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Old 29th March 2017, 15:43   #31
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

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Originally Posted by carmayogi View Post
high capacity ones over 1000 kilowatt and we always suggested a setup where full load of the user would be about 75% of the machine's rated output. This way, the machines ran under reduced strain even though at the same RPM.
Quote:
Originally Posted by Jeroen View Post
So going by your rule of thumb if I need a continuous 1000 Kw, I need to buy a 1000/0.75 = 1333 Kw or it would become unreliable? That doesnít make sense.
I think we are discussing two separate aspects here. What carmayogi is mentioning is the strain or in other words, the maximum stresses the engine can take when producing 1000KW. If its built for a 100PSI maximum pressure on the cylinder head during combustion, then at 75% i.e 75PSI itself, the total achievable power of 1000KW is reached. In this case, the factor of safety for this engine is 33% ((100-75)/75), and it is precisely this reason why these engines become reliable because they are running at much less than the maximum stresses they are designed for. Ofcourse, this also depends on the quality of supporting components like Injectors, Pistons etc.

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Originally Posted by Par_neon View Post
If we consider the torque figures at 4200 rpm then for 140 HP engine the torque is 240 Nm, for the 170 HP engine torque is 285 Nm and for 190 Hp it is 325 Nm.
The generated torque is directly proportional to the amount of fuel burnt in the 4 stroke cycle.
This clearly indicates that the engine is burning different amount of fuel at each configuration which also means that it is also supplying different amount of fuel at each configuration.
For a same injector the fuel supply can be controlled by varying the fuel injection pressure. Thus i feel that every engine has the same hardware when it comes to fuel supply and control and the computer electronically controls the system i.e a different engine map.
Help me understand this. The Power rating of an engine is due to the amount of fuel the engine burned and the Torque is based on the stroke of the engine at this particular power. Is it not?

And talking about efficiency, the efficiency would depend on the air-fuel mixture. If 1mm3 of diesel requires 100mm3 of Air to burn completely, then the ideal air-fuel mixture is 100:1. Now since this is difficult to achieve practically in a high compression engine, a turbo is employed which tries to force in as much air as possible to bring it close to the ideal air-fuel mixture. Now, with the use of different turbo units, what engineers are effectively doing is for the same quantity of fuel supplied, they are achieving different power/torque figures thereby impacting efficiency. Bigger turbos increase the amount of air and thus produce more power for the same amount of Diesel burnt. Ofcourse most of this stuff being electronically controlled.

Hence we see that in two cars of the same weight powered by the same engine, the engine employing the bigger turbo and producing more power output is the more efficient of the two.
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Old 29th March 2017, 16:34   #32
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

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Originally Posted by racer_ash View Post
I think we are discussing two separate aspects here. What carmayogi is mentioning is the strain or in other words, the maximum stresses the engine can take when producing 1000KW. If its built for a 100PSI maximum pressure on the cylinder head during combustion, then at 75% i.e 75PSI itself, the total achievable power of 1000KW is reached. In this case, the factor of safety for this engine is 33% ((100-75)/75), and it is precisely this reason why these engines become reliable because they are running at much less than the maximum stresses they are designed for. Ofcourse, this also depends on the quality of supporting components like Injectors, Pistons etc.
We can let Carmayogi comment himself, but thatís not what he wrote:

He states:
Quote:
high capacity ones over 1000 kilowatt and we always suggested a setup where full load of the user would be about 75% of the machine's rated output
So again, when you need 1000Kw he would sell you a 1333Kw unit so it becomes more reliable.

If an engine is designed to handle 1000Kw continuous output it handles all associated stresses that come with producing that output. You donít quantify that as 100% or 75%. Again, I have mentioned this before, there is this persistent misconception that engines under full load are stressed to the max. This is not necessarily the case.


Quote:
Originally Posted by racer_ash View Post
Help me understand this. The Power rating of an engine is due to the amount of fuel the engine burned and the Torque is based on the stroke of the engine at this particular power. Is it not?
Power is simply put a function of torque per time unit. Fuel or rather ignition of a fuel-air mixturepushes down the piston, creating tongue. Torque per time unit is power.

Quote:
Originally Posted by racer_ash View Post
And talking about efficiency, the efficiency would depend on the air-fuel mixture. If 1mm3 of diesel requires 100mm3 of Air to burn completely, then the ideal air-fuel mixture is 100:1. Now since this is difficult to achieve practically in a high compression engine, a turbo is employed which tries to force in as much air as possible to bring it close to the ideal air-fuel mixture. Now, with the use of different turbo units, what engineers are effectively doing is for the same quantity of fuel supplied, they are achieving different power/torque figures thereby impacting efficiency. Bigger turbos increase the amount of air and thus produce more power for the same amount of Diesel burnt. Ofcourse most of this stuff being electronically controlled.
Adding a turbo increase power output for the same engine (i.e. size/weight) So more power from the same package (weight/size). Turbo by itself doesnít do anything for efficiency. The high compression you mention has nothing to do with the turbo. In fact, by adding a turbo, you usually have to lower the compression ratio.

A turbo canít make the same amount of diesel produce more power. What it does is to compress the air, in the same space, i.e. the cilinder, so therefor more fuel can be added too. And that creates more power.

Quote:
Originally Posted by racer_ash View Post
Hence we see that in two cars of the same weight powered by the same engine, the engine employing the bigger turbo and producing more power output is the more efficient of the two.
No not necessarily, that would suggest in order for engines to become more efficient they would have to bigger, more powerful and turbo charged.

We own the smallest Ford Fiesta with a tiny, tiny engine non-turbo and it is the most efficient of the total range which are all more powerfull. (It wonít accelerate but it uses virtually no fuel!

Jeroen
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Old 29th March 2017, 19:45   #33
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

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Originally Posted by racer_ash View Post
I think we are discussing two separate aspects here. What carmayogi is mentioning is the strain or in other words, the maximum stresses the engine can take when producing 1000KW. If its built for a 100PSI maximum pressure on the cylinder head during combustion, then at 75% i.e 75PSI itself, the total achievable power of 1000KW is reached. In this case, the factor of safety for this engine is 33% ((100-75)/75), and it is precisely this reason why these engines become reliable because they are running at much less than the maximum stresses they are designed for. Ofcourse, this also depends on the quality of supporting components like Injectors, Pistons etc.
Quote:
Originally Posted by Jeroen View Post
We can let Carmayogi comment himself, but that’s not what he wrote:

He states:


So again, when you need 1000Kw he would sell you a 1333Kw unit so it becomes more reliable.

If an engine is designed to handle 1000Kw continuous output it handles all associated stresses that come with producing that output. You don’t quantify that as 100% or 75%. Again, I have mentioned this before, there is this persistent misconception that engines under full load are stressed to the max. This is not necessarily the case.

Jeroen

There are few aspects to this:

1) If a particular block design, in the case here is the VW 2.0 TDI, is capable of accepting a certain amount of load and heat without breaking, that would be the maximum capacity of that engine block - forget other parts that are added. If the block can run at 10PSI (random number chosen) then when running at 6 or 7PSI it is not close to breaking point. Over years of use and abuse, this will tell in terms of the durability of an engine. This is why service intervals for highly tuned OEM engines are shorter. Less repeated strain, particularly when there is sloppy maintenance from the user, or there are extreme weather or use conditions, results in lower damage/better reliability. Why does Toyota, a company that surely knows how to generate high power from an engine, always provide lower power outputs for a given displacement?

2) Any ideal situation, we would happily run generators at 100% and did not force the customer to buy up. However, just as an example of VW selling a 110 version to a commercial user rather than a higher power unit, we would, instead of detuning a bigger engine, suggest to run under reduced load. Remember that this customer may use the engine 10 years later without checking oil levels, in 50 degrees centigrade summer with dust clogging the filters and the cooling system not turned on - this is REAL WORLD. In such a situation, over the 80+ year history of our company, we found that building in certain amount of redundancy helped with reliability. If our customers were all T-bhpians, we would never sell a replacement part, only consumables!

3) When we talk of load in modern diesel generators, the RPM is always constant, it's the loading caused by the alternator demanding more current which in-turn causes the engine electronics to pump more air and fuel. It's like pressing the accelerator more to maintain the same speed in the same gear once you hit a slope. No change in speed but loading, i.e. pressures & stresses within the engine, have changed. This somewhat explains what racer_ash is saying.

3) If you check an engine's parameters operating at full load v/s 75% load, you will see all pressures and temperatures are higher. This absolutely increases wear and tear no matter which world you live in.

4) Heavy fuel generators are inherently running lower state of tune than a diesel generator and you need a larger generator for the same output as a diesel. They also run a lower speed. Low speed, low tune, low output fuel = long life. This is why heavy fuel units are used for continuous power generation even though they are larger and more capital intensive. Diesel generators are used as backup when the electricity grid fails. However, we often had builders who didn't get their connections done but sold property and had to run the DG for a while until sorting other stuff out.

5) Your example of high speed marine engine was still a question of overload causing breaking. In your case, high speed was the overload, like someone madly revving his engine in neutral and having it go bust.
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Old 29th March 2017, 21:51   #34
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

Assuming you're agreeing with me (one can't be quite certain!)
Quote:
Originally Posted by Jeroen View Post
So itís probably true that "the great god of parts rationalization has been greatly diminished in statureĒ. But he isnít gone completely. He is working in tandem with various other techniques and technologies!
lets see how this plays out in the 'engines identical, only differing in turbos, fuel delivery systems, and the cartographers bag of tricks' scenario.

Today's manufacturing processes mean that breakeven (using breakeven for want of a better word) can be attained with a much shorter production run (as far as the production process goes) compared to yesteryears. What has ballooned is the cost of the development phase. However when we are talking about a family of products, the development cost, to a large extent, is spread over the entire family. So individualised members of a family, each with a smaller production run make more sense economically. Even when we say 'smaller production run' in the auto world the numbers are mindboggling. Multiply even a couple of USD by this number, and soon we are talking of serious money! (Incidentally (and perhaps anecdotally) I think Ford had a policy where only the board could sign off if the BOM of a car increased by more than a couple of dollars).

So IMHO these engines - brothers of the same family - certainly. But identical twins wearing different clothes - have serious doubts.

It would be great if someone could trawl through the parts catalogues and compare SKUs.

Incidentally in your opinion, what are the items/ modules you think would need to be 'strengthened' for reliability if one ups the power? (Lets keep the discussion to diesels ie no or negligible rpm increase). Any cost implication for these?

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Sutripta
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Old 29th March 2017, 22:02   #35
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

If this
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Originally Posted by d3mon View Post
I think what is generally not understood very well is the concept of an engine producing different power levels at the same RPM, and the impact that it has on operating efficiency.
...
About the 190 PS engine producing 140PS of power more efficiently than a 140PS engine producing 140 PS of power - I hope that these curves make things more clear.
is the explanation for

Quote:
Originally Posted by d3mon View Post
For instance, if you slap a bigger turbo on to the same engine, like they've done for the 170/190PS models, once the turbo is on boost, it's providing more air, and hence more efficient combustion to produce 100 PS than the 140PS engine. Makes sense?
I must say that I'm still all at sea.

In the graphs, if one keeps rpm the same, and goes up and down the y axis, what are the variable being changed, and what are the variables (parameters) being held constant, or changing based on some other set of rules?

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Old 29th March 2017, 23:56   #36
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

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Originally Posted by carmayogi View Post
3) If you check an engine's parameters operating at full load v/s 75% load, you will see all pressures and temperatures are higher. This absolutely increases wear and tear no matter which world you live in.

Your example of high speed marine engine was still a question of overload causing breaking. In your case, high speed was the overload, like someone madly revving his engine in neutral and having it go bust.
It seems you live in the sales world and I live in the design and engineering world.

Let me illustrate using the high speed marine engine example.
High speed was not the cause. This concerned the Stork Werkspoor TM410 engines as installed on many ocean going tugs, supply and anchor handling vessels in the years gone by.

See:

https://www.civilengineeringhandbook...or-diesel.html



These vessels all have variable pitch propellors. During normal operations, through one handle both the engine RPM and propellor pitch adjust to ensure maximum propellor and engine efficiency are obtained. So there is a predefined (designed) handle angle versus RPM/pitch correlation. (In fact there are multiple curves included, powering up, powering down, forward, reverse.)

These vessels need to be able to handle a lot of close quarters, tricky manoeuvring. Getting close to an oil rig in heavy seas, or a ship that’s on fire in the middle of the ocean, requires the ability to very quickly adjust power and pitch settings continuously.

Some captains preferred to run the engines at a fixed RPM, about 2/3 of the nominal maximum rating (so no overspeed) and only use the pitch adjustment. So the deviated from the combined RPM/Pitch control. They found they could manoeuvre a little bit more aggressively, get slightly better response. However, this practice lead to massive problems with the bearings, or more precisely the bearing saddles that started cracking.

It was a result of the inertia forces developed by the moving piston and con rod being substantially higher than the counter force about the piston being developed by the diesel fuel / air mixture igniting whilst the engine were running at this approx 2/3 nominal RPM with little load and then going to max load and back again.

Simply put, because the pressure above the piston was too low to counteract the inertia forces the bearings were subjected to a force that proved too much. So the pressure wasn’t to high, it was actually to low. It did not counteract the inertia forces!

This is a phenomena that is fairly specific to fixed RPM type of engine applications. The engine, and therefor the crankshaft, the piston, the con rod are all spinning around at a give RPM. Creating huge inertia force. But depending on the actual loading of the engine, the overall balancing of the total system will be very different. At low loadings the crankshaft could be pulled up in the bearings and at high loading they are likely to be pushed down.

You tell me what causes more wear and tear?

High loading and therefor a well balanced equilibrium between inertia forces and combustion related forces. (I.e. low loading of bearings)

Or the problems associated with low loading and letting the inertia forces overcome the combustion forces and tear into the bearing and such?

Another example: Piston rings and cilinder lining. A difficult match at the best of times. You want to have an as airtight seal between the piston ring and the liner, but at the same time you want to make sure lubrication is as efficient as can be, to avoid wear.

Piston rings achieve that by mechanical force (i.e. spring) and by the pressure on top and behind them (which pushes the rings outward). Designing them to run perfect at low loading is of no use, as it will not work at all at high loading. So you design them for high loading to be as airtight and to get the best lubrication as well. Then you make sure that at low loading things are still reasonable.

Again, a case where the engine from a wear and tear point of view is actually designed to do better at high loads then low loads.

This might not be the stuff that is discussed during the sales process of an engine. But it is the stuff that gets discussed during the design of an engine. And engineers live with the aftermath of the outcome of these discussions.

Most engine design tends to be the result of many design compromises. It’s necessary to allow it to work across a different range of power settings and RPMs where applicable. So it’s rarely as straight forward as this or that is high, therefor there will be wear or no wear.

But what do I know, I’m just a clapped out designer/engineer. And if you have followed some of my other posts you will have noticed I keep warning everybody not to believe/trust anything or anybody on the Internet! Always make up your own mind.

Enjoy

Jeroen

Last edited by Jeroen : 30th March 2017 at 00:02.
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Old 30th March 2017, 00:16   #37
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

A few things:

1. Drag coefficient is a big factor (reason Yeti fares worse than others)
2. The FE ratings are under "typical" conditions - whatever that means. What are typical urban streets - the streets of old Hyderabad or the zippy lanes of Greater Noida?!
3. VW was the same company involved in Dieselgate where they fudged figures for tests. Tests that were conducted by external agencies all across the world. They fooled the whole world for a long time. Even when they got caught, little or nothing happened to them in India http://www.team-bhp.com/forum/images...rustration.gif

In light of this, I don't know if I can trust their FE figures. Others are free to trust a "scammy" company like VW, I will consider everything that VW does as a potential scam - especially agency numbers


Hence (apart from the addition of turbos and dual clutches) the only way higher performance is achieved is by compromising FE. It's the laws of physics - you can't have both with the same engine. (Interesting to know if anyone gets 15.26 kmpl from their A6 - not the number on the display panel but actual distance divided by volume) http://www.team-bhp.com/forum/images/smilies/LOL.gif
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Old 30th March 2017, 01:01   #38
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

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Originally Posted by Sutripta View Post
Assuming you're agreeing with me (one can't be quite certain!)

What has ballooned is the cost of the development phase. However when we are talking about a family of products, the development cost, to a large extent, is spread over the entire family.

So IMHO these engines - brothers of the same family - certainly. But identical twins wearing different clothes - have serious doubts.

Incidentally in your opinion, what are the items/ modules you think would need to be 'strengthened' for reliability if one ups the power? (Lets keep the discussion to diesels ie no or negligible rpm increase). Any cost implication for these?
I think on this one we are in agreement. A couple of additional thoughts/comments.

This spiralling of development cost is not unique to the automotive industry I think. The same, if not worse, can be seen in for instance the world of (military) aviation.

I was just reading up on the Lockheed SR71 the other day. It was designed by Lockheed Skunkworks in a matter of months in the late 50s/early 60s.

Some of the technology they used did not or hardly existed. They lacked some fundamental research om Mach 3 supersonic flight. Still they had a plane in the air, doing Mach 3 within the space of less then a few years. Huge succes.

Current programs like the F22/F-35 run for decades and seem to be plagued with trouble and endless problems. Some say you canít compare because these modern planes are so much more complex. But each plane was at the cutting edge of technology at itís respective conception point in time. So I donít buy that argument at all.

Personally, I donít think it has to do with technology so much (or the lack thereof). I think it is down to how people worked, how the oversight is/was arranged, so more on the cultural aspects then any hardcore technical differences. But we could fill a whole internet forum with that debate alone.

About reliability. First we need to distinguish between the overall reliability of the total engine as a system and the reliability of its individual components.

As a simple example. If you take a NA engine and bolt on a turbo (assuming it would run with no other changes) the Turbo version would be, theoretically, less reliable than the NA version. For no other reason, it has one additional part that can go wrong! Simply put, if you donít have a turbo, you are never going to suffer from Turbo related problems.

But letís forget about the system approach, lets look at individual components.
If we take an engine of a given size (cilinder volume) and a given RPM range, the only way to increase itís output is to get more fuel and air into the combustion chamber. Bigger bang (Higher combustion pressure and temperature ) leads to a bigger force on the piston etc.

So whatever else, at the bare minimum, we will be seeing higher combustion pressures and temperatures. Obviously, Cilinder head, head gasket, valve seals, head bolts and all need to be re-looked at. Obviously, a lot will depend on how much output increase you are aiming for!

I seem to recall that it is actually the connecting rods that are very often the weakest link. They need to deal with the additional forces that push on them coming from the piston. Here we assumed the RPM would not vary, but if the engine is going to run at higher RPMs as well, the con rod will take a double whammy: Just look at my earlier post. Inertia forces lead to tensile forces on the connecting rod and the bearings as well near the TDC.

The crankshaft and its bearings and saddles will definitely need looking at as well.
At some point in time you are likely to needing a different harmonic damper, different flywheel etc.

To be more precise, all mechanical bits which are likely to be subjected to higher pressures (and some to higher temperatures as well) need to be re-evaluated and strengthened where appropriate / deemed necessary

Now, going back to our discussion on lean manufacturing / parts rationalisation. I would still assume that an engine gets designed in such a way that most parts are common, or at least the expensive bits.

Somebody, earlier on mentioned injectors. You need to inject more fuel into a higher pressure. So again at some point in time you need different injectors and maybe a different fuel system all together.

So, one approach could be to have as many common parts as could be, and only add bits (e.g. turbo, inter cooler) to increase power / Torque. But in all honesty, I just donít know how itís done in practice for car engines. I can easily think up which parts are effected, but not how that is taken into the design phase.

In my good old days, on marine diesels, it wasnít a big issue. If you needed more power you went from say a 6 cilinder to an 8 cilinder! Easy enough!

It would be interesting to hear from somebody currently involved in car engine design how this really works.

Jeroen
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Old 30th March 2017, 20:49   #39
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

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Originally Posted by Jeroen View Post
Now, going back to our discussion on lean manufacturing / parts rationalisation. I would still assume that an engine gets designed in such a way that most parts are common, or at least the expensive bits.
And I think otherwise. Except possibly for the block. Anyway, being opinions, can't be resolved here

Why not the block? If properly designed, normal production processes (esp. true of CI) result in blocks which are far stronger than required. (Remember the BMW F1 engine?) Block problems with higher outputs usually are heat management problems leading to mechanical problems. That is a design problem, and once sorted should not add to the cost.

A note on conrods: IMO conrods (and even more so the cap bolts) landed up with their fearsome reputation for failure from too many tuners trying to eke out extra power from poorly designed long stroke British engines!

Regards
Sutripta

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Old 30th March 2017, 21:10   #40
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

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Originally Posted by Sutripta View Post
And I think otherwise. Except possibly for the block. Anyway, being opinions, can't be resolved here
I agree on the block. As I said, I really donít know, not even an educated guess, more a shot in the dark really. Maybe a little bit of wishful thinking from my own profession thrown in. In my Telecom Networks I want to have as few different parts/configurations as possible.

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Old 31st March 2017, 01:46   #41
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

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Originally Posted by smartcat View Post
Let's take a look at the curious case of 2.0 TDI engine which is shared between Volkswagen, Skoda and Audi. This engine is available in four states of tune - from 110 BHP/250 Nm to 190 BHP/400 Nm. The advantages of having a single engine with different power/torque outputs are obvious - you don't need to have 3 separate engines for 5 or 6 models.

Attachment 1623003

Questions :

1) How different are the engine internals in its different iterations? Is it the same exact engine, but with different ECU or fuel/air mixture settings? Or is it possible that the engine in Rs. 70 Lakhs Audi A6 is packed with (invisible) technology when compared to its twin in Rs. 25 Lakh VW Jetta?
Among the vehicles listed, Yeti & Jetta uses the older EA189 engines while the rest now have the updated EA288 series of engines.

I do not have the expertise to speak from reliability/cost point of view, but since VW parts database is extensively documented freely on the internet, for example here (Octavia 2016 Engine parts catalogue), one can scroll the engine internals / external aggregates and see the variations. Apart from what has already been mentioned in terms of different turbo charger, ecu mapping, injectors etc there are also difference in high pressure fuel pumps, fuel rails, absence/presence of variable valve timing, cooling system (different rating for coolant pumps in some cases), different intercoolers, different cam profiles (not 100% sure on it). Compression ratios are also different in some cases (Eg: 16.2 for 150PS variant and 15.8 for 190PS variant, achieved with different cylinder heads). The core engine internals are pretty much the same in terms of the block/crankcase, crankshaft, pistons, conrods,valves,valve springs, rollers/lash adjusters, various seals/gaskets etc.

Minor variations (especially peak torque) are often in connection with the gearbox to which these engines are paired to (associated change in engine maps). For example, among the DSGs used along with 2.0TDI across the various transverse engined VAG cars, there are currently three variants: DQ250 (6-speed wet clutch), DQ380/381 (7-speed wet clutch), DQ500 (7-speed wet clutch) - in increasing order of rated torque capacities. Cars like A4, Q5, A6 have longitudinal engine layout (though essentially the same 2.0TDI) which previously had CVT/torque converters in India and now being offered with the longitudinal DSG DL501 (another 7-speed wet clutch).

Quote:
2) Audi A6 (191 BHP/400 Nm) has an ARAI FE of 15.2 kmpl. But the same engine in a Skoda Octavia (143 BHP/320 Nm) offers a FE of 19.3 kmpl. Now this makes sense, because one would assume - higher the power, lower the fuel economy

However, look at the weight columns - Octavia weighs 1.4 Tonnes and A6 weights 1.8 Tonnes. So the difference in the fuel economy is probably due to weight difference, rather than power/torque output difference. If we look at the "Fuel Economy Per Tonne" (I know ), the same engine in different states of tune offers roughly the same Fuel Economy (in a theoretical 1 tonne car) -> 25 to 27 kmpl.

Basically, VW guys are increasing power/torque by 50% plus but with no change in fuel economy. Another way to look at this - detuning this VW 2.0 TDI engine doesn't seem to offer any fuel economy benefits. How on earth is this possible (or what exactly is happening here)?
I believe the whole of 110 PS or 150 PS or 190PS or the peak torque is not being requested during the driving cycles by which ARAI/EU certify fuel efficiency. Owing to identical engine internals; parasitic losses via heat rejection, frictional losses and through exhaust gas flow also remain pretty much the same between various iteration of the 2.0TDI engine. So when you normalize the FE for weight and final drive ratios, all of them produce similar results in identical testing scenarios. This is my understanding. If you look at the case of same engine producing different power outputs in the same car, for eg: Yeti 4x2 with 110PS and Yeti 4x4 with 140PS, Laura MT 110 PS vs Laura DSG 140PS, or the CO2 ratings for Superb 190PS vs 150PS, you will see that they are indeed very close.

Quote:
3) Why reduce the power output in a Jetta/Octavia? Why not offer it in 190 BHP guise, especially since there doesn't seem to be power vs fuel economy issue?
To distinguish the premium and variants primarily. Also a 190PS variant would need uprated brakes/tyres/wheels, which they would happily sell you as a 'vRS' variant elsewhere. Case is similar for 2.0TSI also when you look abroad. The 2.0TSI in an Octavia is always a vRS or a GTI in Golf, but just another variant when the identical powertrain (and even brakes/tyres) goes inside a Superb or Passat.

Also particular to our market, consumers won't be pleased by an Octavia that costs more than a Superb. Not the case, say in EU, where you can buy a Octy vRS that costs more than multiple variants of the Superb.

Last edited by avinash_clt : 31st March 2017 at 01:59. Reason: Added info
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Old 31st March 2017, 16:40   #42
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

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Originally Posted by smartcat View Post
Let's take a look at the curious case of 2.0 TDI engine which is shared between Volkswagen, Skoda and Audi. This engine is available in four states of tune - from 110 BHP/250 Nm to 190 BHP/400 Nm. The advantages of having a single engine with different power/torque outputs are obvious - you don't need to have 3 separate engines for 5 or 6 models.

Questions :

1) How different are the engine internals in its different iterations?..

2) Audi A6 (191 BHP/400 Nm) has an ARAI FE of 15.2 kmpl. But the same engine in a Skoda Octavia (143 BHP/320 Nm) offers a FE of 19.3 kmpl...

3) Why reduce the power output... ?
This is explained below.

First thing to note is that to produce more horse power (HP), one needs higher torque or higher rpm or a combination of both. It is torque that is key here, not HP. The torque comes from gas pressure that is exerted on the piston top (crown). Higher the pressure, more is the torque. So, the key to understanding is to know, how the engine designers vary the pressure to achieve higher torque, and therefore HP and even fuel efficiency.

To achieve the different pressure curves, the engineer needs to fiddle with a few things, such as..

Advance Angle (AA): which is the position or angle of the crankshaft throw, when the diesel fuel is injected. Typically expressed at degrees before Top Dead Center. For a given in-cylinder pressure, varying the AA gives you different Peak Combustion Pressure (PCP). Generally, higher PCP gives you higher torque, for a given engine.

In-Cylinder pressure, prior to combustion: Higher this pressure, more is the PCP, as mentioned above. This pressure is varied in a few ways. One is jacking up the turbo boost pressure by employing different turbos, other is to vary the inlet air temperature. Colder air is more dense resulting in higher PCP. So, have a larger intercooler/aftercooler. VVT, Waste-gate, Injection rate shaping, are additional methods. The last one is also used for emissions control.

Fuel Injector and common rail pump: Different CR pumps gives different fuel injection pressure. Lesser the fuel injected, lesser the PCP. Minor variations of nozzle hole angle possible, but this has to be selected very carefully, else the high-pressure fuel can wet the liners, before it burns out, resulting in poor combustion, smoke, and sometimes it can even cause turbo reliability issues.

Piston Bowl Design: Primarily to change the air flow pattern inside the combustion chamber. This affects combustion rate and hence PCP

ECU: This computer controls only a few things - the firing angle, turbo waste-gate and VVT position. Higher emission control engines have additional things to control such as the EGR valve, Lube oil vane pump position etc. To control these few items, ECU takes sensor data for Inlet air pressure, ambient temperature, exhaust gas temperature, fuel temperature, coolant temperature, oil temperature, turbo speed etc. For a given engine family, typically all ECU and even the software are the same. The engineer selects the 'map' for each configuration.

Changing the above items should help the engineer get different torque from the same engine block. But remember, when one changes these things, there are additional items that get affected. Higher HP also means higher heat rejection from cylinder. So, you need - higher flow rate water pump, oil pump, different piston cooling jet, gaskets, bearings, additional sensors, oil pan size, possible con-rod changes etc. At the end, it is possible that only the block is remaining same, rest of the engine has a complete different set of parts.

So, what is the advantage? For one, the block is one big casting and requires a lot of machining. Communizing the block gives you a lot of advantage in terms of supply chain, tooling cost etc. Another is packaging near similar engine size in the engine bay along with easier configuration control. The advantages spill over in many ways than I have listed here.

Hope this helps
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Old 31st March 2017, 18:04   #43
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

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Originally Posted by avinash_clt View Post

I do not have the expertise to speak from reliability/cost point of view, but since VW parts database is extensively documented freely on the internet, for example here (Octavia 2016 Engine parts catalogue), one can scroll the engine internals / external aggregates and see the variations. Apart from what has already been mentioned in terms of different turbo charger, ecu mapping, injectors etc there are also difference in high pressure fuel pumps, fuel rails, absence/presence of variable valve timing, cooling system (different rating for coolant pumps in some cases), different intercoolers, different cam profiles (not 100% sure on it). Compression ratios are also different in some cases (Eg: 16.2 for 150PS variant and 15.8 for 190PS variant, achieved with different cylinder heads). The core engine internals are pretty much the same in terms of the block/crankcase, crankshaft, pistons, conrods,valves,valve springs, rollers/lash adjusters, various seals/gaskets etc.
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Originally Posted by Czarcarsm View Post

Changing the above items should help the engineer get different torque from the same engine block. But remember, when one changes these things, there are additional items that get affected. Higher HP also means higher heat rejection from cylinder. So, you need - higher flow rate water pump, oil pump, different piston cooling jet, gaskets, bearings, additional sensors, oil pan size, possible con-rod changes etc. At the end, it is possible that only the block is remaining same, rest of the engine has a complete different set of parts.
Specifically for the 2.0TDI engines in discussion, even between its 110PS and 170PS (EA189 series) or between 143/150/177/190PS variants (EA288 series), core engine internals are the same. Same crankshaft, block, sump, pistons, conrods, oil pumps,valves, valve springs, gaskets, oil seals, bearings etc. Part catalogues are available to verify the same. External aggregates are uprated of course. Major internal difference were seen however in the case of the 240PS bi-turbo 2.0TDI which VW has in EU.


If someone could list out the critical components which they expect to remain same and to be different, we could fish the part numbers for them and have a comparison between different output variations of the 2.0TDI in both EA189 series and EA288 series.
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Old 31st March 2017, 19:40   #44
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Default Re: VW 2.0 TDI: Different Power & Torque outputs - How & why?

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Originally Posted by Czarcarsm View Post
This is explained below.

It is torque that is key here, not HP. The torque comes from gas pressure that is exerted on the piston top (crown). Higher the pressure, more is the torque. So, the key to understanding is to know, how the engine designers vary the pressure to achieve higher torque, and therefore HP and even fuel efficiency.

Advance Angle (AA):

In-Cylinder pressure, prior to combustion:

Fuel Injector and common rail pump:

Piston Bowl Design:

ECU:

Changing the above items should help the engineer get different torque from the same engine block.

So, what is the advantage? For one, the block is one big casting and requires a lot of machining. Common block gives you a lot of advantage in terms of supply chain, tooling cost etc. Another is packaging near similar engine size in the engine bay along with easier configuration control. The advantages spill over in many ways than I have listed here.

Hope this helps
Thank you! This certainly helps my understanding. In short may I summarize that moving more fuel and air through the same displacement engine gives you more torque and horse power. This means that other components, sensors and control logic needs to be adequately optimized to maintain efficiency and reliability. Advantage being parts commonality and common sizing in the engine bay. Of course if one makes use of the additional torque / power, one would burn more fuel.
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Old 31st March 2017, 20:25   #45
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Quote:
Originally Posted by avinash_clt View Post
Specifically for the 2.0TDI engines in discussion, even between its 110PS and 170PS (EA189 series) or between 143/150/177/190PS variants (EA288 series), core engine internals are the same. Same crankshaft, block, sump, pistons, conrods, oil pumps,valves, valve springs, gaskets, oil seals, bearings etc. Part catalogues are available to verify the same. External aggregates are uprated of course. Major internal difference were seen however in the case of the 240PS bi-turbo 2.0TDI which VW has in EU.

So looks like this engine is designed at max conditions for parts commonality.

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Originally Posted by MinivanDriver View Post
Thank you! This certainly helps my understanding. In short may I summarize that moving more fuel and air through the same displacement engine gives you more torque and horse power. This means that other components, sensors and control logic needs to be adequately optimized to maintain efficiency and reliability. Advantage being parts commonality and common sizing in the engine bay. Of course if one makes use of the additional torque / power, one would burn more fuel.

Yes fuel and it's burn rate are the primary drivers. Diesel engine thermal efficiency is currently at around 44-45%. That is, out of the total chemical energy stored in fuel, about 45% is converted to work. Rest escapes as noise and heat. So the only way to increase torque is to increase fueling with other factors remaining more or less same. Of course there are max fuel limits.
One key advantage I missed out in previous post is on NVH. For any vehicle, all excitation that drive vehicle vibrations, comes from 2 things, the tyre/road interface and from engine. The first one is from road irregularities and the second one from the explosive combustion. Now, how a structure behaves when excited, depends on how stiff the structure is and how heavy it is (mass). The engine block along with crankshaft and cylinder head forms approximately 90% of the total engine weight. As these 3 remain the same across the family, the engine weights remains approximately same. Again with these 3 being same, the stiffness of the structure is same as well. This means, all engines in the family has the same vibration response irrespective of the HP produced ! This makes the job of downstream engineers much simpler. The engineer designing chassis, body, mounts, instrument panel etc has a comparatively simpler job. They can now focus more on the structure response to excitation from tyres since the engine response, natural frequency etc are known and already tackled in other models.

Last edited by Czarcarsm : 31st March 2017 at 20:34.
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