Because tractor is designed for farm which is very rough, uneven and highly zigzag surface. because of this surface there may be chances of damage of exhaust system if it designed as a car. So, it designed for up front with turbocharger engine.

mayb to avoid direct emission onto the vegetation!!!!!

Some tractors do have the exhaust running under towards the back (FORD 9N). I believe this practice was stoped because the hot exhaust pipe can ignite dry grass.

Initially, cost!....no need for expensive or complicated ducting of the exhaust gasses.

Minimisation of fire risk (as said above)

Due to the "enhanced ventilation" available in the early tractors (ie there was no enclosed "cab") there was no need to prevent a build-up of exhaust gasses around the cab.

Diffusion of highly flammable dusts (such as during harvest) reaches a lower ignition/explosion risk at slightly higher levels.

Prevention of both grounding and blockage due to the environment.

No exhaust blowing onto the pickers/packages following the tractor.

Probably a few more to boot!

I know why we using front silencer in track tor because its help to remove Exhaust burn gas's to engine exhaust port easily othere coast coting

Tractors are designed for agricultral purpose,so when the exhaust is at bottom there may damage due to water etc in field .so it mounted on top of engine

The car requires aesthetic look so you cant fit an exhaust in front of the car and it disturbs the view of the driver but in tractor aesthetic is not much worried compared to performance and the exhaust wont disturb much the view of the driver

Lot of time these tractors are towing something in the back, so you prob don't want the exhaust blowing on it. Same with big trucks. Hot air rises, so easier and quicker to pipe it up too.

some people say in tractor  silencer is fitted on front side and it is   aesthiticaly not good seen and but  in tractor is  not consider aesthitic ,and second thing is tractor is  mostly used for agriculture purpose .  when we silencer fitted in lower side of the tractor then sometime  some accident is happen then this silencer is damaged ,theirforein tractor silencer is fitted on front side .

Its' because tractor's are mostly used on agricultural purposes mostly in dry lands, and if fitted under way, it will distract emissions by blowing more dust, at the same time when under way there is high risk of contracting fire to dry materials such as grass and others, also high risk of exhaust silencer being damaged due to an even service along the ground where the tractors worked on 

There are 3 reasons for this point. "Why Tractors have vertical exhaust in the front"

1. Design level reason : Tractor is made of 2 piece construction. The rear portion (with the rear axle and drive line) can be seperated from the front portion (with engine, transmission). Hence, the silencer and exhaust tail pipe has to be kept along with the front part of the tractor. If the exhaust was to be facing the ground, then the hot gas will blow on the Driver's legs and will cause uncomfort for the user. Hence, the exhaust gas is sent vertically upward.

2. Functional level reason : If Silencer has to be placed facing the rear, (as in car), then the silencer has to be kept at the bottom. If the exhaust tail pipe is kept at a lower level, the fast blowing exhaust gas will lift up the loose sand in the crop field, now, this has multiple negative impacts 

2.1. Top layer of any crop field is the fertile sand, which will get blown-off if tractor silencer is fitted like in cars. If this is allowed, every time, tractor is used, the crop field will loose its fertile sand and ultimately will become barren land.

2.2. Another effect, is these blown-off loose sand, will fall and settle on the crops, forming a layer which will cover the crop and thus stopping the Photosynthesis process of the crops. So the crop yield will be badly affected

3. Yes, keeping the silencer and tail pipe at the bottom will have other packaging issue, where, due to the articulation in crop fields, there is every chance of the silencer getting damaged due to ground hits.

By the way , I m in Automobile Service Industry for the last 12 years.

Tractor can take ride on low lying water streams in the terrain areas. There are chances to get water inside to the exhaust system. may be the reason to arrange like this to upward.

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To go under water. Filter is also high.

Anybody suggested me!

I am Bangladeshi.. Now I am study at Diploma mechanical engineering. 

How can I opportunity in BSC  at canada.? or out of country! 

Tractor as agric implement is to avoid the farm from burning when there is dry grass.

If you  take the silencer pipe to rear end,  the flue gas will turn around due to wind speed while tractor running in 10 to 15km/hr speed.. Which makes driver uncomfortable and heatup whole tractor space. 

Tractor is a heavily vahicle to produced more power. In this vahicle filter and exhaust system are top of the vahicle two reasons,

1. First is exhausted gas easily out of the vahicle and help to produced more power.

2.Second is water entering in the exhaust system.

Because tractors are designed for farms which is very rough, uneven and highly zigzag surface. because of this surface there may be chances of damage of exhaust system if it designed as a car. So, it designed for up front with turbocharger engine.

Maximum horse power for engine. Less exhaust back pressure. Faster air can go in and out, the more you can increase fuel mixture, hince more power. The fire safety comments would be important also.

Ease of design and construction. The exhaust is closer to the combustion chamber.

For saving crops and soils from exhaust gasses 

In case of tractors all the agricultural functions are at back,  so there should not be any disturbance of smoke. 

And it is very unconvenient to pass exhaust line to back there will be heating essues