Mufflers are widely used to reduce the exhaust and intake noise of fluid machines for different applications. Every muffler has to be tailored carefully to the engine to which it is connected. One very important tool of muffler design is the measurement of its properties, acoustic performance, and pressure drop.
The introduction of flow is a key issue as it simulates a real engine situation. The two-source technique has been proven to be the most stable and most efficient technique to characterize the full scattering matrix of the muffler. At several companies and research institutes, this has become a standard measurement which is repeated frequently throughout the design process. This is a new platform to measure the passive (e.g. Transmission Loss) and active (flow-generated noise) properties of mufflers. Stepped sine excitation is used with simultaneous excitations from both sides of the muffler. The stepped sine excitation is optimized to reduce the needed time without jeopardizing the quality of the measurement. Measurement of flow background noise, microphone coherence, and pressure drop are also performed. This platform is based on a combined JAVA/NI software and National Instruments Data Acquisition cards, to automate the measurement accounting for different theoretical and practical considerations.
Our solution for the measurement of muffler acoustic performance includes the following standard components:
This is the test rig for the measurement of the acoustic properties of mufflers for different exhaust/intake and HVAC applications. We offer 3 standard inner diameter sizes of 25, 50, and 100 mm. Other pipe sizes are available upon request. The rig can handle flow up to 100 m/s and air temperature up to 100oC. It can be further modified for higher flows, higher temperatures, and specific gases.
The SIDLAB Acquisition Rig solution consists of:
Two adaptors for the connections to the test objects. More adaptors can be manufactured by the user based on different sizes.
Optional add-on: Fan to provide the flow, and a frequency inverter to change the fan speed.
We provide the necessary Data Acquisition System from National Instruments (NI) to be able to conduct the measurement. The Data Acquisition System consists of 8 inputs, 4 outputs and the interface with the computer via USB port. The system is supplied with all necessary cabling to the microphones, amplifier and loudspeakers, all fitted in a carrying case.
If you have your own National Instruments Data Acquisition System, we can use it. However, this is the subject to the specifications of the current Data Acquisition System that you have.
The components provided with the SIDLAB Data Acquisition System are:
Optional add-on: Necessary cards for Fan control and Measurement of mass flow, gas temperature, and pressure drop across the muffler. The details are described in the SIDLAB Acquisition Flow kit part.
To facilitate the measurement with flow, the rig is equipped with extra sensors that are connected to the same data acquisition system. The rig is connected to a fan to provide the flow, and a frequency inverter to change the fan speed. The fan speed can be controlled from the SIDLAB Acquisition Software, and all the sensor readings are fed automatically into the software.
It is also required to measure the pressure drop across the test objects and plot the pressure drop curve at different speeds. This can be done by varying the fan speed, and measuring the differential pressure between the inlet and outlet of the test object. The loss coefficient of the muffler can be calculated by the software.
This item includes:
Six microphones are normally used for this measurement to cover a wide frequency range within the plane wave range of the measurement pipes. Two microphone spacing on each side of the muffler are used to cover low and high frequencies. Special microphones are used, that are designed for the in-duct measurement of sound fields. ¼ inch microphones to provide good accuracy for the wave decomposition using the two-microphone technique. The microphones are calibrated with Class 1 microphone calibrator.
If the frequency range of interest is rather narrow, then it can be enough to use 4 microphones. If there is an interest to measure beyond the plane wave range, then 10 microphones can be used to measure the higher order modes.
This item includes:
The commissioning includes Packaging, Shipping, Installation, and 2 days onsite hands-on training. The training will be offered by one of our experts and will cover the following topics:
The whole system will be packaged inside a wooden box, made of plywood, for transportation. The box is equipped with custom designed internal structure for secure fastening of the test rig components.
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