Christopher Morehouse Julie Maier Ted Zachwieja Caroline Bills NOISE REDUCTION FOR INTERNAL COMBUSTION ENGINE

 Objectives:  Sound attenuation for performance cars (i.e. Formula Team)  Minimal performance degradation  Understand phenomenon of sound  Engine - lawnmower (Briggs & Stratton) PROJECT OVERVIEW

 Engine Firing Frequency ENGINE NOISE CHARACTERISTICS Pressure Waves  Sound Sources  Mean Effective Pressure

ENGINE NOISE CHARACTERISTICS

DESIGN OPTIONS  ABSORPTION MUFFLER  CONCENTRIC TUBE RESONATOR  HELMHOLTZ RESONATOR  ACTIVE NOISE CANCELLATION  Pursued by another Senior Design Team

 CONCENTRIC TUBE RESONATOR RESONATOR DEMONSTRATION MODULE  HELMHOLTZ RESONATOR

RESONATOR TEST SET-UP Helmholtz Tests: -1. Vary frequen cy Concentric Tube Tests: -1. Vary Frequency -2. Vary Length SPEAKERS CONCENTRIC TUBE RESONATOR HELMHOLTZ RESONATOR TONE GENERATOR (LAPTOP) SOUND LEVEL METER

CONCENTRIC TUBE TEST 1 RESULTS  Fixed Length, Vary Frequency  Predicted:  ½ & ¼ -> max reduction  Magnitude ~ 10 dB  Result:  Max 4dB  Offset from Predicted

CONCENTRIC TUBE TEST 2 RESULTS  Fixed Frequency, Vary Length  Locations offset from wavelength multiples  Reduction increases with frequency  Max Attenuation:  550Hz, 10.3 dB (LCT)  550 Hz 8.4 dB (SCT)

 Prediction:  High reduction  Narrow Band  Result:  Reduction offset  Higher F -> higher reduction  Errors Sources:  Simple Equation HELMHOLTZ RESONATOR TEST RESULTS

ABSORPTION MUFFLER: OVERVIEW  Outer steel casing  Perforated inner steel pipe  5 shapes  Steel end caps  Packing material in cavity  3 materials  3 densities

 Fiberglass  Mineral Wool  Steel Wool  Fiberglass & Mineral Wool:  175, 200, and 225 g/L  Steel Wool:  Grades 0000, 1, and 4 ABSORPTION MUFFLER: MATERIAL & DENSITY OPTIONS

ABSORPTION MUFFLER TESTING  Test 1: Optimal Packing Material & Density  Standard Shape Option only  Test 2: Optimal Shape  Optimal Material & Density only

OPTIMAL MATERIAL RESULTS

OPTIMAL SHAPE RESULTS Baseline Standard Short Cavity Thin Sine

POSSIBLE ERROR SOURCES 1.Repeatability 2.Non-uniform engine performance 3.Non-uniform packing 4.Noise contamination from environment  Loaded engine, constant RPM  Anechoic chamber?

 Concentric Tube Resonators  Require further testing  Follow-on  Research Offset  Recordings of Engines  Helmholtz – performed as expected  Absorption  Steel wool better material, but best geometry needs further testing  Follow-on  Higher densities steel wool  Composite packing  Endurance testing  SAE application  Recommend small Helmholtz with Steel Wool packed muffler CONCLUSIONS

 References:  Bell, Lewis H. Industrial noise control: Fundamentals and Applications. New York : M. Dekker, Print.  rules.pdf QUESTIONS??