共查询到19条相似文献,搜索用时 390 毫秒
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《工程热物理学报》2010,(11)
均质混合气压燃(HCCI)燃烧受爆震和NO_x排放的限制,高负荷拓展是一个难题。本文提出利用理论空燃比SICI组合燃烧作为汽油机中高负荷运行区域的高效低污染燃烧模式。在试验台架上研究了理论空燃比SICI组合燃烧的排放特性及其对三效催化剂(TWC)转换性能的影响。研究发现,通过外部EGR与点火控制相结合,理论空燃比SICI组合燃烧可以在指示平均有效压力(IMEP)0.65~0.82MPa范围内稳定实现;与传统SI燃烧相比,理论空燃比SICI组合燃烧燃油经济性提高近10%,NO_x排放降低80%以上,但HC排放有所增加;SICI组合燃烧与传统SI燃烧类似,TWC空燃比特性的高效区间在理论空燃比附近,但对HC排放的催化能力提出了更高的要求。 相似文献
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二甲醚HCCI燃烧高温反应动力学分析 总被引:1,自引:0,他引:1
应用单区燃烧模型对二甲醚均质压燃燃烧的化学反应动力学过程进行了数值模拟研究。通过分析在内燃机压燃燃烧边界条件下二甲醚高温氧化反应过程中的关键基元反应速度、关键中间产物以及自由基的浓度随曲轴转角的变化,得到了二甲醚燃烧氧化的高温反应途经。结果表明,二甲醚均质压燃燃烧具有明显的两阶段放热特性,即低温反应放热和高温反应放热。高温反应阶段又可分为蓝焰反应阶段和热焰反应阶段,其中蓝焰反应阶段是甲醛氧化成CO的过程,热焰反应主要是CO氧化成CO2的过程。二甲醚氧化产物之一甲酸(HOCHO)在蓝焰反应阶段分解生成CO2。 相似文献
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柴油燃料HCCI燃烧影响因素的试验研究 总被引:4,自引:0,他引:4
本文采用在进气上止点附近进行柴油喷射,利用缸内高温残余废气促进燃油蒸发形成均质混合气,实现了柴油燃料的均质压燃(HCCI)。试验结果表明柴油燃料HCCI燃烧的放热规律呈现低温和高温放热两个阶段,并且NOx排放可以降低95%-98%。本文主要研究了影响HCCI燃烧的因素,指出负荷增大、进气温度增加和负气门重叠期的增加使HCCI着火提前,而外部EGR率的增大可以推迟着火。因此对于低温自燃性好的燃料,冷EGR是控制其HCCI着火燃烧过程的有效措施。 相似文献
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本文利用直接数值模拟方法对均质压燃(HCCI, Homogeneous Charge Compression Ignition)工况下氨氢混合物的着火和燃烧特性进行了研究。结果表明,着火首先从局部孤立区域处发生,随后发展到整个计算区域;最高燃烧温度和热释率随着掺氢比的增加而增加;通过与零维计算结果对比,发现湍流和热分层使得氨氢混合物着火提前。利用直接数值模拟数据计算了反应锋面的位移速度,并据此分析了自着火和火焰传播这两种燃烧模式。发现在低掺氢比的情况下,燃烧模式以自着火为主;而在高掺氢比的情况下,燃烧模式以火焰传播为主。 相似文献
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根据碳氢燃料化学反应系统具有层次结构的特性,本文通过分析二甲醚(DME)与液化石油气(LPG)的详细化学反应机理,构建了反映DME/LPG混合燃料均质压燃(HCCI)燃烧的详细化学反应机理.采用该机理应用单区燃烧模型对DME/LPG混合燃料HCCI燃烧的化学反应动力学过程进行了数值计算.计算结果与试验结果对比表明,所构建的DME/LPG混合燃料氧化的详细化学反应机理能够准确预测DME/LPG混合燃料的两阶段放热特性,对低温和高温着火始点的预测很好;但高温反应过程预测欠佳,高温反应机理需要改进. 相似文献
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《工程热物理学报》2021,42(6):1591-1599
在产品级重型多缸机上对三种不同压缩比条件下的汽柴油双燃料燃烧在全工况平面内进行了优化,重点分析了压缩比对双燃料燃烧全工况范围内燃烧和排放特性的影响,提出了双燃料燃烧在全工况范围内应用的高效清洁燃烧控制策略,并研究了柴油氧化催化器(DOC)对THC和CO排放的净化效果。结果表明:小负荷采用活性控制压燃(RCCI)燃烧模式,中高负荷采用均质混合气引燃(HCII)燃烧模式能够实现汽柴油双燃料全工况范围内的高效清洁燃烧。降低压缩比能够有效拓展中高负荷的最高汽油比例,获得更低的NO_x和Soot排放。使用DOC能够有效净化双燃料燃烧各个工况的THC和CO排放。通过使用上述高效清洁燃烧控制策略以及简单后处理装置DOC,汽柴油双燃料燃烧的NO_x、Soot、THC和CO四项排放物在欧洲稳态循环(ESC)测试中的综合比排放均能满足国5法规,而且综合比油耗与原机纯柴油模式处于同一水平。 相似文献
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《Combustion Theory and Modelling》2013,17(2):417-433
This study used a numerical model to investigate the combustion process in a premixed iso-octane homogeneous charge compression ignition (HCCI) engine. The engine was a supercharged Cummins C engine operated under HCCI conditions. The CHEMKIN code was implemented into an updated KIVA-3V code so that the combustion could be modelled using detailed chemistry in the context of engine CFD simulations. The model was able to accurately simulate the ignition timing and combustion phasing for various engine conditions. The unburned hydrocarbon emissions were also well predicted while the carbon monoxide emissions were under predicted. Model results showed that the majority of unburned hydrocarbon is located in the piston-ring crevice region and the carbon monoxide resides in the vicinity of the cylinder walls. A sensitivity study of the computational grid resolution indicated that the combustion predictions were relatively insensitive to the grid density. However, the piston-ring crevice region needed to be simulated with high resolution to obtain accurate emissions predictions. The model results also indicated that HCCI combustion and emissions are very sensitive to the initial mixture temperature. The computations also show that the carbon monoxide emissions prediction can be significantly improved by modifying a key oxidation reaction rate constant. 相似文献
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进气中CO2浓度对预混合燃烧和排放影响的试验和模拟研究 总被引:4,自引:0,他引:4
本文研究了进气中CO2浓度对燃烧和排放特性的影响.研究表明在所有的预混合燃料比下,当CO2浓度增加时,NOx排放随之大幅减少,烟度排放有小的变化。利用KIVA3V和湍流与化学反应交互的燃烧模型对柴油机预混合燃烧进行了模拟研究,对缸内OH浓度的模拟计算表明,随着CO2浓度的增加,着火前期OH生成浓度明显向后推移,这表明燃料的氧化速率随CO2浓度的增加变慢,从而延长了着火滞燃期。进气中CO2浓度变大时,燃烧温度降低,有利于降低NOx的排放。 相似文献
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Dhananjay Kumar Srivastava Kewal Dharamshi Avinash Kumar Agarwal 《Optics and Lasers in Engineering》2011,49(9-10):1201-1209
In this paper, laser-induced ignition was investigated for compressed natural gas–air mixtures. Experiments were performed in a constant volume combustion chamber, which simulate end of the compression stroke conditions of a SI engine. This chamber simulates the engine combustion chamber conditions except turbulence of air–fuel mixture. It has four optical windows at diametrically opposite locations, which are used for laser ignition and optical diagnostics simultaneously. All experiments were conducted at 10 bar chamber pressure and 373 K chamber temperature. Initial stage of combustion phenomena was visualized by employing Shadowgraphy technique using a high speed CMOS camera. Flame kernel development of the combustible fuel–air mixture was investigated under different relative air–fuel ratios (λ=1.2?1.7) and the images were interrogated for temporal propagation of flame front. Pressure-time history inside the combustion chamber was recorded and analyzed. This data is useful in characterizing the laser ignition of natural gas–air mixture and can be used in developing an appropriate laser ignition system for commercial use in SI engines. 相似文献
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《Proceedings of the Combustion Institute》2023,39(4):4851-4860
This paper presents a joint numerical and experimental study of the ignition process and flame structures in a gasoline partially premixed combustion (PPC) engine. The numerical simulation is based on a five-dimension Flamelet-Generated Manifold (5D-FGM) tabulation approach and large eddy simulation (LES). The spray and combustion process in an optical PPC engine fueled with a primary reference fuel (70% iso-octane, 30% n-heptane by volume) are investigated using the combustion model along with laser diagnostic experiments. Different combustion modes, as well as the dominant chemical species and elementary reactions involved in the PPC engines, are identified and visualized using Chemical Explosive Mode Analysis (CEMA). The results from the LES-FGM model agree well with the experiments regarding the onset of ignition, peak heat release rate and in-cylinder pressure. The LES-FGM model performs even better than a finite-rate chemistry model that integrates the full-set of chemical kinetic mechanism in the simulation, given that the FGM model is computationally more efficient. The results show that the ignition mode plays a dominant role in the entire combustion process. The diffusion flame mode is identified in a thin layer between the ultra fuel-lean unburned mixture and the hot burned gas region that contains combustion intermediates such as CO. The diffusion flame mode contributes to a maximum of 27% of the total heat release in the later stage of combustion, and it becomes vital for the oxidation of relatively fuel-lean mixtures. 相似文献
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Xinyan Wang Hui Xie Liyan Xie Lianfang Zhang Le Li Tao Chen 《Combustion Theory and Modelling》2013,17(1):142-166
SI-CAI hybrid combustion, also known as spark-assisted compression ignition (SACI), is a promising concept to extend the operating range of CAI (Controlled Auto-Ignition) and achieve the smooth transition between spark ignition (SI) and CAI in the gasoline engine. In this study, a SI-CAI hybrid combustion model (HCM) has been constructed on the basis of the 3-Zones Extended Coherent Flame Model (ECFM3Z). An ignition model is included to initiate the ECFM3Z calculation and induce the flame propagation. In order to precisely depict the subsequent auto-ignition process of the unburned fuel and air mixture independently after the initiation of flame propagation, the tabulated chemistry concept is adopted to describe the auto-ignition chemistry. The methodology for extracting tabulated parameters from the chemical kinetics calculations is developed so that both cool flame reactions and main auto-ignition combustion can be well captured under a wider range of thermodynamic conditions. The SI-CAI hybrid combustion model (HCM) is then applied in the three-dimensional computational fluid dynamics (3-D CFD) engine simulation. The simulation results are compared with the experimental data obtained from a single cylinder VVA engine. The detailed analysis of the simulations demonstrates that the SI-CAI hybrid combustion process is characterised with the early flame propagation and subsequent multi-site auto-ignition around the main flame front, which is consistent with the optical results reported by other researchers. Besides, the systematic study of the in-cylinder condition reveals the influence mechanism of the early flame propagation on the subsequent auto-ignition. 相似文献
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Dongil Kang Aleksandr Fridlyand S. Scott Goldsborough Scott W. Wagnon Marco Mehl William J. Pitz Matthew J. McNenly 《Proceedings of the Combustion Institute》2019,37(4):4699-4707
Robust surrogate formulation for gasoline fuels is challenging, especially in mimicking auto-ignition behavior observed under advanced combustion strategies including boosted spark-ignition and advanced compression ignition. This work experimentally quantifies the auto-ignition behavior of bi- and multi-component surrogates formulated to represent a mid-octane (Anti-Knock Index 91.5), full boiling-range, research grade gasoline (Fuels for Advanced Combustion Engines, FACE-F). A twin-piston rapid compression machine is used to achieve temperature and pressure conditions representative of in-cylinder engine operation. Changes in low- and intermediate-temperature behavior, including first-stage and main ignition times, are quantified for the surrogates and compared to the gasoline. This study identifies significant discrepancies in the first-stage ignition behavior, the influence of pressure for the bi- to ternary blends, and highlights that better agreement is achieved with multi-component surrogates, particularly at lower temperature regimes. A recently-updated detailed kinetic model for gasoline surrogates is also used to simulate the measurements. Sensitivity analysis is employed to interpret the kinetic pathways responsible for reactivity trends in each gasoline surrogate. 相似文献
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Simulation is performed to analyse the characteristics of turbulent spray combustion in conventional low and high speed diesel engine conditions. Turbulence–chemistry interaction is resolved by the Conditional Moment Closure (CMC) model in the spatially integrated form of an Incompletely Stirred Reactor (ISR). After validation against measured pressure traces, characteristic length and time scales and dimensionless numbers are estimated at the locations of sequentially injected fuel groups. Conditional flame structures are calculated for sequentially evaporated fuel groups to consider different available periods for ignition chemistry. Injection overlaps the combustion period in the high rpm engine, while most combustion occurs after injection and evaporation are complete in the low rpm engine. Ignition occurs in rich premixture with the initial peak temperature at the equivalence ratio around 2–4 as observed in Dec [2]. It corresponds to the most reactive mixture fraction of the minimum ignition delay for the given mixture states. Combustion proceeds to lean and rich sides in the mixture fraction space as a diffusion process by turbulence. The mean scalar dissipation rates (SDRs) are lower than the extinction limit to show stability of diffusion flames throughout the combustion period. 相似文献