An exhaust pipe connects the exhaust manifold and the muffler. Where two exhaust manifolds are used, as in V-8 engines, the two exhaust pipes — each connecting one exhaust manifold, submerge into one pipe which is connected to the muffler. The exhaust pipe is usually 5 cm in diameter and 2 mm thick. The connection between the exhaust manifold and exhaust pipe is flanged. Both the exhaust pipe and muffler are usually mounted so as to eliminate metal-to-metal contact and to prevent the transfer of vibration and exhaust noise to the car body. This is done by insulation—rubber, rubber-impregnated fabric, or similar flexible material between the exhaust pipes, mufflers, and mounting brackets. This flexible material also allows for engine movement and for expansion and contraction with the change of temperature.
If the high-pressure exhaust gases were allowed to enter the atmosphere directly from the exhaust manifold, a loud unpleasant noise would be heard like the firing of a gun. This noise is due to the large difference in pressure between the exhaust gases and the atmosphere. For the quiet operation of the motor vehicle, it is desirable to reduce this noise as much as possible. This is done by using a muffler (or silencer) in the exhaust system. A muffler is connected between the engine exhaust pipe and the tail or outlet pipe. The function of the muffler is to reduce the pressure of the exhaust gases sufficiently to permit them to be discharged into the atmosphere silently. To reduce the pressures, the exhaust gases are permitted to expand slowly and cool in the muffler. The capacity of the muffler should be sufficiently large to permit the gases to expand to nearly atmospheric pressure before they are discharged into the air. Also, the muffler should not have any appreciable restriction to flow that will raise back pressure excessively.
In some designs, the outer shell of the muffler is made oval in shape to permit adequate clearance with the ground. Many of the outer shells of mufflers are made of steel coated with lead-tin alloy or aluminum to resist corrosion, particularly that caused by the exhaust condensate. Most of the mufflers are provided with small drain holes in the outside shell to drain out the condensate from the exhaust gases and to resist corrosion.
Types of mufflers-
- Baffle type.
- wave cancellation type.
- Resonance type.
- Absorber type.
- Combined resonance and absorber type.
It consists of a number of baffles spot welded inside the cylindrical body. The purpose of the baffles is to dose the direct passage of the exhaust gases, thus the gases travel a longer path in the muffler. There are many designs of the baffles used in the muffler. The figure shows two types of such mufflers. The major drawback of this type of muffler is its low efficiency. Due to the restricted flow of the exhaust gases. back pressure increases causing the loss of engine power.
Wave cancellation type muffler-
|Wave cancellation type muffler
In this type of muffler, the exhaust gases entering the mufflers are divided into two parts to flow in the muffler. The lengths of these paths are so adjusted that after they come out of the muffler, crests of one wave coincide with the troughs of the second wave, thus canceling each other and reducing the noise to zero theoretically. This is achieved if the lengths of the two paths differ by half the wavelength. But this is not practically achieved, because the noise created by exhaust gases is a combination of different frequencies at different engine speeds. However, appreciable noise is reduced.
Resonance type muffler-
It consists of a number of Helmholtz resonators in series through which a pipe having access port passes. Helmholtz is the name of a person who originated the idea of this type of muffler. The exhaust gases flow through this pipe. The resonators eliminate the fundamental and higher harmonics of the engine noise.
|Absorber type muffler
It consists of a perforated tube, around which a sound-absorbing material, like fiberglass or steel wool, is placed. The exhaust gases pass through the perforated tube. The sound-absorbing material reduces the high pressure fluctuation of the exhaust gases, thus reducing the noise intensity. These mufflers may be either straight-through type or reverse flow type.
Combined resonance and absorber type-
Sometimes, a resonance chamber is provided at one end or in the middle of the straight-through absorber-type muffler to reduce the pressure and noise still further. In some designs, a resonance chamber is a separate unit called a resonator, which is connected in series to the muffler.