Study on effect of heat transfer space non-uniformity of combustion chamber components on in-cylinder NOx emission formation in internal combustion engine

The components of combustion chamber (cylinder head-cylinder liner-piston assembly-oil film) were taken as a coupled body.Based on the three-dimensional heat transfer numerical simulation of the coupled body,a coupled three-dimensional calculation model for in-cylinder working process and the combustion chamber components was built with domain decomposition and boundary coupled method,which implements the coupled three-dimensional simulation of in-cylinder working process and the combustion chamber components.The model was applied in the influence investigation of the space non-uniformity in heat transfer among combustion chamber components on the generation of in-cylinder emissions:NOx.The results showed that the heat transfer space non-uniformity of combustion chamber components directly influences the formation of in-cylinder NOx.The main area being influenced was the accessory area on the wall,while the influence on the generation of NOx in the central area couold be omitted.     

Experimental study of effects of oxygen concentration on combustion and emissions of diesel engine

Effects of oxygen concentration on combustion and emissions of diesel engine are investigated by experiment. The intake oxygen concentration is controlled by adjusting CO₂. The results show that very low levels of both soot and NO _x emissions can be achieved by modulating the injection pressure, timing, and boost pressure at the low levels of oxygen concentration. However, both CO and HC emissions and fuel consumption distinctly increase at the low levels of oxygen concentration. The results also indicate that NO _x emissions strongly depend on oxygen concentration, while soot emissions strongly depend on injection pressure. Decreasing oxygen concentration is the most effective method to control NO _x emissions. High injection pressure is necessary to reduce smoke emissions. High injection pressure can also decrease the CO and HC emissions and improve engine efficiency. With the increase of intake pressure, both NO _x and smoke emissions decrease. However, it is necessary to use the appropriate intake pressure in order to get the low HC and CO emissions with high efficiency. Supported by the National Natural Science Foundation of China (Grant Nos. 50636040, 50676066)     

A New Method for Computing Radiation Heat Flow of In-Cylinder Soot of Diesel Engines

A concise formula for computing radiation heat flow of in-cylinder soot is presented,based on the assumptions that in-cylinder heat transfer of diesel engines is a quasi-equilibrium process and in-cylinder soot particles are spherical. That in this formula there consist neither constants needing adjustments nor variables related to engine types or operating conditions makes it universal and easy to use. Also it can be seen from the formula that radiation heat transfer is proportional to the quotient of in-cylinder soot mass over the average radius of primary particles. Besides, with the help of different algorithms it can be used for predicting cylinders' global as well as local radiation heat flows. As a demonstrative application on its global facet, a three-dimension simulation study about the soot-radiation-related heat flow in the combustion chamber of a diesel engine is carried out. Results show that the range of the soot-radiation-related heat flow computed by this formula agrees well with other researcher's earlier theoretic reasoning and experimental measurements.     

Effect of exhaust gas recirculation and intake pre-heating on performance and emission characteristics of dual fuel engines at part loads

Achieving simultaneous reduction of NO _x , CO and unburned hydrocarbon (UHC) emissions without compromising engine performance at part loads is the current focus of dual fuel engine research. The present work focuses on an experimental investigation conducted on a dual fuel (diesel-natural gas) engine to examine the simultaneous effect of inlet air pre-heating and exhaust gas recirculation (EGR) ratio on performance and emission characteristics at part loads. The use of EGR at high levels seems to be unable to improve the engine performance at part loads. However, it is shown that EGR combined with pre-heating of inlet air can slightly increase thermal efficiency, resulting in reduced levels of both unburned hydrocarbon and NO _x emissions. CO and UHC emissions are reduced by 24% and 31%, respectively. The NO _x emissions decrease by 21% because of the lower combustion temperature due to the much inert gas brought by EGR and decreased oxygen concentration in the cylinder.     

掺烧煤热解气和生物质气对锅炉NOx排放的影响

对煤热解气和生物质气耦合煤粉进行了模拟,研究了不同组分的掺烧气体条件下锅炉NOx排放规律。结果表明,与原煤燃烧相比,掺烧煤热解气和生物质气均可降低锅炉NOx排放量。烟道出口处,原煤燃烧工况下NOx浓度值为244.2 mg/m3,比掺烧煤热解气时的NOx浓度值高出44.7 mg/m3,比掺烧生物质气时的NOx浓度值高出28.1 mg/m3。燃气组分中CHi基元成分越高,NOx排放值越低。     

Simulation of VGT control based on charge oxygen concentration

A turbocharged diesel engine model was built with the GT-Power software,and experimentally verified.Then two different control variables for the control of the variable geometry turbocharger（VGT）were described,and their distinct effects on engine performance,i.e.NOxand soot emissions and fuel consumption,were simulated and compared on the basis of this model.The results showed that NOxemissions decreased obviously with the increase of exhaust gas recirculation（EGR）rate at constant boost pressure condition,but soot emissions and fuel consumption considerably increased.It was a good way to reduce NOxemissions without increasing fuel consumption and soot emissions when VGT was controlled to maintain the excess oxygen ratio unchanged as EGR rate increases.     

某2 027 t/h锅炉变工况掺烧污泥燃烧特性研究

采用Fluent软件,针对某2 027 t/h四角切圆煤粉锅炉不同负荷下单独燃烧煤粉、煤粉和污泥混烧工况进行了数值模拟,研究了炉内流动、燃烧和NOx排放特性。结果表明：模型能够模拟锅炉燃烧过程,模拟误差在10%以内;掺混污泥对炉内速度场影响较小,掺混污泥后,水分蒸发吸热,炉膛整体温度水平下降,中上层燃烧器区域CO和HCN生成量增加,还原性气氛增强,NOx生成受到抑制;掺混10%比例污泥后,600 MW,510 MW,450 MW工况下平均温度峰值分别降低了15.5 K,8.2 K,3.1 K,NOx排放分别降低10.9%,13.1%,8.1%。     

近后喷对高压共轨柴油机燃烧过程影响的数值计算

应用CFD模拟软件FIRE针对车用增压共轨柴油机在高负荷工况下采用近后喷策略的缸内工作过程进行了数值计算。分析了后喷量和主/后间隔角对燃烧过程的影响。研究结果表明,随着后喷量和主/后间隔角度的增加,缸内燃烧压力、放热规律及缸内温度曲线的峰值降低,燃烧重心推迟,燃烧噪音和NOx生成量减少,但经济性有所恶化。同时,增大后喷量一方面可使后喷燃油的贯穿距增大,在壁面附近高温缺氧区域内形成的燃油蒸汽增多,增加了后喷燃油的Soot的生成量,另一方面增强了对缸内流场的扰动效果,使得更多的氧气进入燃烧产物区,加速了Soot的氧化,因此选取适当的后喷量可以获得较低的Soot的生成量。后喷间隔过大时,Soot排放有明显增加的趋势。     

Numerical investigations on HCCI engine with increased induction induced swirl and engine speed

Homogeneous charge compression ignition(HCCI) mode of combustion is popularly known for achieving simultaneous reduction of NOx as well as soot emissions as it combines the compression ignition(CI) and spark ignition(SI) engine features. In this work, a CI engine was simulated to work in HCCI mode and was analyzed to study the effect of induction induced swirl under varying speeds using three-zone extended coherent flame combustion model(ECFM-3Z, compression ignition) of STAR-CD. The analysis was done considering speed ranging from 800 to 1600 r/min and swirl ratios from 1 to 4. The present study reveals that ECFM-3Z model has well predicted the performance and emissions of CI engine in HCCI mode. The simulation predicts reduced in-cylinder pressures, temperatures, wall heat transfer losses, and piston work with increase in swirl ratio irrespective of engine speed. Also, simultaneous reduction in CO2 and NOx emissions is realized with higher engine speeds and swirl ratios. Low speeds and swirl ratios are favorable for low CO2 emissions. It is observed that increase in engine speed causes a marginal reduction in in-cylinder pressures and temperatures. Also, higher turbulent energy and velocity magnitude levels are obtained with increase in swirl ratio, indicating efficient combustion necessitating no modifications in combustion chamber design. The investigations reveal a total decrease of 38.68% in CO2 emissions and 12.93% in NOx emissions when the engine speed increases from 800 to 1600 r/min at swirl ratio of 4. Also an increase of 14.16% in net work done is obtained with engine speed increasing from 800 to 1600 r/min at swirl ratio of 1. The simulation indicates that there is a tradeoff observed between the emissions and piston work. It is finally concluded that the HCCI combustion can be regarded as low temperature combustion as there is significant decrease in in-cylinder temperatures and pressures at higher speeds and higher swirl ratios.     

高压喷射的高速直喷柴油机混合气形成及燃烧过程

为了有效组织燃烧室内气流特性,改进了车用缩口直喷高速柴油机燃烧室结构,并在此基础上基于CFD商用软件FIRE对匹配不同轨压的喷雾特性时燃烧室内气液混合流的速度场、浓度场和温度场的动态分布特性进行了仿真计算分析。研究了高速直喷柴油机的混合气形成规律,并通过试验研究了这种混合气形成特性对燃烧过程及排放特性的影响。结果表明:通过对缩口直喷燃烧室内气流特性和轨压的优化匹配,可以有效地控制燃烧过程的滞燃期、预混合燃烧比例和扩散燃烧过程,从而控制高温燃烧持续期,在保证经济性的前提下,可以有效地降低NOx和烟度排放。     

Effects of H<Subscript>2</Subscript>/CO/CH<Subscript>4</Subscript> syngas composition variation on the NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> and CO emission characteristics in a partially-premixed gas turbine combustor

This paper reports the effects of variations in the fuel composition of H₂/CO/CH₄ syngas on the characteristics of NO _x and CO emissions in a partially-premixed gas turbine combustor. Combustion tests were conducted on a full range of fuel compositions by varying each component gas from 0% to 100% at heat inputs of 40 and 50 kW_th. Flame temperature, combustor liner temperature, ignition delay time, and flame structure were investigated computationally and experimentally to judge whether they are significant indicators of NO _x and CO formation. The characteristics of and reasons for NO _x and CO emissions were investigated by analyzing the emission mechanisms and relationships among fuel property, equivalence ratio, flame temperature, liner temperature, flame shape. The flame structures were investigated using the following flame visualization methods: (1) time-averaged OH* chemiluminescence and its Abel-deconvolution; (2) direct photography; and (3) instantaneous OH-PLIF. The flame structures were greatly changed by the fuel composition and heat input, and they were subjected to key affecting parameters of the temperatures of the flames and the liners. NO _x and CO emissions also largely varied according to fuel composition and heat input, showing neither linearly nor exponentially clear proportional trends toward the syngas compositions because of the singular conditions. For example, only the 100% CO flame at low load emitted lots of CO, whereas complete combustion was observed in other cases. However, the qualitative observations showed that the root causes of NO _x emission behaviors were flame temperature and flame structure, which were directly related to the residence time in the flame. Various sets of practical test results were obtained, and these results could contribute to the optimal selection of the fuel-feeding condition when fuel is changed from natural gas to syngas in order to minimize NO _x and CO emissions with stable combustion.     

Numerical Investigation of the Effects of Rate-Shaped Main Injection on Combustion and Emission in an OPOC Two-Stroke Diesel Engine

The effects of various split injection strategies on the opposed-piston opposed-cylinder (OPOC)diesel engine combustion and emission characteristics have been studied numerically using AVL-Fire CFD tools. The five rate-shaped main injections were used in split injection strategies. The results show that ignition delay from a rectangular injection rate is the shortest. Maximum pressure of the trapezoid injection rate is the largest. And the NO_x emission of the rectangular injection rate is the largest. Meanwhile, the soot emission of the trapezoid injection rate is the least among the five injection rates.     

不同再燃技术降低燃煤锅炉NOx排放的对比分析

目前降低NO_x生成与排放技术中,再燃技术具有改造费用低、锅炉运行效率高、降低NO_x排放效率显著等特点。通过分析超细粉、生物质气、天然气和H₂作为再燃燃料的机理、影响因素、优缺点和实际应用情况,比较了不同再燃技术降低NO_x排放的技术参数和经济性,发现H₂再燃技术降低燃煤锅炉NO_x排放具有较大优越性。     

The effects of EGR and ignition timing on emissions of GDI engine

The effects of EGR and ignition timing on engine emissions and combustion were studied through an experiment carried out on an air-guided GDI engine. The test results showed that the ignition timing significantly affected the GDI engine emissions, that the NO _x emissions significantly reduced when the ignition timing was retarded, and that NO _x emissions decreased with the EGR level increasement. A higher EGR rate could reduce CO emissions while the CO emissions were less affected by the ignition timing. The HC emissions decreased at a lower EGR rate. At 2500 r/min, an appropriate EGR rate could cut down CO emissions. The exhaust gas temperature could significantly decrease with improving the EGR rate, and the exhaust gas temperature at 2500 r/min was clearly higher than that at 1850 r/min. The nucleation mode particles increased clearly, the accumulation mode particle number decreased gradually with the increase of EGR rate, and the typical particle size of nucleation mode particle was in the range of 10–25 nm.     

Characteristics of radiation and convection heat transfer in indirect near-infrared-ray heating chamber

Numerical study was performed to evaluate the characteristics of combined heat transfer of radiation,conduction and convection in indirect near infrared ray (NIR) heating chamber.The effects of important design parameters such as the shape of heat absorbing cylinder and heat releasing fin on the pressure drop and heat transfer coefficient were analyzed with different Reynolds numbers.The Reynolds numbers were varied from 103 to 3×106,which was defined based on the hydraulic diameter of the heat absorbing cy...     

快速压缩机漏气量的计算方法

以自主研发的快速压缩机为研究对象,对燃烧缸内可燃混合气的泄漏量进行了计算。由于密封不好和活塞速度较慢,快速压缩机出现漏气,混合气的泄漏量与压缩比和活塞的速度有关。作者利用已知的缸内压力-时间关系曲线,对活塞的有效漏气面积进行了计算,在根据燃烧时缸内压力变化关系曲线对燃烧缸的漏气量进行了计算。漏气量的计算可以实现对缸内压力曲线修正,同时也可以对燃料的低热值进行修正,研究结果有助于提高计算精度和准确分析燃烧特性。     

基于CMAQ-MCM模型的长三角地区夏季臭氧和大气氧化性影响的研究

传统的空气质量模型多使用简化的光化学反应机制来模拟大气污染物的形成.这些机制主要基于烟雾箱实验拟合的反应速率和产物来模拟二次产物（如臭氧（O₃））前体物的氧化反应，具有一定的不确定性，导致模拟结果产生偏差.针对该问题，本研究将详细的大气化学机理（MCMv3.3.1）与美国国家环境保护局研制的第三代空气质量预报和评估系统CMAQ相结合（CMAQ-MCM），模拟研究长三角地区2015年8月27—9月5日臭氧高发时段的空气质量.CMAQ-MCM模型可以较好地模拟长三角地区6个代表城市O₃和其前体物随时间的变化趋势.对模拟的O₃日最大8 h平均浓度的统计分析表明，徐州表现最好（标准平均误差=-0.15，标准平均偏差=0.23）.在长三角地区，居民源对挥发性有机物（VOCs）的贡献最大，占39.08%，其次是交通运输（33.25%）和工业（25.56%）.能源对总VOCs的贡献最小，约为2.11%.对活性氧化氮（NO_y）的分析表明，其主要组分是NO_x（80%），其次是硝酸（HNO₃）（<10%）.O₃的空间分布与NO_y和NO_x非常相似.HCHO等其他氧化产物的分布与NO_x相似，这很可能是由于在高NO_x条件下VOCs氧化产生的产物.甲基乙烯基酮（MVK）和甲基丙烯醛（MACR）的空间分布与自然源VOCs （BVOCs）非常相似，表明长三角地区MVK和MACR主要由BVOCs氧化生成.长三角地区受到人为源和自然源排放相互作用的影响.     

汽油机缸内富氧燃烧的试验研究

富氧燃烧是一种可以实现节约能源和降低污染物排放的内燃机燃烧技术.通过汽油发动机在同一工况工作时,使进气中氧体积分数分别为20.7％、23.2％和25.4％,实现富氧燃烧.研究不同的进气氧体积分数对汽油发动机的燃烧特性和排放特性的影响.研究结果表明：进气氧体积分数增加,发动机缸内压力和燃烧放热率升高,最高燃烧压力相位提前,降低循环波动,发动机燃烧工作稳定;同时减少THC和CO的排放,但NOx的排放量增大.     

Review: Investigation of Partially Pre-mixed Charge Ignitions (PPCI) Engine Mode

This paper embraces the key points of unpolluted internally combusted engine emissions. Core objective is focused on the recent effort to improve compression ignition(CI) and spark ignition(SI) engine to have fuel-efficient and minimized pollutant emissions. There are many advanced internal combustion engines to overcome the challenges of conventional compression ignition engines of the high level of particulate matter(PM) and oxides of nitrogen emission. One of the latest options on which many ...     

Investigation of the combustion deterioration of an automotive diesel engine under transient operation

With increasingly stringent emission regulations and demand for fuel economy by the public,the combustion and emission problems of automotive diesel engines during transient operation have become vital and urgent issues.In this study,combustion deterioration has been experimentally analyzed using a heavy-duty turbocharged diesel engine running under transient conditions(constant speed and increasing torque).Optimization of the transient combustion process was performed by adjusting the fuel injection parameters.The results indicated that the notable combustion deterioration relative to steady state operation while transient was a function of the delay in the air-supply to the turbocharged engine,and took the form of combustion phasing delay,resulting in rapidly increasing smoke emission and fuel consumption.However,the delay in combustion phasing can be controlled by advancing the fuel injection timing,effectively increasing thermal efficiency.Unfortunately,smoke and NO x emissions increased at the same time.The deterioration in combustion phasing can also be improved by increasing injection pressure,resulting in decreased smoke emission while NO x emission increased.It is worth noting that the effective thermal efficiency first increased and then decreased as fuel injection pressure increased during transient operation.