Fundamental phenomena of noise of internal combustion engines

Motor vehicle noise comes from three main sources: rolling, engine and high-speed aerodynamic sources (interaction of solid surfaces with airflow).

Powertrains are a dominant source of power when vehicles are travelling at low speeds, and this is true at least for internal combustion engines.

Noise reduction in internal combustion engines is one of the most difficult tasks for automotive engineers, because the sources of noise are many and varied, and the phenomena are complex. What's more, users tend to demand more and more silence in modern cars.

To reduce engine noise, you first need to control vibrations. An engine that vibrates is automatically a noisy engine. The vibratory aspects of automobile engines are described in the article "Fundamental phenomena of automobile engine vibrations" [BR2771] . On the other hand, an engine that does not vibrate is not necessarily a silent engine, as there are more sources of noise than those that affect vibrations, and the physical phenomena are significantly different. Indeed, the vibrations of an internal combustion engine act mainly at low and medium frequencies (20 to 800 Hz), and their amplitudes depend mainly on the engine's basic structure. Noise frequencies tend to be in the medium and high frequency range (up to 5,000 Hz). In addition to the basic motor, all components and accessories are potential sources of noise, and all peripheral parts are important in the noise transmission and amplification chain.

This article updates and expands on the topics already presented in the [BM2773] dossier. It provides an overview of the different types of engine noise present in today's automobiles and requiring special treatment. The following are presented: air intake noise, which is part of the aeraulic noise family; combustion noise, which is part of the basic engine noise family; and turbocharger noise, which is part of the component noise family. For each source, the physical phenomenon, the state of the art and applicable technical solutions are presented. The final chapter, devoted to acoustic radiation, summarizes all the noise emitted by the powertrain.