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Gasoline vs Diesel Engines: What's the Difference?

gasoline vs diesel engines

Whether you’re just curious or deciding which engine meets your needs, you’re in the right place. Even though both gasoline and diesel use internal combustion to power your car, they each have advantages and disadvantages depending on your driving habits and budget. They each offer different fuel efficiencies, power, and maintenance service costs. Let’s look at what makes each engine unique and which one is right for you.

Gasoline vs Diesel: Four-Stroke Engine

A stroke is a stage in an engine’s cycle when the piston travels up or travels down. A four-stroke engine means the piston travels down, then up, then down, then up again to complete an engine cycle. Gasoline and diesel engines turn chemical energy into mechanical energy by using air, fuel, and combustion to move the piston, which rotates the crankshaft.

The stages of a four-stroke engine are as follows:

  • Intake stroke: The piston travels down, allowing oxygen-rich air into the cylinder.
  • Compression stroke: The piston travels up and compresses the air.
  • Power stroke: The fuel and air ignite, causing an explosion, which pushes the piston down and rotates the crankshaft. The crankshaft moves the car forward.
  • Exhaust stroke: The exhaust valve opens, and the piston moves upward, expelling the fumes.

Gasoline and diesel car engines are four-stroke engines. As previously mentioned, combustion happens at the third stroke. How diesel and gasoline engines produce an explosion is where they vary.

A gasoline engine relies on a spark plug to create a spark to ignite the fuel and air. Diesel engines do not use a spark because they are compression ignition engines. A compression ignition creates heat by compressing the air. The piston compresses the air in the combustion chamber first in a diesel engine. Because the air is under intense pressure, it heats up. Then vaporized diesel is injected into the combustion chamber, igniting when it hits the air. Since gasoline and diesel engines produce explosions differently, they have different advantages.

Diesel Versus Gasoline Engines: Difference Between Internal Combustion

Compression-Ignition Engine (Diesel)

  • Hot air is compressed in the combustion chamber of the cylinder, heating the air
  • Diesel is injected into the combustion chamber
  • Combustion occurs, forcing the piston downward

Spark-Ignition Engines (Gasoline)

  • Air and gas is compressed in the combustion chamber of the cylinder
  • The piston reaches the top, and spark plugs create a spark
  • Combustion occurs, forcing the piston downward

Why Does The Difference Matter?

The difference in combustion sets the two engines apart in fuel type, fuel efficiency, power, and reliability. Does that make one better than the other? Not necessarily. Your day-to-day driving habits should determine whether a diesel or gasoline engine is suitable for you. In short, city driving is better with a gasoline engine. Highway driving, hauling, and idling are better with a diesel engine.

Diesel vs. Gasoline: Fuel Type and Efficiency

Gasoline and diesel engines use different kinds of fuels, and how the fuel ignites affects its efficiency. Gas is more refined and volatile than diesel fuel. As a result, gasoline evaporates quickly and is more flammable. In other words, gasoline burns faster than diesel fuel. These are why gasoline engines use a spark for ignition in the combustion chamber.

On the other hand, diesel is thicker, which explains why diesel engines are 20% more efficient. Diesel burns slower, which is why diesel is vaporized and injected into compressed air to create combustion. A spark or flame won’t work to ignite diesel. Air compression contributes to fuel efficiency also because it uses thermal energy efficiently, making it a more fuel-efficient vehicle.

Diesel vs. Gasoline: Power Output

The power of a vehicle is made up of torque and horsepower. To keep it simple, torque measures how quickly your car accelerates from a dead stop. Horsepower is the rate at which your engine works. In general, gasoline engines produce more horsepower because they burn fuel faster and have more revolutions per minute (RPM). Higher RPMs mean the engine is working harder, which is why spark-ignited engines produce more horsepower. Diesel engines produce more torque because combustion happens faster than gas engines.

Diesel Engine Pros

  • Diesel is thicker
  • Diesel is 20% more efficient
  • Higher air compression ratio
  • Produces more torque
  • Better for trucks and cargo vans

Gasoline Engine Pros

  • Refined, thin fuel
  • Spark ignited
  • Fuel burns faster
  • Produces more horsepower
  • Better for sports cars and city dwellers

Diesel vs. Gasoline: Reliability

The build of each plays a role in their longevity. Gasoline engines’ design requires precision, chains, and belts. Since there are many moving parts, they wear and tear more than a diesel and require more frequent maintenance. Their life expectancy is up to 150,000 miles. Diesels are more robust and use gears. Since gears are in a fixed position, wear and tear is at a slower rate. Remember that since diesel engines are more efficient, they don’t work as hard, minimizing wear and tear. In fact, their life expectancy is 250,000 - 300,000 miles, according to manufacturers.

Diesel vs. Gasoline: Which is Best For Me?

At a glance, it looks like a diesel engine is the better option, but that is untrue. It’s all about your driving habits. Do you drive to and from work, run errands, and take occasional road trips? Do you drive up to 13,000 miles a year like the average person? If so, you want a gasoline engine. Do you drive on the highway often, tow heavy loads, carry heavy cargo, and sit idle a lot? Are you driving 15,000 miles or more? Consider a diesel engine.

How is your budget? Yes, a diesel is more robust and built to last, but consider what happens when replacing a part. New diesel parts are more expensive than new gasoline engine parts, and so is maintenance service. Even though the cost of diesel fuel is higher, remember it takes less effort for the same amount of work as a gasoline engine. This means a vehicle powered by a gasoline engine requires more fill-ups than a diesel. Fuel costs will be about the same over time.

To summarize everything you’ve learned, a diesel engine is for work. If you have a catering business, construction business, or needs that require towing, idling, and carrying heavy cargo, go for a diesel engine. Everyone else should enjoy the benefits of a gasoline engine just fine.

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