What is the Difference Between Diesel and Gasoline Engines?

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With gas prices rising ever higher and alternative fuels becoming more mainstream, many vehicle owners are reexamining the gasoline engine. Its most prominent competitor is the diesel engine, and while many Americans have heard of diesel, fewer understand the differences between diesel and gas.

First of all, unlike a car powered by electricity or cold fusion, a diesel-powered car is not much different from a gas-powered one. They both contain internal combustion engines that convert liquid fuel into mechanical energy. The main difference between these engines is how their internal combustion processes work. (To briefly explain internal combustion: Explosions generated in the piston chambers push the pistons up, the pistons turn the crankshaft, and the crankshaft spins the wheels.)

In a gasoline engine, fuel is mixed with air inside a piston chamber, compressed by a piston and ignited by a spark plug. In a diesel engine, the air is compressed first, before the fuel is added, which causes it to heat up. When the fuel arrives, no spark plug is necessary to generate the explosion (this is known as direct injection).

Diesel engines outperform gasoline engines on fuel economy. This is due to the fact that diesel is more energy dense than gasoline. Diesel engines can convert heat into energy, instead of piping it out of the vehicle (as gasoline engines do). However, despite this advantage, diesel engines are more expensive than their gasoline counterparts, and because there are fewer of them on the road, parts and labor can be more expensive.

Another strike against diesel fuel is that it is no longer much cheaper than gasoline. That prime advantage has disappeared over time. And while it does get better mileage, a higher engine weight and compression ratio give diesel cars a lower maximum RPM. They’re also noisier, smokier and harder to start in cold weather.