Direct numerical simulations of rich premixed turbulent n-dodecane/air flames at diesel engine conditions

Rich premixed turbulent n-dodecane/air flames at diesel engine conditions are analyzed using direct numerical simulations. The conditions correspond to a parametric variation of the Engine Combustion Network Spray A (pressure 60 atm; oxidizer oxygen level and temperature 21% and 900 K, respectively; fuel temperature 363 K). Three simulations with equivalence ratios of 3, 5, and 7 are performed with a Karlovitz number (Ka, based on flame time) of order 100 to match the estimated Ka of the rich premixed combustion region in Spray A. At these conditions, the reference laminar flames exhibit a complex structure which involves both low-temperature chemistry (LTC) and high-temperature chemistry over a wide range of length scales. In the presence of turbulence, the flame structure is strongly affected in physical space and the reaction zone exhibits a very complex structure in which broken, distributed, and thin regions co-exist, especially for the leanest case. However, the contribution of the LTC pathway is only weakly affected by turbulence. In progress variable space, the mean flame structure, including the chemical source terms, is found to match remarkably well that of the corresponding unity Lewis number laminar flame, particularly for the $?=$ 3 and 5 cases. This behavior is attributed to the strong turbulent mixing occurring throughout the flames/reaction zones, which suppresses differential diffusion effects. Nevertheless, large conditional fluctuations around the mean chemical source terms are identified. These are found to correlate very well with radical species mass fractions such as OH. In addition, a similar functional dependence is obtained from counterflow laminar flames. As such, it appears from these results that laminar flame models have a potential to be used to represent the thermochemical state of rich premixed turbulent flames under diesel engine conditions.     

硅烷化处理对Pt/SAPO-11催化正十二烷临氢异构化反应性能的影响

 利用X射线衍射、N2物理吸附与NH3-程序升温脱附等手段以及异辛烷加氢裂化探针反应研究了硅烷化处理对Pt/SAPO-11催化剂结构和酸性的影响, 并考察了催化剂对正十二烷临氢异构化反应的催化性能. 结果表明,硅烷化处理有效清除了样品外表面的酸性位,减少了发生在外表面的非选择性裂化反应. 硅烷化处理后,催化剂对单支链异构体的选择性明显提高,尤其对单支链端甲基异构体的选择性显著提高,但催化剂的总体异构化选择性有所降低. 硅烷化处理可能造成催化剂的孔口窄化,从而提高单支链异构体的选择性,但同时也导致其微孔孔道内裂化反应的增多.     

Limited Solubility and Critical Exponents for Some Indole + Hydrocarbon Systems

Abstract

The solubility of indole n-octane, n-decane and n-dodecane has been measured at several temperatures. The three systems exhibit limited solubilities with upper critical solution temperatures. The critical exponents of the three systems, evaluated from the experimental data, are found to be the same within the limits of experimental error: β = 0.50 ± 0.4.     

n-Dodecane Hydroconversion over Nickel Supported on Different Mesoporous Aluminosilicates

Introduction The hydroconversion of n-paraffins is achieved over bifunctional catalysts consisting of an acidic support and a hydrogenating/dehydrogenating metal compo-nent.1 During the reaction, the metal catalyses hydrogen transfer reactions, while isomerization and cracking oc-cur on the Br鰊sted acid sites.2,3 This reaction pathway determines that the proper ratio of metal/acid is impor-tant for the catalytic properties of the hydroconversion catalysts. The Pt, Pd or Ni promoted zeolite …     

水-丁醇两相介质合成SAPO-11和MgAPO-11分子筛

在水-丁醇两相介质中合成了SAPO-11和MgAPO-11分子筛.水-丁醇两相介质有利于在SAPO-11中引入更多的Si,从而产生较多的酸性位,以所得SAPO-11为载体的Pt催化剂在正十二烷临氢异构化反应中表现出较高的催化活性.相反,水-丁醇两相介质不利于Mg进入分子筛骨架,导致MgAPO-11上的酸性位减少,Pt/MgAPO-11催化剂的催化活性降低.     

Development and validation of an n-dodecane skeletal mechanism for spray combustion applications

n-Dodecane is a promising surrogate fuel for diesel engine study because its physicochemical properties are similar to those of the practical diesel fuels. In the present study, a skeletal mechanism for n-dodecane with 105 species and 420 reactions was developed for spray combustion simulations. The reduction starts from the most recent detailed mechanism for n-alkanes consisting of 2755 species and 11,173 reactions developed by the Lawrence Livermore National Laboratory. An algorithm combining direct relation graph with expert knowledge (DRGX) and sensitivity analysis was employed for the present skeletal reduction. The skeletal mechanism was first extensively validated in 0-D and 1-D combustion systems, including auto-ignition, jet stirred reactor (JSR), laminar premixed flame and counter flow diffusion flame. Then it was coupled with well-established spray models and further validated in 3-D turbulent spray combustion simulations under engine-like conditions. These simulations were compared with the recent experiments with n-dodecane as a surrogate for diesel fuels. It can be seen that combustion characteristics such as ignition delay and flame lift-off length were well captured by the skeletal mechanism, particularly under conditions with high ambient temperatures. Simulations also captured the transient flame development phenomenon fairly well. The results further show that ignition delay may not be the only factor controlling the stabilisation of the present flames since a good match in ignition delay does not necessarily result in improved flame lift-off length prediction.     

Isentropic compressibilities of chlorobenzene + n-hexane + (n-undecane or n-dodecane) at 298.15 K

In this study, the applicability of the Free Length and the Collision Factor theories to predict multicomponent changes of isentropic compressibilities is analysed and compared. To this end, appropriated expansions for ternary mixtures were derived from the original studies where these theories are developed, and then applied to a mixture containing unlike compounds in terms of functional molecular groups. Experimental data of excess molar volumes from open literature and new experimental isentropic compressibilities of the mixture chlorobenzene?+?n-hexane?+?(n-undecane or n-dodecane) were used to compute the parameters. A good accuracy was obtained when ternary prediction is attempted in this partially soluble mixture at different temperatures by the both methods. These results show the versatility of the models for estimation in complex multicomponent mixtures.     

High pressure measurement of n-dodecane heat capacity up to 100 MPa. Calculation from equations of state

Abstract

Isobaric heat capacities of liquid n-dodecane were measured at temperatures from 313.15 to 373.15 K and at pressures up to 100 MPa using a calorimetric device based on a Calvet calorimeter (Setaram (280). These experimental data were used to perform a comparative study in order to choose, from among the great number of equations of state proposed in the literature, the most appropriate to calculate the isobaric heat capacity.     

低硅铝比ZSM-48分子筛合成及其正构十二烷临氢异构催化性能研究

通过静态水热合成法,溴化六甲二铵作为结构导向剂合成出系列低硅铝比的ZSM48沸石分子筛(Si/Al100),所合成样品中最低硅铝比为38.6(ICP-AES),这将拓宽ZSM-48高硅沸石分子筛的应用范围。制备Pt负载双功能催化剂,用于正构十二烷临氢异构催化反应。结果表明,硅铝比的改变可以影响催化剂的活性,投料硅铝比为70的双功能催化剂具有最优的催化性能,但硅铝比改变对异构产物的分布没有明显的影响,其异构产物以支链在中间位的异构体为主。