In general, gasoline engines are inherently smoother and quieter than diesel engines due to the difference in combustion characteristics. Going by this principle, exhaust system of gasoline engines should need lesser muffler volumes as compared to the exhaust system of diesel engines to achieve similar noise reduction However, the muffler volumes of production gasoline engines are about 5 liters more than that of the corresponding diesel engines. What could be the technical explanation for this in terms of acoustics and vehicle level noise control?
Thank you Mr. Wei for your answer.. I am also in the opinion of some kind of masking effect wherein by virtue of the relative quietness of Gasoline engines as compared to Diesel engines, the exhaust noise becomes more predominant in the former.
Hi
This is a good question.
Mr Wei's explanation may be the right one as Diesels do not rev as high as gasoline engines.
One other factor may be that most Diesels use turbos. The turbo unit takes up some of the exhaust noise. Not all gasoline engines use turbos. Similarly, particle filters take up some of the noise.
I am sure that someone with actual motor design experience can improve on my guesses.
Just my 2 cents
Claes
Thanks Mr Fredo... Nowadays, most SI engines use turbochargers at lease in India.. and the trend is the same when it comes to muffler volumes... !!
Regards,
Dave
IMO, in contrast to SI engine, diesel exhaust gases go through a relatively complex EAS (EGR, DPF, SDPF, etc.) which contributes to reduce the exhaust noise till it reaches the final muffler.
Recently I came across with one interesting fact about muffler size. Maybe this is the main reason but I didn't talk to any muffler design engineers yet.
The fact say that exhaust gas temperature inside the muffler has to be sufficiently high in order to stay in a gaseous state. This is due to the highly corrosive nature of exhaust gases when they turn to liquid (dew point!). So, we need to make sure that the exhaust gas stays hot enough in the muffler. It is known that diesel exhaust temperature after purification is almost half of that gasoline level (~350 C vs. ~600 C, correct me if I am wrong). I suppose this is one of the main reasons, along with acoustics, to design the muffler size. Cheers!
- Badges
- Science topic
- Similar topics
- Engineering
- Mechanical Engineering