Talking to a turbo expert

[pgfpro]

http://autospeed.com/cms/title_Turbod-f ... ticle.html

"Implications

So let’s take a step back. In the comparison shown above of the two 2-litre engines, the turbo engine has better fuel economy, better CO2 emissions, 50 per cent more bottom-end power and 34 per cent more top-end power.

In short, it’s better in every respect (except, it must be said, cost to build)."

Granted there’s a lot of hype for turbocharging. And granted that turbocharging yields more power per unit displacement. But the thought that driving a turbocharger with normally wasted exhaust heat energy sans compounding improves efficiency is just hype. If energy doesn’t do work outside of the system, i.e. propel the vehicle, it’s not improving thermal efficiency. The energy harvested by the turbocharger is used within the system (engine), not to do measurable work –efficiency-, but instead to enhance the engine’s ability to do work -power.

With computer control of engine operating parameters it’s now possible to manage engine operating conditions to greatly optimize efficiency and power, often concurrently. For instance, it’s been mentioned in this thread that 14:1 compression ratio is being used in ICE engines. I suspect that, in order that detonation is avoided, either the VE is being limited by throttling at RPMs below the torque max, or delayed DI is being used to inject fuel only when the cylinder pressure has diminished. The higher CR allows for more efficient combustion under partial throttle, low combustion pressure conditions. This can be useful in both boosted and NA engines, but is more likely to be found in the more highly developed and sophisticated turbocharged engines. But it doesn’t mean that turbocharging is intrinsically more thermally efficient, only that all the costly efficiency driving features haven’t been applied to the more prosaic NA engines.

To match turbocharging power a NA engine will need more displacement to pump a comparable volume of air at a given RRM. However, with the same attention to engine management, the NA engine will show better efficiency with a minor weight penalty.

These are the images from Ford's pdf.

IMO this shows that a turbo engine with today's new technology can broaden the lower numeric BSFC Islands for a more usable efficient BSFC range of power.

IMO the turbo is helping with atomization of the fuel making combustion more complete. This also increases the burn rate or flame speed in which you can run less ignition advance to help get max cylinder pressure at the correct crank angle with less cylinder pressure before TDC.

IMO with a turbo you can run a more efficient engine delta p.verses N/A.

[nipo]

Wow u guys really belong to this forum... so much technical insight!

I have none of that to offer but I think I've read an article that says when you boost up an engine with a turbo you basically force more air into the engine, which then allow you to burn more fuel in each cycle, hence more power.

So the "more power" still came from "more fuel". Just that it burns at a faster rate so it gives you "more power". In this very theoretical and pure sense, nothing is gained in terms of efficiency.

It's like your credit card's limit just got increased - but the interest charged for every penny you owe is still the same... Yes you can spend more now with the card, but you also pay more as you spend more so it is not a better deal (not more efficient).

Anyway - I suppose there are 2 very practical reasons why smaller turbo engines are replacing larger NA engines for similar power output on production cars. (1) Taxes are charged based on displacement, so this is a "trick" to lower the price tag of the car you sell. (2) The so called turbo-lag seems not so much a problem nowadays and turbo engines are much more user-friendly for normal family cars, whereas in the past it was usually for performance vehicles and more serious drivers.

For F1, I suppose turbo was introduced in the past to give a massive advantage in power relative to engine size / packaging flexibility. Now it seems more like a "green" tag to the sport - I do hope in this new engine race (which goes completely against cost-saving, I agree) produces some kind of road-relevant technology to bring another level of efficiency to road cars.

Of course if they allow the 1000+ hp super beefed-up turbo engines in the old days, they get my vote!

[olefud]

[quote="pgfprothe lower numeric BSFC Islands for a more usable efficient BSFC range of power.

IMO the turbo is helping with atomization of the fuel making combustion more complete. This also increases the burn rate or flame speed in which you can run less ignition advance to help get max cylinder pressure at the correct crank angle with less cylinder pressure before TDC.[/quote]

This again compares an optimized turbocharged engine with a pedestrian NA engine.

Here’s how the NA engine needs to be optimized to compete. With CR at the max for WoT and the other goodies such as DI, the engine MAP needs to modulate the RPM by such as a CV transmission. Thus the engine will normally run at WoT to maintain optimum combustion efficiency and the transmission will change the gear ratio in response to the throttle input to modulate power. In essence, each power stroke will produce the same max power and optimum efficiency from the individual single power event. Total power output will be controlled by increasing or decreasing the number of power strokes per unit time. This keeps the NA engine in the BSFC sweet spot.

Fuel atomization is independent of turbocharging; it primarily a result of direct injection. The main fuel charge effect of turbo charging is higher temperature

[WhiteBlue]

OK what about Fords Ecoboost V6
http://www1.eere.energy.gov/vehiclesand ... 2011_o.pdf

The Ecoboost project aims for 25% improvement in fuel economy. Of that target 18% are related to downsizing from large NA V6 to small turbo I4. I think that 18% is a realistic and valuable target for a downsizing by turbo project.

[pgfpro]

[quote="pgfprothe lower numeric BSFC Islands for a more usable efficient BSFC range of power.

IMO the turbo is helping with atomization of the fuel making combustion more complete. This also increases the burn rate or flame speed in which you can run less ignition advance to help get max cylinder pressure at the correct crank angle with less cylinder pressure before TDC.

This again compares an optimized turbocharged engine with a pedestrian NA engine.

Here’s how the NA engine needs to be optimized to compete. With CR at the max for WoT and the other goodies such as DI, the engine MAP needs to modulate the RPM by such as a CV transmission. Thus the engine will normally run at WoT to maintain optimum combustion efficiency and the transmission will change the gear ratio in response to the throttle input to modulate power. In essence, each power stroke will produce the same max power and optimum efficiency from the individual single power event. Total power output will be controlled by increasing or decreasing the number of power strokes per unit time. This keeps the NA engine in the BSFC sweet spot.

Fuel atomization is independent of turbocharging; it primarily a result of direct injection. The main fuel charge effect of turbo charging is higher temperature

Looking at my book "McLaren Honda Turbo A Technical Appraisal" on page 63 they have four graphs.
1) Effect of equivalence ratio on power and B.S.F.C. (Equivalence increases, power increases)
2) Effect of Intake temperature on power and B.S.F.C. (Intake temp increases, power decreases)
3) Effect of fuel temperature on power and B.S.F.C. (fuel temp increases, power decreases)
4) Effect of boost on power and B.S.F.C. (Boost Pressure increases, power increases while B.S.F.C. decreases by 3%)

One other thing worth noting on page 60 of this book it shows graph of power verse engine rpm(6k to 13k). On the RA 168E its best B.S.F.C. was at 12k at 272g/KW*h. Is this something that could be replicated in NA form?
IMO rpm hurts B.S.F.C. in a major way in NA form.

Question why does static compression help an engines efficiency?

What does dynamic compression do to efficiency in NA and a boost engine?

[Tommy Cookers]

the NA Grand Prix/F1 engine has never been asked to be fuel-efficient (since 1913)

(intentionally) the tankage limits (a recent development) on NA F1 cars have never stopped them running on very rich mixtures
this is simply throwing away quite a lot of fuel unburnt for quite a small gain in power ie worse BTE
the Honda paper clearly shows this

the Honda turbos improved in BTE (and greatly suffered in power) when they had a hard limit of fuel quantity

[olefud]

Question why does static compression help an engines efficiency?

What does dynamic compression do to efficiency in NA and a boost engine?

Static compression compresses a given fuel charge into a smaller volume that then expands upon ignition into a larger volume as the piston moves during the power stroke. With a higher static compression, the smaller compressed volume both provides a faster combustion and confinement of the combustion products to an initial smaller volume which in turn develops greater pressure and resulting force on the piston. The pressure stays higher though diminished through the power stroke, i.e. until the exhaust valve opens. Engine power is the area under the curve for the pressure force through the effective stroke. Since the greater pressure results from a given fuel charge, efficiency also increases with compression –up to detonation. The only “cost” is higher octane requirement.

Since NA and boosted engines can tolerate the same compression pressures –adverse aspects of a hotter mixture in the boosted engine aside- there is no thermal efficiency advantage one way or the other between boosted and NA from compression pressure per se. But the many other parameters do affect efficiency –too many to consider.

I discussed this topic with David Vizard awhile back. He has the knack of explanation in simple terms backed by a profound knowledge. If you are really interested, Google David Vizard and compression ratio –or most any other topic since he’s widely published. One caveat, he sometimes shills for a product.

[WhiteBlue]

the NA Grand Prix/F1 engine has never been asked to be fuel-efficient (since 1913)...

I do not fully agree with that statement. In the nineties there was a mighty battle between V8, V10 and V12s which was handsomely won by the V10 format. It was primarily because the V12 were not as fuel efficient and needed to carry too much fuel or required too much refuelling time. So fuel efficiency of a design was certainly a competitive factor and influenced the development of the F1 engines of the last 30 years.

In the meantime I have also investigated the fuel consumption of the three super sport cars in the EU cycle:

McLaren 11.7 L/100km
Ferrari 13.3 L/100km = +14%
Lamborghini 13.7 L/100km = +17%

The turbo powered McLaren has the highest power and the highest acceleration together with a lower fuel consumption. I'm not saying that the fuel consumption is very relevant for most buyers of super cars. I was just pointing out that downsized turbo engines are offering better fuel economy at comparable power levels. On top they seem to have more grunt at low revs which obviously helps with acceleration. The 18% targeted for the Ford ECOBOOST turbo engine are in the same ball park.

I want to emphasise that I do not condemn all petrol heads that would buy a NA powered car for emotional reason like the TOPGEAR testers. Everybody is entitled to his choice if he can afford such a luxury. I was simply pointing out that the turbo engine offers greater fuel economy in the super car segment with high power engines as well as in family sedans.

I'm inclined to believe what pgfpro posted on the previous page. The turbo downsized engine has combined greater thermal efficiency and better mechanical efficiency through the higher torque delivery at lower revs.

[noname]

In the meantime I have also investigated the fuel consumption of the three super sport cars in the EU cycle:

McLaren 11.7 L/100km
Ferrari 13.3 L/100km = +14%
Lamborghini 13.7 L/100km = +17%

The turbo powered McLaren has the highest power and the highest acceleration together with a lower fuel consumption. I'm not saying that the fuel consumption is very relevant for most buyers of super cars. I was just pointing out that downsized turbo engines are offering better fuel economy at comparable power levels. On top they seem to have more grunt at low revs which obviously helps with acceleration. The 18% targeted for the Ford ECOBOOST turbo engine are in the same ball park.

I think if we look at BSFC of these engines we could assess their efficiency better. Things like curb weight should be taken into account as well. Also, as usual in the real world, there are compromises to be made - in this case efficiency vs. performance. They are not directly opposite to each other, but they are not walking hand in hand.

When we are talking about low end of the family cars (vide ECOBOOST) we should not forget it comes at the price of power at high revs, the turbos are just that small they can not flow enough when the revs climb up. That would be unacceptable in the world of performance car, but to reverse the situation one need to accept turbo lag... or expensive turbo with variable turbine geometry. Common in diesels, but there is still a lot to do when it comes to gasoline engines. Just ask Porsche

However, overall downisizing and downspeeding are being used to bump up efficiency of the ICE.

[WhiteBlue]

I think if we look at BSFC of these engines we could assess their efficiency better. Things like curb weight should be taken into account as well. Also, as usual in the real world, there are compromises to be made - in this case efficiency vs. performance. They are not directly opposite to each other, but they are not walking hand in hand.

You often do not have access to those data. Btw, I have included power/weight ratio in the original post further up. The are identical for the McLaren and the Ferrari (0.41 bhp/kg) and slightly worse for the Lambo (0.42bhp/kg). The performance according to all tests is slightly superior with the McLaren, which incidentially also posts the highest absolute power figure.

When we are talking about low end of the family cars (vide ECOBOOST) we should not forget it comes at the price of power at high revs, the turbos are just that small they can not flow enough when the revs climb up. That would be unacceptable in the world of performance car, but to reverse the situation one need to accept turbo lag... or expensive turbo with variable turbine geometry. Common in diesels, but there is still a lot to do when it comes to gasoline engines. Just ask Porsche

I would recommend to read the reviews on the Ford 1L 3cylinder ECOBOOST engine. They contradict all your claims. The engine has massive grunt in low revs and there is no reported turbo lag. The engine has header integrated exhaust manifolds that feed a very small high revving (250k rpm) turbo. Brilliant little engine with up to 123 bhp and massive torque. The high end of the turbo engines is equally performant as our little survey into super sports cars show. Drivebility also improves for a turbo versus a NA. Testers speak of diesel like torque and no need to switch gears as often as you have to for NA engines.

However, overall downisizing and downspeeding are being used to bump up efficiency of the ICE.

Yeah, I agree if we add "by turbo charging" to the downisizing and downspeeding.

[pgfpro]

Question why does static compression help an engines efficiency?

What does dynamic compression do to efficiency in NA and a boost engine?

Static compression compresses a given fuel charge into a smaller volume that then expands upon ignition into a larger volume as the piston moves during the power stroke. With a higher static compression, the smaller compressed volume both provides a faster combustion and confinement of the combustion products to an initial smaller volume which in turn develops greater pressure and resulting force on the piston. The pressure stays higher though diminished through the power stroke, i.e. until the exhaust valve opens. Engine power is the area under the curve for the pressure force through the effective stroke. Since the greater pressure results from a given fuel charge, efficiency also increases with compression –up to detonation. The only “cost” is higher octane requirement.

Since NA and boosted engines can tolerate the same compression pressures –adverse aspects of a hotter mixture in the boosted engine aside- there is no thermal efficiency advantage one way or the other between boosted and NA from compression pressure per se. But the many other parameters do affect efficiency –too many to consider.

I discussed this topic with David Vizard awhile back. He has the knack of explanation in simple terms backed by a profound knowledge. If you are really interested, Google David Vizard and compression ratio –or most any other topic since he’s widely published. One caveat, he sometimes shills for a product.

DI does help with the hotter mixture in a boosted engine by not injecting any fuel while the intake valve is open and providing a positive cooling air charge during valve IV/EV overlap. There is no loss in fuel with the overlap and the results are a nice clean cool combustion with no residual exhaust contamination.

One other thing that makes the DI/turbo engine work efficient is the new advance lean turbocharge technology. You will see very lean power with great B.S.F.C.

So these new DI turbo engines are a high compression N/A versions with a turbo.

[350matt]

the biggest new thing withthe ecoboost and the other new downsized engines is the introduction of 'cooled' EGR this allows the turbocharged engine to run at MBT and close to Lambda 1 at full load


this is unprecendented and the main reason why the engines fuel economy is so good as a normal turbo installation will run anything up to lambda 0.65 under full load to protect the turbo from melting

[Dragonfly]

Will the new engines use EGR?

[noname]

I would recommend to read the reviews on the Ford 1L 3cylinder ECOBOOST engine. They contradict all your claims. The engine has massive grunt in low revs and there is no reported turbo lag. The engine has header integrated exhaust manifolds that feed a very small high revving (250k rpm) turbo. Brilliant little engine with up to 123 bhp and massive torque. The high end of the turbo engines is equally performant as our little survey into super sports cars show. Drivebility also improves for a turbo versus a NA. Testers speak of diesel like torque and no need to switch gears as often as you have to for NA engines.

I can not agree there is any contradiction.

Ecoboost has really good low end, but high end is highly compromised (as an owner of its 1.6L incarnation I have 1st hand experience ). Max torque is in the 1600-3700 range, and than falls from a cliff. 150 or 180 KM is a nice number for a family car, but not that impressive. In WRC/WTC version this engine can make twice as much, but to do this you need bigger turbo (apart from few other measures), pushing max torque to 4000 RPM and making strong and responsive low end nonexistent. And there is also a clever anit-lag system, not without the reason.

In contrary turbocharged McLaren MP4-12C @ 2000 RPM makes less than 50% of its max torque, you need to revv it up to ~4000 RPM to wake it up.

http://blogs.insideline.com/straightlin ... 4-12c.html

So one can not have both - strong low end and high performance. Yes, you can broaden power band, you can improve drivebility and have diesel-like torque (but with this extra smoothness and without rattling), but there are still compromises to be made.

[WhiteBlue]

I can understand that you get disappointed if you ask for WRC torque and grunt from a family sedan. I guess you have to compare likes and likes. The question would be if a naturally aspired engine in a Fiesta would do a better job? I doubt it having read several test which all rave about that little engine.

I also concede that not every road going turbo engine may be as responsive as a comparable NA engine. Much depends of the technology used and what the compromises are. They use twin scroll, twin turbos and now even electric assisted turbo compound as in F1 2014. I'm wondering what that technology will do to hybrid road cars. I'm guessing it will be smooth and very fuel efficient.


I also read the engine test on the MP4-12C. It features the nice dyno comparison of the McLaren and a Porsche 911 GT2 RS. It goes on to compare turbo technology of the two engines and points out that valve and turbo tec of the McLaren are still rather pedestrian in its early incarnation. When MCLaren have played for several decades with turbo as the folks from Weissach did they will come out with something that is seriously refined.

I would love to see a dyno comparison of the McLaren vs a Ferrari Italia.