共查询到19条相似文献,搜索用时 125 毫秒
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利用低功率电弧放电辅助甲烷燃烧,研究了在不同甲烷/空气比例的情况下,等离子体对甲烷燃烧的影响。采用发射光谱仪进行光谱诊断,比较有/无等离子体辅助甲烷燃烧火焰发射光谱的异同,讨论了等离子体辅助燃烧可能发生的过程和机理。比较有/无等离子体辅助甲烷燃烧火焰温度的变化。利用气相色谱和烟气分析仪对甲烷燃烧产物中的CH4、CO 和O2 进行分析。实验结果表明,加等离子体后,火焰的温度升高,尾气中的可燃性成分减少,氧气含量降低,在很大程度上提高了甲烷的燃烧效率;甲烷/空气的比例越低,燃烧效率的提高越明显;甲烷的富燃燃烧极限从16%调高到21%。 相似文献
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基于气液相间滑移的影响,建立了适用于湿天然气凝结系统的水蒸气-甲烷双组分自发凝结流动数理模型,研究了水蒸气在以甲烷为载气的超声速流动中的凝结规律,对比了不考虑相间滑移的单流体模型与加入了相间滑移因素的双组分模型在自发凝结过程中的凝结规律的区别,分析了压力、温度对湿天然气在Laval喷管中自发凝结的影响.结果表明,湿天然气中相间滑移作用对凝结参数影响较大,本文建立的包含相间滑移因素的双组分模型能更准确的预测湿天然气的凝结特性;在凝结初始阶段相间滑移速度较大达到7.2 m/s,对湿天然气的自发凝结规律影响较大,随凝结过程的不断进行气液两相逐渐达到平衡,相间滑移速度逐渐降低至1.8 m/s;随入口温度的降低、入口压力的升高最大凝结成核率位置向入口方向移动。 相似文献
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在10 m3的爆炸罐中对体积分数为8%的甲烷和75 g/m3煤尘的混合物进行了系统的燃烧爆炸实验。分别利用光测方法和压力方法得到了爆炸物的层流燃烧速度、火焰传播速度、火焰厚度、马克斯坦长度以及爆炸特征值的变化规律。结果表明,在常温常压下,当点火能为40 J时:利用光测法得到的8%甲烷与75 g/m3煤尘混合物的燃烧速度为0.437 m/s,而根据压力-时间关系得到的混合物燃烧速度为0.459 m/s,两者符合较好;用火焰厚度与马克斯坦长度判定的火焰发展趋势相同,即向外传播的火焰趋于稳定;爆炸物的爆炸特征值最大值出现在0.5 m处,壁面的爆炸特征值偏小。 相似文献
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冉景煜^祁文杰王蕊蕊 《工程热物理学报》2014,(6):1244-1247
采用详细化学反应机理对甲烷空气预混气体在不同粗糙度下微通道内催化燃烧进行了数值模拟。结果表明:粗糙度的存在使得微通道内甲烷转化率减小,出口温度降低,粗糙表面将阻碍催化反应的进行,而且粗糙度越大这种阻碍作用越大;在同一粗糙度下,随着当量比、混合气入口速度的增加,粗糙度对催化反应的阻碍作用越明显,粗糙度越大,燃烧效率越低。 相似文献
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《工程热物理学报》2016,(7)
通过数值模拟研究了入口温度对贫燃H_2/air混合气燃烧效率的影响。结果表明:当量比为0.5时,即使入口温度为300 K也能获得很高的燃烧效率,而当量比为0.3和0.4时,由于火焰尖端发生分裂,导致燃料泄漏和燃烧效率下降。入口温度上升50~100 K时,火焰尖端分裂得到显著改善。分析表明:一方面,依据Arrhenius定律,提高混合气温度可以直接增加燃烧反应速率;另一方面,提高入口温度在一定程度上可以增加混合气的有效Lewis数;此外,提高入口温度可使火焰高度变小,削弱火焰拉伸效应的影响。总之,对于贫燃H_2/air火焰来说,小幅提高混合气的初始温度就能明显增加火焰尖端的燃烧强度,抑制火焰尖端分裂现象的发生,提高燃烧效率。 相似文献
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为了获得可燃气体的放电及等离子体发射光谱特性,进一步揭示等离子体助燃作用下燃料在稀燃状态的点火与燃烧特性,在常压下以氩气作为载气对预混的甲烷和空气进行放电研究。实验基于平行板电极射频(13.56 MHz)介质阻挡放电的等离子体发生装置,首先在常压下对体积分数为90%氩气/10%空气的混合气体开展放电研究;再在90%氩气含量不变的情况下,调节空气含量并加入与之能形成燃烧化学当量比Φ=1的甲烷,氩气/甲烷/空气的混合气体同样能实现稳定而均匀的放电;最后分别在90%氩气含量不变,甲烷和空气在当量比为Φ=0.4~1.9六种情况下进行放电实验。由光谱仪记录不同放电工况下的发射光谱信息,诊断反应产物类型,利用观测到的氮分子第二正带系(0-2)380.4 nm和(1-3)375.4 nm处的发射谱线,与自编程序计算的模拟谱线拟合,得出分子转动温度(即气体温度)。研究结果表明:通过拟合模拟光谱与实验所测发射光谱的方法推测分子转动温度,进而获得气体的平动温度,氩气/空气放电的气体温度可达到1 150 K,氩气/甲烷/空气Φ=1时放电气体温度升高到1 390 K;甲烷与空气形成不同当量比时,所测等离子体气体温度相对于90%氩气/10%空气混合气体温度的温升在70~240 K范围变化;由光谱信息观测到CH,H,OH和CH2O等活性粒子的存在以及气体温度的升高,表明可燃成分混合气在射频电场放电作用下发生等离子体燃烧化学反应并释放出化学热。 相似文献
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超低浓度煤层气由于甲烷含量低、浓度变化大而较难加以利用。采用实验和数值模拟的方法,研究了超低浓度煤层气在流化床中燃烧特性,得到燃烧产物的轴向分布规律,分析了进气浓度、床层温度、流化风速等因素对甲烷浓度轴向分布的影响。研究结果表明:随着床层高度的增加,无量纲甲烷浓度逐渐减小,在床层表面达到最小值,然后突然增加,随后达到稳定。实验范围内,CO浓度均小于20mL/m~3减小进气浓度、增加床层温度、降低流化风速部会使相同床层高度处的无量纲甲烷浓度减小。燃烧反应主要发生在密相区,随着进气浓度的减小、床层温度的增加、流化风速的降低,反应区域逐渐向床层下部移动。 相似文献
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Wei-Dong Hsieh Shuhn-Shyurng Hou Ta-Hui Lin 《Proceedings of the Combustion Institute》2005,30(1):267-275
Traditionally, research has focused on positive stretch in the stagnation flow and negative stretch along the Bunsen flame. Only a very limited amount of research has been devoted to studying the behavior of a conical Bunsen flame established in a stagnation flow, which is significantly affected by the combined effects of the curvature stretch and the aerodynamic straining. This investigation is aimed at studying the characteristics of laminar conical premixed flames in an impinging jet flow experimentally and theoretically. First, we analyze the transport processes of a nonreactive impinging jet flow numerically. For lower burner-to-plate distance, the potential core becomes concave at the top. Hence, a conical Bunsen flame established in such a flow field may suffer positive flow stretch. The predicted flame shapes using a simple model incorporated with the numerical results agree well with the experimental observations. Flame shapes exhibit double-solution characteristics in a certain range of methane concentrations. Experimentally, by following different paths of adjusting methane concentration (decreasing from rich to lean or increasing from lean to rich), two different flame configurations (planar or conical flame) may exist at the same flow conditions, namely burner-to-plate distance, inlet velocity, and methane concentration. At the higher (or lower) critical methane concentration, the transition from a flat flame to a conical flame (or from a conical flame to a flat flame) occurs. The calculation of stretch and measurement of flame temperature for the low inlet velocity, 0.8 m/s, show that the stretch of a conical flame established in a stagnation flow is negative (dominated by the flame curvature). However, it is important to emphasize that at high velocity, e.g., Uin = 1.6 m/s, a negatively stretched flame tip can suffer positive flow stretch. This significant finding has been verified in the experiment since the conical flame tip is higher than the positively stretched flat flame. 相似文献
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An experimental study has been conducted to find the heat transfer characteristics of methane/air flames impinging normally to a flat surface using different burner geometries. The burners used were of nozzle, tube, and orifice type each with a diameter of 10 mm. Due to different exit velocity profiles, the flame structures were different in each case. Because of nearly flat velocity profile, the flame spread was more in case of orifice and nozzle burners as compared to tube burner. Effects of varying the value of Reynolds number (600–2500), equivalence ratio (0.8–1.5) and dimensionless separation distance (0.7–8) on heat transfer characteristics on the flat plate have been investigated for the tube burner. Different flame shapes were observed for different impingement conditions. It has been observed that the heat transfer characteristics were intimately related to flame shapes. Heat transfer characteristics were discussed for the cases when the flame inner reaction cone was far away, just touched, and was intercepted by the plate. Negative heat fluxes at the stagnation point were observed when the inner reaction cone was intercepted by the plate due to impingement of cool un-burnt mixture directly on the surface. Different heat transfer characteristics were observed for different burner geometries with similar operating conditions. In case of tube burner, the maximum heat flux is around the stagnation point and decay is faster in the radial direction. In case of nozzle and orifice burner, the heat transfer distribution is more uniform over the surface. 相似文献
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用分子动力学模拟研究石墨狭缝中甲烷的吸附,考察狭缝宽度和温度对甲烷吸附的影响.模拟发现甲烷在石墨狭缝中出现分层现象,吸附层中甲烷具有类液特征,第一吸附层内甲烷中总有两个氢原子的连线与另外两个氢原子的连线分别位于平行于狭缝壁的两个平面内,游离层中甲烷呈现气体的特征;碳原子间的平均作用势说明吸附层中甲烷分子间结合能力大于游离层,吸附态是甲烷在石墨狭缝中的主要赋存形式之一;伦敦力以及由吸附层净电荷产生的电场力是甲烷吸附和分层的主要原因;甲烷的吸附量随狭缝宽度增大或温度升高而减少,当狭缝宽度小于16.46Å时,甲烷仅以吸附形态存在.甲烷在第一吸附层中的扩散能力最弱、游离层中最强,甲烷扩散系数随狭缝宽度的增大或温度的升高而增大. 相似文献
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在压力2.5~4 MPa, 质量流量0.7~1.7g/s, 入口温度20~250 ℃的实验条件下, 对煤油在内径1 mm, 长度300 mm竖直上升圆管中的流动及传热不稳定现象进行了实验研究.结果表明, 当热流密度增大到一定程度后, 传热不稳定开始发生.不稳定发生的起始热流密度随压力和流量的增加而增大, 随入口油温的升高而减小, 且当入口油温升高到一定程度后无不稳定现象发生.不稳定发生的初始时刻, 出口油温迅速增加, 管道壁温明显下降, 传热系数增大; 实验段局部流速增大, 进而在管道内部形成压力脉动并产生声音.不稳定结束后, 出口油温几乎保持不变, 壁温会缓慢增加, 直至下一次不稳定发生. 相似文献
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Accurate, repeatable heat transfer and pressure-drop measurements have been made for condensation of CFC-113 with downflow inside enhanced microfin tubes and tubes containing twisted-wire inserts. In the latter case measurements have also been made for CFC-113/air mixtures. The heat transfer rate was calculated from the coolant flow rate and temperature rise, the latter measured using a 10-junction thermopile with careful attention paid to adequate coolant mixing and isothermal immersion of the thermopile leads. The surface temperature was found from thermocouples embedded in the tube wall. One plain tube, nine microfin tubes (with different fin heights, helix angles, and number of fins), and four twisted-wire inserts (with different wire densities) were tested. Enhancement ratios (i.e., vapor-side heat transfer coefficient for the enhanced tube divided by that for a smooth tube at the same vapor-side temperature difference and vapor inlet velocity) between 1.6 and 5.6 for the microfin tubes and between 1.2 and 1.6 for the twisted-wire inserts were found, with values depending on vapor-side temperature difference, vapor inlet velocity, and air inlet mole fraction in the case of CFC-113/air mixtures. The microfin tubes showed moderate pressure-drop penalties of around 50% compared to the plain tube, while the twisted-wire inserts showed increasing pressure-drop penalty with increasing wire density. 相似文献