Gasoline vs. Diesel Engine – What is the Difference?

Gasoline and diesel engines seem identical on the look. They both have pistons that move up and down inside cylinders by using internal combustion.

The pistons are linked to a crankshaft which turns their back-and-forth action into the rotating movement needed to propel a vehicle. Both engines produce energy by igniting fuel, but the major difference between the two is in the ignition mechanism.

Both engines have significant differences in operation, cost, and efficiency. Learn all about those differences, including the advantages and disadvantages of each in this article.

Engine Work Mechanism

Gasoline Engine:

In a gasoline engine, the combustion cycle is a four-stroke. The intake stroke begins at the top of the cylinder, and the piston travels to the bottom.

As the piston descends, the intake valve opens, enabling a mixture of air and fuel to enter the engine. As the piston returns to its starting position, the gas-air combination is compressed once more. The spark plug is activated at the top of the compression stroke, igniting the mixture.

The combustion stroke is completed when the piston is pushed down by the expanding gas. This is followed by a piston movement back to the top of the cylinder, which causes the exhaust valve to force the exhaust gasses out.

Diesel Engine:

The four-stroke cycle of a diesel engine is nearly identical to that of a gasoline engine, except for one key difference. A diesel engine’s intake stroke consists solely of air, unlike a gasoline engine’s.

When the piston rises and compresses the air, it gets heated. Fuel is pumped into the cylinder at the top of this stroke. Combustion is sparked by the compressed air’s heat, which causes the piston to drop back down.

Major Differences Between Gasoline and Diesel Engines

Spark Plugs:

Gas engines require a spark plug to start the combustion process in the combustion chamber. On the other hand, diesel engines don’t need spark plugs since they utilize the heat of compressed air.

However, glow plugs can be used in certain diesel engines. This is due to the compressed air not being hot enough to ignite the fuel in a cold cylinder.

Diesel engines might have difficulty starting in cold weather. To get the engine to start, glow plugs employ electrically heated wires to warm up the combustion chamber. As a result, the engine reaches its optimum working temperature.


Source: chemistryworld

Diesel engines frequently outperform their gasoline equivalents in terms of fuel economy. With self-ignition, diesel engines are able to generate substantially higher pressures during the compression stroke resulting in increased overall efficiency.

In gas engines, on the other hand, the self-ignition temperature must never rise before the spark plug sparks. As a result, the cylinder’s compression will be decreased, resulting in lower overall efficiency.

Compression ratios in gas engines are almost never higher than 14:1. On the other hand, diesel engines have a ratio of 18:1 or more.


Diesel engines typically last two to three times as long as their gasoline counterparts. The nature of the fuel is part of the reason behind this. In comparison to gasoline, diesel fuel acts more like a thin viscosity oil and lubricates everything it comes into contact with.

Advantages & Disadvantages of Gasoline Engines


  • Low-cost price tag
  • More widely available
  • Reduced repair expenses


  • Lower fuel economy
  • Life expectancy is reduced
  • Increased depreciation rate

Advantages & Disadvantages of Diesel Engines


  • Excellent torque for the size of the engine
  • Longer life expectancy
  • Greater fuel economy


  • It’s more expensive
  • Higher insurance rates
  • Increased repair expenses

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Christopher Alaban
Christopher Alaban
1 year ago

Thank you for sharing this is a big help for the new mechanic