FIGHT­BACK TECH­NOLOG IES

Car (South Africa) - - TECH -

The rea­son that diesels fell out of favour was poor real-world emis­sions re­sults (that in­fa­mously led to Diesel­gate). It there­fore makes sense that en­gi­neers tar­get the main con­cern head-on: prov­ing diesels can be en­vi­ron­men­tally friendly, but can also com­ply with the strict Euro 7 emis­sion stan­dards that reg­u­la­tors are plan­ning for 2023. Ac­cord­ing to Siegfried Pint, with the in­tro­duc­tion of Euro 7, there will be no dif­fer­ence be­tween the emis­sions re­quire­ments for diesels and petrols, plac­ing the two ICE types on an equal foot­ing. 48 V MILD-HY­BRID SYS­TEMS This tech­nol­ogy con­sists mainly of an in­te­grated starter mo­tor (ISG) and a small lithium-ion bat­tery pack (round 0,5 kwh) that runs a 48 V sys­tem. The ISG is an elec­tric mo­tor con­nected to the en­gine via the aux­il­iary belt and can re­cu­per­ate ve­hi­cle ki­netic en­ergy during brak­ing or down­hill sit­u­a­tions by gen­er­at­ing elec­tric­ity when the ve­hi­cle’s brakes are ap­plied. In the up­com­ing new Audi A8, the sys­tem gen­er­ates up to 12 kw of elec­tric power.

Us­ing this stored elec­tric en­ergy, it can also per­form a boost­ing func­tion by adding to the en­gine out­put. This sys­tem low­ers emis­sions in both diesel and petrol pow­er­trains, but in diesels, known for high lev­els of noise, vi­bra­tion and harsh­ness, it of­fers a much smoother stop/start func­tion than achieved with the con­ven­tional starter mo­tor. ELEC­TRI­CALLY HEATED CAT­A­LYSTS With re­gard to cat­alytic con­vert­ers, a down­side of a diesel en­gine is that its ex­haust gas is much cooler than the equiv­a­lent petrol ver­sion’s. This means long heat-up times for cat­a­lysts that func­tion ef­fi­ciently only at op­er­at­ing tem­per­a­ture. How­ever, a new type of cat­a­lyst, show­cased by Con­ti­nen­tal at the 2017 Techshow, has an elec­tric heater el­e­ment that im­proves heat-up times con­sid­er­ably and keeps the cat­a­lyst at op­ti­mum tem­per­a­ture. This helps fur­ther lower emis­sions during, for ex­am­ple, low loads or when the en­gine stops during stop-start sys­tem oper­a­tion. This tech, to­gether with a 48 V mild-hy­brid sys­tem, was demon­strated on a Volk­swa­gen Golf GTD, the re­sult of which was 60% less CO emis­sions com­pared with the stan­dard car. Se­lec­tive cat­a­lyst-re­duc­tion sys­tems and diesel-par­tic­u­late fil­ters (DPF) are manda­tory after-treat­ment sys­tems to meet strict emis­sions reg­u­la­tions.

DOU­BLE-DECKER IN­TAKE MAN­I­FOLDS

To achieve ef­fi­cient and com­plete diesel com­bus­tion and min­imise emis­sions, it is im­por­tant that all the diesel that’s in­jected mixes with the air be­fore com­bus­tion takes place. To achieve this, two tech­niques are em­ployed: swirl, where the air cir­cles the com­bus­tion cham­ber; or tum­ble, where the air tum­bles like a wave into the com­bus­tion cham­ber during the in­take (and com­pres­sion) stroke.

For the first time, Audi is em­ploy­ing a dou­ble-decker in­take man­i­fold de­sign in its new 3,0-litre TDI en­gine in which the air can ei­ther flow through the top or bot­tom sec­tions, re­sult­ing in ei­ther swirl or tum­ble. This al­lows en­gi­neers to choose the most ef­fi­cient method of mix­ing de­pend­ing on the en­gine’s speed and load con­di­tion. High-pres­sure in­jec­tion sys­tems (2 500 bar) and mul­ti­ple in­jec­tions per cy­cle help fur­ther.

ELEC­TRIC TUR­BOCHARG­ERS

As we know, elim­i­nat­ing turbo lag im­proves driveability in tur­bocharged en­gines. Hav­ing an elec­tric tur­bocharger in par­al­lel with the con­ven­tional turbo achieves zero lag be­cause the elec­tric unit can reach peak boost in less than a quar­ter of a sec­ond. There­after, the con­ven­tional turbo takes over. The turbo is pow­ered by the 48 V mild-hy­brid sys­tem we men­tioned ear­lier and this tech­nol­ogy is used on diesel and petrol en­gines. The Audi SQ7 TDI is the first pro­duc­tion model fea­tur­ing this tech.

LOW-PRES­SURE EGR SYS­TEM

During part-load con­di­tions in a diesel, some of the burnt ex­haust gasses are re­cy­cled back into the in­take to lower the oxy­gen con­tent in the com­bus­tion cham­ber via the ex­haust gas-re­cir­cu­la­tion (EGR) valve. The ef­fect is re­duced com­bus­tion tem­per­a­tures during the part-load con­di­tion and fewer NOX emis­sions. The tra­di­tional, high-pres­sure EGR sys­tem routes hot ex­haust gases be­fore the turbo back to the in­take man­i­fold after the in­ter­cooler. The prob­lem is that the pres­sure dif­fer­en­tial is not enough to al­low ad­e­quate EGR flow rates. A new sys­tem is now used which takes colder ex­haust gas after the DPF and pipes it to the in­take sys­tem be­fore it gets to the turbo’s com­pres­sor. Adding low pres­sure EGR flow to the high EGR flow fur­ther re­duces emis­sions.

THE AUDI SQ7 IS THE FIRST PRO­DUC­TION CAR WITH AN ELEC­TRIC TUR­BOCHARGER

Golf GTD fi ed with Con­ti­nen­tal emis­sion test de­vice.

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