Is Diesel Flammable? (And Dissolve in Water?)


Diesel is used as an energy source by several businesses and industries. It will be ideal to become familiar with some of the properties of diesel if you use it in any capacity. Its flammability is among its fundamental properties. Is diesel flammable, then?

We can determine whether diesel has a flash point, burns, or is flammable. But first, let’s clarify the difference between flammable and combustible. Are you interested in learning whether or not diesel will catch fire with a spark or why diesel is less flammable than diesel? Read on.

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Does Diesel Burn?

Diesel ignites slowly compared to kerosene or gasoline, but it does burn. Before you notice a fire after introducing a flame to diesel, you must wait a while. Additionally, the fire won’t spread quickly even once it gets going. It’s also possible that a diesel flame won’t last without much pressure.

The fact that makes it is slower to burn also means that it is harder to put out. Because diesel types vary, you can ignite diesel with a spark or a flame. Diesel must heat above its flashpoint due to environmental conditions or other heat sources to burn.

Difference Between Flammable vs. Combustible

OSHA defines flammable liquids as those with a flash point of less than 100°F for general industry. Combustible liquids are those with flash points higher than 100°F. But other characteristics set flammable and combustible apart.

The differences between flammable and combustible are as follows:


  • When a flammable liquid or material comes in touch with a flame, it ignites immediately.
  • For flammables, the boiling point is lower.


  • When you introduce a flame, combustible liquids or materials will take some time to ignite.
  • A combustible material will require a higher temperature to ignite.
  • At room temperature, combustible substances do not produce vapor.
  • For combustibles, the boiling point is higher.
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Flashpoint of Diesel

Diesel has a flash point that varies from 100 to 180°F. Diesel fuel comes in four different types, which accounts for the variance. However, 140°F is the generally accepted value for the flash point of diesel. Any diesel fuel with a flash point lower than 140°F is flammable. Diesel fuels above 140°F are combustible.

A flashpoint is the lowest temperature at which a liquid will vaporize and ignite when a flame is present. Due to its high flash point, diesel is unlikely to present an explosion hazard at outdoor temperatures. Diesel’s flash point is the temperature at which it begins to evaporate in the presence of a flame. You can use any heating surface instead of using a flame.

Will Diesel Ignite With a Spark?

No diesel will not ignite with a spark. You must raise the temperature above a particular point (the flash point) for diesel to ignite. It is the vapors that burn. Hence heat diesel first to give off sufficient vapor. The vapor must then mix with air for the diesel to burn.

Diesel engines lack spark plugs because a spark cannot ignite the diesel fuel. You’ll have to heat the diesel first to ignite. As a result, diesel engines initially use a compression ignition and glow plug to warm the combustion chamber. Diesel fuel begins to vaporize once the combustion chamber reaches operating temperature.

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Is Diesel Considered a Flammable Liquid?

The NFPA (National Fire Protection Association) classifies diesel as a class 2 combustible liquid. Class 2 liquids are those with flash points that are higher than 100°F but lower than 140°F. NFPA, therefore, classified them as combustible liquids. It bases its classification system on the flash point of a liquid. 

The organization uses these classifications to determine various fire protection requirements. 

When combustible liquids reach their flash point, they evaporate to form a gas concentration.  The other examples of class 2 liquids are camphor, kerosene, paint thinner, and mineral spirits. 

Does Diesel Dissolve in Water?

Water and diesel do not mix. In diesel, water is a contaminant. Additionally, having water in your engine tank is a severe disaster since diesel does not dissolve in water. Diesel rises to the top of your fuel tank while the water sinks to the bottom. The water makes the tank rust, and algae grow.

See what happens between water and diesel:

Water will freeze first during winter because diesel and water do not mix. Did you know that diesel freezes faster than water? Water freezes at 32°F while diesel does so at 20°F. It will result in corroded fuel components, worn injectors, power loss, and clogged filters. Your engine’s lifespan will be shorter, and maintenance could be expensive.

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You have water in your diesel fuel if your equipment’s idling or the engine cuts out while accelerating.

Why is Diesel Less Flammable Than Gasoline?

Diesel has a higher flash point than gasoline, making it less flammable. Diesel has a flashpoint of 140°F, while gasoline has a flashpoint of -45°F. Gasoline will produce enough fumes to ignite at -45°F. Hence gasoline is more flammable than diesel as a result. Once you introduce a flame or a spark, gasoline will ignite immediately.

See the difference between the flammability of diesel and gasoline: 

The fact that gasoline is more refined than diesel contributes to its greater flammability. That makes gasoline thinner in density and more likely to evaporate in normal temperatures. Hence gasoline tends to burn faster. On the other hand, diesel is thicker in density and evaporates more slowly. 

Can You Light Diesel With a Lighter?

Using a lighter to light the diesel will take some time. Only at extremely high pressure would diesel vaporize before igniting. Whether the diesel will light with a lighter will depend on its flash point. If the temperature of the lighter is below 100°F, it will not light the diesel. 

Diesel is difficult to evaporate, and a lighter won’t heat it quickly enough. But you can spread the fuel across a sizable surface where it can more easily evaporate. The diesel will evaporate and ignite when the lighter is held close to it for a short period.

Diesel fires tend to last a little bit longer, which is a plus, even though lighting diesel with a lighter takes a long time. Most people light their bonfires with diesel since it burns hot and long. Compared to other fuels like gasoline and kerosene, diesel is safer to use. It is less toxic and flammable than other fuels.

Frequently Asked Questions

Does Kerosene Burn The Same as Diesel? 

Kerosene has no additives like diesel as it’s made from a distilling process. Kerosene burns hotter than diesel due to its purity from the distillation process. Diesel and kerosene have different ignition temperatures. The fuel whose ignition temperature is lowest will ignite first.

Kerosene has an auto-ignition temperature of 428°F, while diesel has an auto-ignition temperature of 410 °F. The term “autoignition temperature” refers to the temperature at which the fuel will burn hotly on its own without an outside source of ignition.

Will Diesel Burn With a Torch? 

You can use kerosene, gasoline, or diesel for your torch. The mixture amounts of the fuel will depend on your preference. When temperatures exceed 75°F, the best blend is 60% diesel/kerosene and 40% gasoline. The combination can be 50:50 when the temperature is lower than 75°F. Make sure you don’t ever use more gasoline than 50%.

Does Diesel Kill Grass? 

Diesel is a toxic compound that kills grass as well as ornamental plants, worms, weeds, and insects. You’ll struggle to clean up the mess if diesel spills, splashes, or sprays on your grass. The plants harmed by the diesel spill won’t recover since it will take a long time for the diesel to break down.

There is a good chance that nothing will grow there as long as the diesel does not degrade. In less than an hour, diesel will destroy the grass, and the entire plant will rot within 48 hours. A tiny spill can kill plants in a large area. Most plants will die rapidly.


The most significant characteristics of diesel are its flash and ignition points. It is also essential to understand that diesel burns slowly yet continuously. Your diesel engine will be at risk if it comes into contact with water since it does not dissolve in water. Water that freezes during winter might seriously harm your car’s engine.

Diesel is less flammable than gasoline, so you must be careful when using gasoline. When using a lighter to ignite diesel, take your time because it won’t happen immediately. You’ll have to wait until diesel is hot enough to release vapors. Find out if your area has red diesel if you have off-road vehicles. It is cheaper than regular diesel. 

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