Efficiency Obstacles

An internal combustion engine works by igniting gasoline in a confined space to create an explosion, displacing a piston. Energy stored in gasoline gets transformed into kinetic energy as the pistons move. That kinetic energy is processed through the transmission and the drive train to deliver enough power to the wheels to overcome the car's tendency to stay at rest. The heavier the car is, the more energy is required to set it into motion.

To move, a vehicle must overcome Isaac Newton's first law of motion:

An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

In addition, there are other forces the pistons' kinetic energy must overcome:

Drag: The greatest obstacle during highway driving, drag is amplified by the height, width, and shape of the car. The bigger the car, the more kinetic energy it takes to overcome the car's drag. Some hybrid cars have special aerodynamic designs to reduce drag.
Friction: Leaking energy in the drive train between the pistons and the tires, friction can be reduced through alternate transmission types. The Toyota Prius has a power split device and the Honda Insight has a continually variable transmission to reduce friction.

On top of all that, a majority of the energy stored in gasoline never even makes it to becoming kinetic energy. More than 60% of your gasoline dollars create nothing more than heat. The gasoline that your car burns does more to raise the needle on the temperature gauge of your engine than the needle on your speedometer.

About 17% of the energy in gasoline is lost while an engine idles at a red light or in traffic. That's energy leaked away while the vehicle isn't even moving. In some hybrid cars, like the Toyota Prius, the gasoline engine shuts off to save fuel while the car is stopped, even if it's for a few seconds.

Only about 18% of the energy available in gasoline makes it to the drive train, where about 5% is lost before it reaches the wheels. A typical car is left with only 13% of the energy in its tank reaching its wheels.

Recall from Newton's law that an object in motion tends to stay in motion. That's great, but cars need to stop or slow down all the time. When it is time for a car to slow down, the brakes are applied. The brake pads create friction, which converts the kinetic energy of the vehicle's forward motion back into heat. All that work the engine did to create kinetic energy from gasoline is lost when the car brakes.

Learn how hybrid car technologies like regenerative braking are designed to mitigate the wasteful aspects of traditional cars by retaining kinetic energy.