Experiment Study on the Exhaust-Gas Heat Exchanger for Small and Medium-Sized Marine Diesel Engine

This paper aims to design a special exchanger to recover the exhaust gas heat of marine diesel engines used in small and medium-sized fishing vessels,which can then be used to heat water up to 55°C–85°C for membrane desalination devices to produce fresh water.A new exhaust-gas heat exchanger of fins and tube,with a reinforced heat transfer tube section,unequal spacing fins,a mixing zone between the fin groups and four routes tube bundle,was designed.Numerical simulations were also used to provide reference information for structural design.Experiments were carried out for exhaust gas waste heat recovery from a marine diesel engine in an engine test bench utilizing the heat exchanger.The experimental results show that the difference between heat absorption by water and heat reduction of exhaust gas is less than 6.5%.After the water flow rate was adjusted,the exhaust gas waste heat recovery efficiency was higher than 70%,and the exhaust-gas heat exchanger’s outlet water temperature was 55°C–85°C at different engine loads.This means that the heat recovery from the exhaust gas of a marine diesel engine meets the requirement to drive a membrane desalination device to produce fresh water for fishers working in small and medium-sized fishing vessels.

Effect of indirect non-thermal plasma on particle size distribution and composition of diesel engine particles

To explore the effect of the gas source flow rate on the actual diesel exhaust particulate matter（PM）, a test bench for diesel engine exhaust purification was constructed, using indirect nonthermal plasma technology. The effects of different gas source flow rates on the quantity concentration, composition, and apparent activation energy of PM were investigated, using an engine exhaust particle sizer and a thermo-gravimetric analyzer. The results show that when the gas source flow rate was large, not only the maximum peak quantity concentrations of particles had a large drop, but also the peak quantity concentrations shifted to smaller particle sizes from 100 nm to 80 nm. When the gas source flow rate was 10L min^-1, the total quantity concentration greatly decreased where the removal rate of particles was 79.2%, and the variation of the different mode particle proportion was obvious. Non-thermal plasma（NTP） improved the oxidation ability of volatile matter as well as that of solid carbon. However, the NTP gas source rate had little effects on oxidation activity of volatile matter, while it strongly influenced the oxidation activity of solid carbon. Considering the quantity concentration and oxidation activity of particles, a gas source flow rate of 10L min^-1 was more appropriate for the purification of particles.

A 3D basin modeling study of the factors controlling gas hydrate accumulation in the Shenhu Area of the South China Sea

Great advancement has been made on natural gas hydrates exploration and test production in the northern South China Sea.However,there remains a lot of key questions yet to be resolved,particularly about the mechanisms and the controls of gas hydrates enrichment.Numerical simulaution would play signficant role in addressing these questions.This study focused on the gas hydrate exploration in the Shenhu Area,Northern South China Sea.Based on the newly obtained borehole and multichannel reflection seismic data,the authors conducted an integrated 3D basin modeling study on gas hydrate.The results indicate that the Shenhu Area has favorable conditions for gas hydrate accumulation,such as temperature,pressure,hydrocarbon source,and tectonic setting.Gas hydrates are most concentrated in the Late Miocene strata,particularly in the structual highs between the Baiyun Sag and the Liwan Sag,and area to the south of it.It also proved the existence of overpressure in the main sag of source rocks,which was subject to compaction disequilibrium and hydrocarbon generation.It also shown that the regional fault activity is not conducive to gas hydrate accumulation due to excess gas seepage.The authors conjecture that fault activity may slightly weaken overpressure for the positive effect of hydrocarbon expulsion and areas lacking regional fault activity have better potential.

通过进气道优化改进柴油机的性能

利用仿真软件FIRE建立了6V150柴油机进气道的三维仿真模型,在用稳流吹风实验验证了仿真的结果后,分析了进气道内部的三维流场,然后采用缩小气门杆后部气流停滞区的方法提高了进气道的流量,而且该方法对气缸盖布置及进气门结构的影响也很小。最后,在仿真软件BOOST建立的整机仿真模型中,对柴油机的性能进行了分析。分析结果显示,在保证空燃比不变的前提下,在柴油机进气量增加的同时也加大其燃油量,可以提高柴油机的有效功率和指示平均有效压力(IMEP),改进了柴油机的动力性。

柴油机燃烧室的系统设计方法研究与应用

为使柴油机燃烧室设计走向系统化和正规化,提出了柴油机燃烧室系统设计的概念。通过对因子处理方法和响应分析方法的梳理总结了9种因子-响应组合方法,选取其中1个燃烧室设计方法进行方法展示。此方法以一款四气门直喷式柴油机作为研究对象,建立了缸内气体瞬态流动模型,以缸内气体流速和湍流动能作为评价标准,在压缩比基本保持不变的前提下,对比分析了缩口率分别为16.4%、6.1%、9.8%、9.8%且底面凸台形状不同的A、B、C、D 4种ω型燃烧室对缸内流场的影响。研究结果表明,燃烧室几何结构对柴油机进气阶段和压缩阶段前期的缸内气流运动影响较小,对压缩阶段后期缸内气流运动影响显著。在上止点前后20°曲轴转角区段,底面凸台呈锥形的C型燃烧室的平均挤流速度、逆挤流速度比底面凸台呈球形的D型燃烧室分别高25.2%、26.4%;缩口率为16.4%的A型燃烧室内气体平均湍流动能比缩口率为9.8%的D型燃烧室高25.4%。与底面凸台呈椭球形的A型和呈球形的D型燃烧室相比,底面凸台呈45°锥形的B、C型燃烧室在湍流动能强度和逆挤流强度方面的保持性更好。该文研究结果可为柴油机燃烧室结构设计和优化提供参考。

柴油机喷嘴喷孔内气液两相湍流场三维数值模拟

柴油机喷嘴内部空穴流动是影响喷雾特性极为重要的因素。在开发了喷嘴流动区域三维实体参数化生成软件的基础上,对完全发展了的空穴流动建立起三维空穴两相流动数学模型,提出将计算区域的出口边界延伸至气缸内部,以减小出口对喷孔内部求解区域的影响。对多孔垂直喷嘴进行了喷孔内部空穴两相湍流流动的三维数值模拟,得出喷嘴内部燃油流动的压力降基本发生在喷孔入口处,喷孔入口锐边过渡,使得该处必定出现空穴现象,且会延伸至喷孔出口,增加液流紊乱,引起燃油在喷孔出口的初次雾化。

柴油机全可变配气缸内流场三维仿真分析

为了改善柴油机动力性、提高经济性并降低排放,本文采用全可变配气技术实现了气阀配气参数的柔性调节,突破了传统柴油机凸轮型线的限制。基于中高速柴油机的气缸结构和进排气系统,使用SolidWorks软件建立柴油机气道-气阀-气缸精确模型,通过ICEM CFD软件实现高质量、速度快的动态层网格。改变进气阀开启、关闭相位和最大升程,使用FLUENT流体计算软件开展可变配气参数下的缸内流动性能CFD仿真研究。仿真结果揭示了缸内流场在不同配气参数下的发展变化规律,为中高速柴油机全可变配气参数优化和控制提供理论基础。

四气门柴油机进气过程三维数值模拟

为减少柴油机的污染物排放、降低油耗和燃烧噪音,通过计算流体力学(Computational Fluid Dynamics,CFD)数值模拟,对车用电控四气门柴油机进气系统进行不同气门升程下气流稳态流动的数值研究,揭示四气门柴油机的进气流动特点以及气门开度对缸内涡流形成的影响和变化规律.仿真结果为电控四气门柴油机的气道设计、喷雾与燃烧的组织与优化提供理论依据.

柴油机分段喷射下混合气形成及其对燃烧排放的影响

基于数值模拟计算,研究了不同预喷策略下某非道路直喷柴油机混合气形成和燃烧过程,分析了挤流和涡流对主、预喷燃油当量比分布和燃烧的影响。结果表明:适当的主预喷间隔(20°)能够使预喷燃油在挤流带动下进入燃烧室凹坑;适当强度的进气涡流比(1.5~2.0)能使预喷油束偏转并在相邻两束主喷油束之间燃烧。二者都可以改善主喷和预喷油束的重叠,并且可以充分利用预喷燃油的放热量促进主喷燃油的混合和提升燃烧速率。优化喷油策略结合适度的进气涡流可以提高发动机功率,降低碳烟排放,但会使NOx排放增加。