Can you explain how gasoline powers cars, including the science behind internal combustion engines go?

-Karthik Gurumurthy

When people ask me how gas makes a car go, I explain it’s all about controlled burning. Gasoline is burned inside an engine—that’s why we call it an internal combustion engine, unlike steam engines or Stirling engines where fuel burns externally.

Most cars use what’s called a four-stroke combustion cycle, or the Otto cycle, named after Nikolaus Otto who invented it back in 1876.. When you put a small amount of high-energy fuel in a confined space and ignite it, it releases tremendous energy as expanding gases.

In a car engine, these expanding gases push pistons that turn a crankshaft, which transmits the motion to the wheels. Several hundred explosions happen every minute, creating smooth acceleration.

It starts with the chemical energy stored in gasoline molecules, which are hydrocarbons formed from ancient organic matter that’s been compressed underground for millions of years.

The four-stroke engine cycle is what converts this chemical energy into mechanical motion:

1. Intake stroke: A piston moves downward, creating a vacuum that draws in a mixture of air and atomized gasoline through an open intake valve.
2. Compression stroke: The intake valve closes, and the piston moves upward, compressing this fuel-air mixture into a much smaller space, making it more explosive.
3. Power stroke: At the perfect moment, the spark plug ignites the compressed mixture. The rapid combustion creates expanding gases that forcefully push the piston downward, which is the only stroke that generates power.
4. Exhaust stroke: The exhaust valve opens, and the piston moves upward again, pushing out the spent gases.

This process happens in each cylinder simultaneously but at different stages, creating continuous power. The pistons are connected to a crankshaft, which converts their up-and-down motion into rotational motion.

The crankshaft connects to the transmission, which provides different gear ratios to optimize power delivery. The transmission then connects to the driveshaft (in rear-wheel drive cars) or directly to the differential (in front-wheel drive cars), which allows the wheels to turn at different speeds when cornering while still receiving power.

The entire system relies on precise timing, controlled by the engine’s computer in modern cars. This computer regulates exactly when the spark plugs fire, how much fuel is injected, and when the valves open and close, all calibrated to maximize power and efficiency.

The engine also requires cooling systems (typically water-based) to prevent overheating, and lubrication systems to reduce friction between all the rapidly moving parts. That’s why there’s growing interest in hydrogen-based fuel systems and other alternatives that would mean cleaner fuel and less dependence on foreign oil markets.