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Variable CR con rodswitches compressionratio from 13:1 to 17:1SHOULDthe diesel engine betossed onto the scrapheap?Headline writers shouldn’ tforget that all combustionengines produce nitr ogen oxides. Whilediesel NOx is higher than petrol (Euro6NOx limits allow 80mg/ℓ for diesel and60mg/ℓ for gasoline), the ro llout of newNOx after-treatment systems will allowdiesel to match gasoline. Chris Brace,automotive propulsion professor at Bathuniversity, believes today’s ‘after-treatments will fixemissions and airqualityissues. Whenreal dr ivingemission tests are enforc ing Euro 6.2 in2017, the air qualityissue will be largely``````beaten. Then it’s back to CO2 businessas usual.’ Of course, that’s where denserdiesel fuel has the edge, containingabout 15% moreener gythan petrol, plusdiesel engines are ab out 20% moreefficient. The downside is that dieselproduces 2.65kg of CO2 per kilo burnt,compared to 2.3kg for petrol. However,since diesel consumes 25% less fuel thana gasoline engine, it emits 15% less CO2.And that’ll be vital to help car makersavoid a €95 (approx. R1500) fine forevery gram emitted over 95g/km– PERcar sold – from 2021. Reason enough forthe bean-counters to sanction theseNOx-beating technologies...``````Don’t letVW’swoesfoolyou intothinkingdieselisdead.It’smore efficientthanpetrol,and willget cleanerstill5 technologiesto save the dieselDepending on the engine and vehiclesize, different exhaus t gas treatment(EGT) systems will be empl oyed.Bosch has developed modularsystems that incor porate a NOxStorage Convertor ahead of a doubleselectiv e catalyst reduction (SCR).The NOx trap appears to be tailor-madefor many urban traffic situa tions``````due to the lower te mper ature limitof its oper ating range. The firstSCR, with AdBlue urea inje ction,combined with a diesel pa rticulatefilter (DPF) reduces low te mper atureurban exhaus t emissions; a second,optional, SCR further cleans thehigh temper ature exhaus t gase s, ifnecessary.1Exhaust after-treatmentsToday’ s Golf al ready has cylinderdeactivation – but onits 1.4petrol (above). But for diesel?Tula Technology’s Dynami cSkip Fire (DSF) uses audioelectronics-derived digi tal signalprocessing to continu ously varythe number of cylinders firingat any one time, controllingdiesel exhaus t te mper atureindependent of engine load.Dies el after-treatment devi ceshave a relatively narrow windowof temper atures in which theyare effectiv e. A commonproblem with NOxtraps and SCR``````catalysts is that, at low loads,the exhaus t is actually too coldfor the after-treatment devi cesto work at peakeffectiv eness.Running DSF allows control ofthe exhaus t te mper ature so thesystems operate more effectiv ely.As a separate but relatedadvantage, wit h DSF it is easierto achi eve the te mper atures andequivalence ratios requir ed toregenerate a particula te filter.3Cylinder deactivationVariable CR con rodswitches compressionratio from 13:1 to 17:1``````Because compression ratio (CR) isfixed across all oper ating boundariesit is a compromise. A high CR isused for cold ambient star t andengine warm-up – improving star ting,hydrocarbon/carbonmonoxide (HC/CO) reduction and increased thermalefficiency. With increased in-cylindertemper ature at the star t of inje ctionthe rate of igniti on is improved andstab ilised, resulting in more complete``````combustion and reduced HC/COemissions. It is also used for part loadin warm engine conditio ns to increasethe combustion’s therma l efficiency,decr ease CO 2 emission and fuelconsumption. A reduction in CR isneededas the engine load increasesto protect components. For high erloadsthe amount of fuel and cylindercharge isincreased along with cylinderpeakpressure.2Variablecompression ratioTECHKNOW96 TOPCAR.CO.ZA|January 20 16The innovations transforming our driving worldTECH KNOW