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同济大学：《汽车构造》课程电子教案（课件讲稿）第十二章发动机有害排放物的控制系统 Control System of Harmful Emissions in Engine Exhaust

12.1 Harmful Emissions in Automotive Engine Exhaust 汽车发动机的有害排放物 12.2 Emissions Control Devices in Gasoline Engine 汽油机的排放控制装置 12.3 Other Emissions Control Devices 其他排放物的控制装置 12.4 Emissions Control Devices in Diesel Engine 柴油机的排放控制装置

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2014/5/8 1 1/45 同济大学汽车学院《Automotive Configuration》 Lecturer ： Dr. Li Liguang/Professor Department：School of Automotive Studies, Tongji University Contact： liguang@tongji.edu.cn Lecture Schedule：12-13 2nd Semester Week 1~8 2/45 同济大学汽车学院 Chapter 12 Control System of Harmful Emissions in Engine Exhaust 第六章发动机有害排放物的控制系统 12.1 Harmful Emissions in Automotive Engine Exhaust 汽车发动机的有害排放物 12.2 Emissions Control Devices in Gasoline Engine 汽油机的排放控制装置 12.3 Other Emissions Control Devices 其他排放物的控制装置 12.4 Emissions Control Devices in Diesel Engine 柴油机的排放控制装置 3/45 同济大学汽车学院 European emission standards for passenger cars ( g/km) 4/45 同济大学汽车学院 §12.1 Harmful Emissions in Automotive Engine 汽车发动机的有害排放物 Exhaust Types of harmful emissions : CO、 HC、 NOX、PM、SOX. (1) CO: Hydrocarbon fuel uncompleted combustion product, it will reduce the ability to absorb and transport oxygen in blood, after being inhaled(人体吸入后). Formation mechanism: (形成机理) Oxygen deficit(缺氧); Low combustion temperature; Short combustion time;  Inhomogeneous mixture(混合不均). Generation rate of CO is mainly influenced by coefficient of excess air (过量空气系数):a 5/45 同济大学汽车学院 The formation of HC in combustion ： lack of oxygen, gap effect（缝隙效应）, chilling and quenching（激冷与淬熄）. Include unburned and incomplete combustion fuel and lubricating oil steam. 包括未燃和未完全燃烧的燃油和润滑油蒸汽。 HC and NOx can form photochemical smog(光化学烟雾) in sunlight, which is harmful to human and environment. (2) HC: HC in exhaust accounts for 60% of the total HC; HC in crankcase leap gas (曲轴箱窜气)accounts for 25% of the total HC; HC in fuel supply system steam(供油系统的HC蒸气) accounts for around 15% ~ 20% of the total HC. Source: 6/45 同济大学汽车学院 (3) NOX： Composition: NO (95%), NO2. High temperature High oxygen concentration Long duration Formation mechanism: NOx and HC can form photochemical smog(光化学烟雾) in sunlight, which is harmful to human and environment. 7/45 同济大学汽车学院 (4) Particulate Matter emissions: the dry soot(碳烟) in diesel engine exhaust + the soluable organic fraction adsorbed on their surface(表面吸附的可融性有机物). Formation mechanism: soot is cracked(裂解) by hydrocarbon fuel under high temperature and oxygen deficit（高温缺氧）. Harm: particles below 0.1 um are the most harmful to human body, after being inhaled into lung ,they will be adsorbed on the lung cells. And soluble organic fraction(可溶性有机物), polycyclic aromatic hydrocarbons(多环芳香烃) are cancercausing toxins(致癌物质). 8/45 同济大学汽车学院 (5) SOX： Composition: most of SOX is SO2, the quantity of SO3 is quite little in engine exhaust. SOX come from the sulphur ( 硫) in the fuel(Gasoline or diesel oil) oxidated by oxygen in combustion process. Harm: SOX are harmful to human body.  After being emited into the air ,they will form acid rain(酸雨), moreover, 50% of SOX will become sulfates(硫酸盐) which is part of PM. SOX will poison three-way catalyst(三效催化剂) in aftertreatment system. As emission regulations have become increasingly restrictive, the quality of SOX in the fuel(Gasoline or diesel oil) has been less. 9/45 同济大学汽车学院 §12.2 Emissions Control Devices in Gasoline Engine 汽油机的排放控制装置 1. Catalytic converter(催化转化装置); 2. Devices to reduce HC emissions at low temperature; 3. Lean NOx catalytic conversion device(稀薄NOx催化转化装置); 4. Exhaust Gas Recirculation System(废气再循环系统);

2014/5/8 2 10/45 同济大学汽车学院 Types Oxidation catalytic conversion device(氧化催化转换装置); Reduction Catalytic conversion device(还原催化转换装置);  Three-way catalytic converter（TWC）(三效催化转换装置); 1. Catalytic converter(催化转化装置); Structure: honeycomb ceramic supporters (蜂窝状陶瓷载体)and alloy supporters(金属载体). Catalyst: Pt(铂), Pd(钯), Rh(铑).etc 11/45 同济大学汽车学院 (1) Oxidation catalytic conversion (氧化型催化转化器):  CO, HC(in the exhaust) are oxidized into CO2 and H2O, and is also known as dual catalytic converter（二元催化转换器).  Generally, it works with secondary air(二次空气) as oxidant. H O H O HC O CO H O CO O CO 2 2 2 2 2 2 2 2 2 2 4 5 4 2 2 2        Secondary air supplying system(二次空气供给系统)： Second air-injection system(二次空气喷射方式) The pressure pulsation of exhaust pipe(排气管压力脉动方式) 12/45 同济大学汽车学院 (2) TWC (三效催化转换装置) TWC can reduce CO, HC and NOx emissions at the same time. NOx → N2 +O2 with using CO+HC in the exhaust gas as the reductant (还原剂), while CO +HC are oxidized into CO2 + H2O. When air-fuel ratio (A/F = 14.7) , the the oxidation - reduction reaction reaches equilibrium(氧化- 还原反应达到平衡), CO, HC and NOx emissions are minimum at the same time. Exhaust gas conversion efficiency and a 13/45 同济大学汽车学院 14/45 同济大学汽车学院 The principles of using TWC (三元催化转换装置的使用原则)  Quality of fuel(油品): cannot use leaded gasoline (加铅汽油),or it will disable catalyst (使催化剂失效)  Exhaust temperature: catalytic converter works in condition over 350℃, →so it is installed in the back of Exhaust manifold.  Mixture composition(混合气成分): air-fuel ratio must be around 14.7. If mixture is too thick or too lean, catalytic efficency will decrease. 15/45 同济大学汽车学院 2. Devices to reduce HC emissions at low temperature(降低低温HC排放装置) (1) Catalyze directly(直接催化) it is installed in the back the exhaust pipe→catalyst temperature increasing rate↑( 催化剂温升速率)→reducing HC under the cold condition effectively. Issue: catalyst is affected by high temperature of exhaust pipe, it needs to improve the heat resistance of the catalytic device(提高催化装置的耐热性). (2) Utilize electric heating catalytic conversion device(利用电加热催化转化装置) heat catalytic in advance through external electricity(通过外部电力提前加热催化), main defects(缺点): high power consumption, poor durable reliability(耗电量大，耐久性较差). (3) The secondary combustion device(二次燃烧装置) send a part of fuel or rich mixture to catalytic conversion device, then ignite to promote catalysis. main defects: complex structure. 16/45 同济大学汽车学院 (4) Utilize the HC trap(采用HC捕捉器) Use zeolites and activated carbon as adsorbent. 利用沸石或活性炭作为吸附剂. It’s usually installed at the back of the TWC. 17/45 同济大学汽车学院 3. Lean NOx catalytic conversion device(稀薄NOx催化转化装置) Air-fuel ratio in lean combustion is more than theory air-fuel ratio, so conventional TWC device no longer works, there’re two new types: Direct decomposition of NOx (NOx直接分解型): use HC as reductant to reduct NOx in lean mixture. Adsorption and reduction of NOx (NOx吸附还原型). 18/45 同济大学汽车学院 Fundamental of EGR: ↓NOX. (1) work: high speed, medium load . (2) not work:  low temperature, low speed;  heavy load . 4. Exhaust Gas Recirculation System(废气再循环系统 )

2014/5/8 3 19/45 同济大学汽车学院 (1) Gasoline evaporation control system (汽油蒸发控制系统) § 12.3 Other Emissions Control Devices (其他排放物的控制装置) Function: prevent the evaporation of fuel in fuel tank and the carburetor float bowl(化油器浮子室) diffusing into air and causing pollution. Solution: collect the gasoline vapor and store it in the activated carbon tank(活性炭罐), then send it into cylinder and be burnt when the engine is started. 20/45 同济大学汽车学院燃油蒸发（EVAP）控制系统 1-汽油箱 2-燃油泵 3-蒸发阀 4-双通阀 5-碳罐 6-EVAP控制电磁阀 7-进气软管 -节气门 9-滤网 10-量孔 21/45 同济大学汽车学院 (2) Positive crankcase ventilation system (PCV) 强制式曲轴箱通风装置（ PCV系统） Fundamental: When engine is working, send part of the fresh air from the air filter(空气滤清器) to cylinder head cover(气缸盖罩) by the hose(软管), then the air go into the crankcase(曲轴箱) through the hole that is connected cylinder head and body, and mix with crankcase gas. finnaly,the mixtures go into the intake manifold through the PVC valve. 22/45 同济大学汽车学院 23/45 同济大学汽车学院 (3) Constant temperature of intake charge (恒温进气) To supply a high temperature and guarantee mixture form well in cold start or light load. The vacuum degree of intake manifold affects on the vacuum control membrane box 7, and dominates control valve8 open or close. (进气管真空度作用在真空控制膜盒7上，控制控制阀8开大或关小) 24/45 同济大学汽车学院 1. Characteristics of Diesel engine emissions; 2. EGR system; 3. Diesel oxidation catalytic converter (柴油氧化催化转化器); 4. The NOx reduction catalytic converter (NOx还原催化转化器); 5. Diesel Particulate Filter (DPF)颗粒捕捉器. §12.4 Emissions Control Devices in Diesel Engine (柴油机的排放控制装置) 25/45 同济大学汽车学院 Features: (1) have no fuel evaporative emissions problem; (2) compared with gasoline engine, HC and CO emissions are much less, and the NOx emission is in the same order of magnitude(同一数量级); (3) particulate matter (PM) emission is high. Difficult points: (1) the exhaust is always in the oxidation atmosphere (excess air coefficient ＞ 1), the NOx reduction is hard;废气总是处于氧化氛围（过量空气系数大于1）中，NOx难以还原； (2) the exhaust temperature is lower than that of gasoline engine exhaust temperature, soot oxidation is hard;排气温度明显低于汽油机的排气温度，碳烟难以氧化 (3) the exhaust contains a lot of SOx and particles, cause catalyst poisoning easily.排气中含有大量的SOx和微粒，容易导致催化剂中毒 1 Characteristics of Diesel engine emissions 26/45 同济大学汽车学院 27/45 同济大学汽车学院 2 EGR system Q the quanlity of ch e o the cylinder with EGR Q the quanlity of ch e o the cylinder without EGR Q Q Q EGR rate EGR W OEGR W OEGR W OEGR EGR arg int arg int 100% / / /         Low pressure circuit type (低压回路方式)  High pressure circuit type (高压回路方式) Internal EGR External EGR EGR Types:

2014/5/8 4 28/45 同济大学汽车学院  Low pressure circuit type(低压回路方式) connect compressor inlet side(压气机7 入口端) and the exhaust turbine outlet 5 (废气涡轮5出口)to realize the EGR directly. Due to compressor inlet side 7 is negative pressure(负压), exhaust turbine outlet 5 is positive pressure(正压), so it can realize the EGR by pipe 6 easily. But due to exhaust flow through the compressor and inter-cooled 8(中冷器8) directly, it's easy to cause corrosion of the compressor and pollution of inter-cooled(压气机的腐蚀和中冷器的污染). (1) External EGR: 29/45 同济大学汽车学院  High pressure circuit type(高压回路方式） connect inter-cooler 8(中冷器8) and the exhaust turbine inlet 5 (废气涡轮5入口)to realize the EGR directly. Due to exhausts do not flow through the compressor and inter-cooler ,there is no corrosion and pollution of compressor(压气机和中冷器的腐蚀和污染问题), but EGR rate is determined by the difference of the exhaust pressure and inlet pressure. Especially in the medium and heavy load(中、大负荷), it’s difficult to realize EGR because of the increased pressure in manifold. 30/45 同济大学汽车学院 need no exhaust throttle（排气节流）, → not affect the pumping losses（泵气损失）→not affect fuel economy; need no EGR valve and EGR pipe→ structure is simple. (2) Internal EGR add internal EGR CAM(增设EGR专用凸轮),at appropriate moment in intake stroke open the exhaust valve to make exhaust flow back into the cylinder with the help of EGR CAM(使排出的废气回流到气缸内部), to realize the EGR. Use pulsation of gas in inlet and exhaust pipes(利用进、排气管中的气体脉动进行EGR的方式). during the intake stroke, make one cylinder appear positive pressure wave near the exhaust valve. At this point, open the exhaust valve, it can realize the EGR.(使某一缸在进气过程中，其排气门处出现正压波,此时，如果能再次开启排气门，就可实现EGR)。 Advantages: Types: 31/45 同济大学汽车学院 3. Diesel oxidation catalyst(DOC)(柴油机氧化催化转化器) Fundamental: With the help of catalyst Pt or Pd, CO+THC are oxidized into CO2+H2O,  SOF in PM can be also oxidized into CO2+H2O,  Polycyclic aromatic hydrocarbons(多环芳香烃), acetaldehyde(乙醛) can be also oxidized. But sulphur(硫) in diesel oil can be oxidized into RSO4 and RSO3 which are part of PM, maybe add the emission of PM. So the fuel in diesel engines with DOC should contain little sulphur. 32/45 同济大学汽车学院 33/45 同济大学汽车学院 4. The NOx reduction catalytic converter (NOx还原催化转化器) Types: Selective Noncatalytic Reduction(SNCR)(选择性非催化还原); Selective Catalytic Reduction(SCR)(选择性催化还原); Non Selective Catalytic Reduction(NSCR)(非选择性催化还原). NH3 - SCR HC - SCR SCR Disadvantages: Low transformation efficiency Service life is not long, Complicated system 34/45 同济大学汽车学院 SNCR technology can only work in a temperature range (800 ~ 1000℃), and diesel exhaust could not achieve such a high temperature, therefore only injecting ammonia(氨水) into the cylinder in expansion process can realize SNCR, but the effect is not very ideal, the technology is widely used in the power plant only. SNCR 技术只能在一定的温度区间(800～1000 ℃) 使用,而柴油机排气不可能达到这样高的温度, 因此只能通过在柴油机膨胀过程中,向气缸中喷入氨水来实现,但效果不很理想,该技术仅在发电厂得到了广泛应用. (1) SNCR(选择性非催化还原) 35/45 同济大学汽车学院 A reduction that react with oxygen in the gas phase firstly,then react with NOx in the presence of catalyst. 在催化剂存在的条件下,若还原剂优先与气相中的氧发生反应,再与 NOx发生反应的还原过程称非选择性催化还原。 Inject reductant (such as CH4, CO, H2) into the exhaust pipe under the action of Pt or Pd, then reduct NOX. NSCR 将还原剂( 如CH4 ,CO ,H2) . 喷入排气管中,在铂或钯催化转换器的作用下与废气中的NOx进行反应。 Because of the exhaust contains much oxygen, the reductant is easy to be oxidized directly, so the consumption of reductant is great. 由于尾气中含氧量较高,还原剂很容易直接被氧化,故消耗量极大。 (2) NSCR(非选择性催化还原) 36/45 同济大学汽车学院 Utilize a small amount of HC in the exhaust to reduction N0x when A/F is large. 富氧时利用尾气中含有的少量HC来选择性还原NOx。 (3) SCR(选择性催化还原) HC-SCR HC + NOx + O2—>N2 + CO2 + H2O

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