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

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Article Highlights:

While flex-fuel vehicles were once widespread in the auto market, they have dwindled to a select few models today. These cars, designed to utilize ethanol-based gasoline, represented a noteworthy segment of the alternative energy sector. However, with governmental incentives shifting towards electric cars and plug-in hybrids, flex-fuels have taken a backseat.

Let's delve deeper into what flex-fuel cars are and the types of fuels they use.

Understanding Flex Fuel

Flex fuel refers to a vehicle's ability to operate on either conventional gasoline or ethanol-blended fuel. Typically, E85 is the most common ethanol-based fuel, containing up to 83% ethanol during the summer. This percentage drops in colder months in certain regions to minimize cold start issues.

The inception of E85 was twofold: firstly, to harness America's capacity to produce bio-ethanol, generally from corn, supporting domestic agriculture and reducing oil import dependence. Secondly, it was perceived as more eco-friendly compared to the conventional gasoline/ethanol blend of 90/10. However, this claim remains debated.

A downside of E85 is its reduced fuel efficiency. The EPA suggests that vehicles running on E85 may experience mileage that's 15 to 27% less efficient compared to conventional gas engines, though this can be somewhat offset by its typically lower cost at the pump.

Distinguishing Features of Flex-Fuel Vehicles

Modern vehicles can handle some ethanol content in their fuel, but raising this content to 83% necessitates that the fuel system is constructed from materials resistant to ethanol's corrosive nature, particularly due to the extra moisture in E85.

Flex-fuel vehicles employ sensors to recognize the fuel type being used and adjust the combustion process appropriately. It's also possible to mix regular gasoline with E85 without causing any harm, although it offers no particular advantage.

Identifying Flex-Fuel Capable Vehicles

Today, the only new flex-fuel-compatible vehicles are large pickups and cargo vans from Ford and General Motors. In the past, flex-fuel cars were more widespread across different models. Indicators such as a "flex fuel" badge, a yellow ring around the filler, or a yellow filler cap can help identify these vehicles. Additionally, the owner's manual can provide confirmation.

Energy metrics in this discussion are estimated based on stop-and-go city driving as per the EPA FTP-75 Test procedure.

Diesel engines inherently have lower energy losses and are about one-third more efficient than gasoline engines. Recent advancements in diesel technology and fuel options are enhancing their appeal.

Innovations like variable valve timing and lift (VVT&L), turbocharging, direct fuel injection, and cylinder deactivation can help reduce energy losses.

In gasoline vehicles, a significant portion of fuel energy is lost as heat in the engine. Lesser amounts are lost due to engine friction, air pumping, and combustion inefficiencies.

Energy is also lost through the transmission and driveline. Technologies such as automated manual transmissions (AMTs), dual-clutch, lock-up transmissions, and continuously variable transmissions (CVTs) can mitigate these losses.

Energy losses from accessories like electric door locks and signal lights are negligible, but those from seat heaters, steering wheel warmers, and climate control fans are more noticeable.

Electrical components like lights, windshield wipers, navigation systems, and entertainment systems consume energy, impacting fuel economy.

Systems such as the water pump, fuel pump, oil pump, ignition system, and engine control use up energy produced by the engine.

Energy Losses During Braking

When brakes are applied in conventional vehicles, the energy expended to overcome inertia and move the car forward is lost as heat due to friction.

Lighter vehicles use less energy for movement, reducing energy wastage from braking. Weight reduction can be achieved through lighter materials and technologies.

Hybrid, plug-in hybrid, and electric vehicles use regenerative braking to recapture some of the braking energy that would otherwise be lost.

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Wind Resistance and Aerodynamic Drag

A vehicle requires energy to displace air as it moves, with resistance increasing with speed.

This resistance is influenced by the vehicle’s shape and frontal area. Aerodynamic designs have already significantly reduced drag, but further reductions of 20%-30% are feasible.

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Rolling Resistance and Tire Efficiency

Rolling resistance is the frictional force when a tire deforms while rolling on a flat surface.

New tire designs and materials can reduce rolling resistance. For cars, a 5%-7% reduction in rolling resistance can improve fuel efficiency by 1%, although these enhancements must balance traction, durability, and noise levels.

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