2. Combustion noise

In an internal combustion engine, most noise and vibrations are directly or indirectly related to combustion. In this article, the term "combustion noise" is defined as the noise made directly by the combustion of fuel in the chambers. The difference in technology between gasoline and diesel engines has a decisive influence on combustion noise. In gasoline engines, combustion takes place by spark ignition, and the flame front spreads progressively throughout the mixture, producing a continuous increase in pressure. In diesel engines, on the other hand, combustion takes place by self-ignition under high compression. The air-diesel mixture ignites spontaneously when pressure and temperature conditions are right. Near-simultaneous ignition throughout the chamber leads to a sudden increase in cylinder pressure. Combustion noise is therefore a diesel issue. This section presents the physical...