直喷式柴油机NO_x和碳烟的预测

本文以直喷式柴油机喷油燃烧过程现象学描述为基础，建立了柴油机准维多区燃烧模型，用以预测直喷式柴油机的NOx和碳烟量，计算结果与实测数据比较接近．     

煤粉燃烧炉膛沿程NOx释放规律的研究

对一维炉内煤粉燃烧，炉膛沿程NOx的释放规律进行了数值模拟和试验研究。研究结果表明：炉内温度升高，NOx的析出峰值升高，位置前移，温度达到一定值后，随温度的升高, NOx 的释放量又呈下降趋势；煤中含氮量越多，NOx释放量越大，NOx的析出峰值位置，随煤种碳化程度的增加而逐渐后移；随过量空气系数的增加，NOx释放量呈明显增加的趋势；NOx的释放量与煤粉粒度的关系中，存在一个煤粉平均粒度临界值dc，当煤粉粒度d≤dc时，随煤粉粒度的减小，NOx的释放量减小，当煤粉粒度d>dc时，随煤粉粒度的减小，NOx的释放量增大；模拟计算同试验结果吻合较好。     

铜精炼阳极转炉氧化期烟气的传热特性

根据能量平衡原理,建立烟气对铜液的传热模型,并对不同空气过剩系数下的烟气平均温度和传热强度进行计算。结果表明:随着空气过剩系数的增大,烟气平均温度和传热强度均有明显下降。为增强烟气对铜液的传热能力,必须适当地减小空气过剩系数。此外,针对燃烧室排烟温度较高的问题,提出采用余热装置回收烟气余热的合理建议。     

一种含能硝基化合物对低燃速低燃温双基推进剂性能影响

为进一步降低低燃速低燃温双基推进剂的燃速、燃温,对一种含能硝基化合物的降温、降速效果进行了实验研究,设计了系列含无机铅盐、有机铜盐及过渡元素金属催化剂的双基配方。通过燃速测试及高压差示扫描量热法(PDSC)研究上述推进剂的燃烧性能和热分解特性。含该硝基化合物的推进剂DSC曲线呈三峰放热,放热峰峰温分别在200℃、280℃、350℃左右,第三峰不明显。结果表明:该含能硝基化合物能有效降低推进剂的燃速、燃温,但使推进剂的压强指数增大,而加入催化剂能改善推进剂的燃烧性能,使压强指数降低,分解放热量也降低。     

Ignition and chemical mechanisms of volume combustion synthesis of titanium diboride

Reaction ignition and chemical mechanisms in volume combustion synthesis of TiB₂ via TiO₂–B₂O₃–Mg precursors were studied using in-situ differential thermal analysis, X-ray diffraction, scanning electron microscopy and thermochemical modeling. Mg–TiO₂ samples ignited at 607 °C through a sudden single step solid-solid reaction while Mg–B₂O₃ samples ignited at 810 °C after melting of magnesium. X-ray diffraction analysis revealed that reduction of TiO₂ occurs in multiple steps and forms intermediate compounds. Results showed that heat released from the first reaction between TiO₂ and Mg ignites the reactions between Mg, Ti and B₂O₃ resulting in the formation of TiB₂. Samples with larger TiO₂ particle size or a higher sample surface to volume ratio showed a two-step reaction behavior and the released heat in the first solid state reaction was insufficient for the propagation of the reaction throughout the sample. In addition, Mg₃B₂O₆ undesired by-product was formed as a result of this two-step reaction.     

Rapid fabrication of Al4SiC4 using a self-propagating high-temperature synthesis method

As a promising high-temperature ceramic, aluminum silicon carbide (Al₄SiC₄) has attracted much attention. Al₄SiC₄ is usually synthesized at high temperatures with a long reaction time in an electric furnace. Self-propagating high-temperature synthesis (SHS) is a promising technique for rapid synthesis. In this study, Al₄SiC₄ was prepared by the SHS method from a mixture of silicon, aluminum and carbon black with the addition of poly(tetrafluoroethylene) (PTFE) as an exothermic promoter. The experimental results showed that the use of a high-pressure Ar atmosphere could retain the gaseous materials in the pellet mixture, and the PTFE additive promoted the formation of silicon carbide. In addition, the oxide layer present on the surface of silicon particles inhibited the reaction between silicon and carbon. As a result, high-purity Al₄SiC₄ could be synthesized from aluminum, silicon, and carbon black with 15 wt% PTFE under 1.0 MPa Ar atmosphere in several seconds by the SHS method.     

Biofuels (alcohols and biodiesel) applications as fuels for internal combustion engines

The increasing industrialization and motorization of the world has led to a steep rise for the demand of petroleum-based fuels. Petroleum-based fuels are obtained from limited reserves. These finite reserves are highly concentrated in certain regions of the world. Therefore, those countries not having these resources are facing energy/foreign exchange crisis, mainly due to the import of crude petroleum. Hence, it is necessary to look for alternative fuels which can be produced from resources available locally within the country such as alcohol, biodiesel, vegetable oils etc. This paper reviews the production, characterization and current statuses of vegetable oil and biodiesel as well as the experimental research work carried out in various countries. This paper touches upon well-to-wheel greenhouse gas emissions, well-to-wheel efficiencies, fuel versatility, infrastructure, availability, economics, engine performance and emissions, effect on wear, lubricating oil etc.     

Large-Eddy/Reynolds-averaged Navier–Stokes simulation of combustion oscillations in a cavity-based supersonic combustor

Combustion oscillations in a supersonic combustor with hydrogen injection upstream of a cavity flameholder are investigated numerically using a hybrid RANS/LES (Reynolds-Averaged Navier–Stokes/Large-Eddy Simulation) method acting as a wall-modeled LES. A turbulent boundary layer with thickness of δ_inf = 2.5 mm is considered and a recycling/rescaling method is adopted to treat the unsteady inflow. The results show that combustion oscillations can mainly be attributed to two mechanisms. One is the unsteady flame spreading from the cavity shear layer to the main stream, which is greatly influenced by the interaction of the jet-with-cavity shear layer. This mechanism leads to relatively low-frequency oscillations that correspond to the cavity-shear layer oscillations. The other is the auto-ignition of the combustible fluid packets formed around the fuel jet accompanied by the generation of the hairpin-like vortices, which leads to relatively high-frequency oscillations that correspond to the jet instabilities.     

基于微燃烧量热仪的典型人造革火灾特性实验研究

通过对家居、办公等场所中主要采用人造皮革种类的调研,分别选择一种高档与中档人造皮革材料,基于微燃烧量热仪,对其主要火灾特性进行了实验研究与对比。实验结果表明,高档人造皮革材料的火灾危险性比中档人造皮革材料更小,即,这些高档人造皮革在给人们带来更舒适的物质享受的同时,在降低室内火灾危险性方面具也有一定的优势。     

Modeling percolative fragmentation during conversion of entrained char particles

A numerical model of carbonaceous particle conversion under chemical and external diffusion control is proposed. The model accounts for different classes of particles which undergo chemical conversion in parallel with percolative fragmentation. It applies to typical conditions of entrained flow reactors. The system of algebraic and differential equations has been numerically solved. Results include the total carbon conversion as well as the determination of particle properties along the reactor. The model correctly predicts the change of the conversion rate at varying temperature, initial oxidant concentration and excess oxidant ratio. The influence of percolation parameters is also relevant and claims further investigations for more accurate determination. A comparison with experimental data available in literature is also provided