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Old 30th March 2010, 14:00   #16
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Originally Posted by Stratos View Post
The exhaust on a front engine truck is easy to direct on the roof as there is space behind the cabin but it would be difficult in case of buses where everything behind the driver is passengers and luggage.
I guess roof mounted exhausts are essential in all the cities of India, and not impossible since most metros are now inducting buses with rear engines into their fleet.

Even in Delhi, with buses running on CNG, some badly maintained DTC buses (the new Tata Marcopolo ones) still spew out smoke from their exhaust pipes which are placed very low. It's a harrowing experience for anyone who is on a two-wheeler, or even if you have the windows of your car rolled down. With Delhi holding the dubious distinction of being the most polluted city in the country, it is more of a necessity.
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Old 30th March 2010, 14:47   #17
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What a coincidence? I was just talking about this on the thread here & the same topic has appeared as new post after 2 days.

@Stratos - Ever since you commented I was just thinking how is it difficult is it for the front engined vehicles. I perfectly understand there're good engineering thoughts that goes into it during design, however I'd my own questions on it - is it not possible to just extend the pipe from the existing position to the rear for the front engine bus & then mount it to the top? Does that lead to some power loss?

Agreed for the bus on the part of passengers, how about our good old lorries/trucks? They still have a small cabin & the exhaust could be roof mounted that should considerably improve the air quality at breathing level right?

Last edited by aargee : 30th March 2010 at 14:49.
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Old 30th March 2010, 18:30   #18
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Originally Posted by aargee View Post
is it not possible to just extend the pipe from the existing position to the rear for the front engine bus & then mount it to the top? Does that lead to some power loss?
Correct, atleast one loss that comes to my mind is "Pumping loss", i.e. the power required to pump the exhaust gases away, any exhaust design has a simple funda "Assisting easy exit of exhaust gases", any other thoughts?

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Old 31st March 2010, 03:04   #19
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In addition, top exhaust is probably easier to fit on a low floor city bus.

One would expect a world class company like Volvo to rise over and above the rules and make a statement. What are they doing for their low floor buses.

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Originally Posted by Stratos View Post
The exhaust on a front engine truck is easy to direct on the roof as there is space behind the cabin but it would be difficult in case of buses where everything behind the driver is passengers and luggage.
yes it would be difficult and require some extra insulation and possible loss of seating. The idea suggested by aargee below is probably the best

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Originally Posted by aargee View Post
position to the rear for the front engine bus & then mount it to the top? Does that lead to some power loss?
yes, very much possible. Powerloss will be minimal and well worth the extra benefit.

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Originally Posted by SPIKE ARRESTOR View Post
any exhaust design has a simple funda "Assisting easy exit of exhaust gases", any other thoughts?
Pumping loss is the work done during intake. This is exhaust work caused by additional back pressure but its well worth the effort methinks.
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Old 31st March 2010, 06:35   #20
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I cant understand why would it be so difficult to implement .For a fact our tractors have them here , then why not the buses and trucks ?

Quote:
yes, very much possible. Powerloss will be minimal and well worth the extra benefit.
So does that mean these roof mounted exhausts in the vehicles abroad do have a power loss associated with it ? From what I see here most of the Freightliner's/Kenworths/Macks simply blast thru the Interstate Highways and for a fact these are mostly loaded.

They do churn out a good amount of thick smoke, however since the exhausts are roof mounted hardly causes any hassle to fellow motorists.
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Old 31st March 2010, 07:53   #21
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I cant understand why would it be so difficult to implement .For a fact our tractors have them here , then why not the buses and trucks ?
@RJ - its not so difficult; tractors have front engine & its easy to mount the exhaust over there at the cost of fumes hitting the driver's face. However, when the same is done on buses, imagine the smoke not only on the driver's face but also on the passengers. This is exactly what Stratos was saying.

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They do churn out a good amount of thick smoke, however since the exhausts are roof mounted hardly causes any hassle to fellow motorists
Very very true; in that case, the exhaust needn't be extended for the trucks, they simply need to be roof mounted in the front.

Last edited by aargee : 31st March 2010 at 07:54.
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Old 31st March 2010, 08:04   #22
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So does that mean these roof mounted exhausts in the vehicles abroad do have a power loss associated with it ?
No what I meant is that in a front engine bus (indian style), you take the exhaust all the way to back and then up, the overall path is little longer than usual.
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Old 31st March 2010, 10:07   #23
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Quote:
Originally Posted by SPIKE ARRESTOR View Post
Correct, atleast one loss that comes to my mind is "Pumping loss", i.e. the power required to pump the exhaust gases away, any exhaust design has a simple funda "Assisting easy exit of exhaust gases", any other thoughts?

Spike
I think this would be very negligible for truks/buses etc. since they have usually high torque/power diesel engines. Also the hot gases tend to move up on their own which will aid its flow. The design should be in such a way that for the front engined vehicles, the exhaust outlet does not have to be taken to the back end of the vehicle. It should be routed vertically at the front end itself. (Tractor exhausts!)

There should be a CMVR rule to enforce it.
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Old 31st March 2010, 15:30   #24
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Quote:
Originally Posted by aargee View Post
@RJ - its not so difficult; tractors have front engine & its easy to mount the exhaust over there at the cost of fumes hitting the driver's face.
aargee I was referring to the trucks. Sorry if my previous post wasn't clear. I know it would be a herculean task for the front engine buses to have an exhaust pipe running all the way to the rear and then to the roof.

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No what I meant is that in a front engine bus (indian style), you take the exhaust all the way to back and then up, the overall path is little longer than usual.
Makes sense, however with a rear engine bus am sure they could have implemented this. Surprising that the current generation volvo and marcopolo buses here still have exhaust pipes to their sides.
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Old 31st March 2010, 19:41   #25
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The DTC buses about two to three decades earlier had such roof level exhausts. Moreover tractors also have high rising exhausts. That should be no problem for commercial vehicle makers.
With the non AC Maruti 800 that I was using, the truck/ bus exhaust pipes would be located right at the centre of this car's window level. At traffic junctions, if such an exhaust pipe was found nearby, the plight can well be imagined.
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Old 9th April 2010, 08:34   #26
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I think they should route it to the top. If the exhaust is bent towrd the ground, it will be like a blower.
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Old 9th April 2010, 18:14   #27
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Quote:
Originally Posted by Stratos View Post
It might not be possible or be very difficult to have that exhaust on front-engined buses. Even though many metropolitan cities in India have a lot of Volvos, Kinglongs, Starbuses going around, major amount of the commercial vehicle population is ruled by front-engine configurations.
Still they can be moved to the top, albeit in the front side.
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Old 12th April 2010, 22:08   #28
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Its technically feasible to manufacture a truck/bus with a roof mounted exhaust.But it has its own limitations as there may be a radical redesign of the exhaust system as a whole. As of now there are additional mufflers given in our trucks and buses to qualify for the ARAI noise norms. So this is to be balanced in the new system.The pumping loses to be properly balanced too for a better performance of the engine.
Because of all these difficulties manufactures are staying away from this model and it ill be effective only if enforced through ARAI.
But can anyone list out some major cities in Europe, North America where this is being enforced?

Kindly find the AL3135 show cased in Auto Expo- 2008 having this type of exhaust system. All though these are used in deep mining applications, it shows the technical feasibility of using the this type of exhaust system in high power engined vehicles.

Roof Mounted Exhausts for Trucks & Buses-3135.jpg
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Old 12th April 2010, 22:38   #29
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It is not at all difficult to route the exhaust pipe of a front engined heavy vehicle to the extreme rear and then route it upwards through a corner.

The exhaust pipe is basically a 2 inch (or more) wide mild steel pipe. It would not require any insulation while running under the body (probably inside the chassis channels), but would require multiple layers of insulation when routed above the chassis levels. With an outermost layer of detached metal frame insulation with FRP panes for cosmetic purposes, and heat retardant (asbestos substitutes) fibre wound around the pipes, this should not pose any difficulty.

Having seen same engines used on heavy vehicles and passenger boats (AL 370 engines, on buses, trucks and the KeSTRTC's Vypeen - Ernakulam boat service), I can assure that this is feasible.

The cynics arguing about additional energy spent on sending the exhaust gases UP should remember that exhaust gases are well above 200deg C in temperature, and hot gases move up.
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Old 22nd April 2010, 15:48   #30
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At least our Trucks could get Roof Mounted Exhausts of not the buses.
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