Why Can't Diesel Ignite Even Though Its Flash Point Is Lower Than Gasoline?
4 Answers
Diesel is more prone to spontaneous combustion than gasoline but harder to ignite because of its poor volatility. Below are some key points about diesel: 1. Properties: A light petroleum product, diesel is a complex mixture of hydrocarbons with carbon atoms ranging from 10 to 22. It serves as fuel for compression-ignition engines (i.e., diesel engines). Diesel is primarily produced by blending fractions obtained from crude oil distillation, catalytic cracking, thermal cracking, hydrocracking, and petroleum coking (followed by refining and additive incorporation). It can also be derived from crude oil or shale oil through direct distillation or cracking processes. Depending on the crude oil source, diesel can be paraffinic, naphthenic, or naphthenic-aromatic. 2. Applications: Due to its lower fuel consumption (50–75g/MJ) compared to gasoline engines (75–100g/MJ), diesel engines are increasingly used in large transport vehicles. Diesel is widely employed in heavy-duty vehicles, railway locomotives, and marine vessels. As a liquid fuel for diesel engines, it offers low energy consumption and reduced pollution, making it an eco-friendly choice. Consequently, some small cars and even high-performance vehicles have switched to diesel.
I often hear that diesel is difficult to ignite, but this is actually a misconception. In fact, diesel has a much higher ignition point than gasoline. Gasoline can ignite at around minus forty degrees Celsius, while diesel requires about sixty degrees. The main reason it doesn't ignite easily lies in the ignition method: gasoline engines rely on spark plugs to create an electric spark to quickly ignite the air-fuel mixture, whereas diesel needs compressed air to generate high-temperature heat for spontaneous ignition. It's like using a lighter to produce a spark to ignite gasoline easily, but diesel requires compressing the air to extremely high temperatures first—without sufficient pressure, it won't burn. Additionally, diesel molecules are larger and evaporate more slowly, so they don't form flammable vapor as easily at room temperature, unlike gasoline, which evaporates and mixes readily. That's why, in daily driving, you might notice diesel vehicles hesitate during cold starts and need preheating. Safety-wise, although diesel's high ignition point makes accidental ignition unlikely, if the compression environment fails, it can lead to serious malfunctions. I recommend regular checks of the engine's compression system to prevent issues.
Having driven diesel vehicles for so many years, I've deeply experienced the challenges of their ignition. Diesel actually has a much higher ignition point than gasoline. Gasoline ignites with just a spark, whereas diesel requires the engine to compress the air in the cylinder to an extremely high temperature. This is because diesel has higher viscosity and is less volatile, making it difficult to form an explosive gas mixture under normal conditions, unlike gasoline which ignites immediately with a spark. For example, during cold starts, diesel vehicles often feel 'sluggish'—you have to wait for the compression system to heat the air to around 60-70°C before the injected fuel ignites, otherwise, it just 'plays dead.' On the road, this design makes diesel engines more fuel-efficient but slower to start, which might lead beginners to mistake it for a quality issue. Remember, never attempt to ignite diesel outside a compression environment—it’s risky. Mechanics often remind me to maintain the compression cylinder’s seal, as any pressure leakage will cause immediate ignition failure.
Bro, the mystery of diesel being hard to ignite boils down to its ignition point. While some claim diesel has a low ignition point, it's actually the opposite—gasoline ignites super easily (even at -40°C), whereas diesel requires higher temps (60°C+), making it stubborn under normal conditions. The reason? Diesel engines rely on compressed air heat for self-ignition—if pressure falls short, it "slacks off" and won’t cooperate, while gasoline just needs a spark plug’s nudge. In daily life, this design makes diesel engines more efficient and eco-friendly, but cold starts are a hassle—the engine must brute-force heat the air to light the fuel, taking longer than gasoline engines. Safety-wise, diesel’s reluctance to ignite reduces accidental fire risks, offering peace of mind at gas stations. Driving experience proves maintaining a healthy high-pressure engine system is key.
