WLTP ex­plained – the new emis­sions test dis­rupt­ing the fast car world

New emis­sions test­ing pro­ce­dures are mak­ing life dif­fi­cult for man­u­fac­tur­ers, but the sit­u­a­tion is only go­ing to get tougher

Motor (Australia) - - CONTENTS -

YOU’RE FOR­GIVEN FOR NOT spend­ing a great deal of time study­ing the ins and outs of ve­hi­cle emis­sions test­ing. It’s not the world’s most ex­hil­a­rat­ing topic, par­tic­u­larly as we’re bet­ting most MO­TOR read­ers are happy to sac­ri­fice a lit­tle (or a lot, in some cases) fuel con­sump­tion for more power and per­for­mance. How­ever, the reg­u­la­tory net is clos­ing and will force ma­jor me­chan­i­cal changes to the next gen­er­a­tion of per­for­mance cars and be­yond. Let’s start with where we’ve been. The New Euro­pean Driv­ing Cy­cle (NEDC) was in­tro­duced in 1970 to as­sess pas­sen­ger car fuel econ­omy and emis­sions. There are other tests, such as that con­ducted by the En­vi­ron­men­tal Pro­tec­tion Agency in the US, but the NEDC is rel­e­vant in Aus­tralia be­cause it forms the ba­sis for fuel econ­omy and emis­sions test­ing un­der Aus­tralian De­sign Rule 79/04. The NEDC con­sists of an ur­ban driv­ing cy­cle re­peated four times con­sec­u­tively (the ‘ur­ban’ econ­omy fig­ure) fol­lowed by an ex­tra-ur­ban cy­cle (the ‘high­way’ fig­ure), which are then com­bined. If you’ve ever won­dered why your car’s claimed econ­omy is dif­fi­cult to achieve, it’s be­cause the NEDC is not in any way rep­re­sen­ta­tive of real-world driv­ing. We won’t bore you with the nit­tygritty de­tails, but es­sen­tially the en­tire test is spent at idle, cruis­ing, or gen­tly ac­cel­er­at­ing and de­cel­er­at­ing at a rate that even your grand­mother would call leisurely. The most en­thu­si­as­tic ac­cel­er­a­tion is dur­ing the ini­tial 0-15km/h phase, which is re­quired to take four sec­onds, the equiv­a­lent of 0-100km/h in 26.6sec. Is it any won­der that mod­ern cars are pre­dom­i­nantly pow­ered by low-ca­pac­ity, highly boosted en­gines with stop­start sys­tems and as many gears as pos­si­ble? Thus equipped, the NEDC can be com­pleted off-boost at low rpm and with the en­gine off for a large pro­por­tion of the test. The NEDC has rightly been crit­i­cised for its lack of real-world cor­re­la­tion and has now been re­placed by the World­wide Har­mo­nized Light Ve­hi­cles Test Pro­ce­dure (WLTP), which came into force in Europe from Septem­ber 1, 2018. Again, we’ll save you the specifics, but WLTP is a longer test split into four cy­cles (low, medium, high and ex­tra-high speed) that, cru­cially, re­quires much more dy­namic driv­ing. The ac­cel­er­a­tion and de­cel­er­a­tion events are still un­re­al­is­ti­cally slow, but there are more of them. In lay­man’s terms, WLTP econ­omy and emis­sions fig­ures will be closer to those of the real world. For ex­am­ple, the VW Up GTI’s fig­ures of 5.76L/100km and 110g/km CO2 in­creased to 6.73L/100km and 127-129g/km CO2 un­der WLTP. This is good news for cus­tomer knowl­edge, but bad news for man­u­fac­tur­ers. For some, par­tic­u­larly the Volk­swa­gen Group, it has caused chaos. Porsche sus­pended orders for its en­tire model range, Audi sus­pended the SQ5, the VW Golf GTI was re­moved from sale, and the Golf R lost 7kW. And that’s just some of the VAG im­pact. Else­where, BMW killed the M3 and the base M2 early, Jaguar re­moved its petrol XJs from sale and slimmed down its XF range, and Peu­geot sus­pended sale of its 308 GTi 270. The prob­lem goes be­yond just greater fuel use and emis­sions, though that’s bad enough when by 2021 a man­u­fac­turer’s fleet av­er­age emis­sions must be below 95g/km CO2. The real is­sue is that most of the ‘tricks’ used by man­u­fac­tur­ers for the NEDC don’t trans­late to the WLTP. This isn’t Diesel­gate-style cheat­ing, but tun­ing de­signed to achieve the best pos­si­ble re­sults. Many cars use 1:1 air-fuel ra­tios (known as sto­i­chio­met­ric) at light loads to im­prove econ­omy only to add fuel to con­trol tem­per­a­tures and pro­tect com­po­nents such as the tur­bocharger un­der heavy loads. This is where it gets tricky for fu­ture per­for­mance cars, par­tic­u­larly as it’s likely that the as-yet-un­con­firmed Euro7 emis­sions reg­u­la­tions will force man­u­fac­tur­ers to use sto­i­chio­met­ric air-fuel ra­tios at all times, end­ing the prac­tice of us­ing fuel as a cool­ing agent. This gives man­u­fac­tur­ers a choice: re­duce power, make com­po­nents able to with­stand higher tem­per­a­tures, or in­tro­duce tech­nol­ogy like hy­brid tur­bocharg­ers, wa­ter in­jec­tion or vari­able-com­pres­sion. How­ever, the most likely out­come is that th­ese reg­u­la­tions will sim­ply ac­cel­er­ate the de­vel­op­ment of pure-elec­tric cars.


BELOW Audi’s 2.9-litre twin-turbo V6 is one of many new-age, down­sized, boosted en­gines, but the new test regime isn’t kind to such con­fig­u­ra­tions

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