Mechanical Engineering & Automotive Projects

[hash4u]

great stuff!
i am sure u and ur work would always be supported here!

[Kartoos90]

@ebad bro Wsalam
Really liked to see a fellow M.E on PW. It will take another year for me to complete my M.E from Uni.Hertfordshie..
Tell me are u going back to Pak? U still have till Apr 2012 for Applying work permit innit??

[ebad_ali]

@ hash4u: thanks alot for your support! hope you keep reading, posting new stuff now

@ Kartoos90: happy you are glad to see me here...good luck with your studies, im already in Pak...will get the work permit just in case!

KEEP READING FOLKS

[ebad_ali]

So i have finally gotten the time to post some more stuff on my exhaust study...

The FS has very strict rules on exhaust sound levels. The sound is tested at a 45 degree angle and 1m from the exhaust opening. The car should not exceed more than 90dBA at this level under the regulations. In most cases, sound attenuation in the exhaust comes at the cost of performance. The thing that hinders performance in an exhaust is known as back-pressure. This can be caused by anything that interrupts the flow of exhaust gasses making the engine do more work to expel them. Therefore this study was immensely important to analyze the perfect mixture of performance and sound.

Starting off, it is worth mentioning that exhaust sound is attenuated by either the resonating principle or the by absorption. The Helmholtz chamber as it's known after the inventor, uses the resonating principle. In this type of muffler, special plates are located inside which reflect sound waves at a certain degree so their reflection cancel out the preceding wave causing the sound to attenuate. A cross section of one such muffler is given below:

As you can probably imagine, mufflers employing this principle cause back-pressure as the plates cause interruption in the exhaust gas flow. Most stock cars employ the resonant type of mufflers as they attenuate the greatest levels of sound using the cancelling technique discussed above.

The other type of muffler uses the absorption principle to attenuate sound. In these type of mufflers, a perforated pipe is present inside. This perforated pipe is covered with sound insulation material such as glass beads, polymer fibre sheets etc. When the exhaust gas travels through the perforated pipes at high pressure, it expands through the holes into the insulating material allowing sound to be attenuated (see picture below). Even though the sound attenuation is not as great as the resonant chambers, there is considerably less back-pressure involved. These mufflers are also known as straight through design and is employed by most performance aftermarket mufflers.

Now we know the two major types of mufflers involved in attenuating sound, in the next section i shall discuss my study on mufflers.

keep reading!!!

[ebad_ali]

Moving on, once these principles were deeply studied (above i have just given a tiny summary, i have 10,000 words on this report :S ). It was time for me to get some work done regarding the FS. So what i did was I outlined 6 different muffler designs to test on the race car. Three out of the six design were manufactured by me personally for the testing phase. For the experiment, i needed two important readings. These were the back-pressure caused by the muffler and the muffler sound in dB. The exhaust back-pressure readings were taken by a pressure gauge placed carefully on the exhaust down-piping and the sound was measure using an electronic Sound Pressure Level (SPL) meter. The exhaust designs are given below:

1) Orignal Yamaha R6 titanium muffler (resonant + absorptive)
2) JDM toyota corolla silencer (resonant)
3) Aftermarket Muffler - HKS first copy (absorptive)
4) Self Made 75mm diameter and 400mm length
5) Self Made 100mm diameter and 500mm adjustable length (500-400-300)
6) Self Made 125mm diameter and 400mm length

Note: All self made exhausts are absorptive type

Given below is an image of the rear of the FS car showing the R6 titanium exhaust.

Shall post details on my self made exhaust in the next post

[ebad_ali]

So now it was time to manufacture my exhaust mufflers. The first thing that was done was to manufacture the shell of the mufflers. For this I used Mild steel sheet that was cut to the required length and breadth to give the correct dimensions. The sheet was then rolled using a mechanical roller and welded at the ends. One such empty shell is shown in the image below:

Once the shells of the three different sizes were ready, I bought in 1.5 m length of perforated tube (2inch diameter) which was then cut in the required length using a vertical saw. The pictures of the perforated tubes are given below:

Once this was complete, I had to manufacture the endplates to the mufflers. To do this I took a solid aluminium round and cut it. The solid rounds were then machined on a lathe to give the correct inside and outside diameter. A lip on the end of the endplates was kept to allow proper sealing. For the variable length end plate an O-ring was used in the plate with a depression to allow easy movement withing the casing. given below are pictures of the manufacturing process, assembly and the completed mufflers.

Once the end caps were ready, for the sound insulation I used sheets of fire-proof fibre glass. Fibre glass has high noise attenuation properties (due to the high surface area) and was readily available at the university. Following on is the completion of the muffler assembly.

[ebad_ali]

More Pictures of the Self made mufflers and the other test mufflers.

[ebad_ali]

Will post pictures of the testing and conclusion of the results later on,
meanwhile please feel free to comment
Enjoy

[ebad_ali]

bump

[hassanazeem]

Great Bit on the manufacturing of exhausts... can you share some insight on what would be the method if one wanted to fabricate a replica EMPI Stinger exhaust... Thanks

[ebad_ali]

Thanks @ hassanazeem: leme do dome reasearch, will let you know then

[ebad_ali]

jhatka/bump (no one interested in the technical side i believe)

Pakwheels is flooded with ricers

[murtaza_murti]

Great thread! How long did it take you to complete your degree in Mechanical Engineering? I plan on doing Automotive Engineering next year.

[ebad_ali]

Thanks @ murtaza_murti....bro i did it from england so 3 years BEng followed by 1 year MEng....good luck with your admissions, let me know if you need any guidance!

[murtaza_murti]

Thanks @ murtaza_murti....bro i did it from england so 3 years BEng followed by 1 year MEng....good luck with your admissions, let me know if you need any guidance!

Thanks for the prompt reply, will definitely contact you if I need help

[ebad_ali]

This is the last installment for the muffler study. In a brief recap, my study was to find a muffler solution for the FS racecar powered by a 600 cc yamaha r6 engine. To do so i needed to keep in mind the performance and the sound emitted (limited to 90dB). Therefore I selected a few mufflers from the market and manufactured 3 myself as stated above. The list of these mufflers is given below:
1) Orignal Yamaha R6 titanium muffler (resonant + absorptive)
2) JDM toyota corolla silencer (resonant)
3) Aftermarket Muffler - HKS first copy (absorptive)
4) Self Made 75mm diameter and 400mm length
5) Self Made 100mm diameter and 500mm adjustable length (500-400-300)
6) Self Made 125mm diameter and 400mm length

The three self made mufflers allowed me to analyze the impact of diameter and length both (using the absorptive principle, discussed above). The self made mufflers allowed me 3 configurations for length (300-400-500mm) and three configurations for the diameter (75-100-125mm). Further i also had 3 other exhausts. Therefore in total i had 3*3+3=12 experimental configurations.

In the experiment I had to determine the backpressure cause by the mufflers and the level of sound attenuated by each. Given below are pictures of the experimental setup and procedure (you can also see the variable length muffler in one of the pictures).

Results & Conclusion:

1) The R6 titanium muffler had the greatest sound attenuation and the second highest backpressure. The back pressure was due to the fact that it uses the resonance principle and the attenuation was greatest as it was designed for this engine.

2) The JDM toyota silencer has the second greatest sound attenuation and the highest backpressure.

3) The Aftermarket HKS first copy had the lowest backpressure and the lowest sound attenuation.

4) The self made exhausts had the second lowest back pressure and low levels of sound attenuation, however all three of them in the full length still emitted sound which was within the acceptable limits. However an important discovery was that with increasing length and diameter the sound attenuated was greater. Therefore the level of sound attenuated was directly proportional to increasing both the diameter and length.

Therefore the theory was proved. The greater the sound attenuation, the greater the back-pressure. Also another important revelation from the experiment was that at low engine frequency (low RPM) the resonance principle worked better however at high frequency (high RPM) the absorptive principle worked better.

Hope you guys enjoy and learn from my experiment. Do comment and ask any questions possible!

Regards,
Ebad

[nfssaad]

very good

[nfssaad]

now i know what to do with the spare fibreglass sheet i have lying around me home

great research... you going to write a paper on that?

[ebad_ali]

@ nfssaad: already written a paper on this.... thanks for appreciating bro

[osk89]

great work bhai keep it up . i am a mechanical engineer from UET lahore and loving the work you r doing