23. Study of Noise and Vibration Problems Related to Heavy Duty Diesel Engines

Noise can be described as what is heard, and vibration as what is felt by a person. The pulsation of air particles in contact with vibrating structure or fluctuating flow causes noise. Noise from the engine due to exhaust and inlet flows are predominant at lower frequencies and at high frequencies it is usually structure related. Noise from the cooling fan is not negligible. Noise at steady state is studied but more annoying is transient noise. The pass-by and interior noise are the net effect of the noise from the engine, tires, vehicle panels, the fan and the exhaust silencer. Exhaust noise and engine noise are the loudest components of the pass-by noise from diesel trucks and buses. Vibration on the other hand, is mainly due to inertia forces left unbalanced by design as well as inevitable manufacturing tolerances to the masses and linear dimensions. Further, the side thrust to the cylinder walls and the forces at the bearings induce a vibrating torque about the crankshaft axis, proportional to the brake mean effective pressure. This chapter is written under three subtitles namely, noise at steady state, transient noise and engine vibrations.