2009 Winter Auto Guide
A close up of rusty nails and bolts
auto
Hybrids not the only answer

Hybrid cars are not the only answer to increasing gas mileage. Carmakers are employing an array of other promising -- but less ballyhooed -- technologies and one may soon be sitting in your garage.

Government fuel-efficiency requirements -- often referred to as CAFE, or Corporate Average Fuel Economy, standards -- refer to the average fuel economy, expressed in miles per gallon, of a manufacturer's fleet of passenger cars or light trucks.

Recently, Congress mandated that cars and light trucks combined achieve 35 mpg by 2020. To achieve that number, passenger cars will have to jump from 27.5 mpg to 35.7 mpg and light trucks from the current 23.5 mpg to 28.6 mpg between 2011 and 2015. That's roughly a 25-percent increase.

To meet this requirement means automakers -- particularly those lacking a hefty portfolio of diesel-powered or hybrid vehicles -- will have to enhance current internal combustion engine, or ICE, technologies and develop some new ones.

Internal combustion engines produce power by sucking an air-gas mixture into a cylinder, compressing it with a piston and igniting it with a spark. The resulting explosion forces the piston down, which generates power.

Here are some of the technologies we can expect to see in greater use during the next decade:

Cylinder deactivation. GM calls this Displacement on Demand, or DOD, and Chrysler uses Multiple Displacement System. Whatever the terminology, cylinder deactivation rests certain cylinders when power demand is low.

At cruising speed, an ICE is working only at about 30 percent of power and the throttle valve is only partially open, limiting the amount of fuel and air. This makes the engine work harder to draw air -- wasting power that could be used to propel the vehicle.

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Shutting down four of the eight cylinders at cruising speed opens the throttle valve more fully, enabling the engine to "breathe" easier and reducing piston drag. The change in the number of "firing" cylinders is seamless. This can save as much as 25 percent of fuel, depending on the vehicle and the driver's habits.

Turbocharging. The best way to boost a gasoline engine's power is to increase the amount of air and fuel it burns. This used to be done by increasing the number and/or size of the cylinders. However, that's counterproductive when the goal is to increase fuel efficiency.

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