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Old 24th August 2009, 11:10   #16
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Originally Posted by sgiitk View Post
Basically colder air is denser, so the power will be more. I am not aware of any engine which gives more output with warmer air.
Simple and precise answer to your Question, samu san. Cooler air = better performance. Be it old gen or new gen engines, unless you are running in siberia where engine and fuel charge needs warming up and for that hot air induction might come in handy.
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Old 24th August 2009, 12:34   #17
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Not necessarily. One is talking of efficiency of combustion, extraction of energy in the fuel and hence absolute power delivery, i.e. everything one expects to see on the dynamometer under ideal circumstances. One is not accounting for apparent performance sensed from the vehicle. Does one actually measure all the technical parameters on road? No, one goes by feel - expectations and observations together telling one of the situation. "Working better" need not be the same as "delivering output most efficiently". Our logical minds are always expecting a text-book profile, not the non-obvious ones.

It all depends on mechanical tolerances and resolution. There are some situations with injection fed from in-line or distributor pumps, where in situations that need minimum or fine adjustment of injected fuel, the 'feeling' of the engine is better with the slightly less oxygen of the warm air. The 'feeling' and fuel consumption are never simultaneously measured , but these situations - even though they sound counter-intuitive - actually result in lesser vibrations from the engine.

Psychologically one has always associated 'vibrations' with 'inefficiency' and 'inability to take load' (and exactly the opposite for lack of vibrations). Traditionally, pump fed DI or IDI diesel engines' inherent on-load vibrations (not shaking, that's different) are actually an indication of complete combustion (better explosion in the cylinder) rather than lack of it. At lower RPMs, this is more manifest because one 'feels' it more; at higher RPMs this gets evened out. Check the signal of a vibration sensor mounted on the head with an oscilloscope to see the difference.
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Old 24th August 2009, 12:43   #18
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@Der: so does that mean hot air is good for old gen engine?
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Old 24th August 2009, 13:43   #19
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Quote:
Originally Posted by Jaggu View Post
@Der: so does that mean hot air is good for old gen engine?
Not neccessarily: And I guess thats what he's mentioned!
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Old 24th August 2009, 13:45   #20
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A simplistic explanation based on thrmodynamics is given below ofcourse the real engine is much more complex but still fundamentals remain same.

The laws of thermodynamics can no be avoided. Any IC engine including a non common rail diesel is basically a heat engine so Carnot cycle is applicable.

Carnot theorem says no engine can exceed efficiency of carnot engine.

and efficiency = 1 - ( Heat entering the system) / (Heat exiting the system)

Colder intake air implies also implies lower heat entering the system thus efficiency will be more ( Apart from additional oxygen from dense cold air)

Question arises does EGR actually reduces the efficiency of engine as per carnots cycle and just required to prevent nox emission ?
Theoretically the answer should be actually no if you see EGR as the part of the system ( recirculated heat).
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Old 24th August 2009, 14:18   #21
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Quote:
Originally Posted by Jaggu View Post
@Der: so does that mean hot air is good for old gen engine?
May be, may not be - depends on what was felt as 'better'. For example, if for the same power delivery (not equal to peak power) vibrations were less, quite likely yes. Or some such parameter which influences something in the complex interaction of injection quantity with other parameters.

It is not that when we say 'warm air' we are talking of oxygen levels so reduced that people would find it difficult to breathe. Nor 'cold' meaning icicles are forming on mustaches, though I have heard of electrical heaters used in the intake manifold of Russian diesel engines (trucks, gensets) used in Siberia.

It is an inexact science, especially since we are not scientifically measuring performance, but relying on subjective human judgment. This is quite similar to the speculation of a widened power band felt after an apparent ECU firmware upgrade! It is like the role of 'catalysts': doesn't participate in a reaction hence no known scientific reason; yet industrial experience proves the production efficiency with or without!!!
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Old 24th August 2009, 14:21   #22
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Quite fantastic information in the posts here, I'd like to get some information about a specific case though. This weekend, we fitted a K&N filter into a Scorpio. The filter mouth and the air intake pipe were slightly different in dia, so we had to use a pvc adapter pipe as a go-between. Now my query is this, until now, the Scorpio OEM filter box was fed from a pipe that pulled in air from the front of the vehicle (cooler than engine bay air). Now, we have removed the filter box, and have an open K&N in its place. As the filter is open, its receiving warm air from the engine bay as well as whatever pulled in air the feed-pipe gives it.

Q1. Will the resultant warmer air affect the performance of the engine?
Q2. Will the filter being open, get dirtier, quicker, than the OEM enclosed filter?
Q3. Is just the filter change enough, or is there anything I need to do along with it.

After the filter got put in, the performance has improved noticeably. The car seems to be much quicker, and the accelerator seems to be lighter, and any throttle input much more responsive.

PS: This Scorpio is HVK's 2+ lakh kms old MDI beast. The reason for the K&N is to allow better performance at higher altitudes. Though I have a sneaky feeling, that 'The Transporter' HVK is never going to take it off after the performance bump he's getting!

Cheers,
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Old 24th August 2009, 15:18   #23
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I guess Samu would be more confused after reading all this, anyways with my experience (feel factor), cold air works better, so ill keep loading the engine bay with bags of ice as usual
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Old 24th August 2009, 15:21   #24
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no, at least with my turbo-intercooled IDI indica engine
http://www.team-bhp.com/forum/techni...ndigo-tdi.html (Sluggish Pick Up at Hot Engine - Indigo TDI)
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Old 24th August 2009, 16:14   #25
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Quote:
Originally Posted by greenhorn View Post
Glad to know that your Indica also confirms to laws of thermodynamics
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Old 24th August 2009, 19:35   #26
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Quote:
Originally Posted by Samurai View Post
Does this apply to Diesel engines? I know cool air helps petrol engine, but I was told diesel engines work better with hot air.

Edit: I heard this from a top expert, or else I would have ignored it.
Did the expert tell you the the reasion to why the old diesel engines worked better with hot air?
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Old 24th August 2009, 20:17   #27
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Quote:
Originally Posted by dinar View Post
Did the expert tell you the the reasion to why the old diesel engines worked better with hot air?
He did, but it was raining hard, we were in the Jeep and it flew right over my head.
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Old 25th August 2009, 19:59   #28
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Originally Posted by Samurai View Post
He did, but it was raining hard, we were in the Jeep and it flew right over my head.
OK, but could please get the info if it's not too much of hassle, I would really like to know as to why.
I know from expirence that warmer air helped the engine start , but would get good power from both IDI as well as the DI engined jeeps, I drove[had], with bit noise increase in cold weather. warmer climate mad the jeeps loos power, I stay on a hill so in the mornings the jeeps could climb in third gear and as the temperature increased , same slop had to be taken in second.

Did he mean the cold weather considering the rains?
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Old 25th August 2009, 21:05   #29
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My answer to Q.1 & 2 is yes. I was using the Green Storm Cotton filter in my Scorpio and went to Leh with that. Since mine too is a MDI like HVK's, I didn't see any improved performance at high altitudes. Rather the performance fell but I would not attribute this to the filter. I had to disconnect the EGR valve to get more power in the rarefied atmosphere.

My Scorpio was belching smoke like a brick kiln. When I reached Manali and reconnected the EGR, everything was hunky-dory.

Now in HVK's case, since the K&N is open and is also drawing hot air from the engine bay, he would face problems on altitudes as the hot air will any case be more thinner than the already thin cold air..

The "Transporter" is getting a performance bump in the plains where the air is denser and the engine is getting more and proper air than what the OEM filter used to provide. It will be different in altitudes.

Quote:
Originally Posted by sriku View Post
Quite fantastic information in the posts here, I'd like to get some information about a specific case though. This weekend, we fitted a K&N filter into a Scorpio. The filter mouth and the air intake pipe were slightly different in dia, so we had to use a pvc adapter pipe as a go-between. Now my query is this, until now, the Scorpio OEM filter box was fed from a pipe that pulled in air from the front of the vehicle (cooler than engine bay air). Now, we have removed the filter box, and have an open K&N in its place. As the filter is open, its receiving warm air from the engine bay as well as whatever pulled in air the feed-pipe gives it.

Q1. Will the resultant warmer air affect the performance of the engine?
Q2. Will the filter being open, get dirtier, quicker, than the OEM enclosed filter?
Q3. Is just the filter change enough, or is there anything I need to do along with it.

After the filter got put in, the performance has improved noticeably. The car seems to be much quicker, and the accelerator seems to be lighter, and any throttle input much more responsive.

PS: This Scorpio is HVK's 2+ lakh kms old MDI beast. The reason for the K&N is to allow better performance at higher altitudes. Though I have a sneaky feeling, that 'The Transporter' HVK is never going to take it off after the performance bump he's getting!

Cheers,

Last edited by gd1418 : 25th August 2009 at 21:08.
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Old 28th August 2009, 14:34   #30
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Quote:
Originally Posted by headers View Post
EGR is Exhaust Gas Recirculation - A device that is present in the exhaust manifold that senses unburnt gases and feeds a portion of that into the intake again.

2 effects - 1: Improve Nox Emissions
2: Improve FE

Most modern diesel engines have EGR nowadays!
EGR does not feed unburnt gases. The principle of EGR is to feed burnt gas (which is devoid of oxygen/ has very less oxygen) to reduce Nox. When the exhaust gas mixes with the fresh air from the turbo, it reduces the overall oxygen content of the air (charge air) entering the cylinder. This helps in reducing the Nox.

But, the exhaust gas is not always mixed with the fresh air. Depending on the engine operating points, the EGR valve operates mainly in the region of high Nox.
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