Does Diesel Engine Have Spark Plugs – How Spark Plug Works?

Like all oil engines, diesel engines also have spark plugs for the primary ignition to start the combustion process inside the engine.

But what if we tell you diesel engines don’t have any spark plugs?

Although it might shock you, this is the reality. Diesel engines, of course, need ignition to start and work. But it uses glow plugs instead of the conventional spark plugs for the purpose. Glow plug combines with different engine parts to function as a heater to ignite the diesel engine.

Yes, some diesel engines would still have spark plugs. But it is not a common phenomenon and an essential part of the engine. We will discuss this special occasion broadly in the following part.

do diesel engines have spark plugs?

Generally speaking, despite being an oil engine, a diesel engine doesn’t have any spark plugs. This may shock you, but diesel engines’ unique design and combustion method enable them to do away even without the spark plugs.

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These engines follow a simple rule of physics that allows them to ignite and start without any spark plugs. When the engine is turned on, air will heat up inside the compressor here. Within the cylinder, it squeezes up fast, and the internal temperature works with the compressed air to ignite the engine.

The compressed air helps the diesel to transfer and inject right into the ignition chamber. When the diesel reaches the ignition chamber, the engine ignites and gets going.

The explanation may seem easy and short, but many things go inside the diesel engine cylinder to help it ignite without the proper spark plugs.

To understand how this complicated process accomplishes, you need to learn the spark plug working process.

Read also >> How Long Do Shocks Last On A Car? (Signs Of Bad Shocks)

How Spark Plug Works?

Spark plugs will supply the essential spark to the engine cylinder to ignite its air and fuel mixture. It creates the required explosion that the engine needs to generate enough power to drive the automobile comfortably.

The standard spark plug comes with a center electrode made of copper. A nickel alloy surrounds it, and you can easily see the nickel alloy right at the tip of the plug. There is a porcelain housing to protect the electrode core.

The p9orcelain housing also transfers and dissipates the heat to help the engine maintain an optimal temperature to prevent any damages.

Depending on the working process, spark plugs are of two kinds-

1. Hot plugs

Hot spark plugs are found in most standard engines these days. It has additional insulation that keeps the temperature inside sufficiently high. The high temperature will burn down the extra carbon deposits inside the engine’s cylinder.

However, spark plugs need more gasoline which is a concerning issue due to the price hike of gases.

2. Cold plugs

If an automobile has a high-compression and high-horsepower engine, it is more likely to use a cold spark plug. The cold plug has less insulation, so the heat dissipates soon, resulting in engine damages due to improper ignition.

why don t diesel engines have spark plugs?

We now know that diesel engines don’t require any spark plugs for their proper functioning. Plus, we also know how a spark plug works to ignite and start any engine.

But how does a diesel engine work without a spark plug? Also, why doesn’t it need any spark plug?

Thank me later for these two valid questions. To begin with, diesel engines are entirely different from standard gasoline engines. Instead, it compresses the air using injected fuel. On the contrary, a typical gas-powered engine uses a spark plug to compress air and ignite the engine.

The compressed air inside the cylinder heats up quickly to reach an optimum temperature. Thus, inside the cylinder, the air is in a pressurized and heated state. Once the ECM (Electric Control Module) detects that the compressed air has reached the appropriate temperature, it sends signals to the injectors.

After that, the injectors will release more fuel right into the combustion chamber. Inside the chamber, there’s already extra hot gas. The fuel helps the hot gas to put pressure on the connected piston. Finally, depending on your gear position, the piston will move up or downward to produce power. It then transforms into motion and passes through the axles and crankshafts to help the car move forward or backward.

A diesel engine works on compressed air to reach the right temperature and release the essential pressure inside the combustion chamber to help the engine ignite. Since it uses direct combustion and heat, it doesn’t need any spark plugs.

How do diesel engines run without spark plugs >> Check out the video below:

Is There Any Diesel Engine With Spark Plugs?

Although the standard diesel engine doesn’t include a spark plug for ignition, some special diesel engines still use spark plugs.

The list includes-

  1. Combustion turbine
  2. Engines with compression ignition

Compression-ignition engines are relatively modern-day diesel engines. These engines are found mostly in automobiles. The engine includes one or more standard spark plugs for every cylinder. The number of spark plugs for the cylinder depends on the type and configuration of the diesel engine.

Nonetheless, older-style diesel engines mostly don’t have any spark plugs. Since these engines lack the spark plug for ignition, the supply of heated and compressed air comes from mainly the crankcase heater. The gas heater is mainly mounted either on the side or front of the automobile engine. At times, the engine uses a hot air generator instead of a gas heater to help the compressed air reach the optimal air.

Since these engines use high-induction temperatures, it helps in eliminating the ignition delay. So, you can accelerate the automobile quickly as soon as you start it. That’s why the advanced sports car uses these diesel engines to help a quick boost to the motor and accelerate rapidly.

Advantages & Disadvantages of Using Diesel Engines

Yes, diesel engines don’t use spark plugs for ignition. Yes, it works differently than a gas-powered engine. But does this bring any added benefit for the diesel engine in a car or automobile? Also, does it have any disadvantages?

Let’s see what we find-

Also, it is important to know if you are planning to get a new car and have little to no knowledge of diesel engines.

a car engine on a black background

The key benefits of diesel engines include-

  • The main advantage of the diesel engine is its increased mileage. Car experts, in fact, report that a diesel engine has got 25% to 30% better mileage and fuel-efficient than a gasoline engine.  So, it could be a great money-saving option for people.
  • Compared to all fossil fuels available in today’s market, diesel is surely the most energy-dense fuel on the list. It means it has more fuel density per volume than any fuel. So, it is also good at fuel economy. Since it has improved fuel density, it delivers better efficiency. So, you will need fewer gallons of diesel for the engine.
  • Since the diesel engine works without any spark plugs for ignition, it saves you from the essential tune-ups of the ignition. So, you need less maintenance of the car.
  • The design of the diesel engine enables it to work continuously in higher combustion and compression. Their excellent design allows them to perform longer than any gasoline engines ad also needs less repair.
  • A diesel engine generates much more torque than any standard gas-powered engine. So, it delivers more torque to the crankshaft. So, you can accelerate the passenger cars rapidly and drive them with an enhanced speed that a gasoline engine fails to perform.

You may be wondering that diesel engines are all perfect. But it has a few disadvantages that you have to consider before getting one of them for your automobiles.

The main disadvantages of diesel engines are-

  • The price hike of gallons of diesel these days has made it almost as expensive as any gas. So, its fuel efficiency is diminishing quickly.
  • The diesel engine is a bit complicated. So, it needs regular maintenance to help it running well and perfectly. If you don’t maintain the engine regularly, it may break down soon and cost you dearly.

Nonetheless, the benefits of a spark plug-free diesel engine outnumber its disadvantages. So, you should be good to go with a diesel engine car for your daily commuting and fun rides.

Final Words

The standard diesel engines don’t use any spark plugs as means of ignition. It, instead, uses compressed air at a high temperature for the ignition. The diesel engine is easy to maintain and has a longer lifespan since it is void of any spark plug.

The diesel engine works on a glow engine and supports an efficient driving experience. Also, it helps in the rapid acceleration of your passenger car and is ideal for fun rides.

Who Worked on This?



I'm the guy responsible for ensuring that every blog post we publish is helpful for our reader.

Mahir Ahmed


I'm the guy responsible for ensuring honest, informative, accurate and helpful guide to the reader.

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