New de­vel­op­ments to help im­prove fuel econ­omy.

Ev­ery mo­torist wants to save money on fuel, so it’s for­tu­nate that plenty is be­ing done to help us. Chris Randall looks at some of the lat­est de­vel­op­ments.

Car Mechanics (UK) - - Contents -

Dur­ing the 60 years that Car

Me­chan­ics has been pub­lished, ar­ti­cles on sav­ing money on fuel have been a reg­u­lar fea­ture. From handy driv­ing tips to ad­vice on main­tain­ing your car so it runs as ef­fi­ciently as pos­si­ble, we’ve strived to help you spend less of your hard-earned cash at the pumps.

When it comes to car-mak­ers, ever more strin­gent leg­is­la­tion has meant their fo­cus on im­prov­ing econ­omy and emis­sions has never been greater. Right now they are hav­ing to get to grips with new test­ing regimes – the World­wide Har­monised Light Ve­hi­cle Test Pro­ce­dure (WLTP) is far stricter than the pre­vi­ous New Euro­pean Driv­ing Cy­cle test – and, by 2021, an EU tar­get de­mand­ing a cor­po­rate av­er­age of just 95g/km of CO2 will present fur­ther chal­lenges.

The re­cent de­mon­i­sa­tion of diesel cars hasn’t helped, plus there’s the pro­lif­er­a­tion of elec­tric and hy­brid mod­els on the mar­ket.

So where does that leave things for the in­ter­nal com­bus­tion en­gine? Let’s take a look at what’s be­ing done to make ev­ery gal­lon go fur­ther.


Weight is one of the arch-en­e­mies of fuel econ­omy. As cars get big­ger and more buy­ers are tempted by an SUV, mak­ing ve­hi­cles lighter is cru­cial. One of the big­gest ad­vances is in the ma­te­ri­als used for bodyshells, with many car-mak­ers opt­ing for a multi-ma­te­rial mix that en­sures ex­cel­lent strength and rigid­ity while be­ing much lighter in weight.

Com­bin­ing the likes of high-strength and ul­tra-high-strength steel ( both hot- and cold-formed), alu­minium, mag­ne­sium and com­pos­ites such as car­bon-fi­bre re­in­forced plas­tic can yield sig­nif­i­cant sav­ings.

For ex­am­ple, at the launch of the cur­rent As­tra, Vaux­hall claimed that it was up to 200kg lighter than its pre­de­ces­sor, with the body-in-white sav­ing of around 20% (280kg in­stead of 357kg), while the cur­rent Audi Q7 SUV re­put­edly saved a whop­ping 325kg over­all. The re­cently-launched Ford Fo­cus’s 88kg re­duc­tion com­pared to the out­go­ing model was helped by lighter win­dow reg­u­la­tors re­in­forced with glass­fi­bre fab­ric.

Stream­ing ser­vice

Stream­lin­ing isn’t ex­actly a new area in car de­vel­op­ment, but it is worth not­ing how much work is be­ing done on main­stream cars to re­duce drag. Tak­ing the lat­est Ford Fo­cus as an ex­am­ple, the man­u­fac­turer’s data reck­ons that aero­dy­namic im­prove­ments (along with the weight re­duc­tion) con­trib­ute to a 10% im­prove­ment in fuel ef­fi­ciency. This af­ford­able fam­ily ve­hi­cle now has a co­ef­fi­cient of drag of 0.273 and ben­e­fits from fea­tures such as an Ac­tive Grille Shut­ter, which closes to re­duce drag when less cool­ing is re­quired, as well as ‘air cur­tains’ that guide air­flow across the front wheels to re­duce tur­bu­lence and en­hance­ments to un­der­body air­flow due to pan­elling over the cen­tral tun­nel, fuel tank and rear axle.

In­te­grated Starter Gen­er­a­tor (ISG)

Be­com­ing com­mon on a wide range of premium and bread-and-but­ter mod­els, an ISG com­bines the func­tion of the starter mo­tor and al­ter­na­tor. It can be known by dif­fer­ent names – Audi calls it a belt al­ter­na­tor starter – and some en­gines also re­tain a con­ven­tional starter mo­tor for use dur­ing cold starts, but they all work in es­sen­tially the same way. Con­nected to the en­gine by a belt, it has a num­ber of ben­e­fits, in­clud­ing a quicker-act­ing stop/start sys­tem and the abil­ity to re­cover en­ergy un­der brak­ing which is then fed back to the car’s electrics. That abil­ity to sup­ply ‘free’ en­ergy and pro­vide elec­tri­cal as­sis­tance to the pow­er­train con­trib­utes to fuel econ­omy.

Mild-hy­brid sys­tems

ISG is also a key com­po­nent in mild­hy­brid sys­tems. These dif­fer from full hy­brids by not ac­tu­ally driv­ing the wheels di­rectly, but can still pro­duce use­ful sav­ings. Audi and Mercedes­benz are keen em­ploy­ers of such sys­tems, but they aren’t con­fined to premium brands. For ex­am­ple, Suzuki uses the same tech­nol­ogy to save fuel with its Smart Hy­brid Ve­hi­cle by Suzuki (SHVS) set-up. Us­ing an ISG and a sep­a­rate lithi­u­mion bat­tery to store re­cov­ered en­ergy, the sys­tem can har­vest power from re­gen­er­a­tive brak­ing (up to 12kw in the case of Audi’s sys­tem), power that can then be used to as­sist the en­gine dur­ing take-off from rest and dur­ing ac­cel­er­a­tion. More com­plex sys­tems also in­cor­po­rate ‘coast­ing’ func­tions, of­ten in con­junc­tion with 48-volt elec­tri­cal sys­tems, and when com­bined with smaller-ca­pac­ity, more ef­fi­cient en­gines, it’s easy to see how mild­hy­brids can boost econ­omy.

48-volt electrics

Al­though pretty much lim­ited to more ex­pen­sive mod­els at present, this tech­nol­ogy will be fil­ter­ing down to more af­ford­able cars in the next cou­ple of years. Able to pro­vide four times the power of cur­rent 12-volt sys­tems that are con­sid­ered to be at the limit of their ca­pa­bil­i­ties, it’s seen as a cru­cial de­vel­op­ment to sup­port tech­nol­ogy such as mild-hy­brid sys­tems and au­tonomous driv­ing, as well as pow­er­ing elec­tric tur­bos or su­per­charg­ers and cli­mate con­trol com­pres­sors. Com­bin­ing 48-volt sys­tems with starter-gen­er­a­tors also means quicker en­gine restart­ing and al­lows higher lev­els of brake en­ergy re­cu­per­a­tion. And be­ing ca­pa­ble of higher volt­ages with a lower cur­rent draw, there’s less need for heavy-duty elec­tri­cal com­po­nents, so wiring can be thin­ner and lighter.


Pop­ping the gear­box into neu­tral and coast­ing – or free­wheel­ing – was once frowned upon be­cause you were deemed to not be in full con­trol of the ve­hi­cle. How­ever, in con­junc­tion with so­phis­ti­cated au­to­matic and dual-clutch trans­mis­sions, it has be­come an es­sen­tial part of sav­ing fuel. Es­sen­tially, the elec­tron­ics put the gear­box into coast­ing mode, de­cou­pling it from the en­gine and dis­en­gag­ing clutches to re­duce me­chan­i­cal drag, in some cases switch­ing off the en­gine at the same time.

Dur­ing this op­er­a­tion, the bat­tery (some­times a sep­a­rate lithium-ion unit) sup­plies power to elec­tri­cal equip­ment and the en­gine is restarted al­most in­stan­ta­neously via an ISG. In Audi’s sys­tem, the mode can be ac­ti­vated at speeds between 34mph and 99mph.

As­sis­tance sys­tems

It’s not just me­chan­i­cal im­prove­ments that save fuel. Elec­tron­ics are play­ing an ever greater role and nowhere is that more true than with sys­tems that help you drive more ef­fi­ciently.

Audi’s Pre­dic­tive Ef­fi­ciency As­sis­tant claims to re­duce fuel con­sump­tion on coun­try roads by up to 10%. It works by pulling to­gether a num­ber of dif­fer­ent tech­nolo­gies, in­clud­ing adap­tive cruise con­trol, satel­lite nav­i­ga­tion and traf­fic sign recog­ni­tion (plus coast­ing func­tions in some mod­els), tak­ing into ac­count fac­tors such as speed lim­its, the traf­fic ahead and route to­pog­ra­phy. Able to ad­just speed to road con­di­tions and alert the driver to slow down for cor­ners, junc­tions and round­abouts, it pro­motes smoother, more ef­fi­cient driv­ing.

BMW’S ECOPRO sys­tem works in a sim­i­lar fash­ion, us­ing a gearshift in­di­ca­tor and the stop-start sys­tem, as well as coast­ing and a route aheadas­sis­tant, to achieve fuel sav­ings of up to 20%.


You could find cars fit­ted with three-cylin­der en­gines back in the 1980s, but they’ve made a strong come­back over the last few years. With the im­prove­ments that have taken place in tur­bocharg­ing and elec­tronic man­age­ment sys­tems, a wide range of car-mak­ers see three-cylin­der en­gines as an ideal way of of­fer­ing de­cent per­for­mance with im­pres­sive econ­omy.

In the Vaux­hall As­tra 1.0 ECOTEC, for ex­am­ple, you get 0-60mph in 10.5 sec­onds plus a claimed 64mpg. And if you think these en­gines are only suit­able for ur­ban run­abouts, you couldn’t be more wrong. In fact, around a dozen man­u­fac­tur­ers of­fer mod­els with three-cylin­der en­gines, in ev­ery­thing from the sporty MINI to SUVS and the use­fully large Ford Mon­deo.

Cylin­der shut­down

Shut­ting down in­di­vid­ual cylin­ders to save fuel isn’t a new idea, hav­ing been found on main­stream cars since the early 2000s. Of­ten ap­plied to larger, multi-cylin­der units, it has be­come more wide­spread in re­cent years with Volk­swa­gen the first to in­tro­duce Ac­tive Cylin­der Tech­nol­ogy on four­cylin­der en­gines back in 2012. Tak­ing VW’S cur­rent 1.5-litre TSI petrol unit as an ex­am­ple, the sys­tem op­er­ates between 1400-3200rpm un­der lowload con­di­tions and at speeds of up to 81mph. It’s the two in­ner cylin­ders that are de­ac­ti­vated (the changeover al­most im­per­cep­ti­ble, with the driver no­ti­fied by ‘2 cylin­der mode’ ap­pear­ing in the in­stru­ment dis­play) as a pair of ac­tu­a­tors dis­en­gage the cam lobes from the in­let and ex­haust valves for those cylin­ders, so the valves re­main closed and fu­elling is cut. VW claims the 130PS ver­sion of this en­gine is 10% more fuel-ef­fi­cient than a com­pa­ra­ble petrol en­gine.

Ford has got in on the act: the com­pany’s process of cylin­der de­ac­ti­va­tion on three-cylin­der units is a world-first, with its Ecoboost unit able to dis­en­gage or re-en­gage a cylin­der in just 14 mil­lisec­onds – as they point out, that’s 20 times faster than the blink of an eye!

Spark Con­trolled Com­pres­sion Ig­ni­tion (SPCCI)

This lat­est tech­no­log­i­cal ad­vance is ex­pected to ap­pear in 2019. Devel­oped by Mazda for its SKY­AC­TIVE-X en­gine, it com­bines the spark ig­ni­tion of a petrol en­gine with the com­pres­sion ig­ni­tion of a diesel, flip­ping seam­lessly between the two. It works by switch­ing from the sto­i­chio­met­ric 14.7:1 air/fuel ra­tio to a lean-burn mix­ture of 29.4:1. When the en­gine is cold or op­er­at­ing at high revs, con­ven­tional spark ig­ni­tion is used; in lean-burn mode (around 80% of the time, ac­cord­ing to Mazda), the spark plug ig­nites a small amount of fuel-rich mix­ture in­jected di­rectly into the cylin­der dur­ing the com­pres­sion stroke. Com­pres­sion ig­ni­tion then takes over, re­sult­ing in a more com­plete and pow­er­ful burn of the mix­ture and there­fore a stronger power stroke. It prom­ises ef­fi­ciency gains of 20-30% com­pared to Mazda’s cur­rent SKYAC­TIV-G petrol range.

48-volt sys­tems are al­ready fit­ted on high-level mod­els. The tech­nol­ogy should fil­ter down to af­ford­able ve­hi­cles in the not-too-dis­tant fu­ture.

Smart Hy­brid Ve­hi­cle by Suzuki (SHVS) is a mild hy­brid that re­cov­ers en­ergy from brak­ing, stor­ing it in a lithium-ion bat­tery to as­sist the petrol en­gine later.

Mazda’s new SKY­AC­TIVE-X en­gine will com­bine the spark ig­ni­tion of a petrol with the com­pres­sion ig­ni­tion of a diesel.

Ford’s three-cylin­der en­gine has the abil­ity to shut down a cylin­der when cir­cum­stances al­low.

BMW’S ECOPRO elec­tric sys­tem helps achieve fuel sav­ings of up to 20%.

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