European vehicle manufacturers group ACEA is committed to cutting fleet average emissions to 140g/km by 2008 and to just 120 g/km by 2012. A study by the European Federation for Transport and Enviroment says 15 of 20 major brands sold in Europe are not on track to meet this target. So the IC engine has to become more efficient, and quickly. But as well as the need to cut CO2, legislation on tailpipe emissions will tighten under Euro V and VI, and may affect fuel consumption in the wrong way. Gasoline engines have obviously the greatest margin for improvement. Combustion knock limits compression ratio but bioethanol fuels can help because in high blends they have a higher octane rating, although naturally aspirated engines cannot take full advantage. A report by the European Commission finds strong downsizing with turbocharging the single most effective gasoline powertrain technology for CO2 reduction: at 12%. Smaller engines hawe lower frictional losses but to substitute one for a larger capacity unit without sacrifing driveability means developing the same torque. Torque is proportional to engine capacity and mean effective pressure (MEP). So a downsized unit needs more air: forced induction is the simplest route but lag must be avoided. This has been seen already with Volkswagen's 1.4 litre TSI twin charge engine: turbo- and supercharged to develop 168 bhp and 240 Nm at 1750rpm with CO2 of 175 g/km. Renault recently announced its 1.2 litre TCE 100 engine with 100 bhp, and Fiat will fit 1.4 litre T-JET engines of 120/150 bhp into the new Bravo. BorgWarner believes that within five years 30 % of gasoline engines made in Europe will be turbocharged; today around 11 % are. Driveability and good transient response require good low speed torque - something downsized engines cannot always provide, hence VW's supercharger. Variable turbine geometry (VTG) turbochargers seek to adress this by cutting lag but, until recently, were confined to diesel applications because of higher exhaust gas temperatures. Withstanding elevated temperatures require high nickel alloys for the turbine wheel and ensuring robust operation of the vanes and adjustment mechanism raises cost. Ricardo adresses this issue with a downsizing concept of its own: the lean boost direct injection engine (LBDI). More effective engine control also has potential to improve economy but not without cost. Automotive consultancy Integral Powertrain is developing an electrically driven compressor combined with a belt-driven starter/generator that also provides torque assist from energy captured during regenerative braking, allowing a claimed 170 bhp from 1.4 litres, enabling taller gearing and therefore downsizing and downspeeding to emit only 120 g/km CO2. Diesel engines are under pressure: already far more expensive to manufacture than gasoline, they are also the primary target of Euro V for PM emissions, and Euro VI for NOx.
The return of gasoline. Powertrain
Die Rückkehr des Benzins. Antriebsstrang
Automotive Engineer ; Dez ; 26-27
2006
2 Seiten, 3 Bilder
Aufsatz (Zeitschrift)
Englisch
Anwendung im Motorenbau , Dieselmotor , Otto-Motor , Kraftfahrzeugmotor , Kohlendioxid , Abgasturboaufladung , Kompressoraufladung , EU-Norm , Abgasemission , Downsizing (Rechnernetz) , Benzindirekteinspritzung , Verdichtungsverhältnis , Oktanzahl , Trend (Entwicklung) , Kraftstoffverbrauch , Ethanol , Drehmomentenverlauf , Abgastemperatur , Reibungsverlust , Rekuperationsbremsung
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