Gas, electric, diesel or a combo pack?

Today's auto powertrains offer many different ways to improve fuel efficiency

By Jil McIntosh Wheels.ca

May 29, 2014 4 min. read

Article was updated 9 years ago

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At one time, choosing a car was a lot easier, since almost all of them just had regular gasoline engines.

It's a lot tougher today. Rising gas prices, stricter fuel-economy and emissions standards, and new technologies have resulted in several types of vehicles. It?s not always easy to figure out exactly how they work, so here?s a list of the ones you're most likely to see.

These are sometimes called 'alternative powertrains.' The powertrain is the overall system that powers the car, including the engine and transmission, while alternative refers to anything other than a traditional gasoline engine working by itself.

Hybrid: These vehicles, such as the Toyota Prius, use a gasoline engine coupled with an electric motor. Most hybrids can run on gasoline alone, on electricity alone, or a combination of the two. The system switches between them automatically, depending on such factors as speed and acceleration. You don?t plug them in. Instead, they recharge their batteries using the gasoline engine, and with kinetic energy captured when decelerating.

The gas engine shuts off at idle, such as when you're stopped at a light, although the lights, stereo, climate control and other functions continue to operate. (This feature, called start/stop, is now available on some regular gasoline vehicles, too.)

Hybrids save fuel because the gas engine doesn't run all the time. As well, they can use a smaller, more efficient gasoline engine, since the electric motor provides additional fuel-free power when needed.

Plug-in Hybrids: These hybrids, such as the Toyota Prius Plug-In and Ford C-Max Energi, can be plugged into the wall.

Once charged, they?ll run for about 20 km on electricity alone. When that runs out, the car works as a hybrid, running on gasoline and electricity, and recharging the battery itself. You have to plug it back in again to get that initial electricity-only range.

It will run even if you never plug it in, but depending on your commute, you could do most of your driving on electricity alone if you charge it regularly.

Electric Cars: Purely electric cars, such as the Nissan Leaf, Mitsubishi i-Mi-EV, and Tesla must be plugged into the wall. If you drive until the charge depletes, the car stops running.

Range is the major hurdle with electric cars. Bigger batteries go farther, but also cost and weigh more, and take longer to charge. Tesla?s Model S can travel up to 480 km on a charge, but it also starts at $79,000, and it?s closer to $90,000 for the longest-range model.

Extended-Range Cars: These are electric cars with a small gasoline engine for backup, such as the Chevrolet Volt and Cadillac ELR. Once charged from a wall socket, they run on the battery.

When the charge depletes, the gasoline engine automatically starts up, but instead of driving the wheels, it works like a generator to make more electricity. The battery-only range is generally more than in a plug-in hybrid, but less than an all-electric car.

The benefit is that as long as you have gas in the tank, the car will continue to run when the stored charge is gone.

Light Electrification: Systems like GM's eAssist use an electric motor alongside a gasoline engine that?s smaller, and therefore inherently more fuel-efficient, than on a gas-only model.

The car can't run on electricity alone, but when more acceleration is needed, the electric motor automatically starts up and adds fuel-free power. These cars don?t get plugged in.

Diesel: Once almost exclusive to trucks, diesel is now becoming more common in cars. Diesel engines are more efficient than gasoline so they get better mileage, and can go much farther on a tank of fuel.

Improvements in both the engines and fuel have eliminated the 'rotten egg' smell, and any black guck spewing from the tailpipe. Most are now much quieter than before, and they all start right away, without a long wait for the glow plug to warm up.

Almost all require diesel exhaust fluid, or DEF. It's automatically squirted into the exhaust system, where it breaks down certain pollutants into harmless gases. The DEF tank is easy to fill, and automakers size it so it usually needs filling about the same time that you?re due for an oil change.

Turbocharging: Turbos compress more air into the engine to make more power. The engine uses more fuel when this happens, but the turbo only comes on under load, such as hard acceleration.

Automakers used to use turbos strictly for raw power. Today, some put them on smaller engines, providing power when needed, without the thirst and weight of a larger engine. Possibly the best-known system is Ford's EcoBoost.

Gasoline direct injection: This technology injects fuel and air directly into the cylinder, burning it more efficiently. Once restricted to expensive cars, GDI has come down in price, and can now be found on some entry-level vehicles. It doesn't save fuel by itself, but allows engineers to tweak the engines for better efficiency.

CVT: Stands for Continuously Variable Transmission. Instead of gears, these fully-automatic units use pulleys connected by a belt or chain. Because it continually changes the gear ratio, a CVT always keeps the engine at its most efficient r.p.m.

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