Making conventional gasoline and diesel engines more fuel-efficient is the quickest way to reduce transport emissions.
 | Head in the sandManufacturers have so far used fuel savings to make bigger, heavier, more powerful vehicles instead of more fuel-efficient ones. (Photo: Reuters) |
Making global transportation more fuel-efficient and climate-friendly is a bit like turning a big ship. Manufacturers and consumers embrace new technologies slowly. Although the automotive industry has begun shifting towards hybrid and electric technology, it could take decades for “green cars” to become the norm.
In the meantime, existing and “near-to-market” technologies for improving conventional combustion engines could increase fuel efficiency by 30 percent, says the International Transport Forum. That would in turn stabilize global carbon dioxide emissions from transport for the next 20 years.
One of the most promising of these technologies is arguably the simplest: stop-start systems that switch off the engine when the car is not moving. French carmaker Citroen uses a system that cuts the engine when the driver applies the brakes and just before the car comes to a halt (anything below six kilometers per hour). The engine remains on “standby” until the driver releases the brake pedal, when the engine starts up again. Citroen claims that this reduces fuel consumption and emissions in congested city areas by ten percent.
Efficient engines also employ fuel-injection technology that delivers fuel at high pressure into the engine’s combustion chamber more precisely than traditional carburettors. Fuel-injected diesel engines are the most fuel-efficient engines available.
Meanwhile, superchargers can force more air into the combustion chambers, improving the explosive power that drives the car, but at lower speeds. Cars with superchargers can cruise up steep hills in top gear instead of revving harder to change gears. Fewer revolutions mean less fuel use.
 | Animation (click on the image to enlarge)Ten ways to make cars more efficient (Animation: Allianz) |
Valve-control systems regulate the intake of fuel and air into the engine, and the expulsion of exhaust fumes. Sophisticated systems control the valves to deliver more or less fuel/air when accelerating or driving slowly. French company Valeo uses electromagnetic controls to open and shut valves, and each valve can operate independently from the others. Valeo says the system can cut fuel consumption and CO2 emissions in a car by up to 20 percent.
Valve-control systems can also be used at low speeds to shut down some of the cylinders driving the crankshaft that turns the vehicle’s wheels. Italian manufacturer Fiat reckons its new “Multiair” system can make a two-cylinder engine perform like a four-cylinder one, even though it will use 20-percent less fuel.
Germany’s Daimler is taking it a bit further, using a combination of variable valve-control, fuel injection, and supercharging to develop an engine that can switch between operating as a gasoline and a diesel motor. The “DiesOtto” engine acts like a petrol engine with spark plugs igniting fuel and air in its cylinders, and relies on that engine at high speeds. But at lower speeds, it switches into diesel mode.
The key is to use these new technologies to improve fuel economy. So far, in most industrialized countries, fuel savings from better engines have resulted in bigger and heavier cars rather than more fuel-efficient ones. The demand for power, performance, and safety has trumped fuel efficiency.
That may be changing with rising oil prices and greater taxation of gas-guzzling vehicles, particularly in Europe. And in emerging economies like India and China, small, low-power cars already match or exceed US fuel efficiency targets set for 2020. The future of conventional motoring will look less like the Hummer, and more like the Tata Nano, the world’s cheapest car.
editor: James Tulloch
publishing date: October 6, 2008
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