2007 Volkswagen Golf GT TSI

Recipe for fun: take a turbo and add a blower

Powerful small-displacement engines have always been a European specialty. But even in Europe, an engine that puts out more than 75 kilowatts (100 horsepower) per liter of displacement is notable. So one that gets 125 kW (168 hp) and 240 newton meters of torque from 1.4 liters is quite an achievement. Throw in fuel consumption of 7.2 liters per 100 kilometers (33 miles per gallon), and you’ve really got something to cheer about.

So let’s hear it for Volkswagen’s Golf GT with the TSI Twincharger engine. VW’s goal was to reduce carbon dioxide emissions while maintaining power, torque, and driving characteristics in an engine that could be produced in high volumes for a variety of vehicles. The resulting engine delivers the highest specific power of any mass-produced 4-cylinder, and the same torque as a 2.3-L engine while using 20 percent less fuel.

VW’s engineers opted for the conventional approach to maximizing kilowatts per liter: start with small displacement, and coax out every possible kilowatt. To do this, their unusual trick was to use both a supercharger and a turbocharger. Each is essentially a pump that pushes more air into the cylinder, allowing more fuel to be used, thereby increasing an engine’s power. But a supercharger is basically an air pump driven by gears or a belt from the engine’s crankshaft, while a turbocharger is a small turbine spun by the force of escaping exhaust gases.

Because it’s driven off the crankshaft, a supercharger can supply additional air to the combustion process even at low engine speed. On the other hand, a turbo has to “spool up” to its operating speed, which happens only when the engine is running fast enough to generate significant exhaust pressure to spin it. The delay between a driver accelerating and the turbo boost coming on is called “turbo lag.” VW’s supercharger compensates for that lag.

Below 2400 revolutions per minute, the supercharger can increase the pressure of the air provided to the combustion process by up to 150 kilopascals (about 1.5 atmospheres). Under acceleration from 2400 to 3500 rpm, the supercharger stays engaged while the turbo spools up. Once the turbo nears its maximum boost of 250 kilopascals (2.5 atmospheres), a bypass flap switches the air supply from the supercharger to the turbo. The integration of the two provides high torque from 1750 rpm to 4500 rpm.

Chevrolet Volt / Concept

GM's vision of an electric-drive future

Hybrid-electric vehicles have been available for a decade now. And within a few years, so?called plug-in hybrids will offer beefier batteries that can be recharged from a wall socket, as well as by the vehicles internal-combustion engine. But both variants are still adapted from the same design handed down during a century of mechanically driven cars, in which the engines torque is transferred mechanically to the wheels.

A more radical design is the series hybrid electric car—driven by one or more electric motors powered by batteries that can be recharged by the combustion engine. In the series configuration, the combustion engine cannot drive the wheels directly; it switches on, only as needed, to run a backup generator that recharges the batteries on trips that exceed the cars all-electric range.

The Chevrolet Volt, which stole the show at Detroits North American International Auto Show in January, is the first-ever series hybrid concept vehicle shown by a major carmaker. Its 1-liter, 3-cylinder turbocharged engine runs an onboard 53-kilowatt generator that recharges a 16-kilowatt-hour lithium-ion battery made up of 80 4-volt cells.

That battery powers the car through a 120-kW electric motor delivering 320newton meters of peak torque, giving an all-electric range estimated at 65 kilometers (about 40miles). The plug-in recharge time likely will be 6.5 hours or less. And the 45-L gasoline tank gives almost 1000 km between refuelings.

On paper, anyway. We dont have a battery pack yet for the concept, acknowledges Tony Posawatz, the vehicle line director, who confirmed that the car shown in Detroit doesnt yet run—so its range has been estimated from lab tests. Among other qualifications for automotive use, lithium-ion battery packs must last 10 years or longer through more than 4000 full charge-discharge cycles.

The Volt is the first of several concepts that are expected to use what GM calls its E-flex platform for electrically driven vehicles. Starting around 2010, GM plans to build a variety of subcompact vehicles the size of an Opel Astra on a basic architecture that accommodates E-flex components. Some will have combustion engines, some are likely to be parallel hybrids with plug-in capability, and others may be serial hybrids like the Volt.

GMs announcement that it would produce cars using E-flex changed the Volt from just another shiny concept to a possible precursor of a truly radical shift in drive technology. During the Volts unveiling, Robert A. Lutz, GMs vice chairman for product development, was clear: GM intends to sell cars powered by electricity. But, understandably, the company wont commit to a date for doing so until it can get sufficiently powerful and durable lithium-ion batteries for automotive use.