Do Diesel Engines Have Spark Plugs? Simple and Quick Answer

This is a very common question that lots of people are asking about diesel engines. Do diesel engines have spark plugs? What is the difference between diesel fuel and gasoline? Here you can find both simple answers and detailed explanations of these questions.

Do Diesel Engines Have Spark Plugs? Simple Answer: No!

Do Diesel Engines Have Spark Plugs
Diesel engine glow plugs. Source: Bostech Auto.

Diesel engines do not have spark plug systems to ignite the fuel that comes inside the cylinder. Instead of spark plugs, they have glow plugs that help start the engine at first start. This is the main difference between diesel engines in general.

Why Diesels do not Have Spark Plugs?

To answer this question, we need to elaborate on the spark plugs and their working principle of them. First of all, we need to state that only gasoline engines have spark plugs. Spark plugs are the systems that provide high voltage electric spark inside the engine cylinder to ignite the gasoline air mixture. Without this spark, a ignition will not take place.

But if we take a look at diesel engines, there are certain differences because of the diesel fuel. The structure of diesel fuel is different than that of gasoline. Diesel is a thicker fluid if we compare it with normal gasoline. So there is a special vaporizer system which we call a diesel pressurizing and injection system that increases the pressure of the diesel and makes the diesel to a mist form. In this form, the diesel fuel becomes more and more inclined to burn. And diesel systems do not need spark plugs for the combustion inside the cylinder.

And another reason why diesel does not need spark plugs is, the compression ratios in diesel engines are much higher than the gasoline engines. Because of this, the pressure and temperature levels are much higher than the gasoline engines. This is also another important factor that diesel engines do not need spark plugs.

What Diesel Engines Have? Glow Plugs!

Instead of spark plugs, diesel engines have glow plugs. Glow plugs are basic coil system that provides the required heat to burn the high-pressure and misted diesel fuel when you first cold start the engine.

Once you open the electrical system of your diesel car, an electrical current goes through the glow wires. And this causes the glow plug to coils heat. And when the diesel injection system provides the first high-pressure diesel fuel inside the cylinders, the glow plugs make them combust. After the combustion takes place, the diesel engişne starts to work and does not need the glow plugs after that point.

So these are the general difference between diesel engines.

Which is Better; Diesel or Gasoline?

It depends. Because of the system of the engines and the difference in the gasoline, there are certain differences between these engines.

  • The first difference is torque. Diesel engines produce much more torque with the same amount of power. For example, talking about the 155 hp gasoline and diesel engines. The power of the diesel engine will be much higher. But in terms of speed, the gasoline engine will be better. Do not forget that, this is a generalization. You can find various examples of it.
  • Because the torque of diesel engines is higher, they are generally used for heavy-duty applications such as trucks, tractors, locomotives, and ships. The biggest engines that you can see both in traffic and commercial vehicles are diesel engines.
  • But also, diesel engines are available in passenger cars. Because of the higher pressures and higher temperatures of ignition, diesel engines generally have higher mileage than gasoline engines. 
  • Also, diesel engines require much higher maintenance costs than gasoline engines. The main reason for this, they have a more detailed and complex fuel injection system. This provides extra maintenance costs. So, if you need to decide between different selections, you need to make general cost comparisons.
  • In terms of design and sound, diesel engines are generally lower class than gasoline engines. Because diesel engines generally have higher sounds because of the higher compğression rates and higher pressures inside the engine components. And because of this, people generally do not prefer to use them for high-end cars.

So, these are the general points that we can state about this topic.

Last Words on Do Diesel Engines Have Spark Plugs

So, as you understand that the working principle of diesel engines is slightly different than that of gasoline engines. With this post, you understand the general differences and why diesel engines do not have spark plugs and glow plugs.

If you have additional comments and questions about this topic, please leave them below. Your precious feedbacks are very important to us.


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Why does a diesel engine not have a spark plug?

It is because the diesel engine does not need an external trigger for the burning of diesel fuel inside the cylinder. Because the pressure and the temperature of the air and fuel mixture in a diesel engine are very hot that makes the diesel fuel ignites it. They only have a glow plug that lets the diesel engine ignite at the start.

Do modern diesel engines have glow plugs?

Most diesel engines need glow plugs for the cold start. Because they need an initial temperature level to ignite the high-pressure and misted fuel.

Can diesel run without glow plugs?

The simple answer is no. Maybe, the diesel fuel does not burn with the help f the glow plug temperature. But without glow plugs, youı can not even start the engine.

How long do diesel glow plugs last?

Glow plugs are generally very high-quality applications that you can use even 100.000 miles.

Uğur Uygun

Hello everyone, I am Uğur. I am a mechanical engineer who has experience in different R&D departments of HVAC companies. With my best friend, I decided to build this website to share out knowledge and experience. And also, I am interested in automotive. So, I am writing about automotive and automotive-related articles here. Sharing my knowledge and experiences on these topics is a very big pleasure for me. I am willing to answer all of the questions people have about these topics.

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