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Lesson12CommercialVehicleEmissionsinPerspectiveTheindividualpollutantsareisolatedandweighedandtheamountdividedbythelengthofthe‘testdrive’toarriveataresultmeasureding/km.各种污染物被分离、称重，所得的量除以试验过程的长短，从而得到以g/km为单位的结果。Theseindividualresultsaregivenweightingstorepresentareal-worldoperatingregimefortheengineandthetotalisadjustedforthepoweroutput,andtheresultsgivening/kW·h.这些结果被加权以表示发动机的实际工作状态，其总量根据功率输出修正，所得结果以g/kW·h为单位。Assumingthecarisreturning12.7km/l(7.851/100kmor36mpg)andthetruck5.3km/l(18.8l/100kmor15mpg),thecarwillproduce14.3g(HC+NOx)/landthetruck38.7g/l,orsomewhatlessthanthreetimesasmuch.1gallon=4.55l;1mile=1.61km假设小汽车油耗为12.7km/l而卡车为5.3km/l，小汽车将产生14.3g(HC+NOx)，而卡车为38.7g，略小于其3倍。OnthissamebasisthecarproducestwiceasmuchCOperlitreoffuelasthetruckandthedieselcarproduces50%morePMperlitreoffuelthanthetruck.在相同的基础上，每消耗1升燃料轿车产生2倍于卡车的CO，而柴油车产生多出50%的PM。Asimpler,andnolessvalidcomparisoncanbemadebasedonthetotalamountoffuelused,asultimately,itistheamountoffuelburnedandtheefficiencywithwhichitisburnedthatdeterminestheoverallamountofpollutioncreated.基于总的燃料消耗可以得到一个简单而有效的比较，最终正是消耗的燃料和它燃烧的效率决定所产生污染的数量。Byusingwellestablisheddataforthevariousvehicleparcsandmakingrealisticassumptionsoffuelconsumptionandannualmileagesforthevariousdieselpoweredvehiclegroupstheauthorhasdevelopedamatrixofdieselusage.通过使用公认的数据并对燃料真实消耗和不同柴油机车的平均里程作出合理的假设，作者列出了一个柴油使用的真值表。Atthesametime,althoughtruckdieselemissionsarewellcontrolledthereisnolegislationcoveringthenon-truckapplication,soitissafetoconcludethatoveralltruckemissionsarelessthanthestrictlyproportionfuelusagestatisticswouldsuggest.同时，尽管载重汽车柴油机排放被很好地控制，但没有法规约束柴油机在其他方面的应用。所以，可得出结论：若严格按载重汽车燃油消耗量统计比例来算，其总排放小于应占的比例。Overthelast40yearsorsotheoverallenergydemandhasnotonlygrownbutthepatternofusagehaschangedtoo.经过了过去的40年，不仅总能量需求增长了，而且其使用模式也改变了。