Marine Engine Air Intake Plenum with Helmholtz Attenuators
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Solution Overview
Problem
Existing marine drive air intake systems struggle to effectively attenuate a wide range of sound frequencies, particularly in the mid-frequency range of 500 Hz to 800 Hz, within the limited space of a marine engine's powerhead compartment without interfering with other engine components.
Innovation Solution
A novel air intake plenum with a three-dimensional airbox and Helmholtz-style attenuator devices is designed to convey intake air to marine engine throttle devices while attenuating different sound frequencies, utilizing a combination of inlet and outlet duct geometry, expansion volume, and strategically placed attenuation chambers and holes to minimize sound emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional air intake systems are used, then the structure is simple and space is saved, but sound attenuation capability is insufficient especially in mid-frequency range
Solution Approach 1:
The Helmholtz attenuator devices are integrated within the airbox structure, with attenuation chambers formed as cavities inside the airbox walls. This nesting approach allows sound attenuation functionality to be embedded within the existing intake system volume, adding noise control capability without significantly increasing overall device complexity or space requirements.
Solution Approach 2:
Helmholtz resonator structures are introduced as intermediary elements between the noisy engine and the external environment. These resonators act as acoustic filters that selectively attenuate mid-frequency sound waves (500-800 Hz) while allowing airflow to pass through, thereby mediating between the conflicting requirements of noise reduction and maintaining simple system structure.
2Object-affected harmful factors
If sound attenuation devices are added to reduce noise, then sound pressure levels decrease, but the available space in the powerhead compartment is reduced
Solution Approach 1:
The attenuation chambers are nested within the airbox structure, utilizing the existing volume of the air intake system for sound attenuation purposes. This allows the Helmholtz resonators to be accommodated within the powerhead compartment without requiring additional external space, as they are integrated into the existing airbox geometry.
Solution Approach 2:
The Helmholtz attenuator devices utilize the vertical and lateral dimensions of the airbox structure rather than requiring additional horizontal space. By forming attenuation chambers as cavities within the airbox walls and utilizing the thickness of the airbox structure, the design accommodates sound attenuation functionality within the existing three-dimensional envelope of the powerhead compartment.
3Object-affected harmful factors
If Helmholtz attenuator devices are installed, then mid-frequency sound attenuation is improved, but airflow restriction may increase
Solution Approach 1:
The Helmholtz attenuator devices are strategically positioned at specific locations within the air intake system where they can effectively target mid-frequency sound waves (500-800 Hz) generated by the engine. The attenuators are located to intercept noise paths while minimizing interference with the main airflow path to the throttle devices, thereby achieving localized noise control without significantly impacting overall airflow rate.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces sound pressure levels across various engine speeds and frequencies, with enhanced attenuation in the mid-frequency range, while maintaining minimal flow restriction and efficient airflow, thus addressing the challenge of sound attenuation in a compact engine compartment.
Implementation Method 1
first and second Helmholtz-style attenuator devices at the first and second outlets, respectively. Together the first and second inlets, the expansion volume, and the first and second Helmholtz-style attenuator devices are configured to attenuate different frequencies of sound emanating from the marine engine
Data Source
AI summary
An intake plenum is for a marine engine, the marine engine having first and second throttle devices for controlling flow of intake air to the marine engine. The intake plenum has an airbox providing an expansion volume, first and second inlets that convey the intake air in parallel to the expansion volume, first and second outlets that convey the intake air in parallel from the expansion volume to the first and second throttle devices, and first and second Helmholtz-style attenuator devices located at the first and second outlets, respectively. Together the first and second inlets, expansion volume, and first and second Helmholtz-style attenuator devices are configured to attenuate different frequencies of sound emanating from the marine engine via the first and second outlets.