NOISE REDUCTION FOR INTERNAL COMBUSTION ENGINE Christopher Morehouse

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

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

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

ENGINE NOISE CHARACTERISTICS

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

RESONATOR DEMONSTRATION MODULE CONCENTRIC TUBE RESONATOR HELMHOLTZ RESONATOR

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

CONCENTRIC TUBE TEST 1 RESULTS Fixed Length, Vary Frequency Predicted: § ½ & ¼ -> max reduction § Magnitude ~ 10 d. B Result: § Max 4 d. B § Offset from Predicted

CONCENTRIC TUBE TEST 2 RESULTS Fixed Frequency, Vary Length Locations offset from wavelength multiples Reduction increases with frequency Max Attenuation: § 550 Hz, 10. 3 d. B (LCT) § 550 Hz 8. 4 d. B (SCT)

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

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

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

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?

CONCLUSIONS 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

QUESTIONS? ? References: § Bell, Lewis H. Industrial noise control: Fundamentals and Applications. New York : M. Dekker, 1982. Print. § http: //students. sae. org/competitions/formulaseries/rules/2011 fsae rules. pdf