[Jeroen]

Originally Posted by katchkamalesh

As per my understanding, the use of turbo is to force more air i.e increase the pressure of the air, thereby leading to a finer atomization of fuel. finer the atomization more the power(more efficient the engine).

First and foremost a turbo increases the power per kilogram of weight of the engine. So you get more horsepower out of the same engine block.

So for a given size and weight of an engine, adding a turbo increases the horsepower. It does not necessarily make it a more efficient engine perse.

Jeroen

[katchkamalesh]

Originally Posted by Jeroen

First and foremost a turbo increases the power per kilogram of weight of the engine. So you get more horsepower out of the same engine block.

So for a given size and weight of an engine, adding a turbo increases the horsepower. It does not necessarily make it a more efficient engine perse.

Jeroen

Nope!!! When you compare 1.5L normally aspirated engine with same 1.5l engine but with a Turbo charger (Apple to a turbo charged apple) under SAME driving conditions, you will get more power, more mileage and reduced emission from the turbo charged engine (apple).

Now for people who think that since turbo offers these benefits, why aren't all cars fitted with turbo chargers. The answer is, Turbo charger and its accessories cost a bomb. Hence manufacturers avoid it.

[kaizanfan]

Originally Posted by bsdbsd

Here are some real life facts, notwithstanding all technicalities:

1. Colleagues 1.2L (or 1.1?) i10 AT -Mileage: 7-8 Kms.
2. My Santrao 1.1L AT - Mileage: 9-10 Kms. 15 in long drives.
3. My Honda 1.5 AT - Mileage: 9 Kms. Long drives not tested.
4. Colleagues 1.6 Verna AT - Mileage: 8.5 Kms.
5. Colleagues 2.4 (or 2.6 or ??) New Honda Accord AT - Mileage: 8.5 Kms

I see that a wide range of engine sizes from 1.1 to 2.6 liters ALL ARE returning approximately between 8-9 kms per liter! Thus, I decuce that engine size does not drastically alter mileage in a real life scenario (at least under Bangalore driving conditions).

Thanks bsdbsd.

This kind of data is really useful at arriving at a general consensus on whether or not engine size matters or perhaps what really matters among the cars in the market.
I would like to add couple more piece of data:
6. Santro Petrol AT 1.1L - 8-9km in city
7. Fortuner Diesel AT 3L - 10km in city
8. i20 Petrol AT 1.4L - 8km in city
9. Innova Diesel 2.5L - 11 in city

All with 100% A/c On.

bsdbsd, Is that Verna AT Petrol version? It better be otherwise it's beyond me how it could give lesser mileage than my Fortuner AT?

[bsdbsd]

Originally Posted by kaizanfan

Thanks bsdbsd.

This kind of data is really useful at arriving at a general consensus on whether or not engine size matters or perhaps what really matters among the cars in the market.
I would like to add couple more piece of data:
6. Santro Petrol AT 1.1L - 8-9km in city
7. Fortuner Diesel AT 3L - 10km in city
8. i20 Petrol AT 1.4L - 8km in city
9. Innova Diesel 2.5L - 11 in city

All with 100% A/c On.

bsdbsd, Is that Verna AT Petrol version? It better be otherwise it's beyond me how it could give lesser mileage than my Fortuner AT?

First of all, you are welcome.

All the cars mentioned in my list are Petrol cars. There is one more Diesel Verna AT in my office (1.5 or 1.6...not sure), which goes 10-11 kms for a litre of Diesel.

So its very reasonable to assume that 8-11 is the average range for all types of moving contraptions, across fuel types and engine sizes (AT), under standard Indian city driving conditions. Add 10-15% for non AT vehicles. If you get something better, then its good for you.

I am interested in experts take on this real life data.

[Aroy]

Efficient engine also plays a part in FE. My K10's 1L engine gives 9-10 in very short distances (0.5 to 1km between stops), but in normal Delhi B2B traffic it increases to 12, where as the City with its 1.5L engine gives better average.

[Jeroen]

Originally Posted by katchkamalesh

Nope!!! When you compare 1.5L normally aspirated engine with same 1.5l engine but with a Turbo charger (Apple to a turbo charged apple) under SAME driving conditions, you will get more power, more mileage and reduced emission from the turbo charged engine (apple).

.

Well, you must live in a different universe that adheres to different physical and thermodynamical laws. The more power is as per my earlier post, that's what a turbo does.

Any increase in mileage and reduced emission come from a host of different bit and pieces that need to be added and several design adjustedment on the cilinder head, injection system etc in conjunction to installing the turbo.

Jeroen

[katchkamalesh]

Originally Posted by Jeroen

Well, you must live in a different universe that adheres to different physical and thermodynamical laws. The more power is as per my earlier post, that's what a turbo does.

Any increase in mileage and reduced emission come from a host of different bit and pieces that need to be added and several design adjustedment on the cilinder head, injection system etc in conjunction to installing the turbo.

Jeroen

Hi Jeroen and experts in the forum, feel free to correct me if am wrong. Theoretically speaking, all we should get out of the tail pipe is water. Water is the result of complete or 100% combustion process in the cylinder. In reality, 100% combustion does not take place and this results in tail pipe emission. DO you agree?

All turbo does is increase the volumetric efficiency of the engine which translates that it aids better combustion resulting in lower emission. You are right with "The more power is as per my earlier post, that's what a turbo does" it is the primary objective of turbo, it also provides secondary benefits i.e, decreased emission and increased mileage (Again Turbo charged vehicles are fun to drive and turns people into jeremy clarkson wanting more POWEEEEEEEEEEEER. People tend to have fun leading to drop in mileage).

Again I would like to insist that under "SAME CONDITIONS" turbocharged engine returns better mileage.

[arunphilip]

Originally Posted by katchkamalesh

Theoretically speaking, all we should get out of the tail pipe is water. Water is the result of complete or 100% combustion process in the cylinder. In reality, 100% combustion does not take place and this results in tail pipe emission. DO you agree?

Umm, fuels are hydrocarbons (CnHn), so the product of perfect combustion will be water/water vapour and carbon dioxide.

Naturally, we don't pipe in pure oxygen but atmospheric air, so we also get various oxides of nitrogen, and carbon monoxide due to incomplete combustion.

[Jeroen]

Originally Posted by katchkamalesh

All turbo does is increase the volumetric efficiency of the engine which translates that it aids better combustion resulting in lower emission. You are right with "The more power is as per my earlier post, that's what a turbo does" it is the primary objective of turbo, it also provides secondary benefits i.e, decreased emission and increased mileage
Again I would like to insist that under "SAME CONDITIONS" turbocharged engine returns better mileage.

Sorry, you are mistaken. Volumetric efficiency is not a measure of fuel efficiency perse. There are several definitions around, but give or take it is along the following lines: It is defined as the volume flow rate of air into the intake system divided by the rate at which volume is displaced by the piston. Nothing to do with fuel efficiency.

Sometimes you'll see a definition about how effectively an engine system can pull an intake charge through the cylinder.

There are two different things we are sort of discussing. One, and we seem to be in agreement on this one, a turbo increases power for a given engine weight and size. And two, whether a turbo increases the fuel efficiency. You claim it gives better combustion and resulting in lower emission. But you don't say how it does that. You'd be hard pressed to go into the details, because essentially it doesn't. Why does it give better combustion? I wouldn't know, please explain.

Several members already pointed out that in order to increase power you need more fuel. Engines are designed to run at a very specific air to fuel ratio. Basically so many air molecules to fuel molecules. The engines runs most efficient at a given ratio and every modern car is chock a block full of electronics, sensors, flow meters and what have you that regulate the air to fuel ratio in a very narrow band. Next to that, there are all sort of other design features that enable to burn fuel as efficiently as possible and are really an integral part of the overall design of a (turbo) engine. Such as compression ratio, size and shape of the inlet/outlet channel, size and shape of the cilinder head, exhaust system etc. They are specific to a turbo being part of an engine design as I tried to point out earlier.

When you add a turbo to an engine, you put more air molecules into the cylinder. Therefor you can add more fuel, but the ratio stays the same. So there is no efficiency gain whatsoever. Your ECU sees to that! There are quite a few other factors that we do need to take into consideration. As the turbo actually compresses the inlet air, it also increase the inlet temperature, and as most of us know that is detrimental to engine performance! Rest assured, the power increase offsets that effect, unless we are talking about really high turbo boost pressures in which case you will see intercoolers coming into play.

Now, due to the higher differential pressure across the engine (higher inlet pressure due to turbo boost) there is probably some positive scavenging effect.
That might again, produce some more HP or maybe make the combustion process more efficiently. Essentially better scavenging ensures more residual exhaust gasses get spewed out of the cylinder. To get the maximum effect out of this the cilinder head, inlet, outlet channels and exhaust system need to be designed to allow this. (see my earlier post where I mention this).

Also, turbo charged engines tend to operate on higher average cilinder pressure and higher maximum combustion pressure. Again, that explains the higher HP output and might allow for a more efficient combustion. But again, to my earlier point, you need to add a whole bunch of stuff and design it specifically so, see above.

The problem in this discussion is that we are trying to discuss something theoretical, whereas most of our experiences are in the real world. But bolting a turbo onto an engine and think it will run more efficiently is simply not going to happen. You'd be lucky to get an increase in power.

What is true, as agreed, is that turbo's give a higher HP output. In addition, modern turbo charged cars, tend to have a much better torque curve, allowing for easier acceleration, less shifts etc. So what you actually see is that car manufacturers are using smaller engines, with turbo's. That gives a weight advantage. Also, smaller engines tend to more thermodynamically efficient, and because of the turbo you get a better power/torque curve. All of that results in a more fuel efficient car/engine combination.

So to go back to the original question of this thread whether bigger engines are less efficient than smaller ones. If the smaller one is designed with a turbo and produces the same HP as the bigger one, the smaller one is likely to be more fuel efficient!

Jeroen

[PGA]

Hi
I feel we have mixed up the discussion a bit here. Coming back to the moot question "Engine size inversely proportional to fuel efficiency". Frankly there is no term as fuel efficiency.

Theoretically power produced in the engine is directly proportional to only two things ie mass in the cylinder and calorific value of the fuel used. Mass in cylinder is mixture of air and fuel. Behaviour of gases in the cylinder is governed by Ideal gas equation stating that PV=nRT, where P = pressure, V= volume, n=mass of gas, T= Temp and R is gas constant.
Linking up the above two aspects we can say that power of an engine is directly proportional to pressure in the cylinder head when it is in fully compressed position, Volume of the cylinder(ie size) and inversely to temperature of the gas. (density of gas gets covered in this equation)

As an engine designer your job is to get best/desired power output with least amount of fuel consumption. (One of the QRs) So you tinker with pressure, volume and operating temperatures and try to work out the best combination to achieve the objective. Use of turbo chargers, cam setting, fitment of swirlers, multiport injections, type of fuel to be used various octane nos or cetane nos etc the list is pretty long, all come under adjustment for the three critical factors. These days electronics have made the job easier as inputs and outputs can be sensed and controlled more accurately.

Fuel consumption of an engine is measured not by the number kms done by it but by the amount of fuel used to generate one unit of power.

It can be seen that for checking fuel consumed/km above factors are constant and we have discussed quite elaborately in the thread that fuel consumption/ km is a different ball game and dependent on various other factors beside the above stated.
Cheers

[Jeroen]

Originally Posted by PGA

Hi

As an engine designer your job is to get best/desired power output with least amount of fuel consumption. (One of the QRs) So you tinker with pressure, volume and operating temperatures and try to work out the best combination to achieve the objective. Use of turbo chargers, cam setting, fitment of swirlers, multiport injections, type of fuel to be used various octane nos or cetane nos etc the list is pretty long, all come under adjustment for the three critical factors. These days electronics have made the job easier as inputs and outputs can be sensed and controlled more accurately.

Fuel consumption of an engine is measured not by the number kms done by it but by the amount of fuel used to generate one unit of power.

Cheers

Thanks, for putting it this way. I agree fully. The turbo allows you to put more fuel in the cylinder, but the efficiency (i.e. how much power is generated per unit of fuel) comes from all these other things, design and bits and pieces you bolt onto the engine.

Fuel efficiency or mileage expressed in km/l is a different factor, although the above weighs in pretty hefty obviously. But lots of other factors, ranging from aerodynamics, tires make and size, gearbox, etc.

There are a few cars on the market with are available in a certain engine size (e.g. 2.0 liter) with and without turbo's. You will find that for some the turbo version is slightly more fuel efficient (i.e. better mileage, km/l). That is no so much due to the turbo version being able to extract more power out of a unit of fuel as it is to the other factors I mentioned. Different torque curve and they will (just about all) come with a different gearbox than the non turbo version. Again, only to make optimal use of the specific power/torque delivery of the turbo based engine.

Jeroen

[katchkamalesh]

Originally Posted by Jeroen

Sorry, you are mistaken. Volumetric efficiency is not a measure of fuel efficiency perse.

One, and we seem to be in agreement on this one, a turbo increases power for a given engine weight and size. And two, whether a turbo increases the fuel efficiency. You claim it gives better combustion and resulting in lower emission. But you don't say how it does that. You'd be hard pressed to go into the details, because essentially it doesn't. Why does it give better combustion? I wouldn't know, please explain.

When you add a turbo to an engine, you put more air molecules into the cylinder. Therefor you can add more fuel, but the ratio stays the same.

Jeroen

I will refrain from using technical jargon for the benefit of other forum members who might not be technically inclined.

“Engines rely on the downward stroke of a piston to create a low-pressure area (less than atmospheric pressure) above the piston in order to draw air through the intake system. Most naturally aspirated engines cannot inhale their full displacement of atmospheric density air. The measure of this loss or inefficiency in four stroke engines is called volumetric efficiency. If the density of the intake air above the piston is equal to atmospheric, then the engine would have 100% volumetric efficiency. Unfortunately, most engines fail to achieve this level of performance”

This means that in order to create a single unit of power, more fuel is sent with lower quantity of air (This is done with help of electronics). This is called a rich mixture.

WRT increased fuel efficiency, what I meant is that under ideal conditions just the right quantity of air and fuel are mixed to create a single unit of power.

Your consideration is that with more air being sent, more fuel is required to create more power.

Working of turbo:

Turbo works with the help of exhaust gases, when you depress the accelerator, the engine produces more (hot) exhaust gases and this gas runs the turbo. With the help of turbo, a depressed accelerator increases the pressure of intake gas.

At lower RPM, there is not enough exhaust gases and this is not effective to run the turbo, this is called Turbo lag.

Ways to increase the level of atomization (A fine microscopically dispersed fuel in air)

One way is to create a fine mist of fuel using injectors. The other is by increasing the density of intake air (done with the help of turbo and intercooler).

For people who want to know more on how these systems works, feel free to google some videos.

Here are the answers your questions.

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.

I agree with the accessories parts and electronics part, I wanted to simplify things and not make it complicated.

Theoretically, turbo aids (end result) in better combustion leading to better usage of fuel to produce a single unit of power.

Theory assumes that all the conditions are ideal and in that case, yes, smaller engines consume less fuel to produce a unit of power.

I have attached a couple of links to back up my views with respect to turbos.

Jeroen, I rest my case.

Sources:

http://www.youtube.com/watch?v=rNTDBjfrx0Q

http://www02.abb.com/global/CNABB/CN...1!OpenDocument

http://innovatize.blogspot.in/2012/0...ine-power.html

http://www.ijceronline.com/papers/Vo...3301770180.pdf

[kaizanfan]

Found useful information on the following pages:
http://auto.howstuffworks.com/question685.htm
http://auto.howstuffworks.com/question395.htm
http://auto.howstuffworks.com/10-way...ine.htm#page=0

[Jeroen]

Originally Posted by katchkamalesh

I will refrain from using technical jargon for the benefit of other forum members who might not be technically inclined.

I think if you have more detailed knowledge, pleas use it on this forum. There are lots of opinions, but very few are backed up with factual information. So the more technical detail the better as far as I'm concerned.

Originally Posted by katchkamalesh

This means that in order to create a single unit of power, more fuel is sent with lower quantity of air (This is done with help of electronics). This is called a rich mixture.

Sorry, rich mixture of lean mixtures have not much to do with an engine being more fuel efficient or more power. Actually, the way you describe it, a rich mixture is correctly too much fuel per volume of air is very inefficient.

Rich/lean can be momentarily during acceleration/deceleration but your engine management system will always adjust to the optimal Lambda setting. It will never ever get the emission right otherwise. An engine becomes sustainable more fuel efficient (more HP per unit of fuel) when you increase the combustion efficiency. An engine can be designed to run lean, but that is irrespective of turbo or NA. On planes, like the one I fly, you control the mixture separately and at higher altitudes, i.e. lower densities, you "lean" the mixtures, which gives you a better fuel efficiency. Technically, its not leaning. Its just adjusting for a different number of air molecules. The ratio stays the same

See also: http://en.wikipedia.org/wiki/Air–fuel_ratio

Originally Posted by katchkamalesh

WRT increased fuel efficiency, what I meant is that under ideal conditions just the right quantity of air and fuel are mixed to create a single unit of power.

That is what your cars electronics do all the time. Supported by the integral design of the engine and all of its components.

Originally Posted by katchkamalesh

Your consideration is that with more air being sent, more fuel is required to create more power.

No, that is incorrect. I'm saying by having more air in the cilinder it will allow you to introduce more fuel. This is the basic principle of the turbo. It gives you more power from the same engine. More air plus more fuel in the correct ratio is more power.

Originally Posted by katchkamalesh

Working of turbo:

At lower RPM, there is not enough exhaust gases and this is not effective to run the turbo, this is called Turbo lag.

Most turbo's will happily spin away at lower RPM's as well. Turbo lag is the feeling of delay the driver gets when he/she presses down on the accelerator and it takes some time for the engine to really pick up. This delays is caused by two factors. It takes a bit of time for pressure and temperature to built up in the exhaust. In addition, the turbo needs to overcome it's own rotational inertia

Originally Posted by katchkamalesh

One way is to create a fine mist of fuel using injectors. The other is by increasing the density of intake air (done with the help of turbo and intercooler).

Uh, again sorry no! Density of the intake air is not a factor really.

There is a general misconception that turbo engines run with higher combustion pressures and temperatures. (i.e higher density) In essence this is not true. Normally aspirated engines are designed in such a way that they already have the most optimal pressure and temperature for the combustion to take place. Think of a petrol engine. Too high a temperature and the petrol will start to burn to early or unevenly, causing knock. So what you will see is that turbo version of NA engines will have a lower compression ratio. Take for instance my Jaguar XJR. 4.0L V8 supercharged engine. Compression ratio 9.0:1. The very same engine sits in the non supercharged NA XJ8. No supercharger but the compression ratio is 10.75:1. Do the math of an adiabatic process and you will find that both the supercharged and the NA engine operate at near enough identical pressure and temperatures at the end of the compression stroke! So there is no difference in pre-conditions to the combustion process when comparing NA engines to supercharged or turbo charged engine.

A turbo or Supercharged engine produces more HP/torgue because its average pressure during the power stroke is higher. If you want more detail, we need to go into the details of making everybody understand a P-V diagram showing how the indicated Horsepower is generated.

Same is true, for some different reason for diesels. Based on the above, I guess you can figure that out.

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. Intercoolers are used in combination with high Turbo boost pressures. These high turbo pressures increase the air intake substantially. If this relatively high temperature is subsequently compressed by the piston, the temperature at the end of the compression stroke would be way too high. Hence intercoolers are introduced, to reduce the temperature of the intake air after it comes out of the turbo and before it goes into the cylinder.

Originally Posted by katchkamalesh

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.

Again, sorry, but fuel efficiency as we've been discussing, ie producing same unit of power with fewer units of fuel is exactly that: more efficient combustion. There is nothing else that will do that. If there is please let me know, because I will patent it immediately.

As I said earlier, there might well be some positive scavenging effects, but I don't know how to quantify those.

Originally Posted by katchkamalesh

I agree with the accessories parts and electronics part, I wanted to simplify things and not make it complicated.

Good to hear we agree on something. Simplify doesn't necessarily work. I'm all for the details. The more the better. The problem with simplifications is that we end up with general tit bits, that really have very little value as they appear as opinions without facts.

Originally Posted by katchkamalesh

Theoretically, turbo aids (end result) in better combustion leading to better usage of fuel to produce a single unit of power.

No, see of all of the above

Originally Posted by katchkamalesh

Theory assumes that all the conditions are ideal and in that case, yes, smaller engines consume less fuel to produce a unit of power.

No, that's not what I said and it is not true, see all of the above.

Originally Posted by katchkamalesh

Jeroen, I rest my case.

Don't; you say you simplify and don't want to use to much technical jargon. I'd like to think I can handle that. I've met quite a few Team BHP forum members in person in Delhi and I know several who will be very happy to see you bring in the detail and the technical knowledge.

Looking forward to your detailed, factual, technical explanation why turbo engines are more fuel efficient. I.e. use less fuel to produce a unit of power compared to NA engine.

Jeroen

[katchkamalesh]

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.