1、汽车新能源与排放控制English versionAutomotive emission and controlBeijing University of Civil Engineering and ArchitectureChapter1:introduction3 Study Aims 学习目标学习目标：Understand the relation of automotive and environment Know about the pollution of main city in China Realize the disadvantage of automotive emiss
2、ion Study points 知识要点：知识要点：the environment and automotive the pollution of main city in China the disadvantage of CO,NOx,HC,PM,CO2 Example:4Read the examples in book.Would you like take an example about pollution?1.1 Air pollution and vehicles1.1.1 Air pollution Air pollution is the introduction of
3、particulates,biological molecules,or other harmful materials into Earths atmosphere,causing diseases,death to humans,and damage to other living organisms.1.1.2 Sources There are various locations,activities or factors which are responsible for releasing pollutants into the atmosphere.These sources c
4、an be classified into two major categories.(1)Anthropogenic(man-made)sources:(2)Natural sources:1.2 Environmental impact the pollution in IranWhy？nFig 1.3 Word map of passenger cars per 1000 people Word map of passenger cars per 1000 peoplethe pollution of main city in ChinaWhat do you see from the
5、table?1.3 Types of emissionsnEmissions that are principal pollutants of concern include CO,HC,NOx,PM and CO2Nitrogen oxides nNitrogen oxides(NOx)-Generated when nitrogen in the air reacts with oxygen at the high temperature and pressure inside the engine.nNOx is a precursor to smog and acid rain.nNO
6、x is a mixture of NO,N2O,and NO2.NO2 is extremely reactive.It destroys resistance to respiratory infection.nNOx production is increased when an engine runs at its most efficient(i.e.hottest)part of the cycle.HydrocarbonsnHydrocarbons-A class of burned or partially burned fuel,hydrocarbons are toxins
7、.nHydrocarbons are a major contributor to smog,which can be a major problem in urban areas.The formation of smogThe formation of smogHydrocarbonsnProlonged exposure to hydrocarbons contributes to asthma,liver disease,lung disease,and cancer.nRegulations governing hydrocarbons vary according to type
8、of engine and jurisdiction;in some cases,non-methanehydrocarbons are regulated,while in other cases,total hydrocarbons are regulated.HydrocarbonsnTechnology for one application(to meet a non-methane hydrocarbon standard)may not be suitable for use in an application that has to meet a total hydrocarb
9、on standard.nMethane is not directly toxic,but is more difficult to break down in a catalytic converter,so in effect a non-methane hydrocarbon regulation can be considered easier to meet.nSince methane is a greenhouse gas,interest is rising in how to eliminate emissions of it.HydrocarbonsCarbon mono
10、xide nCarbon monoxide(CO)-A product of incomplete combustion,carbon monoxide reduces the bloods ability to carry oxygen;n overexposure(carbon monoxide poisoning)may be fatal.nCarbon Monoxide poisoning is a killer in high concentrations Particulate matternParticulate matter Soot or smoke made up of p
11、articles in the micrometre size range:Particulate matter causes negative health effects,including but not limited to respiratory disease and cancer.Volatile organic compounds(VOCs)nVolatile organic compounds(VOCs)-Organic compounds which typically have a boiling point less than or equal to 250 C;for
12、 example chlorofluorocarbons(CFCs)and formaldehyde.n Volatile organic compounds are a subsection of Hydrocarbons that are mentioned separately because of their dangers to public health.Carbon dioxide(CO2)Carbon dioxide is a greenhouse gas.Motor vehicle CO2 emissions are part of the anthropogenic con
13、tribution to the growth of CO2 concentrations in the atmosphere which is causing climate change.Sulfur oxidenSulfur oxide(SOx)-A general term for oxides of sulfur,which are emitted from motor vehicles burning fuel containing sulfur.Reducing the level of fuel sulfur reduces the level of Sulfur oxidee
14、mitted from the tailpipe.nEmissions of many air pollutants have been shown to have variety of negative effects on public health and the natural environment.1.4 Pollution Effects1.5 Emission factors1.6 Pollution reductionConclusionsnThe main factor of pollution automotive emission because of the city
15、 development,energy usage,and so on.nThe heavy pollution in China,and the North is heavier than the South.nAutomotive Emission includes many different contents,such as CO,HC,NOx,PM and CO2Chapter 2:Mechanism on emission controlFig 2.1:CO2 emission prediction2.1 General principleFig2.2:The source of
16、gasoline engine emission2.1 General principle2.1.1 Measures for controlling emissions(1)Spark ignition engineA basic essential for spark ignition engine emission control is an injection system capable of extreme accuracy in metering the fuel supply relative to the air entering the engine.(2)Diesel e
17、ngineDiesel and spark ignition engines produce the same emission.On the other hand,owing to the low volatility of diesel fuel relative to that of gasoline,evaporative emissions are not so significant.2.1 General principle2.1.2 Reduction of emissions:conflicting requirementsFig 2.3 NOx increases when
18、 measures are taken to reduce particulates in different types of engine2.2 Oxides of nitrogen,NOx2.2.1 Formation and reactions The three principal reactions(the extended Zeldovich mechanism)producing thermal NOx are:N2+O NO+NN+O2 NO+ON+OH NO+H All three reactions are reversible.Zeldovich was the fir
19、st to suggest the importance of the first two reactions.2.2 Oxides of nitrogen,NOx2.2.2 NOx from fuel It is estimated that transportation fuels cause 54%of the anthropogenic(i.e.human-caused)NOx.The major source of NOx production from nitrogen-bearing fuels such as certain coals and oil,is the conve
20、rsion of fuel bound nitrogen to Nox during combustion.Although the complete mechanism is not fully understood,there are two primary paths of formation.The first involves the oxidation of volatile nitrogen species during the initial stages of combustion.The second path involves the combustion of nitr
21、ogen contained in the char matrix during the combustion of the char portion of the fuels.2.2 Oxides of nitrogen,NOx2.2.3 Effects of fuel properties on NOx(1)Increasing the cetane numberFig 2.4(left)Tests by BP showing how injection timing influences combustionand therefore NOx output;(right)the infl
22、uence of cetane number on the principal Emissions.2.2 Oxides of nitrogen,NOx(2)Increasing fuel volatilityFig 2.5.NOx emissions with direct and indirect injection2.2 Oxides of nitrogen,NOx(3)Exhaust gas recirculationFig 2.6.Relationship between fuel consumption and NOx emissions with(left)and without
23、(right)charge cooling.2.2 Oxides of nitrogen,NOx(4)Reduction of the rate of swirl Reduction of the rate of swirl is another way of reducing the output of NOx.It increases the time required for the fuel to mix with the air,and therefore reduces the concentration of oxygen around the fuel droplets.Con
24、sequently,the temperature of combustion does not rise to such a high peak.Again,however,it also reduces thermal efficiency.Moreover,unless measures,such as increasing the number of holes in the injector nozzle and reducing their diameter,are taken to shorten the lengths of the sprays,more fuel tends
25、 to be deposited on the combustion chamber walls.2.2 Oxides of nitrogen,NOx(4)Reduction of the rate of swirl Reduction of the rate of swirl is another way of reducing the output of NOx.It increases the time required for the fuel to mix with the air,and therefore reduces the concentration of oxygen a
26、round the fuel droplets.Consequently,the temperature of combustion does not rise to such a high peak.Again,however,it also reduces thermal efficiency.Moreover,unless measures,such as increasing the number of holes in the injector nozzle and reducing their diameter,are taken to shorten the lengths of
27、 the sprays,more fuel tends to be deposited on the combustion chamber walls.(5)Delaying the start of injection Delaying the start of injection has the effect of reducing peak temperatures,and the refore NOx.This is because the combustion process builds up to its peak later in the cycle,when the pist
28、on is on its downward stroke and the gas is therefore being cooled by expansion.However,to get a full charge of fuel into the cylinder in the time remaining for it to be completely burnt,higher injection pressures are needed.Therefore,to avoid increasing the proportion of fuel sprayed on to the comb
29、ustion chamber walls,the holes in the injector must again be smaller in diameter and larger in number.2.2 Oxides of nitrogen,NOx(6)Turbocharging with charge cooling Turbocharging increases the temperature of combustion by increasing both the temperature and quantity of air entering the cylinder.Afte
30、r-cooling,however,can help by removing the heat generated by both compression of the gas and conduction from the turbine.It also increases the density of the charge,and therefore thermal efficiency and power output.The net outcome of turbocharging with charge cooling,therefore,is generally an increa
31、se or,at worst,no reduction in thermal efficiency.2.3 Unburnt hydrocarbons2.3.1 Main reasons Hydrocarbons(HCs)in the exhaust are the principal cause of the unpleasant smell of a diesel engine,though the lubricating oil also makes a small contribution.There are three main reasons for this.First,at lo
32、w temperatures and light loads,the mixture may be too lean for efficient burning so the precombustion processes during the ignition delay period are partially inhibited.This is why some of the mixture subsequently fails to burn.Secondly,because of the low volatility of diesel fuel relative to petrol
33、,and the short period of time available for it to evaporate before combustion begins,HCs are generated during starting and warming up from cold.Thirdly,after cold starting and during warm-up,a higher than normal proportion of the injected fuel,failing to evaporate,is deposited on the combustion cham
34、ber walls.2.3 Unburnt hydrocarbons Another potential cause of HCs is the fuel contained in the volume between thepintle needle seat and the spray hole or holes(the sac volume).After the injector needle has seated and combustion has ceased,some of the trapped fuel may evaporate into the cylinder.Fina
35、lly,the crevice areas,for example between the piston andcylinder walls above the top ring,also contain unburnt or quenched fractions of semi-burnt mixture,Expanding under the influence of the high temperatures due to combustion and falling pressures during the expansion stroke,and forced out by the
36、motions of the piston and rings,these vapours and gases find their way into theexhaust.2.3 Unburnt hydrocarbons2.3.2 Ways to reduce HC emissions In general,therefore,the engine designer can reduce HC emissions in three ways.One is by increasing the compression ratio;secondly,the specific loading can
37、 be increased by installing a smaller,more highly rated,engine for a given type of operation;and,thirdly,by increasing the rate of swirl both to evaporate the fuel more rapidly and to bring more oxygen into intimate contact with it.Reduction of lubricating oil consumption is another important aim as
38、 regards not only control of HCs but also,and more importantly,particulate emissions.Avoidance of cylinder-bore distortion can play a significant part in the reduction of 22 oil consumption.2.4 Carbon monoxideFig 2.7:Model(left)and Ball-and-stick model(right)of carbon monoxide Carbon monoxide occurs
39、 in various natural and artificial environments.Exhaust from automobiles is about 100200 ppmv in typical concentrations per million.2.5 Particulate Matter2.5.1 Definition Particulate matter(PM)or particulates is microscopic solid or liquid matter suspended in the Earths atmosphere.The term aerosol c
40、ommonly refers to the particulate/air mixture,as opposed to the particulate matter alone.Sources of particulate matter can be man-made or natural.They have impacts on climate and precipitation that adversely affect human health.Human activities,such as the burning of fossil fuels in vehicles,power p
41、lants and various industrial processes also generate significant amounts of particulates.2.5 Particulate Matter2.5.2 Control technologies(1)Better atomization of the fuel Measures appropriate for reducing the fuel and oil content of the particulates are the same as those already mentioned in connect
42、ion with HC emissions,The overall quantity of particulates can be reduced by increasing the injection pressure and reducing the size of the injector holes,to atomise the fuel better.2.5 Particulate Matter(2)Reduction of the sulphur content Reduction of the sulphur content of the fuel also reduces pa
43、rticulates.Although the proportion of sulphate+water is shown in Table 2.1 as being only 2%of the total,if the insoluble sulphur compounds are added,this total becomes more like 25%.Fig 2.8 Relationship between particulate emissions and fuel quality,as established by Volvo2.5 Particulate Matter(3)An
44、 ingenious methodTable 2.1 ANALYSES,EXPRESSED IN PERCENTAGES,OF PARTICULATES FROM DIFFERENT TYPES OF DIESEL ENGINENote:Horrocks(Ford Motor Co.)differentiated between the carbon and other ash(at 41%and 13%respectively),making the total 44%.2.6 Influence of fuel quality on diesel exhaust emissionsHow
45、individual emissions are influenced by different fuel properties have been summarised by the UK Petroleum Industry Association as follows NOx Increases slightly with cetane number.Decreases as aromatic content is lowered.CO No significant effects.HC Decreases slightly as cetane number increases.Decr
46、eases with density.Relationship with volatility inconsistent.Black smoke Increases with fuel density and decreases with aromatic content.Is not significantly affected by volatility.Increases with injection retard(e.g.for reducing NOx).Particulates Reduced as volatility is lowered.Reduced as cetane n
47、umber is lowered,though inconsistently.Unaffected by aromatic content.Reduced as sulphur content is lowered.2.7 Black smoke The effect of sulphur content on the formation of particulates has been covered in Section 2.5.Other factors include volatility and cetane number.As regards visibility,however,
48、the carbon content is much more significant.The reason is that each engine is designed to operate at maximum efficiency over a given range of speeds and loads with a given grade of fuel.Therefore,at any given speed and load,a change of fuel might increase the combustion efficiency,yet at another spe
49、ed and load the same change might reduce it.The reason why the cetane number does not have a significant effect on the output of black smoke is simple.It is that smoke density is largely determined during the burning of the last few drops of fuel to be injected into the combustion chamber.2.8 White
50、smoke White smoke is a mixture of partially vaporised droplets of water and fuel,the former being products of combustion and the latter arising because the temperature of the droplets fails to rise to that needed for ignition.It can be measured by passing the exhaust through a box,one side of which
