This is what happens when you hit the gas - Shannon Odell

916,854 views ・ 2023-09-05

TED-Ed


Please double-click on the English subtitles below to play the video.

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In 2015, two men drove a Volkswagen across the continental United States
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on just over 100 gallons of fuel.
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Their 81-mile-per-gallon performance doubled the car’s estimated fuel rating,
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and set the record for the lowest fuel consumption ride of a diesel car.
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The duo call themselves hypermilers
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and are experts in techniques that maximize a car’s fuel efficiency,
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such as the pulse-and-glide.
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In the pulse, drivers accelerate slowly
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until they’re traveling slightly above their intended speed.
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They then slowly release the throttle and glide,
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until they’re slightly below, and repeat.
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To understand why this strategy saves fuel,
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we first need to unpack what exactly is going on beneath a car's hood.
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Non-electric cars run on internal combustion engines,
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or ICEs.
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Cars are often advertised as sporting a 4-, 6-, or 8-cylinder engine,
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which refers to this device's main components.
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Within each of these cylinders is a piston,
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which moves up and down,
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spinning a bar known as a crankshaft,
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effectively converting linear motion into a rotary motion
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that can drive the wheels.
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What powers these pistons’ movements
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is what gives these engines their namesake: combustion.
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As the piston lowers, air and fuel are sprayed into the cylinder’s chamber.
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Then as the piston rises, this air and fuel mixture is compressed.
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In gasoline engines, a spark is introduced,
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igniting the gas.
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In diesel engines, the compression alone creates a mini explosion.
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This combustion causes an immediate increase in temperature and pressure,
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propelling the piston down, as it starts the cycle again.
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The gas pedal controls the amount of air and subsequent fuel
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released into the chamber.
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The more fuel in the chamber, the more powerful the combustion,
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making the crankshaft rotate faster.
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Driving down the highway, ICE cars spark thousands of blasts per minute.
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But explosion-power driving is pretty inefficient,
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as much of the energy generated is lost to heat.
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In fact, only 16 to 25% goes towards moving the wheels.
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These explosions also create CO2,
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and ICE engines produce 15% of the total global carbon emissions.
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The pulse-and-glide can increase efficiency for two reasons.
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First, when accelerating to higher speeds during the pulse,
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the engine works at a higher efficiency
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compared to traveling at a constant lower speed.
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And second, modern car engines shut off fuel injection or idle,
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when decelerating.
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Meaning that as the car glides,
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the wheels are driven by inertial energy, rather than combustion,
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ultimately saving fuel.
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But even at their peak performance,
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ICE hypermilers can’t compete with the true champion of fuel efficiency rides:
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the electric vehicle.
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Many EVs run on induction motors, which have two main parts:
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a stator and a rotor.
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The stator is a series of rings, with copper wires wrapped around it.
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By conducting electricity at variable rates,
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these wires create a rotating magnetic field.
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This field induces the rotor with electrical current,
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causing it to spin, and driving the motion of the wheels.
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For EVs, pressing on the accelerator changes the frequency of current
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driven into the wires of the stator,
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in turn increasing the rate at which the rotor spins.
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By utilizing battery power rather than gasoline,
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65 to 69% of the energy consumed by EVs
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goes directly to moving the wheels.
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And since EVs don't create explosions, fewer parts are needed below the hood.
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While a typical ICE vehicle has over 2,000 moving parts
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to help contain, cool, and maintain combustion,
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a typical EV has about 20.
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EVs are completely changing the hypermiling game
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as drivers compete to travel the farthest on the fewest kilowatt-hours.
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And records will likely only get more impressive,
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as the design of EV motors allows for the introduction
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of innovative energy-saving devices.
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For example, most EVs utilize regenerative braking,
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where energy normally lost to friction is conserved.
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As the car slows, the electric motor operates in reverse,
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capturing the vehicle’s kinetic energy to recharge the battery.
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Some companies are even equipping EVs with rooftop solar panels,
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further increasing their range.
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Since they don’t burn fuel, EVs have zero tailpipe emissions.
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That’s not to say they’re always carbon neutral.
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EVs require regular charging of their batteries,
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meaning their emission profile is only as clean
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as the electric utility they plug into.
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So as global grids continue to shift towards renewable sources,
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EVs are also becoming greener,
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making them an even more attractive, hyper-efficient option.
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