Why do Diesel engines have that distinctive sound to them when compared to gasoline engines?
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Because they function much differently. Diesel fuel is harder to ignite than gasoline and is thicker/more oily. In order to get it to ignite you have to get it really hot in the combustion chamber. The flash point of gasoline is -49F the flash point of diesel is 150-180F. To heat it up that high and quickly they use air brought into the engine.
Quick secondary lesson. When you take air and compress it, it increases the temperature of the air. This is also why when you spray something like compressed air in a can as it expands it cools.
So diesels have much higher compression than gas engines because it raises the temperature of the air in the cylinder which allows the diesel to ignite. If you had this much compression in a gas engine it would make it hard to control the gas igniting and would cause it to ignite early harming the engine. Another important thing to note is that gasoline engines use a spark plug to ignite the gasoline. A small spark is enough to ignite it and allows them to better control when it’s ignited. Diesels don’t have spark plugs and rely solely on the increased temperature to make the diesel fuel ignite.
So in order to have the higher compression the engines have to be designed differently and operate at different speeds. Diesel engines are more robust to handle these extreme temperatures and cylinder pressure from all the compression. This is what makes them sound different than gas engines.
The TLDR: is diesels need a lot of compression to ignite their fuel. This means they are designed differently than gas engines. It’s also why you can’t just put gas in a diesel or diesel in a gas and make it run. These differences are what give them their unique sounds.
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