Study of Structural Noise of a Multi-Cylinder Diesel Engine

<div class="section abstract"><div class="htmlview paragraph">The world over has resulted in severe pollution problems. They are classified as air and noise pollution. Air pollution is caused by dispersion of emittents from engine exhaust to the atmosphere at different concentration levels. Similarly, the emission of unwanted sound from engine structure, intake and exhaust are the principal source of noise pollution.</div><div class="htmlview paragraph">In diesel engines structurally, radiated noises have numerous origins. The complexity arises from the fact that the whole engine structure is simultaneously excited by several forces of widely different characteristics. Primary exciting force which is a gas force in the cylinder resulting from the combustion. Secondary exciting forces of considerably different characteristics are generated by the operation slider crank mechanism but related to some primary gas force in some non-linear manner resulting in piston impact, impacts in bearing, impacts in timing gears etc. Force produced in accessories such as valve gear system, fuel injection system etc.</div><div class="htmlview paragraph">In the present study, the structure-born noises are studied by isolating exhaust noise from measurement areas at different moderate loads and speed conditions to see the impact of noise generation of a heavy-duty diesel engine on the test bed. The engine considered was an 80.85 kw multi-cylinder diesel engine on a test bed coupled with a hydraulic dynamo-meter. The engine was manufactured by Tata. The noise was measured at a distance of 1m and 2m at 10 different locations at different load and speed conditions. With this noise contours are plotted to see the behavior of noise emission from engine structure with variation of load and speed.</div><div class="htmlview paragraph">The overall frequency v/s sound pressure level (SPL) graphs were plotted. The impact of the speed of the engine was also studied in the present studies to show the impact of combustion at different speeds on the structural noise emissions.</div><div class="htmlview paragraph">The combined impact of engine noise and load on structural noise and piston slap was also studied.</div></div>