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Case Study
DLW, indian railways, Varanasi. 2600 hp engine test bed noise control
M/s Diesel Locomotive Works (DLW) is the manufacturer of 2600 HP & 1350 HP Loco Engines. These engines are performance tested in a Test Bed, subjecting the engines up to full load conditions prior to assembling on locomotive. DLW proposed to establish 4 Nos. of Engine Test Bed and awarded the contract to M/s Acoustics India Private Limited for design, engineering, manufacture, supply, erection, testing and commissioning. The scope of the project included complete civil work for engine foundation, construction of control room, fuel oil/lube oil/ cooling water circuits, electrical work, control panel, MCC, cables, piping, water rheostat type load boxes, cooling tower, heat exchangers, sound proof enclosures for the test beds, test bed ventilation system, sound proofing the control room, air conditioning, engine exhaust silencers etc. on turnkey basis.

In this paper, we would cover only the Noise Control part of the test bed, control room, ventilation and air conditioning.
 
The noise levels measured around the engines are as below:
Freq (Hz) 63 125 250 500 1k 2k 4k 8k
Engine noise (at 1.5m distance)
SPL dBA
91 97 98 99 97 95 94 91
Engine Exhaust (at 3.0m distance)
SPL dBA
93 102 98 91 90 90 84 72
The noise control system was designed to reduce the noise level within 85 dBA at 1m distance from the Enclosure and within 55 dBA inside the control room.
 
THE COMPLEXITY OF THE PROJECT
Being test beds, engine will have to be loaded/unloaded everyday on the test bed. Hence loco engines exhaust ducting and fresh air intake ducting should not be a fixed installation. Performance of the Acoustic Enclosure system/Silencer designed should not get deteriorated due to flexibility of connections.

Dismantling the acoustic panels of the test bed acoustic enclosures would not be possible everyday as the engines had to be loaded on the test bed almost on daily basis.

Enormous amount of heat rejected by the engine would have to be exhausted, limiting the temperature raise inside the enclosures.

The broadband noise generated by the engine which is fluid borne in the exhaust line will have to be controlled within the limit.
1.  TEST BED ACOUSTIC ENCLOSURE 4.  ENGINE EXHAUST SILENCERS
2.  AIR HANDLING UNIT WITH DUCT SILENCERS 5.  SOUND PROOF CONTROL ROOM
3.  AIR FILTRATION UNIT WITH DUCT SILENCERS  
Fig 1. Engine Test Bed Project Layout
The turbocharger noise evidently with peak amplitude in the higher frequency required a very careful design to limit the noise emission.

THE SCHEME
The noise control package was divided in to the following

  • Test Bed Acoustic Enclosures.
  • Engine Exhaust Silencers.
  • Turbocharger intake Silencer
  • Ventilation system with duct silencers with air washer based Air-Handling Unit (AHU).
  • Turbocharger air intake filtration system with intake Silencer.
  • Sound proofing of the control room with sound proof glass windows including air conditioning of the large control room.
The major requirement that was considered while designing the acoustic enclosure was the provision for loading the engine inside the enclosure from the front and from the rooftop. Each of the 4 Nos. acoustic enclosures was designed to have a dimension of 5500mm width x 12900mm length x 4040mm height. The acoustic enclosure was constructed with acoustic panels and brick wall with acoustic panel lining.
Fig 2. Engine Exhaust Silencer
The front side of the acoustic enclosure was designed with motorized sliding twin doors enabling the engine front-loading trolley to move inside the test bed enclosure. The roof loading arrangement was designed with a motorized sliding panel on the rooftop to have a clear opening of 3400mm width x 6500mm length, which enabled top loading of the engine from the rooftop using EOT crane.

The operations of the motorized mechanism of the sliding doors are controlled from the control desk in the control room.

The engine exhaust system consists of a reactive and absorptive silencer with the associated ductwork and acoustic insulation. A flexible connection was used for coupling the engine exhaust connector to the fixed exhaust piping.

The turbocharger intake air was ducted from an air filtration package, ducted to each of the 4 Nos. test bed, and connected to the inlet of turbocharger through flexible coupling. The noise emission from the turbocharger was attenuated through the duct silencers.
Fig 3. Air handling Unit

Being a test bed a very effective cooling system was designed to ensure evacuation of heat dissipated from the engine. This comprises of separate air washer based air handling unit with supply air ducting with duct silencers to each of the enclosure ensuring a cool environment inside the acoustic enclosure.
The control room sidewalls and roof were acoustically treated with acoustic panels and soundproof doors. The dimension of the control room is 26.5m length x 4.5m width. The control room was air conditioned with centralized unit and duct silencer. Each of the 4 acoustic enclosures dividing wall between the control room and the acoustic enclosure was provided with triple glazed industrial sound reducing glass windows to ensure visibility of test bed from control room and at the same time attenuating the test bed noise to restrict within 55 dBA inside the control room.
Fig 4. Control Room Acoustic Enclosure
 
 
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