Do Diesel Engines Have Spark Plugs?

Published on 03/15/2023

do diesel engines have spark plugs

Many commercial applications, such as construction, farming, and even logistics, rely on vehicles capable of pulling or pushing high loads. Diesel engines excel at generating high levels of torque for relatively little fuel, making them extremely common as heavy-duty performance vehicles. 

However, while gasoline and diesel vehicles may look the same on the outside, they have many notable differences that affect their maintenance, parts, and longevity. While hopefully, you’ll never need a mobile diesel repair service in the San Francisco Bay Area, our team at All Bay Diesel shares the following information, as knowing the key differences between diesel and gas engines can help save you lots of trouble on the road.

Diesel vs. Gasoline Engines

All internal combustion engines work on the same principle: fuel and air mix in a chamber and undergo a reaction that releases heat and combustion gases. The gases released during this reaction expand rapidly and push a piston, which rotates the crankshaft and provides power to the wheels through the vehicle’s powertrain. 

Where diesel and gasoline engines differ is how the combustion process starts. Gasoline engines use spark ignition, where an arc of energy to the gas-air mixture is enough to start the combustion process by igniting the gas-air mixture in the chamber. 

Diesel engines work slightly differently. Instead of mixing diesel and air in the combustion chamber, the chamber only contains pressurized air. The fuel injector atomizes the diesel before it enters this chamber, while glow plugs heat it up, creating the conditions necessary for ignition. Then, when the diesel combines with the oxygen in the combustion chamber, it reacts and releases gases that push the piston and move the drivetrain. 

Why Don’t Spark Plugs Work On Diesel Engines?

The reason gasoline and diesel internal combustion engines have different ignition modes is due to the differences in volatility and ignition points between the two fuels. One of the common measures of volatility is the flash point, the lowest temperature at which a liquid gives off enough vapors to form an ignitable air/gas mixture.

Gasoline is significantly more volatile and has a flash point of -43°C, while diesel is less volatile and has a flash point of 52°C. This means that a system that works for igniting gasoline won’t work on diesel, and using gasoline in a diesel engine can be extremely dangerous. 

Instead of having a single electrical arc act as an ignition source, diesel engines use a combination of glow plugs that heat the diesel to make it more volatile and atomizing the fuel as it hits the air to result in a consistent combustion reaction. Since glow plugs are only responsible for raising the temperature of the diesel, it’s possible to start a diesel engine without using glow plugs as long as the ambient temperature is high enough and the fuel injector atomizes the diesel correctly. However, having functioning glow plugs speeds up the ignition reaction and allows the engine to run more efficiently. 

Phases Of Glow Plug Ignition

Glow plugs consist of heating coils housed in a ceramic or metal casing filled with ceramic powder to act as an electrical insulator. These plugs can heat up to 1000°C within several seconds, sufficient to assist in the ignition process. Ceramic glow plugs can heat up even faster and retain heat for longer, making them a more efficient and durable option than their traditional metal counterparts.

Glow plugs go through two separate phases during normal ignition, namely:

  • Engine start: When you start a diesel vehicle, the glow plugs will heat up rapidly. Once they’ve reached the correct temperature, the fuel injector will atomize the incoming diesel fuel and blow it across the glow plug. This process causes the diesel to reach its ignition temperature, and once it comes into contact with pressurized air in the combustion chamber, it will readily combust and start the engine. 
  • Continuous heat: Glow plugs will maintain a constant temperature for several cycles to ensure the engine is running correctly before turning off. The heat generated by the combustion reaction is enough to keep any new incoming fuel hot enough to burn.  

How Diesel Ignition Methods Affect The Engine

Diesel combustion chambers experience a lot more pressure due to the compressed air inside them than gasoline engines. This increased pressure leads to diesel-specific problems that inexperienced mechanics may fail to diagnose. 

One of the most common issues diesel engines experience is blow-by, where some diesel gas leaks into the crankcase and past the piston rings, putting additional pressure on the engine. Since diesel engines run at higher pressures than gas engines, they have a higher chance of blow-by, which can dramatically reduce the torque the engine generates. 

The increased pressure associated with a diesel compression ignition strains almost all engine components. By creating more force against moving parts, the compression increases the friction of these parts against each other, leading to faster wear and tear. Oil additives and detergents can alleviate some of this friction, and using diesel-specific oil can dramatically extend the lifespan of your diesel vehicle’s engine. 

Another common problem for diesel engines is carbon buildup. This buildup happens because the initial ignition reaction affects a larger surface area and involves more diesel molecules. As carbon builds up, it can affect ignition efficiency and reduce engine performance. An oil treatment that removes stiction can help combat this carbon buildup and restore ignition efficiency and engine performance

Diesel engines have plenty of advantages that make them ideal for heavy-duty commercial vehicles, but they come with their share of quirks. Understanding the differences between a diesel truck and your ordinary daily driver can help you handle any small issues that may arise from using a diesel engine.

It's Time To Give Us A Call

If you're having problems, like your diesel engine not starting, it may be time to call the professionals. At All Bay Diesel, we are an experienced diesel vehicle servicing company that offers repairs, maintenance, and even a mobile truck repair service in the SF Bay Area. Give us a call at (925) 522-1780 to find out how we can keep your fleet on the road today!

Call Now: (925) 522-1780