How Does a Diesel Engine Work?

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Diesel engines excel in areas where gasoline engines simply can't compete. Shipping trucks, buses, generators, construction, agriculture, and locomotive transport are a few diesel dominated areas. Let's cover what makes them different from gasoline engines.


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Differences in Ignition between Diesel and Gasoline Engines


The Difference in Ignition

Both engines are similar in that they have internal combustion to drive power. However, gasoline and diesel engines experience combustion in two different ways. Gasoline combusts through the use of compression paired with a spark plug, while diesel fuel combusts without a spark because of the higher compression and temperature in the cylinder. Both engines require three things to be efficient:

  • Fuel
  • Heat
  • Air

One clear difference in both combustion chambers are that diesel engines have glow plugs, and gasoline engines have spark plugs. So what's different about them?


Diesel Engine Glow Plugs

Unlike gas powered engines, diesel ignition is caused by compression without a spark. The compression stroke in a diesel engine is hot enough to ignite the fuel-air mixture, sometimes reaching 2,000 degrees. In cold temperatures however, a glow plug is required to start. The glow plug heats up the combustion chamber, then shuts off once the engine starts running. We have a selection of glow plugs available on our website.


  • Heats the combustion chamber
  • Doesn't ignite the fuel
  • Used in cold temperatures


Gasoline Engine Spark Plugs

Spark plugs are required for the ignition in gasoline engines. They differ from glow plugs because they're used in every power stroke.

Gasoline Engine Spark Plug | Highway & Heavy Parts

  • Required to ignite the gasoline
  • Used with every power stroke


How Does a Diesel Engine Turn Fuel into Power?


Turning Fuel Into Power

It's no secret that diesel engines are very powerful. The reason for this power is attributed to the way compression occurs in the combustion chamber. A diesel engine operates by cycling between four different strokes:

  1. Intake Stroke - The piston starts at the top of the cylinder, as it moves downward the intake valves open and an air-fuel mixture is introduced into the combustion chamber. The mixture enters the low pressure zone caused by the piston movement.

  2. Compression Stroke - This stroke begins with the piston at the bottom of the cylinder. After the fuel-air mixture has filled the cylinder and the intake valves have closed, the piston begins rising for compression. At the top of the cycle, the mixture has nowhere to go, and is ignited.

  3. Power Stroke - This stroke begins after ignition. The valves remain closed, and the ignited mixture expands and pushes the piston back down. 

  4. Exhaust Stroke - Once the power stroke ends, the exhaust valve opens and the used mixture is expelled as the piston returns to the top.

What are the advantages and disadvantages of the diesel engine?

Diesel engines are very versatile and efficient. Because of the power created by compression, they have great fuel economy, torque, and durability. Gasoline engines require a spark to ignite the fuel, but the pressure and temperature in diesels is so high that it ignites on its own.

Advantages of Diesel Engines:

1. Efficiency - Because of the power generated by compression ignition, the diesel engine uses less fuel and generates more power. 

2. Durability - In order to withstand higher temperatures from compression, the diesel engine is designed more rugged than gasoline engines. As a result, they can last more miles compared to gasoline vehicles before needing part replacement.

3. Torque - More energy emitted from compression means more torque. This additional power is why diesel engines are ideal when hauling heavy items.

4. Resale - The high durability and ability to put on miles attributes to diesel vehicles having better resale value.


Disadvantages of Diesel Engines:

1. Price - You'll find that diesel vehicles can be quite a bit more expensive than gasoline vehicles.

2. Fuel - Diesel fuel is more expensive than gasoline but depending on how often you drive, you won't need to fill up as often. It's still something to keep in mind while considering a purchase.

3. Parts - If general maintenance isn't kept up with, parts and repairs can be more expensive than gasoline vehicles.

You'll find that diesel vehicles have a high cost and fuel price, but generally they're meant to do bigger jobs than gasoline vehicles. More power, torque, and durability makes diesel great for various jobs. However, if you're just looking for something for city driving, a gasoline car would be the way to go. Read our previous blog for some useful tips to help your diesel engine live longer.



Diesel engines deliver more power and efficiency compared to gasoline engines due to compression ignition. Greater fuel economy is also a result, meaning fewer trips to pump. The diesel engine functions through the intake, compression, power, and exhaust strokes. This is similar to a car motor, however gasoline is ignited with the use of a spark plug in gas vehicles. In a diesel engine, fuel injectors release fuel in a fine mist, which is ignited by compression.


Let us help you get the right parts for your engine! We have ASE Certified Techs who can help make sure you're getting the best parts for the job. Call them at 844-304-7688, or request a quote online.