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Old 2nd October 2013, 22:51   #61
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Firstly, I am never of the opinion that volumetric efficiency is a measure of fuel efficiency. I again like to emphasise that higher the Volumetric efficiency more complete the combustion is.

Suppose with 100% Vol efficiency, I retard the timing much much beyond the MBT, will there be still "good" or complete combustion? Does the charging efficiency also help wrt improvement of combustion characteristics ?
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Old 2nd October 2013, 22:59   #62
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Originally Posted by katchkamalesh View Post
That is all I have to say and I have explained what a turbo charger does.

I have all reasons to be believe in what I have posted and I have also backed it up with the links.

I urge all of you you to read all my posts in this thread once again.

And since this is a public forum, Its is not just for you, me or a few who understand these technical terms. Knowledge sharing should be simple. This is my school of thought.
You sound quite desperate. You shouldn't be. This is just a forum, it's not life or death, there is nothing at stake.

Again, I think you're selling yourself short. If you have knowledge why not share it, especially on a public forum. Others can learn. Apart from that as I pointed out a couple of your statements are just factually incorrect. If you don't think so, point it out with counter arguments or facts. If you think an intercooler works differently from what I pointed out, spill it out. If you think my way of articulating turbo lag is incorrect, please correct. If you think the pressure and temperature on turbo engines are fundamentally different than on a NA engine, do the math and show me.

You come with general statements, and call that simplification, but refuse to go into detail. Sorry, but I call that lack of content. I believe I provide more detail than you do and I have no doubt that most members have a pretty good idea of what I'm saying. I'm not using fancy math, complicated science. I'd be very happy too, if need be. I'm pretty good a thermodynamics, have a reasonable good understanding of most aspects of engine design. Or at least I think I can ask some relevant questions. I'll be very happy to share and adjust my views if somebody comes up with good arguments.

On the links provided, for every link that states one particular position (yours) you can find one that states the opposite (mine). I can show you a zillion billion links that concur with what I wrote. Does that make your or my view the correct one? Of course not.

We live in a sad world where research seems to be to find a link on the internet that supports ones own (preconceived) notions and opinions.

To me a public forum is a place where all exchange opinions, exchange what they perceive as facts, challenge and inquire to become more knowledgable or just for a bit of fun and entertainment. I'm not claiming to be right, I just haven't seen a single argument or single fact from you other then very generic statements. And some of those I believe to be factual incorrect. If you don't agree, dig in and come up with your arguments.

Sorry to say, but it seems to me either you don't want to be drawn in a factual detailed discussion or you lack the content to do so. I just don't know. you say you simplify which suggest you know more detail but you don't provide it. On a public forum you can do so and you don't need to give a reason or explain yourself. That's fine.

I have been proven wrong over and over and over again. It's called learning and gaining experience. I have no qualms about that. I enjoy being proven wrong. I don't have anything to gain by being correct. The minute I find myself always right is the moment I stop learning or have surrounded myself with the wrong people.

I believe you should do better than a few very generalist statements and a few internet links.

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Old 3rd October 2013, 07:26   #63
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Default Re: Engine size inversely proportional to Fuel efficiency?

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Originally Posted by SPIKE ARRESTOR View Post
Suppose with 100% Vol efficiency, I retard the timing much much beyond the MBT, will there be still "good" or complete combustion? Does the charging efficiency also help wrt improvement of combustion characteristics ?
Spike
If you're timing isn't correct you are very unlikely to get a good combustion, irrespective of the percentage.

Actually, we are discussing here this very question you're putting up: does charging efficiency improve combustion characteristics as part of turbo's. Everybody agrees that a turbo improves the charging efficiency. Everybody agrees it boosts power output. Not everybody is aligned onto whether it does or does not improve combustion and therefor would allow for better fuel efficiency in terms of unit of power per unit of fuel.

As I said earlier, I do believe there could be a scavenging effect that might have some positive effect. I just don't know. I don't think it does much on the combustion efficiency. One of the reason being, as I explained, that the pressure and temperature under which the combustion takes place in a turbo engine versus NA engine are not that different. So why would the combustion be better. There just happened to be a slightly larger volume of air with an appropiate large amount of fuel in the cylinder. That by itself doesnt make it more efficient, but it will produce more power.

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Old 3rd October 2013, 08:14   #64
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Default Re: Engine size inversely proportional to Fuel efficiency?

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Originally Posted by Jeroen View Post

Contrary to your statement the intercooler doesn't increase the density of the air intake. It lowers the temperature of the intake! So density decreases.
Jeroen
All fluids(air included) with the exception of water increases in density the colder it becomes. How ever if you were to say increase in pressure on a fluid decreases density then you would be spot on and which is the sole reason why we have intercoolers on our engine. In case of water there is a decrease in density below 4 degrees centigrade. Lowering of temperature of the air intake at any point of the air pump increases density. That is also the reason why exhaust pipes should not go over board in girth since increased diameter pipes aft of the exhaust valve decreases temperatures and increases density and hence will require the engine to work harder to push out the dense exhaust gases. Exhaust piping I agree borders on black magic.



Now for the geeks!!
Gases: If the fluid is a gas (and if the temperature remains constant), pressure is inversely proportional to volume for a given mass of gas, ie PV = C where C is a constant.

As volume is the reciprocal of density, P/d = C where d is density.

Liquids: For most purposes liquids are incompressible so density does not change with pressure but at very high pressures density will increase. To calculate this you will need the bulk modulus of the liquid. You can find the bulk modulus of various liquids in Kaye and Laby, Tables of Physical and Chemical Constants [Longmans].

p = -K(dv/v) where K is the bulk modulus.

Example: for water at 15C, K = 2.75/GPa
for a pressure, p = 0.1GPa [ie 1000 atmosphere], dv/v = -0.1 x 2.75
ie dv/v = -0.275 so the original volume, v, is reduced to (1-0.275)v, ie 0.725v.
the density has therefore increased by a factor of 1/.725, ie 1.379

Last edited by drpullockaran : 3rd October 2013 at 08:33.
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Old 3rd October 2013, 08:43   #65
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Default Re: Engine size inversely proportional to Fuel efficiency?

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. Lowering of temperature of the air intake at any point of the air pump increases density.
You are of course 100% correct! What was I thinking, must be some mind warp.

What still puzzles me is the idea that the air density is a factor in getting a better combustion in a turbo engine than a NA engine. Although the airdensity in a turbo engine (with or without intercooler) will be larger at the start at the intake stroke, due to the fact that most turbo engines have lower compression ratio's the maximum pressure and temperature reached at the end of the compression stroke is in fact very similar as to that of a NA engine. Especially true on petrol engines.

So although the intercooler does bring the air density down, I have always worked on the assumption that its main function would be to bring the air intake temperature down. If not, the maximum temperature at the end of the compression stroke would sky rocket.

Any thoughts, is the above correct or am I suffering from another mind bender?

thanks,

Jeroen
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Old 3rd October 2013, 10:15   #66
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Default Re: Engine size inversely proportional to Fuel efficiency?

As far as I can recollect, the idea of turbo is to increase the volume of air so that more fuel can be accommodated (constant air/fuel ratio) in a charge. As fuel is what generates the power, and proper air/fuel mixture is required for combustion. The only way to have more fuel is to have more air and the only way to cram more air into a fixed volume is to make it denser - cool it and/or increase the pressure. The resultant mixture may or not may be more efficient, but it will surely give more power.

Most of the turbos are driven by exhaust gasses as that is one inexpensive way to drive the turbo and at the same time keep its speed proportionate to the engine's. But there are other more efficient methods also - electrical drive controlled by ECU is one such method. It will give you zero turbo lag and more efficient combustion as the ECU is constantly monitoring all the engine parameters and decides on the most efficient turbo RPM.
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Old 3rd October 2013, 11:02   #67
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As far as I can recollect, the idea of turbo is to increase the volume of air so that more fuel can be accommodated (constant air/fuel ratio) in a charge. As fuel is what generates the power, and proper air/fuel mixture is required for combustion. The only way to have more fuel is to have more air and the only way to cram more air into a fixed volume is to make it denser - cool it and/or increase the pressure. The resultant mixture may or not may be more efficient, but it will surely give more power.
Agree, on the power, the debate is on whether the turbo, by itself creates a more efficien combustion. I don't think so, but I've been wrong before.

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Most of the turbos are driven by exhaust gasses as that is one inexpensive way to drive the turbo and at the same time keep its speed proportionate to the engine's. But there are other more efficient methods also - electrical drive controlled by ECU is one such method. It will give you zero turbo lag and more efficient combustion as the ECU is constantly monitoring all the engine parameters and decides on the most efficient turbo RPM.
Interesting, are you saying that these turbo's have a little electrical motor, with speed controlled by the ECU? Of course, you will have to take into account the (electrical) power that is needed to drive the turbo which lowers the power gain by a bit, but I can see it can help overcome turbo lag. And I can see it increasing efficiency as you are able to control it in a much more precise way than to rely on the exhaust gas.

On the big two stroke marine Diesels I used to work, we often had electrical driven turbo's as well as exhaust gas driven ones. The electrical ones used to kick in at low engine RPMs. Low engine RPM on a two stroke marine diesel is maybe 30-40 revolutions per minute! The exchaust turbo's are huge and with so little exhaust gas flowing through them, they just would not produce any boost, in fact they were restricting the exhaust flow. Hence we had to supplement by engaging an electrical drive fan in the intake. NOt sure if modern marine diesels still have this system.

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Old 3rd October 2013, 11:27   #68
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Default Re: Engine size inversely proportional to Fuel efficiency?

Engine size inversely proportional to Fuel efficiency?

Having used a 1.2 engine and a 1.4 engine in the same car with same combination of exhausts, intakes and engine management, i can in my experience say that engine size isn't inversely proportional to fuel economy under real world (read as non WOT, closed loop) driving conditions. I am getting better fuel economy with the 1.4 engine than the 1.2, because of the increased torque i can drive with lesser throttle input for the same load conditions.

Last edited by Sankar : 3rd October 2013 at 11:32.
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Old 3rd October 2013, 11:36   #69
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Default Re: Engine size inversely proportional to Fuel efficiency?

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Originally Posted by Jeroen View Post
On the big two stroke marine Diesels I used to work, we often had electrical driven turbo's as well as exhaust gas driven ones. The electrical ones used to kick in at low engine RPMs. Low engine RPM on a two stroke marine diesel is maybe 30-40 revolutions per minute! The exchaust turbo's are huge and with so little exhaust gas flowing through them, they just would not produce any boost, in fact they were restricting the exhaust flow. Hence we had to supplement by engaging an electrical drive fan in the intake. NOt sure if modern marine diesels still have this system.

Jeroen
Two turbos one driven by electricity and other by exhaust gas are slowly gaining as they can boost the performance (and nett efficiency) more than a single turbo driven either electrically or by the exhaust gasses. Depending on the engine RPM and the exhaust gas pressures you use one or the other or a combination of both to give the maximum efficiency (or power as the case may be)
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Old 3rd October 2013, 11:45   #70
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Default Re: Engine size inversely proportional to Fuel efficiency?

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Originally Posted by Sankar View Post
Engine size inversely proportional to Fuel efficiency?

Having used a 1.2 engine and a 1.4 engine in the same car with same combination of exhausts, intakes and engine management, i can in my experience say that engine size isn't inversely proportional to fuel economy under real world (read as non WOT, closed loop) driving conditions. I am getting better fuel economy with the 1.4 engine than the 1.2, because of the increased torque i can drive with lesser throttle input for the same load conditions.
Did those cars have identical gear boxes / gearing or where they different?
Thanks
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Old 3rd October 2013, 11:46   #71
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Default Re: Engine size inversely proportional to Fuel efficiency?

^ Same gearbox and ratios. No change in drive train components, and the car is the same.

Last edited by Sankar : 3rd October 2013 at 11:55.
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Old 3rd October 2013, 12:08   #72
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^ Same gearbox and ratios. No change in drive train components, and the car is the same.
Interesting, it is in line with what I suggested earlier that the way a turbo engine delivers its power/torque is what makes it more fuel efficient on a l/km basis, but not necessarily on a HP/l basis.

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Old 3rd October 2013, 12:39   #73
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"Honda quietly dropped the 2.4-liter four-cylinder turbo engine in the 2013 Acura RDX and replaced it with a bigger nonturbo engine that gets better fuel economy. The turbo engine, EPA rated at 19 mpg city/24 highway/21 combined, was replaced by a 3.5-liter V6 that is EPA rated at 20 mpg city/28 highway/23 combined."

"...automakers are gaming the EPA's mpg rating system by taking advantage of the agency's test procedures. He said some vehicles are being calibrated to deliver the highest fuel economy label number based on EPA test procedures, which may not match real-world driving conditions.

The EPA's highway fuel economy test, for instance, is run for about 12 minutes, has a top speed of 60 mph and an average speed of 48.3 mph. Such low speeds would produce a high mpg rating for a turbocharged engine."

http://www.autoweek.com/article/2013...news/130619995

http://drivingfueleconomy.com/latest...thats-promised

http://www.greencarreports.com/news/...er-gas-mileage

http://www.autoguide.com/auto-news/2...r-reports.html

http://www.slashgear.com/small-turbo...port-06268300/

Interesting that Honda is going the opposite direction. But like i believed small turbo engines gives better FE under low load conditions and fuel efficiency takes a hit when load and RPM goes up. Thats what is happening with large pickups with relatively small turbo engines with lower low down torque compared to large V8.
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Old 3rd October 2013, 16:49   #74
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Default Re: Engine size inversely proportional to Fuel efficiency?

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As far as I can recollect, the idea of turbo is to increase the volume of air so that more fuel can be accommodated (constant air/fuel ratio) in a charge. As fuel is what generates the power, and proper air/fuel mixture is required for combustion. The only way to have more fuel is to have more air and the only way to cram more air into a fixed volume is to make it denser - cool it and/or increase the pressure. The resultant mixture may or not may be more efficient, but it will surely give more power.
RPM.
Aroy, I am of the belief that denser air and high injection pressures leads to a fine atomization and higher the degree of atomization, higher the completeness of combustion. What is your view on this?

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If you think an intercooler works differently from what I pointed out, spill it out. If you think my way of articulating turbo lag is incorrect, please correct. If you think the pressure and temperature on turbo engines are fundamentally different than on a NA engine, do the math and show me.

On the links provided, for every link that states one particular position (yours) you can find one that states the opposite (mine). I can show you a zillion billion links that concur with what I wrote. Does that make your or my view the correct one? Of course not.
Jeroen
Jeroen, Do not consider this an argument, These are just answers (and one question) that I have for you.

First and foremost, I am not desperate. If I sounded that way, may be I was wrong with usage of words.

All along, I have been talking about what (End result) a turbo a does and not how it does that (I might have touched base at certain instances).

For eg, when I talked about not enough exhaust gases, I meant the temperature and pressure of exhaust gases not enough to kick start the turbo. (automotive turbos, generally do not kick in at idle speeds) I was of the opinion that this is called a turbo lag.

I am confused here. A hypothetical question. Suppose a turbo is designed to kick in at 1500 RPM and the engine idles at 700 RPM. Now, you are driving at a slow pace (you do not need to cross 1300 RPM), in this case, you will still be pressing the accelerator (to go from idle to 1300 RPM) and the turbo will never going to kick in. Is this still called a turbo lag?

Again using a inter cooler as the name suggest is to cool the intake air (whose temperature has been increased due to compression) and the desired end result is increase in the density of air (which I had pointed out).

You are right with a zillion links and websites, As a market researcher it is my duty to filter good sites from the bad ones. The reason I had pasted the links, is that you can look at the content and decide on the worthiness of the website for yourself.

I again suggest you to put on some links to back your theories so that we can have a look at those sites. May be they would have dumbed it to my level.



By the way, times have changed and there are a bunch of people like me (and also in IT industry) who rely on WWW for information. Whether you take the information or not is at your own discretion. To me, the WWW has given me access to knowledge.

I also read some article sometime back, it had mention of a type of turbo using exhaust gas recirculation to harness the energy from the waste gases. Here the end result is increase in fuel efficiency and not increase in power.

Turbos running on electricity is new to me. Wont these put pressure on the batteries/electricals which have been strained all ready?

With BMW recommending people to drive their cars for at least 20 KM per week to maintain the life of the battery, I have reasons to believe that electric turbos will strain the system.
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Old 3rd October 2013, 18:18   #75
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Default Re: Engine size inversely proportional to Fuel efficiency?

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So although the intercooler does bring the air density down,
Any thoughts, is the above correct or am I suffering from another mind bender?
thanks,
Jeroen
Yes another mind bender. The intercooler brings the air density UP or more or in other words increases air density and brings the temperature down.

Not to worry I too go through these episodes more often than not; but thankfully not when I am treating patients.
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