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Chi Hou Chan - One of the best experts on this subject based on the ideXlab platform.
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waveguide fed broadband millimeter wave short Backfire antenna
IEEE Transactions on Antennas and Propagation, 2013Co-Authors: Chi Hou ChanAbstract:A broadband millimeter-wave short Backfire antenna (SBA), excited by a bowtie dipole and fed by an E-band rectangular waveguide, is presented in this paper. Its subreflector is replaced by two simple strips printed on the opposite sides of the same supporting substrate of the bowtie exciter for ease and accuracy of fabrication. For reference of practical designs, detailed parametric studies are performed in this paper. Measurements and simulations show that the proposed antenna can feature an improved operating bandwidth and broadside gain compared to the previously reported conventional SBAs. The measured impedance bandwidth for SWR $\leq$ 2 is 57%, from 55.7 to 100 GHz, in which the measured broadside gain is from 13.8 to 18.5 dBi with the peak gain at 85 GHz. Finally, high illumination efficiency of the bowtie exciter is highlighted by comparisons with a straight dipole excited SBA.
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waveguide fed broadband millimeter wave short Backfire antenna
International Symposium on Antennas and Propagation, 2012Co-Authors: Chi Hou ChanAbstract:A broadband millimeter (mm)-wave short Backfire antenna (SBA), excited by a bowtie dipole and fed by an E-band rectangular waveguide, is presented in this paper. Its subreflector is replaced by two simple strips printed on the same supporting substrate of the exciter for ease and accuracy of fabrication. Measurements and simulations show that the proposed antenna can feature an improved operating bandwidth and broadside gain compared to reported conventional SBAs. Finally, high illumination efficiency of the bowtie exciter to the antenna aperture is highlighted by comparisons with an SBA excited by a straight dipole.
Baigang Sun - One of the best experts on this subject based on the ideXlab platform.
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inducing factors and frequency of combustion knock in hydrogen internal combustion engines
International Journal of Hydrogen Energy, 2016Co-Authors: Qinghe Luo, Baigang SunAbstract:Abstract Hydrogen is a promising energy carrier, and the port fuel injection (PFI) is a fuel-flexible, durable, and relatively cheap method of energy conversion. However, combustion knock as an abnormal combustion phenomenon does not only limit the brake torque and thermal efficiency, but also breaks the piston or engines. This paper uses a four-stoke cycle, displacement of 2.0 L PFI hydrogen internal combustion engine and a calculated model to study the inducing factors and frequency of combustion knock. Results showed that combustion knock occurs at relatively higher engine speed (more than 3000 r/min) than the engine speed occurring knock of gasoline engine. The calculated average temperatures of air–fuel mixture at the end of combustion using thermodynamics dual zone model fall in the range of 1000–1100 K for hydrogen engines, which are higher than gasoline ones (about 200 K). Knock and the other abnormal combustion phenomena (Backfire and pre-ignite) interact with each other. When the Backfire generates, the components in the cylinder will be heated. In the next cycle, the components of the cylinder will release heat to the intake, which can increase the initial temperature at ignition. The high initial temperature will lead to the combustion knock. Otherwise, because of the combustion knock, the temperatures of cylinder components will increase, which generates hot spots and ultimately causes pre-ignite and Backfire. Through the figures of Fast Fourier Transform (FFT) amplitude, the frequency of hydrogen engines is higher than gasoline ones for every kind of mode. The pressure waves of combustion knock spread with radial direction for light combustion knock and with circumferential direction for heavy combustion knock. These conclusions can be used to explore the working conditions close to combustion knock to achieve higher thermal efficiency and provide a guidance to detect the knock in hydrogen engine.
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Backfire control and power enhancement of a hydrogen internal combustion engine
International Journal of Hydrogen Energy, 2014Co-Authors: Junfa Duan, Fu Shui Liu, Baigang SunAbstract:Abstract Frequent Backfire can occur in inlet port fuel injection hydrogen internal combustion engines (HICEs) when the equivalence fuel–air ratio is larger than 0.56, thus limiting further enhancement of engine power. Thus, to control Backfire, an inlet port fuel injection HICE test system and a computational fluid dynamics model are established to explore the factors that cause Backfire under high loads. The temperature and the concentration of the gas mixture near the intake valves are among the essential factors that result in Backfire. Optimizing the timing and pressure of hydrogen injection reduces the concentration distribution of the intake mixture and the temperature of the high-concentration mixture through the inlet valve, thus allowing control of Backfire. Controlling Backfire enables a HICE to work normally at high equivalence fuel–air ratio (even beyond 1.0). A HICE with optimized hydrogen injection timing and pressure demonstrates significant enhancement of the power output.
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Backfire prediction in a manifold injection hydrogen internal combustion engine
International Journal of Hydrogen Energy, 2008Co-Authors: Xing Hua Liu, Baigang Sun, Fu Shui Liu, Lei Zhou, Harold SchockAbstract:Hydrogen internal combustion engine (H2ICE) easily occur inlet manifold Backfire and other abnormal combustion phenomena because of the low ignition energy, wide flammability range and rapid combustion speed of hydrogen. In this paper, the effect of injection timing on mixture formation in a manifold injection H2ICE was studied in various engine speed and equivalence ratio by CFD simulation. It was concluded that H2ICE of manifold injection have an limited injection end timing in order to prevent Backfire in the inlet manifold. Finally, the limit of injection end timing of the H2ICE was proposed and validated by engine experiment.
K A Subramanian - One of the best experts on this subject based on the ideXlab platform.
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control of Backfire and nox emission reduction in a hydrogen fueled multi cylinder spark ignition engine using cooled egr and water injection strategies
International Journal of Hydrogen Energy, 2019Co-Authors: Vipin Dhyani, K A SubramanianAbstract:Abstract The experimental study was carried out on a constant speed multi-cylinder spark ignition engine fueled with hydrogen. Exhaust gas recirculation (EGR) and water injection techniques were adopted to control combustion anomalies (Backfire and knocking) and reduce NOx emission at source level. The experimental tests were conducted on the engine with varied EGR rate (0%–28% by volume) and water to hydrogen ratio (WHR) (0–9.25) at 15 kW load. It was observed from the experiments that both the strategies can control Backfire effectively, but water injection can effectively control Backfire compared to EGR. The water injection and EGR reduce the probability of Backfire occurrence and its propagation due to the increase in the requirement of minimum ignition energy (MIE) of the charge, caused mainly due to charge dilution effect, and reduction in flame speed respectively. The NOx emission was continuously reduced with increase in EGR rate and WHR, but at higher rates (of EGR and WHR), there was an issue of stability of engine operation. It was found from the experimental results that at 25% EGR, there was 57% reduction in NOx emission without drop in brake thermal efficiency whereas, with WHR of 7.5, the NOx emission was reduced by 97% without affecting the efficiency. The salient point emerging from the study is that water injection technique can control Backfire with ultra-low (near zero) NOx emission without compromising the performance of the hydrogen fueled spark ignition engine.
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experimental investigation on effects of knocking on Backfire and its control in a hydrogen fueled spark ignition engine
International Journal of Hydrogen Energy, 2018Co-Authors: Vipin Dhyani, K A SubramanianAbstract:Abstract The experimental study was carried out on a multi-cylinder spark ignition engine fueled with hydrogen for analyzing the effect of knocking on Backfire and its control by varying operating parameters. The experimental tests were conducted with constant speed at varied equivalence ratio. The equivalence ratio of 0.82 was identified as Backfire occurring equivalence ratio (BOER). The Backfire was identified by high pitched sound and rise in in-cylinder pressure during suction stroke. In order to analyze Backfire at equivalence ratio of 0.82, the combustion analysis was carried out on cyclic basis. Based on the severity of in-cylinder pressure during suction stroke, the Backfire can be divided into two categories namely low intensity Backfire (LIB) and high intensity Backfire (HIB). From this study, it is observed that there is frequent LIB in hydrogen fueled spark ignition engine during suction stroke, which promotes instable combustion and thus knocking at the end of compression stroke. This knocking creates high temperature sources in the combustion chamber and thus causes HIB to occur in the subsequent cycle. A notable salient point emerged from this study is that combustion with knocking can be linked with Backfire as probability of Backfire occurrence decreases with reduction in chances of knocking. Retarding spark timing and delaying injection timing of hydrogen were found to reduce the chances of Backfire occurrence. The Backfire limiting spark timing (BLST) and Backfire limiting injection timing (BLIT) were found as 12 0bTDC and 40 0aTDC respectively.
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experimental investigation on effects of compression ratio and exhaust gas recirculation on Backfire performance and emission characteristics in a hydrogen fuelled spark ignition engine
International Journal of Hydrogen Energy, 2016Co-Authors: B L Salvi, K A SubramanianAbstract:Abstract The experimental study was conducted on single cylinder, forced air cooled hydrogen fuelled spark ignition (SI) generator set, which was converted from gasoline fuelled generator set with rated power 2.1 kVA at 3000 rpm. The study was carried out at various compression ratios (4.5:1, 6.5:1 (base) and 7.2:1), spark timings (2–20 °CA before top dead centre (bTDC)) and exhaust gas recirculation (EGR) up to 25% by Volume. Furthermore, the experimental tests were conducted on the engine with varied start of gas injection (SOI) at various compression ratios in order to find the Backfire limiting start of injection (BFL-SOI). The results indicated that engine operation at higher compression ratio improved the brake thermal efficiency and reduced the Backfire occurrence as residual gas fraction decreased with increased compression ratio. However, NOx emission increased with increased compression ratio. In order to reduce the NOx emission at source level, the engine was operated with retarded spark timings and different EGR percentage. The relative NOx emission decreased up to 10% with the spark time retarding of 2° CA bTDC from maximum brake torque (MBT) whereas it decreased about 57% with 25% by volume EGR. The delay in gas injection could reduce the chance of Backfire occurrence and the BFL-SOI decreased with increased compression ratio. A notable point emerged from this study is that in hydrogen fuelled spark ignition engine the spark time retarding is not a suitable strategy for NOx emission reduction whereas the EGR at the optimum level (20%) is a better strategy that could reduce the NOx emission up to 50% as compared to base hydrogen engine without EGR.
Christophe Caloz - One of the best experts on this subject based on the ideXlab platform.
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Uniform Ferrite-Loaded Open Waveguide Structure With CRLH Response and Its Application to a Novel Backfire-to-Endfire Leaky-Wave Antenna
IEEE Transactions on Microwave Theory and Techniques, 2009Co-Authors: Toshiro Kodera, Christophe CalozAbstract:A uniform ferrite-loaded open waveguide structure with composite right/left-handed (CRLH) response and its application to a novel Backfire-to-endfire leaky-wave antenna are presented. The structure consists of a ferrite-filled rectangular waveguide open to free space at one of its small sides and biased perpendicularly to its large sides. Based on the fact that the leakage from the open side represents only a small perturbation in terms of guidance, an analytical dispersion relation for the approximately equivalent perfect magnetic conductor closed waveguide structure is derived. The unique dispersive properties of this structure, including its inherent CRLH balanced response (gapless nonzero group velocity transition between the left- and right-handed bands) and low-loss characteristics due to off-resonance operation, are extensively described, parametrically studied, and concretized by design guidelines. This theory is validated by both finite-element method and finite integration technique full-wave results and demonstrated experimentally. The leakage of the structure is exploited to build a full-space Backfire-to-endfire scanning leaky-wave antenna, which is capable of both fixed-bias frequency scanning and fixed-frequency bias scanning, while being a perfectly uniform structure not requiring any chip tuning components. This feature, and its subsequent design simplicity, represents a fundamental advantage over previous CRLH metmaterial implementations. To the best of our knowledge, the proposed ferrite waveguide is the first and unique uniform structure exhibiting a CRLH response.
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miniaturized mim crlh transmission line structure and application to Backfire to endfire leaky wave antenna
IEEE Antennas and Propagation Society International Symposium, 2004Co-Authors: Minwook Kang, Christophe Caloz, T ItohAbstract:A novel miniaturized metal-insulator-metal (MIM) capacitor composite right/left-handed (CRLH) transmission line architecture has been proposed and demonstrated to exhibit an almost twofold reduction factor in size in comparison with a previously published interdigital CRLH structure. The MIM CRLH transmission line has been demonstrated as a Backfire-to-endfire leaky-wave antenna with excellent scanning performance. The proposed antenna is to be fabricated in LTCC.
Yunliang Long - One of the best experts on this subject based on the ideXlab platform.
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periodic triangle truncated dspsl based antenna with Backfire to endfire beam scanning capacity
IEEE Transactions on Antennas and Propagation, 2017Co-Authors: Zhixi Liang, Juhua Liu, Shao Yong Zheng, Yunliang LongAbstract:A Backfire to endfire beam-scanning antenna based on double-side parallel-strip lines (DSPSL) is presented in this communication. The antenna consists of periodic offset DSPSL structures with triangular truncation. A series of uniform DSPSL and offset DSPSL equations were established to analyze its operating modes, transmission mode, and first higher order. The working band range in the periodic DSPSL structure is shown to assist the design of the proposed antenna. The main beam of the antenna scans from Backfire to endfire as operating frequency increases owing to its periodic structure. Truncating the periodic offset DSPSL improved the current distribution and consequently broadened the impendence, enhancing the radiation patterns. Experimental results showed that the main lobe scans electronically and continuously from the Backfire (-z-direction) to endfire in the yz plane toward the absolute end-firing direction (+z-direction) with two open stopbands when operating frequency increases from 1.2 to 5.9 GHz. The peak gain of the antenna is about 9.7 dBi, and the gain in the whole working band exceeds 4 dBi.
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the Backfire to broadside symmetrical beam scanning periodic offset microstrip antenna
IEEE Transactions on Antennas and Propagation, 2010Co-Authors: Quan Xue, E K N Yung, Yunliang LongAbstract:A Backfire-to-broadside beam-scanning antenna with a periodic structure is described. The proposed antenna consists of the offset double-sided parallel-strip lines (DSPSL). The characteristics of the offset DSPSL have been studied, and then a series of offset DSPSL have been applied as the periodic antenna with a Backfire-to-broadside symmetrical beam scanning capability. Both in plane and plane, main beams symmetrically steer from the Backfire direction to the broadside direction with the increase of the operating frequency. The fractional impedance bandwidth has been broadened to nearly 50% by using the offset DSPSL structure.
