What Are Flex-Fuel Cars and What Types of Fuel Can They ...

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Once a common part of the new-car market, flex-fuel vehicles recently shrunk to just a handful of new models. Designed to take advantage of ethanol-based gasoline, flex-fuel automobiles served as a unique subset of the alternative-energy landscape before government subsidies left them behind in favor of electric vehicles and plug-in hybrids.

Let’s take a look at flex-fuel cars and what types of fuel they are designed to use.

What Is Flex Fuel?

Flex fuel is a term that refers to an automotive drivetrain that can run on either traditional or ethanol-blended gasoline. Flex indicates the ability to use either fuel. The most common form of ethanol-based gas is called E85. During the summer months, E85 contains up to 83 percent ethanol content, while in the winter this amount is reduced in some regions to reduce problems with cold-weather starting.

E85 was created for two reasons. The first was to take advantage of the United States’ ability to produce bio-based ethanol, typically from corn. This had the dual effect of propping up domestic agriculture via subsidies and an attempt to reduce reliance on imported oil. It was also viewed as a renewable resource and therefore more environmentally friendly than the typical 90/10 percent gasoline/ethanol mix found at most pumps. This assertion is not universally accepted.

The drawbacks to using E85 include reduced fuel efficiency. The EPA states that flex-fuel vehicles return mileage that is between 15 and 27 percent worse than a regular gas-fueled engine because of the lower energy content in the fuel. This is offset somewhat by the typically cheaper price at the pump for E85.

What Makes Flex-Fuel Vehicles Different?

Although modern automobiles can tolerate a certain amount of ethanol in gasoline without serious issues, increasing ethanol content to 83 percent requires that the fuel system is made of materials that can resist its corrosive effects, especially in terms of the additional moisture in E85 fuel.

Flex-fuel vehicles use a sensor to detect the type of fuel being fed to the engine and adjust the combustion process accordingly. You can even mix a tank of standard gas with E85 with no risk of damage, although there’s no benefit to doing so.

Which Vehicles Can Use Flex Fuel?

Currently, the only new vehicles compatible with flex fuel are full-size pickups and cargo vans by Ford and General Motors. In the past, flex fuel was more common and available across a wider range of automobiles. Look for the “flex fuel” badge on the body, a yellow ring around the filler, or a yellow filler cap. The owner’s manual will also confirm if you’re driving a vehicle that can use E85 fuel.

Energy requirements in this diagram are estimated for stop-and-go city driving using the EPA FTP-75 Test procedure.

Diesel engines have inherently lower losses and are generally one-third more efficient than their gasoline counterparts. Recent advances in diesel technologies and fuels are making diesels more attractive.

Advanced technologies such as variable valve timing and lift (VVT&L), turbocharging, direct fuel injection, and cylinder deactivation can be used to reduce these losses.

In gasoline-powered vehicles, most of the fuel's energy is lost in the engine, primarily as heat. Smaller amounts of energy are lost through engine friction, pumping air into and out of the engine, and combustion inefficiency.

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Energy is lost in the transmission and other parts of the driveline. Technologies such as automated manual transmissions (AMTs), double-clutch, lock-up transmissions and continuously variable transmissions (CVTs) can reduce these losses.

Losses from accessories such as electric door locks and signal lights are minuscule, while losses from seat and steering wheel warmers and climate control fans are more significant.

Electrical accessories such as seat and steering wheel warmers, lights, windshield wipers, navigation systems, and entertainment systems require energy and lower fuel economy.

The water pump, fuel pump, oil pump, ignition system, and engine control system use energy generated by the engine.

Braking Losses

Any time you use your brakes in a conventional vehicle, energy initially used to overcome inertia and propel the vehicle is lost as heat through friction at the brakes.

Less energy is used to move a lighter vehicle. So less energy is wasted from braking a lighter vehicle. Weight can be reduced by using lightweight materials and lighter-weight technologies.

Hybrids, plug-in hybrids, and electric vehicles use regenerative braking to recover some braking energy that would otherwise be lost.

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Wind Resistance (Aerodynamic Drag)

A vehicle expends energy to move air out of the way as it goes down the road—less energy at lower speeds and more as speed increases.

This resistance is directly related to the vehicle's shape and frontal area. Smoother vehicle shapes have already reduced drag significantly, but further reductions of 20%–30% are possible.

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Rolling Resistance

Rolling resistance is a resistive force caused by the deformation of a tire as it rolls on a flat surface.

New tire designs and materials can reduce rolling resistance. For cars, a 5%–7% reduction in rolling resistance increases fuel efficiency by 1%, but these improvements must be balanced against traction, durability, and noise.

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