A MEMS glass membrane igniter for improved ignition delay and reproducibility

Seo, Daeban,Jeong, Juyoung,Kim, Taekyu,Lee, Jongkwang Elsevier Sequoia 2017 Sensors and actuators. A Physical Vol.258 No.-

<P><B>Abstract</B></P> <P>A MEMS igniter with improved ignition characteristics and reproducibility is described. A glass wafer was selected as the igniter material for high membrane structural stability. To improve the reproducibility of the igniter, the membrane was designed to realize a flat surface and uniform thickness, which are essential factors for reproducibility. A heater is designed at the under surface of the membrane for direct contact with the propellant. It was expected that this would improve ignition delay compared with the previous glass-ceramic membrane igniter. Numerical simulations are performed to predict and compare ignition characteristics. The designed glass membrane igniter is realized as an array-type using a MEMS fabrication process with a glass wafer. Performance evaluation of the fabricated igniter is conducted through a firing test. At the cubesat’s operational voltage of 15V, the measured ignition delay was 17.1ms, which is almost the same as the numerical simulation result. Additionally, this result is 34.45% shorter than the measured ignition delay of the previous glass ceramic membrane igniter. The reproducibility is evaluated by consecutively igniting five igniters at 15V. The calculated average ignition delay and its coefficient of variation are 17.08ms and 12%, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This study describes a MEMS igniter for improved ignition characteristics with high structural stability and a uniform membrane thickness. </LI> <LI> A glass membrane which had a flat surface and uniform thickness was selected as the igniter material for high membrane structural stability. </LI> <LI> Numerical simulations were performed to predict and compare ignition characteristics. </LI> <LI> The designed glass membrane igniter was realized as an array-type using a MEMS fabrication process with a glass wafer. </LI> <LI> The measured average ignition delay and ignition energy were 17.08ms and 25.6mJ, respectively. </LI> </UL> </P>

Application of a novel microwave-assisted plasma ignition system in a direct injection gasoline engine

Hwang, Joonsik,Kim, Wooyeong,Bae, Choongsik,Choe, Wonho,Cha, Jeonghwa,Woo, Soohyung Elsevier 2017 APPLIED ENERGY Vol.205 No.-

<P>An experimental study was carried out to investigate the effect of microwave-assisted plasma ignition on the combustion and emission characteristics in a 500 cm(3) single cylinder direct injection gasoline engine. The microwave -assisted plasma ignition system consisted of a 2.45 GHz magnetron (3 kW), a waveguide, a mixer and a non-resistor spark plug. The first experiments were performed in a 1400 cm(3) constant volume combustion chamber (CVCC) to clarify the mechanism of combustion enhancement by microwave ejection. The combustion tests were performed using an acetylene-air mixture at a range of relative air/fuel ratios (lambda) under initial ambient pressures of 0.3 MPa and 0.5 MPa. The microwave-assisted plasma ignition has more advanced combustion phase than the conventional spark ignition showing larger initial flame kernel size and faster flame speed. The imaging results of the hydroxyl (OH) radical in ignition and flame demonstrated the potential of a faster chemical reaction by applying microwave on combustion. The microwave-assisted plasma ignition had a higher spark intensity and larger covering area than the conventional spark plug. The distribution and intensity of OH radicals on the surface of the flame were also higher with microwave ejection. In terms of engine test, lean limit was extended up to lambda 1.55 and the fuel efficiency was improved by 6% by microwave-assisted plasma ignition. The combustion phase was advanced so the peak of in-cylinder pressure and heat release rate increased more than those of conventional spark ignition. Based on the faster combustion, the combustion stability was enhanced so the lean limit was extended to lambda of 1.57. The microwave-assisted plasma ignition system was advantageous in the reduction of carbon monoxide and unburned hydrocarbon emissions, whereas nitrogen oxide emissions increased due to the higher temperatures in the combustion chamber. The engine test results finally demonstrated that the certain level of microwave ejection energy could improve all of engine performance and emission characteristics than conventional spark ignition system.</P>

Direct numerical simulations of ignition of a lean <i>n</i>-heptane/air mixture with temperature and composition inhomogeneities relevant to HCCI and SCCI combustion

Luong, Minh Bau,Yu, Gwang Hyeon,Lu, Tianfeng,Chung, Suk Ho,Yoo, Chun Sang Elsevier 2015 Combustion and Flame Vol.162 No.12

<P><B>Abstract</B></P> <P>The effects of temperature and composition stratifications on the ignition of a lean <I>n</I>-heptane/air mixture at three initial mean temperatures under elevated pressure are investigated using direct numerical simulations (DNSs) with a 58-species reduced mechanism. Two-dimensional DNSs are performed by varying several key parameters: initial mean temperature, <I>T</I> <SUB>0</SUB>, and the variance of temperature and equivalence ratio (<I>T</I>′ and <I>ϕ</I>′) with different T − ϕ correlations. It is found that for cases with <I>ϕ</I>′ only, the overall combustion occurs more quickly and the mean heat release rate (HRR) increases more slowly with increasing <I>ϕ</I>′ regardless of <I>T</I> <SUB>0</SUB>. For cases with <I>T</I>′ only, however, the overall combustion is retarded/advanced in time with increasing <I>T</I>′ for low/high <I>T</I> <SUB>0</SUB> relative to the negative-temperature coefficient (NTC) regime resulting from a longer/shorter overall ignition delay of the mixture. For cases with uncorrelated T − ϕ fields, the mean HRR is more distributed over time compared to the corresponding cases with <I>T</I>′ or <I>ϕ</I>′ only. For negatively-correlated cases, however, the temporal evolution of the overall combustion exhibits quite non-monotonic behavior with increasing <I>T</I>′ and <I>ϕ</I>′ depending on <I>T</I> <SUB>0</SUB>. All of these characteristics are found to be primarily related to the 0-D ignition delays of initial mixtures, the relative timescales between 0-D ignition delay and turbulence, and the dominance of the deflagration mode during the ignition. These results suggest that an appropriate combination of <I>T</I>′ and <I>ϕ</I>′ together with a well-prepared T − ϕ distribution can alleviate an excessive pressure-rise rate (PRR) and control ignition-timing in homogeneous charge compression-ignition (HCCI) combustion. In addition, critical species and reactions for the ignition of <I>n</I>-heptane/air mixture through the whole ignition process are estimated by comparing the temporal evolution of the mean mass fractions of important species with the overall reaction pathways of <I>n</I>-heptane oxidation mechanism. The chemical explosive mode analysis (CEMA) verifies the important species and reactions for the ignition at different locations and times by evaluating the explosive index (EI) of species and the participation index (PI) of reactions.</P>

On the effect of injection timing on the ignition of lean PRF/air/EGR mixtures under direct dual fuel stratification conditions

Luong, Minh Bau,Sankaran, Ramanan,Yu, Gwang Hyeon,Chung, Suk Ho,Yoo, Chun Sang Elsevier 2017 Combustion and Flame Vol.183 No.-

<P><B>Abstract</B></P> <P>The ignition characteristics of lean primary reference fuel (PRF)/air/exhaust gas recirculation (EGR) mixture under reactivity-controlled compression ignition (RCCI) and direct duel fuel stratification (DDFS) conditions are investigated by 2-D direct numerical simulations (DNSs) with a 116-species reduced chemistry of the PRF oxidation. The 2-D DNSs of the DDFS combustion are performed by varying the injection timing of <I>iso</I>-octane (<I>i</I>-C<SUB>8</SUB>H<SUB>18</SUB>) with a pseudo-<I>iso</I>-octane (PC<SUB>8</SUB>H<SUB>18</SUB>) model together with a novel compression heating model to account for the compression heating and expansion cooling effects of the piston motion in an engine cylinder. The PC<SUB>8</SUB>H<SUB>18</SUB> model is newly developed to mimic the timing, duration, and cooling effects of the direct injection of <I>i</I>-C<SUB>8</SUB>H<SUB>18</SUB> onto a premixed background charge of PRF/air/EGR mixture with composition inhomogeneities. It is found that the RCCI combustion exhibits a very high peak heat release rate (HRR) with a short combustion duration due to the predominance of the spontaneous ignition mode of combustion. However, the DDFS combustion has much lower peak HRR and longer combustion duration regardless of the fuel injection timing compared to those of the RCCI combustion, which is primarily attributed to the sequential injection of <I>i</I>-C<SUB>8</SUB>H<SUB>18</SUB>. It is also found that the ignition delay of the DDFS combustion features a non-monotonic behavior with increasing fuel-injection timing due to the different effect of fuel evaporation on the low-, intermediate-, and high-temperature chemistry of the PRF oxidation. The budget and Damköhler number analyses verify that although a mixed combustion mode of deflagration and spontaneous ignition exists during the early phase of the DDFS combustion, the spontaneous ignition becomes predominant during the main combustion, and hence, the spread-out of heat release rate in the DDFS combustion is mainly governed by the direct injection process of <I>i</I>-C<SUB>8</SUB>H<SUB>18</SUB>. Finally, a misfire is observed for the DDFS combustion when the direct injection of <I>i</I>-C<SUB>8</SUB>H<SUB>18</SUB> occurs during the intermediate-temperature chemistry (ITC) regime between the first- and second-stage ignition. This is because the temperature drop induced by the direct injection of <I>i</I>-C<SUB>8</SUB>H<SUB>18</SUB> impedes the main ITC reactions, and hence, the main combustion fails to occur.</P>

정적연소기에서 토치점화장치의 체적변화에 따른 메탄의 연소특성 파악

권순태(Soontae Kwon),김형식(Hyenogsig Kim),최창연(Changyeon Choi),박찬준(Chanjun Park),엄인용(Inyoung Ohm) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5

Six different size of torch-ignition device were applied in a constant volume combustion chamber for evaluating the effects of torch-ignition on combustion. The torch-ignition device was designed six different volumes and same orifice size. The combustion pressures were measured to calculate the mass fraction burned and combustion enhancement rate. In addition, the flame propagations were visualized by shadowgraph method for the qualitative comparison. The result showed that the combustion pressure and mass fraction burned were increased when using the torch ignition device. And the combustion duration were decreased. The combustion enhancement rates of torch-ignition cases were improved in comparison with conventional spark ignition. Finally, the visualization results showed that the torch-ignition device the torch-ignition induced faster burn than conventional spark ignition due to the earlier transition to turbulent flame and larger flame surface, during the initial stage. And the initial flame propagation was effected torch-ignition volume.

정적연소기에서 토치의 체적 변화에 따른 메탄의 연소특성 파악

권순태(Soon Tae Kwon),박찬준(Chan Jun Park),엄인용(In Young Ohm) 한국가시화정보학회 2011 한국가시화정보학회지 Vol.9 No.1

Six different size of torch-ignition device were applied in a constant volume combustion chamber for evaluating the effects of torch-ignition on combustion. The torch-ignition device was designed for six different volumes and same orifice size. The combustion pressures were measured to calculate the mass burn fraction and combustion enhancement rate. In addition, the flame propagations were visualized by shadowgraph method for the qualitative comparison. The result showed that the combustion pressure and mass burn fraction were increased when using the torch ignition device. And the combustion duration were decreased. The combustion enhancement rates of torch-ignition cases were improved in comparison with conventional spark ignition. Finally, the visualization results showed that the torch-ignition induced faster burn than conventional spark ignition due to the earlier transition to turbulent flame and larger flame surface, during the initial stage. Finally, the initial flame propagation was affected by torch-ignition volume.

Studies on the long-distance ignition circuit for HID lamps

Woo-Cheol Lee,Tae-Hun Kim 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

The electronic ballast for high-intensity discharge (HID) lamps needs a high-ignition voltage produced by a high voltage pulse igniter. However, in the case of a street lamp, the distance from the lamp to the ballast makes it difficult for a conventional pulsed highvoltage igniter to turn on the HID lamps because the ignition voltage is reduced. Therefore, research must be carried out on a resonant ignition to turn on the HID lamps. In this paper, topology and an algorithm for a resonant ignition are compared and verified. First, when a transformer is used in a resonant ignition, the method for reducing the load of the igniter is compared and proposed. Second, the parasitic capacitance, which affects the resonant frequency, is increased depending the length of the cable. The ignition voltage can be increased drastically under the resonant ignition through a frequency sweep. A method for reducing the voltage of the igniter is proposed and analyzed.

직접 접촉식 마이크로 점화기의 성능 평가

정주영(Juyeong Jung),서대반(Daeban Seo),김태규(Taegyu Kim),오현웅(Hyunung Oh),이종광(Jongkwang Lee) 한국추진공학회 2014 한국추진공학회 학술대회논문집 Vol.2014 No.12

MEMS 추력기를 위한 직접 접촉식 마이크로 점화기를 제안하였다. 제안된 점화기는 Pt/Ti 코일을 유리 박막의 하단에 배치하여 점화 특성을 향상시킬 수 있으며, 유리 박막의 두께를 균일하게 제작할 수 있어 성능 재연성을 향상시킬 수 있다. 직접 접촉식 마이크로 점화기의 성능을 확인해보기 위한 수치 해석을 수행하였다. 코일 표면에서 열유속이 5.66 ㎿/㎡인 경우 기존의 유리 박막 보다 점화 지연이 4.86% 짧아졌으며, 점화 지연은 열유속이 증가함에 따라 지수적으로 감소하는 특성을 보였다. 수치 해석 결과 제안한 점화기가 기존의 점화기에 보다 우수한 점화 성능을 가짐을 확인하였다. Micro igniter using direct contact ignition for MEMS thruster was proposed. The Pt/Ti coil was placed under the glass membrane in order to improve the ignition characteristic. Another merit of the proposed micro igniter is the uniform thickness of the glass membrane to enhance the repeatability. The effectiveness of the micro igniter using direct contact ignition was estimated through a numerical simulation. Ignition delay was 4.86 % shorter than previous micro igniter on the glass-ceramic membrane at the input heat flux of 5.66 ㎿/㎡. The ignition delay and energy exponentially decreased as the input heat flux increased. From the numerical simulation, we confirmed that the ignition characteristics of the proposed micro igniter surpassed that of the previous micro igniter.

토치 점화 장치의 체적에 따른 연소특성 파악

권순태(Kwon Soontae),김형식(Kim Hyeongsig),최창연(Choi Changhyeon),박찬준(Park Chanjun),엄인용(Ohm Inyoung) 한국에너지공학회 2010 한국에너지공학회 학술발표회 Vol.2010 No.4

토치 점화 장치의 연소 특성을 파악하기 위하여 6개의 각기 다른 토치 점화 장치를 설계하였다. 토치 점화장치의 체적이 메탄의 연소특성에 미치는 영향을 파악하기 위하여, 토치 점화 장치의 높이(h)와 오리피스 직경(De)는 10㎜와 6㎜로 고정하고, 입구 직경(D)을 12㎜에서 22㎜까지 2㎜씩 증가시키며 토치 점화 장치를 설계하였다. 초기 화염 생성 및 전파는 질량 연소율과 연소 촉진율로 분석하였다. 질량 연소율과 연소 촉진율을 계산하기 위하여 정적 연소실 내의 평균 압력을 측정하였다. 또한 shadow graph법을 이용하여, 초기 화염 생성과 화염 전파과정 전 영역을 가시화하였다. 토치 점화 장치를 사용한 경우에는 일반적인 스파크 점화와 비교하여 질량 연소율의 기울기가 증가하였고, 연소 촉진율도 개선된것을 확인하였다. 토치 점화 장치의 체적이 증가할수록 연소가 개선되었으며, 넓은 점화 표면을 제공하였다. Six different size of torch-ignition device were applied in a constant volume combustion chamber for evaluating the effects of torch-ignition on combustion. The torch-ignition device was designed six different volumes and same orifice size. The combustion pressures were measured to calculate the mass bum fraction and combustion enhancement rate. In addition, the flame propagations were visualized by shadowgraph method for the Qualitative comparison. The result showed that the combustion pressure and mass bum fraction were increased when using the torch ignition device. And the combustion duration were decreased. The combustion enhancement rates of torch-ignition cases were improved in comparison with conventional spark ignition. Finally, the visualization results showed that the torch-ignition device the torch-ignition induced faster bum than conventional spark ignition due to the earlier transition to turbulent flame and larger flame surface, during the initial stage. And the initial flame propagation was effected torch-ignition volume.

Ignition of a lean PRF/air mixture under RCCI/SCCI conditions: Chemical aspects

Luong, Minh Bau,Yu, Gwang Hyeon,Chung, Suk Ho,Yoo, Chun Sang Elsevier 2017 Proceedings of the Combustion Institute Vol.36 No.3

<P><B>Abstract</B></P> <P>Chemical aspects of the ignition of a primary reference fuel (PRF)/air mixture under reactivity controlled compression ignition (RCCI) and stratified charge compression ignition (SCCI) conditions are investigated by analyzing two-dimensional direct numerical simulation (DNS) data with chemical explosive mode (CEM) analysis. CEMA is adopted to provide fundamental insights into the ignition process by identifying controlling species and elementary reactions at different locations and times. It is found that at the first ignition delay, low-temperature chemistry (LTC) represented by the isomerization of alkylperoxy radical, chain branching reactions of keto-hydroperoxide, and H-atom abstraction of <I>n</I>-heptane is predominant for both RCCI and SCCI combustion. In addition, explosion index and participation index analyses together with conditional means on temperature verify that low-temperature heat release (LTHR) from local mixtures with relatively-high <I>n</I>-heptane concentration occurs more intensively in RCCI combustion than in SCCI combustion, which ultimately advances the overall RCCI combustion and distributes its heat release rate over time. It is also found that at the onset of the main combustion, high-temperature heat release (HTHR) occurs primarily in thin deflagrations where temperature, CO, and OH are found to be the most important species for the combustion. The conversion reaction of CO to CO<SUB>2</SUB> and hydrogen chemistry are identified as important reactions for HTHR. The overall RCCI/SCCI combustion can be understood by mapping the variation of 2-D RCCI/SCCI combustion in temperature space onto the temporal evolution of 0-D ignition.</P>