CleviteKid
07-28-2004, 08:16
Subject: A curious enthusiast has a question
To the experts at the diesel page:
For a long time, I've been wondering why unlike gasoline engines, diesel engines produce that distinct metallic clatter. I'd appreciate it if you could give me a good answer.
TanManCanFan
* * * * * * * *
Hello TanMan:
The Clevite Kid, a.k.a. Dr. Lee, will answer your question.
You may have noticed that a gasoline engine with the spark advanced too much, or with a really bad load of gas going up a steep hill in high gear, pings and knocks sort of like a diesel. Both the diesel noise, and a pinging gas engine, are experiencing a high rate of pressure rise due to combustion.
The faster the fuel burns in the combustion chamber, the faster the pressure in the combustion chamber is going up. That wave of pressure hits the cylinder walls and the cylinder head like a hammer. With a low rate of pressure rise, it is like hitting the engine with a soft rubber hammer - spreading out the energy of the impact. With a very rapid rate of rise, it is like hitting the engine with a steel ball pien hammer, concentrating the impact over a very short time. This trys to make the engine ring like a bell. What you are hearing is the structure of the engine block and cylinder heads reverberating and vibrating in response to the impact of the combustion gases slamming against them.
This happens more naturally in the diesel, hence the typical diesel rattle or clatter. Diesel engines are built stronger and heavier to withstand these acoustic impacts, compared to gasoline engines, which are not SUPPOSED to be operated while detonating, pinging, or knocking.
Dr. Lee
To the experts at the diesel page:
For a long time, I've been wondering why unlike gasoline engines, diesel engines produce that distinct metallic clatter. I'd appreciate it if you could give me a good answer.
TanManCanFan
* * * * * * * *
Hello TanMan:
The Clevite Kid, a.k.a. Dr. Lee, will answer your question.
You may have noticed that a gasoline engine with the spark advanced too much, or with a really bad load of gas going up a steep hill in high gear, pings and knocks sort of like a diesel. Both the diesel noise, and a pinging gas engine, are experiencing a high rate of pressure rise due to combustion.
The faster the fuel burns in the combustion chamber, the faster the pressure in the combustion chamber is going up. That wave of pressure hits the cylinder walls and the cylinder head like a hammer. With a low rate of pressure rise, it is like hitting the engine with a soft rubber hammer - spreading out the energy of the impact. With a very rapid rate of rise, it is like hitting the engine with a steel ball pien hammer, concentrating the impact over a very short time. This trys to make the engine ring like a bell. What you are hearing is the structure of the engine block and cylinder heads reverberating and vibrating in response to the impact of the combustion gases slamming against them.
This happens more naturally in the diesel, hence the typical diesel rattle or clatter. Diesel engines are built stronger and heavier to withstand these acoustic impacts, compared to gasoline engines, which are not SUPPOSED to be operated while detonating, pinging, or knocking.
Dr. Lee