Lesson 9 Exhaust Emission and Control

Lesson 9 Exhaust Emission and Control

Marine engine designers in recent years have had to address the challenge of tightening

controls on noxious exhaust gas emissions imposed by regional, national and international

authorities responding to concern over atmospheric pollution.近年来，船舶发动机设计人员不得不应对地区、国家和国际当局(国际组织)为应对大气污染问题而实施的对有害废气排放的严格控制的挑战。

Exhaust gas emissions from marine diesel engines largely comprise nitrogen, oxygen, carbon

dioxide and water vapor, with smaller quantities of carbon monoxide, oxides of sulphur and

nitrogen, partially reacted and non-combusted hydrocarbons and particulate material[1]. 船用柴油机的废气排放主要包括氮气、氧气、二氧化碳和水蒸气，以及少量的一氧化碳、硫氧化物和氮氧化物、部分反应和未燃烧的碳氢化合物和颗粒物。

Nitrogen oxides (NOx)--generated thermally from nitrogen and oxygen at high combustion

temperatures in the cylinder--are of special concern since they are believed to be carcinogenic(致癌物(质)的) and contribute to photochemical smog formation over cities and acid rain (and hence

excess acidification of the soil). 氮氧化物（NOx）—气缸内高温燃烧时由氮气和氧气生成—特别值得关注，因为它们被认为是致癌物质，有助于在城市上空形成光化学烟雾和酸雨（从而导致土壤过度酸化）。 Internal combustion engines primarily generate nitrogen oxide but less

than 10 per cent of that oxidizes to nitrogen dioxide the moment it escapes as exhaust gas.内燃机主要产生氮氧化物，但只有不到10%的氮氧化物在作为废气排出时氧化为二氧化氮。

Sulphur oxides (SOx)--produced by oxidation of the sulphur in the fuel--have an unpleasant

odor, irritate the mucus membrane and are a major source of acid rain (reacting with water to form

sulphurous acid). 硫氧化物（SOx）是由燃料中的硫氧化而产生的，具有难闻的气味，刺激粘液膜，是酸雨的主要来源（与水反应生成亚硫酸）。 Acid deposition is a trans-boundary

pollution problem: once emitted, SOx can be carried over hundreds of miles in the atmosphere

before being deposited in lakes and streams, reducing their alkalinity.酸沉积是一个跨国界的污染问题：SOx一旦排放，可以在大气中传播数百英里，然后再沉积到湖泊和溪流中，降低其碱度。

Sulphur deposition can also lead to increased sulphate levels in soils, fostering the formation

of insoluble aluminum phosphates which can cause a phosphorous deficiency. 硫沉积还会导致土壤中硫酸盐含量的增加，促进不溶性磷酸铝的形成，从而导致磷缺乏。 Groundwater

acidification has been observed in many areas of Europe; this can lead to corrosion of drinking

water supply systems and health hazards due to dissolved metals in those systems[2]. 在欧洲的许多地区已经观察到地下水酸化现象；这可能导致饮用水供应系统的腐蚀，并由于系统中溶解的这些金属（盐）而对健康造成危害。 Forest soils can also become contaminated with higher

than normal levels of toxic metals, and historic buildings and monuments damaged.森林土壤也会被高于正常水平的有毒金属污染，历史建筑和古迹也会受损。

Hydrocarbons (HC)--created by the incomplete combustion of fuel and lube oil, and the

evaporation of fuel--have an unpleasant odor, are partially carcinogenic, smog forming and irritate

the mucus membrane (emissions, however, are typically low for modern diesel engines.)碳氢化合物（HC）是由燃料和润滑油不完全燃烧和燃油蒸发产生的，有一种难闻的气味，会部分致癌，会形成烟雾并刺激粘液膜（然而，对于现代柴油发动机来说，排放量通常较低）

Carbon monoxide (CO)--resulting from incomplete combustion due to a local shortage of air

and the dissociation of carbon dioxide--is highly toxic but only in high concentrations.一氧化碳

（CO）是由于局部空气不足产生不完全燃烧和二氧化碳分解而产生的，但仅在浓度很高时具有很高的毒性。

Particulate matter (PM) is a complex mixture of inorganic and organic compounds resulting

from incomplete combustion, partly unburned lube oil, thermal splitting of HC from the fuel and

lube oil, ash in the fuel and lube oil, sulphates and water. 颗粒物（PM）是无机和有机化合物的复杂混合物，源于不完全燃烧产物、部分未燃烧的润滑油、燃料和润滑油中HC的热裂解产物、燃料和润滑油中的灰分以及硫酸盐和水等物。 More than half of the total particulate mass

is soot (inorganic carbonaceous particles), whose visible evidence is smoke. 总颗粒物质量的一半以上是烟尘（无机含碳颗粒），其可见证据是烟雾。Soot particles (unburned elemental carbon)

are not themselves toxic but they can cause the build-up of aqueous（水的, 水成的）

hydrocarbons, and some of them are believed to be carcinogens. 烟灰颗粒（未燃烧的碳成分）本身没有毒性，但它们会导致水性碳氢化合物的积聚，其中一些被认为是致癌物。

Particulates constitute no more than around 0.003 per cent of the engine exhaust gases.微粒组分在发动机废气中所占比例大约不超过0.003%。

Noxious emissions amount to 0.25-0.4 percent by volume of the exhaust gas, depending on

the amount of sulphur in the fuel and its lower heat value, and the engine type, speed and

efficiency. 有害排放物占废气体积的0.25-0.4%，这取决于燃油中的硫含量及其低热值、以及发动机类型、转速和效率。 Some idea of the actual pollutants generated is provided by MAN

B&W Diesel, which cites an 18 V 48/60 medium speed engine in NOx-optimized form running at

full load on a typical heavy fuel oil with 4 per cent sulphur content. MAN B&W Diesel提供了一些真实产生污染物的理念，在NOx形成优化方面，该公司让一台18 V 48/60中速发动机，用典型的含硫量为4%的重质燃油满负荷运转。 A total of approximately 460 kg of harmful

compounds are emitted per hour out of around 136 tones of exhaust gas mass per hour. 在每小时大约136吨的废气质量中，大约每小时一共排放460千克有害化合物。 Of the 0.35 per cent of

the exhaust gas formed by pollutants, NOx contributes 0.17 per cent, sulphur dioxide 0.15 per cent,

hydrocarbons 0.02 percent, carbon monoxide 0.007 per cent and soot/ash 0.003 per cent.在形成废气的占0.35%的污染物中，氮氧化物占0.17%，二氧化硫占0.15%，碳氢化合物占0.02%，一氧化碳占0.007%，烟尘/灰烬占0.003%。

Carbon dioxide: some 6 per cent of the exhaust gas emissions from this engine are carbon

dioxide. 二氧化碳：这台发动机排放的废气中约有6%是二氧化碳。 Although not itself toxic,

carbon dioxide contributes to the greenhouse effect (global warming) and hence to changes in the

Earth's atmosphere. 尽管二氧化碳本身没有毒性，但它会导致温室效应（全球变暖），从而导致地球大气层的变化。The gas is an inevitable product of combustion of all fossil fuels, but

emissions from diesel engines--thanks to their thermal efficiency--are the lowest of all heat

engines. 废气是所有化石燃料燃烧的必然产物，但柴油发动机的排放是所有热机中最低的，这要感谢它（较高）的热效率。 A lower fuel consumption translates to reduced carbon dioxide

emissions since the amount produced is directly proportional to the volume of fuel used, and

therefore to the engine or plant efficiency. 较低的燃料消耗会减少转化为二氧化碳排放量，因为二氧化碳的产生量与所使用燃料的总量直接成正比，因此与发动机或装置的效率成正比（反比？）。 As a rough guide, burning one tone of diesel fuel produces approximately three

tones of carbon dioxide.粗略地说，燃烧一吨柴油会产生大约三吨二氧化碳。

International concern over the atmospheric effect of carbon dioxide has stimulated measures

and plans to curb the growth of such emissions, and the marine industry must be prepared for

future legislation. 国际社会对二氧化碳对大气影响的关注，促使各国采取措施和计划来遏制

这类排放的增长，航运业必须为未来的立法做好准备。(A switch from other transport

modes--air, road and rail--to shipping would nevertheless yield a substantial overall reduction in

emissions of the greenhouse gas because of the higher efficiency of diesel engines.)（从其他运输方式—航空、公路和铁路—转向航运，将使温室气体的排放总量大幅减少，因为柴油发动机的效率更高。）

The scope for improvement by raising the already high efficiency level of modern diesel

engines is limited and other routes have to be pursued: 现代柴油机的效率已经很高，再提高和改进的余地已经有限，必须寻求其他途径：operating the engines at a fuel-saving service point;

让发动机运行在节油伺服点； using marine diesel oil or gas oil instead of low sulphur heavy

fuel oil; 使用船用柴油或柴油代替低硫重油；adopting diesel-electric propulsion (the engines

can be run continuously at the highest efficiency); 采用柴—电推进（发动机可以最高效率连续运行）； or exploiting a diesel combined cycle incorporating a steam turbine. 或采用包含蒸汽轮机的柴油复合循环。 The steam-injected diesel engine is also promising.蒸汽喷射柴油机也很有前途。

Compared with land-based power installations, fuel burned by much of shipping has a very

high sulphur content (up to 4.5 per cent and more) and contributes significantly to the overall

amount of global sulphur oxide emissions at sea and in port areas. 与陆基电力装置相比，大部分船舶燃烧的燃料含硫量非常高（高达4.5%或更多），对全球海上和港口地区的硫氧化物排放总量有很大贡献。Studies on sulphur pollution showed that in 1990 SOx emissions from ships

contributed around 4 per cent to the total in Europe. 对硫污染的研究表明，在欧洲，1990年船舶排放的SOx约占总排放量的4%。In 2001 such emissions represented around 12 per cent of the

total and could rise to as high as 18 per cent by 2010.2001年，这类排放量约占总量的12%，到2010年可能高达18%。

SOx emissions in diesel engine exhaust gas--which mostly comprise sulphur dioxide with a

small amount of sulphur trioxide--are a function of the amount of sulphur in the fuel and cannot be

controlled by the combustion process. 柴油机废气中SOx的排放量（主要由二氧化硫和少量三氧化硫组成）是燃油中含硫量的函数，不能通过燃烧过程来控制。If the fuel contains 3 per cent

sulphur, for example, the volume of SOx generated is around 64 kg per ton of fuel burned; 例如，如果燃油中含有3%的硫，则每燃烧一吨燃料产生的SOx量约为64千克；if fuel with 1 per cent

sulphur content is used SOx emissions amount to around 21 kg per ton of fuel burned.如果使用含硫量为1%的燃油，则每燃烧一吨燃油，SOx排放量约为21千克。

Chemical and washing/scrubbing desulphurization processes can remove SOx from the

exhaust gases but are complex, bulky and expensive for shipboard applications, and increase

overall maintenance costs[4]. 化学和洗涤/筛洗等脱硫工艺可以去除废气中的SOx，但对于船上应用来说，其工艺复杂、体积庞大、成本高昂，并增加了总体维护成本。The most economical

and simplest approach is thus to burn bunkers with a low sulphur content. 因此，最经济和最简单的方法是燃烧低硫燃油。 (If a selective catalytic reduction system is installed to achieve the

lowest NOx emission levels--see section below--then low sulphur fuels are dictated anyway to

avoid premature fouling of the system's catalyst package.)（如果安装选择性催化还原系统以达到最低的NOx排放水平（见下文章节），则应使用低硫燃料，以避免系统催化组件过早失效。）

A global heavy fuel oil sulphur content cap of 4.5 percent and a 1.5 per cent fuel sulphur limit

in certain designated Sulphur Emissions Control Areas (SECAS)--such as the Baltic Sea, North

Sea and English Channel is sought by the International Maritime Organization (IMO) to reduce

SOx pollution at sea and in port. 国际海事组织（IMO）寻求设定4.5%的全球重油含硫量上限，

以及指定硫排放控制区（SECA）1.5%的燃油含硫限制，如在波罗的海、北海和英吉利海峡等，以减少海上和港口的SOx污染。The European Union strategy for controlling air pollution

calls for all ships in EU ports to burn fuel with a maximum sulphur content of 0.2 per cent, which

would force unit-fuel ships to carry low sulphur fuel specifically for this purpose[5].欧盟为了控制空气污染所采用的策略是：要求所有欧盟港口的船舶必须燃烧低硫燃油，其含硫量最高为0.2%，这将迫使（使用）单一（品种）燃料的船舶专门为此要求而携带低硫燃油。

Exhaust gas recirculation

Exhaust gas recirculation (EGR) is a method of modifying the inlet air to reduce NOx

emissions, an approach widely used in automotive applications. 废气再循环（EGR）是一种改善进气以降低NOx排放的方法，是汽车领域中得到广泛应用的一种途径。Some of the exhaust

gas is cooled and cleaned before recirculation to the scavenge air side. 少量废气在再循环至扫气箱侧之前被冷却和清洗。Its effect on NOx formation is partly due to a reduction of the oxygen

concentration in the combustion zone, and partly due to the content of water and carbon dioxide in

the exhaust gas. 它对NOx形成的影响部分是由于燃烧区中氧气浓度的降低，部分是由于废气中的水和二氧化碳的含量。 The higher molar heat capacities of water and carbon dioxide lower

the peak combustion temperature which, in turn, curbs the formation of NOx[6].而高摩尔热容的水和二氧化碳会降低燃烧室的最高燃烧温度，从而抑制氮氧化物的产生。

EGR is a very efficient method of reducing NOx emissions (by 50-60 per cent) without

affecting the power output of the engine but is considered more practical for engines burning

cleaner bunkers such as low sulphur and low ash fuels, alcohol and gas. EGR是一种非常有效的方法，可在不影响发动机功率输出的情况下减少NOx排放（减少50-60%），对于燃烧清洁燃料的发动机来说，如使用低硫和低灰分燃料、酒精和天然气等的发动机，采用EGR更为切实可行。 Engines operating on high sulphur fuel might invite corrosion of turbochargers,

intercoolers and scavenging pipes.使用高硫燃料的发动机可能会使涡轮增压器、空冷器和扫气道带来腐蚀。

Wartsila acknowledges that EGR leads to reductions in NOx emissions but suggests its

practical application is limited by the fact that it quite soon starts to adversely affect combustion,

leading to increased fuel consumption, particulates, unburned hydrocarbons and carbon monoxide.

瓦锡兰确认（使用）EGR可减少NOx排放，但其实际应用受到以下事实的限制：EGR很快开始对燃烧产生不利影响，导致燃油消耗量、颗粒物、未燃碳氢化合物和一氧化碳等增加。 A

worse drawback is that, even with an insignificant sulphur content in the fuel, cooling down of the

exhaust gas results in a sticky liquid of sulphur acid products, water and soot matter. 一个更糟糕的缺点是，即使燃油中的硫含量很低，废气的冷却也会导致粘性硫酸液体产物、水和烟尘物质。This makes it difficult to maintain the functionality of the cooling device and, above all,

results in a difficult residual product, says Wartsila, which abandoned EGR for diesel engine

applications.瓦锡兰公司说，这使得冷却装置的功能很难维持，最重要的是，会产生难以忍受的残留产品，瓦锡兰公司放弃了EGR技术用于柴油发动机。

For low speed engines, especially those with electronically-controlled exhaust valve timing,

Wartsila suggests that the Water Cooled Rest Gas technique offers an opportunity for NOx

reduction. 对于低速发动机，特别是那些采用电控排气阀定时的发动机，瓦锡兰公司认为，水冷余气（废气）技术为减少氮氧化物（排放）提供了机会。 In this concept some of the exhaust

gas is left in the cylinder, which in normal circumstances leads to increased thermal loading and

inferior combustion. 在这个概念中，一些废气留在气缸中，这在正常情况下会导致热负荷增加和燃烧不良。 These drawbacks are largely avoided, however, if the rest gas is cooled by an

internal spray of water. 然而，如果其余气（废气）通过内部喷水冷却，这些缺点基本上可以避免。As the surrounding combustion space components are rather hot, there will be no

condensation of acid products on the metal surfaces.由于燃烧室周围部件相当热，金属表面不会有酸性产物冷凝。

Fuel nozzles

Different fuel nozzle types and designs have a significant impact on NOx formation, and the

intensity of the fuel injection also has an influence. 不同的喷油嘴类型和设计对NOx的形成有显著影响，燃油喷射的密度也很有影响。

The increased mean effective pressure ratings of modern engines require increased flow areas

throughout the fuel valve which, in turn, leads to increased sac volumes in the fuel nozzle itself

and a higher risk of after-dripping[7]. 现代发动机平均有效压力额定值的增加要求整个喷油器的通流面积增大，这反过来会增加喷油器（针阀）压力室容积并造成燃油后滴漏的风险。

Consequently, more fuel from the sac volume may enter the combustion chamber and contribute

to the emission of smoke and unburned hydrocarbons as well as to increased deposits in the

combustion chamber. 因此，来自（针阀）压力室容积的残油会更多地进入燃烧室，并导致冒黑烟和未燃碳氢化合物的排出，同时增加燃烧室沉积物。 The relatively large sac volume in

a standard design fuel nozzle thus has a negative influence on the formation of soot particles and

hydrocarbons.因此，在标准设计的喷油器喷嘴中，相对较大的（针阀）压力室容积对烟尘颗粒和碳氢化合物的形成有负面影响。

The so-called 'mini-sac' fuel valve introduced by MAN B&W Diesel incorporates a

conventional conical spindle seat as well as a slide inside the fuel nozzle. MAN B&W Diesel推出的所谓的“迷你（针阀）压力室”喷油器包括一个传统的锥形主座以及位于燃油喷嘴内的一个滑块。The mini-sac leaves the flow conditions in the vicinity of the nozzle holes similar to the

flow conditions in the conventional fuel nozzle. “迷你（针阀）压力室”使喷嘴孔附近的流动条件与传统燃油喷嘴中的流动条件相似。 But it’s much reduced sac volume--only about 15 per

cent that of the conventional fuel valve--has demonstrated a positive influence on the cleanliness

of the combustion chamber and exhaust gas outlet ducts. 但它大大减少了（针阀）压力室容积——只有传统喷油器的15%左右——已经证明对燃烧室和废气出口通道的清洁度有积极的影响。 Such valves also reduce the formation of NOx during combustion.这种喷油器还可以减少燃烧过程中氮氧化物的形成。

A new type of fuel valve--essentially eliminating the sac volume--was subsequently

developed and introduced by MAN B&W Diesel as standard to its larger low speed engines. 后来，MAN B&W Diesel公司开发了一种新型喷油器，基本上消除了（针阀）压力室容积，并将其作为其大型低速发动机的标准配置。 The main advantages of this slide-type fuel valve are

reduced emissions of NOx, CO, smoke and unburned hydrocarbons as well as significantly fewer

deposits inside the engine. 这种滑式喷油器的主要优点是减少了NOx、CO、黑烟和未燃碳氢化合物的排放，并且显著减少了发动机内部的沉积物。A positive effect on the cylinder

condition in general is reported.据称，通常对气缸状况有积极影响。

Applying slide fuel valves to a 12K90MC containership engine yielded a 40 per cent

reduction in smoke (BSN10) compared with the mini-sac valve engine, while hydrocarbons and

CO were reduced by 33 per cent and 42 per cent, respectively, albeit from a low level. 滑式喷油器在集装箱船的12K90MC发动机上得到了应用，与“迷你（针阀）压力室”发动机相比，烟度（BSN10）降低了40%，而碳氢化合物和CO分别降低了33%和42%，虽然水平较低。NOx was reduced by 14 per cent, while the fuel consumption remained virtually unchanged and

with a slight reduction at part load.氮氧化物减少了14%，而燃料消耗量事实上维持不变，部分负荷时略有下降。