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射流点火可以有效提高发动机燃烧效率,抑制爆震,预燃室内部火花塞的点火位置对于点火成功率以及燃烧效果有较大影响。采用CFD仿真的方法,研究了被动式射流点火发动机预燃室内部火花塞点火位置对发动机缸内燃烧过程的影响,得到以下结论:适当的将预燃室内火花塞点火位置靠近预燃室喷孔可借助高湍动能气体实现火焰的加速传播;在气流作用下,火焰首先向预燃室末端传播,可减少高温燃气喷射前预燃室向主燃室回流的未燃混合气,提高预燃室内混合气的累计放热量,预燃室内可燃混合气累计放热率最高可提升14.9%。 相似文献
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通过试验手段对比分析了预燃室射流点火模式及火花塞点火模式 (SI)对燃烧性能的影响,结果表明:SI点火模式的发动机受高负荷爆震的限制,仅在中等负荷达到最佳的油耗率和热效率。压缩比(CR)的增加仅在中小负荷对油耗率和热效率有改善效果;相比于SI点火模式,预燃室射流点火模式可实现更快的燃烧速度和火焰传播速度,对SI发动机的爆震有较好的抑制效果,在中等负荷具有更低的油耗率和更高的热效率,但在低负荷及高负荷阶段,油耗率和热效率恶化;采用预燃室射流点火模式,能有效增加缸内燃烧速率,减轻CA50推迟对油耗率恶化的效果,通过提高压缩比实现降低油耗率的潜力和效果更好。 相似文献
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预燃室射流点火是改善汽油发动机热效率的有效手段,为了研究和改善被动预燃室低温冷起动及低负荷时的燃烧稳定性,设计了不同容积、孔面积、材料、喷孔结构的被动预燃室装置,安装在一台涡轮增压汽油发动机上,进行了低温冷起动试验,以及低速、低负荷燃烧稳定性试验。研究结果表明,被动预燃室容积、孔面积、材料、喷孔结构对低温冷起动性能有显著影响。预燃室容积较小时,预燃室内部淬熄层占预燃室容积的比例大,预燃室内部混合气少。较小的孔径或孔面积减少了预燃室内残余废气的排出。旋转孔使得预燃室内部废气分层,火花塞附近废气比例大。较高的导热率使预燃室冷起动时预燃室散热较快。因此,小容积、小孔径、高导热率材料以及旋转喷孔等均不利于发动机冷起动。优化结构的被动预燃室在-20℃~-8℃的冷起动工况下能实现发动机稳定着火起动。点火角和排气VVT对发动机的燃烧稳定性影响较小。进气VVT对预燃室燃烧稳定性影响较大,进气门开起时刻推迟,着火上止点附近缸内湍动能变强;另一方面实际压缩比变大,主燃烧压入预燃室内部的新鲜混合气比例提高,预燃室点火燃烧稳定性显著改善。 相似文献
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根据火花塞点火放电过程中三个阶段等离子流能量的变化,通过改变火花塞电极结构,增大带电粒子的动量进而提高火花塞点火性能。设计了双点火间隙电极结构的等离子流火花塞,该火花塞工作时两个间隙同时点火形成双火核,等离子流能量增大,火焰传播速度快,点火能量及起动性增强。放电测量结果为,当特征长度L+=10mm,电极间隙h=1.0mm时,点火电压为19000V,最大峰值电流为200A,点火能量为103mJ。 相似文献
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内燃机早已成为船舶、车辆和热电厂的主要动力。一般来说,与传统的内燃机相比,均质压燃发动机具有优越的燃油经济性和超低的氮氧化物和颗粒物排放。然而,HCCI发动机本质上是与火花塞和燃油喷射分离的。这意味着HCCI发动机没有直接控制自动点火提前角和随后的燃烧阶段的机制。如果没有根据工况按时控制自动点火提前角的有效策略,HCCI发动机由于冷起动问题、高压比和燃烧噪声,甚至在高负荷时会发生后果严重的故障。 相似文献
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Andrzejak TA Shafirovich E Taylor DG Varma A 《The Review of scientific instruments》2007,78(8):085102
We report a compact microgravity flight apparatus for characterization of high-temperature chemical reactions in single particle systems. The apparatus employs an infrared CO(2) laser to ignite 1-5 mm samples while video images, thermocouple measurements, laser on/off status, and XYZ accelerometer signals are synchronously recorded. Different operating modes permit preignition quenching, ignition, and combustion experiments to be performed. The apparatus was successfully utilized during microgravity experiments on board NASA research aircraft. 相似文献
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Investigations into machining of composites 总被引:2,自引:0,他引:2
Fibre reinforced plastics (FRP) have an important place in the field of engineering materials. Initially, the main emphasis in research was on the development of materials. Currently, however, more attention is being paid to the industrial production of FRP products. Normally, conventional methods for machining of these materials are used, but reports have indicated poor performance of these conventional types of cutting tools during machining of FRP. In this paper, a new approach using electrochemical spark machining (ECSM) for cutting and drilling holes in composites is proposed.
The feasibility of using ECSM for machining FRP was first ascertained. Then a parametric study of the process was performed by planning the experiments using a ‘design of experiments’ concept as well as a ‘one variable at a time’ approach. Kevlar-fibre-epoxy and glass-fibre-epoxy composites as work materials, copper as the tool material and an aqueous solution of NaCl as electrolyte were used.
It is concluded that ECSM is a viable solution for cutting FRP. However, for achieving the desired accuracy, surface finish and economics of the process, the machining parameters need to be optimized. 相似文献
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直流电机工作时换向器电刷产生的电火花会干扰电子设备和通信系统,危害飞行安全。为了减少由于换向火花超标带来的飞行事故,通过分析目前的直流电机换向器火花的检测技术和K8飞机各直流电机换向器火花的电气特性,提出了提取电源回馈信号进行火花检测的新方法,该方法将提取的回馈信号经过滤波、放大胡理、脉冲保持电路,A/D转换送到单片机处理,得到火花等级系数。设计了K8飞机直流电机换向器火花检测仪,经过了反复的平台测试和现场测试,实验证明该仪器真正实现了原位检测,具有无须外接电源、测量准确、操作方便、抗干扰能力强、功耗低等优点。 相似文献
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冷冲压凹模的失效分析与电火花局部强化 总被引:3,自引:0,他引:3
分析了冷冲压凹模工作时内孔边缘易发生早期疲劳断裂的原因 ,采用电火花强化工艺对凹模内孔刃口处进行局部强化 ,解决了凹模早期疲劳失效问题。 相似文献
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小型点燃式发动机国家排放标准主要包括发动机分类方法,排放限值,测试循环,生产一致性保证要求等方面的内容。国标实施将有利于改善环境质量,促进行业技术水平提升,提高产品竞争力。 相似文献
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R. Dwaraka 《Machining Science and Technology》2020,24(4):638-662
AbstractThe performance of electrical discharge machining (EDM) primarily depends on the spark quality generated in the inter-electrode gap (IEG) between the tool and workpiece. A method for obtaining accurate information about the spark gap is required to effectively monitor the EDM process. The rise and fall of thermal energy in the discharge zone at a rapid rate during the dielectric breakdown produces high-pressure shock waves. This work explores the suitability of using acoustic emission (AE) generated from these shock waves and the elastic AE waves released on the workpiece due to the induced stress to monitor the performance and spark gap in EDM. The information content of the AE signals acquired at various machining conditions was extracted using AE RMS, spectral energy and peak amplitude. These features were able to well discriminate the machining condition, tool material, workpiece material, flushing pressure, current density, the initial surface roughness of the tool. Additionally, the AE signal features had a good and consistent correlation with the performance parameters, including material removal rate, surface roughness (Ra and Rq) and tool wear. The findings lay the groundwork to develop an effective, non-intrusive in-situ AE-monitoring system for performance and IEG condition in EDM. 相似文献
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