Questions and Answers
Noisy Engines
Q. Why does a petrol engine make less noise than a diesel engine?
A. Yes, there is no mistaking a diesel engine and a gas engine by just listening to it. I have a Mercedes diesel and when I start it up in a parking lot, people invariably turn around and look at it.
The reason the gas engine is quieter is that the combustion is basically a controlled burn, not an explosion as most people think. A slow burn is naturally quiet. In a diesel the fuel comes a lot closer to exploding. Since the air is hot enough to burn the fuel, as soon as the fuel is injected, it burns explosively. At idle that knocking you hear is actually the fuel burning. When the rpm goes up the noise dies down because the fuel system is working faster and the explosions come closer together. Also a diesel is more efficient at higher rpms.
Additional Information provided courtesy of ALLDATA
