 32% shows the optimized catalyst structure with good physical properties and reducibility from the XRD, BET and H2-TPR analysis, especially when the support of 8YSZ was used. From the methane chemical-looping reforming, hydrogen was produced by methane decomposition catalyzed by Ni on both YSZs. Comparing two YSZ supports of 3YSZ and 8YSZ during the cycling tests, the catalyst with 8YSZ (Ni 32%) exhibits not only the higher methane conversion and hydrogen production but also a faster reaction rate reaching to the stable point.