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