Flexible Fuel Technology: Flex Engines

flex fuel label on Buick vehicle
A lot of people don’t even know they drive a flex-fuel vehicle. A body badge like this, however, is a dead giveaway. Want to learn more? Check out these alternative fuel vehicle pictures.
Courtesy of GM

When you think of flexing green muscle, the Incredible Hulk might first come to mind. But flex-fuel engines are another powerful green machine and, unlike the Hulk, they exist outside of comic books and movies.

Flex engines are found in flexible-fuel vehicles (FFVs), which are sold and operated in countries around the world. In short, a flexible-fuel vehicle is one that can run on fuels other than straight gasoline, such as ethanol or nearly any ratio of ethanol and gas combined in the same tank.


Consumers have had the option to buy FFVs in the United States since 1995. But Brazil is actually the world's biggest flexible-fuel vehicle market. More than 90 percent of vehicles sold today in that country have flex engines [source: Sugarcane.org].

In the United States, the flex fuel that's garnered the most headlines is E85. Depending on seasonal adjustments, E85 is a blend of up to 85 percent ethanol, with the remainder consisting of gasoline. As of this writing, approximately 2,300 United States fuel stations offer E85.

You can't pump E85 into a standard gasoline vehicle's tank without nasty side effects, such as chugging, rough performance and possible engine damage. Instead, you need an FFV designed specifically to work with the chemical corrosiveness and higher octane of ethanol.

Oddly, many consumers own FFVs and they don't even know it. For example, there are roughly 120,000 FFVs in the state of Nebraska and nearly 60 percent of the owners are unaware that they have a flex engine under the hood [source: Nebraska Corn Board]. The most obvious clues? If your car was manufactured after 2008 and it has a yellow gas tank cap, it's an FFV. Your owner's manual will also enlighten you as to your motor type.

Even people who don't know much about FFVs understand that oil consumption is a hot topic. That's where FFVs frequently enter the conversation. Because we can produce ethanol from renewable sources, such as corn and sugar cane, FFVs are often described as more eco-friendly than straight gasoline vehicles.

The supposed environmental friendliness of FFVs, however, is a point of hot contention between various factions in manufacturing, politics and science (more on that later).

On the next page, you'll read about how flex engines are different from their gasoline counterparts. You'll see that these two combustible engine cousins are more alike than you might think.


Fine-tuning a Flex Engine

specially designed flex-fuel engine
Flex-fuel engines are specially designed to withstand the corrosiveness of ethanol. Run ethanol regularly in a regular gas engine and it will rust and break down.
Courtesy of GM

Flex engines aren't wildly different from gasoline engines, nor are they space-age technology. The Ford Model T car, for instance, was a flex engine that burned either gas or ethanol.

FFVs don't cost more to build, and they aren't more expensive in terms of sticker price, either. If you really want to, you can even buy a conversion kit that lets you turn your gasoline motor into one that will happily drink E85.


From a chemical perspective, ethanol is different from gas in two major ways. It's more corrosive and conductive. It also burns hotter, so it has a higher octane rating. A flex engine must be built to handle those technical challenges.

For starters, your car has to know what kind of fuel you're pumping. An onboard computer analyzes fuel composition to optimize engine ignition, adhere to emissions standards and regulate combustion. No matter how much the ethanol-to-gas ratio fluctuates, your flex-fuel car can adjust on the fly.

In flexible-fuel vehicles, the fuel tank and in-tank components are built to withstand ethanol's corrosiveness. Similarly, the fuel lines, gaskets, seals and rubber fuel hoses all must be corrosion-resistant, too, as must the fuel injectors.

The same goes for internal engine components. Valve seats, piston rings, valves and other parts are all made from materials that won't easily corrode. These parts are also built to diminish the possibility that damage will result due to ethanol's tendency to break down and clean away engine lubricants.

Conductivity is another concern. All electrical parts of the fuel system, including wiring, must be insulated against ethanol's higher conductivity. In addition, the fuel filler parts have anti-spark features that reduce the chance of stray sparks or static electricity causing a dangerous flare-up.

Electrical worries aside, ethanol has a lower energy density than gasoline, so the engine needs more fuel to achieve high performance. Thus, fuel injectors are created to achieve higher fuel flow rates --otherwise, your engine would see a drastic reduction in overall power.

In terms of engine construction, those are the most notable distinctions in FFV motors. On the next page, you'll read more about flex engine performance and whether making the switch is logical for you.


Flexing Lobbying Muscle

flex fuel engine fuel injectors
Because ethanol has less energy potential than gas, fuel injectors must spray more fuel to maintain your vehicle’s performance.
Courtesy of GM

For multiple reasons, the eco-friendliness of FFVs is questionable. Cost savings are dubious, too. And as it turns out, it's not necessarily consumer demand or sustainability concerns that are driving the proliferation of FFVs.

Let's start with the basics. There's no change in vehicle performance when you use ethanol. You won't notice a difference in acceleration or horsepower.


The key differences are energy density and CO2 (carbon dioxide) emissions. Lower energy density just means that there's less energy in a gallon of ethanol than there is in regular gasoline, so you have to burn more to travel the same distance that you would with gas.

This, in turn, means you have to burn more fuel to get moving, and your vehicle actually releases more CO2 than it does with gas. However, because that CO2 was derived from a plant source instead of petroleum, you're (in theory) simply releasing it back into the atmosphere, where it would have gone anyway as the plant naturally decayed. Still, the eco-friendliness of FFVs is, at best, unclear.

Fuel efficiency is another thing altogether. As with all things related to mileage, there's a lot of variability here, but mileage per tank drops between 15 percent and 30 percent when you switch to ethanol. And because ethanol fuels are generally about the same price as gas, you might actually spend significantly more money -- perhaps hundreds of dollars per year -- to get around on just ethanol.

Considering these facts, you may wonder why anyone would build or buy FFVs. In the United States, federal Corporate Average Fuel Economy (CAFÉ) standards dictate that auto makers must offer vehicles with a minimum gas mileage of 27.5 mpg (22.2 for light trucks); otherwise, they face stiff fines.

There's a loophole, though: If those companies build vehicles that burn ethanol, they won't be fined nearly as much. Basically, it's a government strategy to encourage the use of more ethanol, which effectively subsidizes American crop farmers and could potentially reduce American dependence on foreign oil.

As for the flex engines themselves, well, they're a mature technology that requires zero skills or adaptation on the part of consumers. All you need to do is find one of thousands of gas stations that offer E85 fuel, and your flex engine will take you as far as you want to go -- just not quite as far as it would if you filled up with gas.


Author's Note

FFVs and E85 are getting more and more common, so the pros and cons of the ethanol business model are being played out in the real world for everyone to witness. Corn growers love FFVs because they create greater demand (and higher prices) for their product. And some environmental lobbyists see E85 as a stepping stone to cleaner-burning fuel sources. But whether ethanol can make a serious, long-term dent in our dependence on foreign oil remains to be seen.

Related Articles



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