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This paper describes a study to demonstrate the feasibility of developing an acoustic encapsulation to reduce airborne noise from a commercial diesel engine. First, the various sources of noise from the engine were identified using Nearfield Acoustical Holography (NAH). Detailed NAH measurements were conducted on the four sides of the engine in an engine test cell. The main sources of noise from the engine were ranked and identified within the frequency ranges of interest. Experimental modal analysis was conducted on the oil pan and front cover plate of the engine to reveal correlations of structural vibration results with the data from the NAH. The second phase of the study involved the design and fabrication of the acoustical encapsulation (noise covers) for the engine in a test cell to satisfy the requirements of space, cost and performance constraints. The acoustical materials for the enclosure were selected to meet the frequency and temperature ranges of interest.

Sound pressure level (SPL) measurements of vehicle coast-by runs of a passenger vehicle were performed across a range of temperatures. A controlled test track was used for the runs with six different sets of tires. A small but significant reduction of noise level with positive temperature increases was observed for some but not all tires. The reduction was evident in two of the tires at 53 kph and five of the tires at 80 kph. The SPL of the other tires showed little or no sensitivity to temperature. Frequency analysis of the tire noise showed that noise content above 1000 Hz is most affected by temperature change and noise in the range of 1200 to 2000 Hz is particularly sensitive to temperature changes. However, differences in SPL due to speed and tire type were much greater than that due to temperature

Very large scale, 3D, viscous, turbulent flow simulations, involving 840,000 finite volume cells and the complete form of the time-averaged Navier-Stokes equations, were conducted to study the mechanisms responsible for total pressure losses in the entire intake system (inlet duct, plenum, ports, valves, and cylinder) of a straight-six diesel engine. A unique feature of this paper is the inclusion of physical mechanisms responsible for cylinder-to-cylinder variation of flows between different cylinders, namely, the end-cylinder (#1) and the middle cylinder (#3) that is in-line with the inlet duct. Present results are compared with cylinder #2 simulations documented in a recent paper by the Clemson group, Taylor, et al. (1997). A validated comprehensive computational methodology was used to generate grid independent and fully convergent results.

IMPLEMENTATION OF A SECOND GENERATION SOUND POWER TEST FOR PRODUCTION TESTING OF EARTHMOVING EQUIPMENT Caterpillar has developed an automated sound power measurement system that measures construction equipment sound levels before they leave the assembly plant. This paper describes the test system and gives the results of verification tests conducted at various manufacturing plants around the world. It was concluded that the new system allows Caterpillar to quickly and accurately acquire the data necessary to assure that their product meets its noise requirements.