Talking to a turbo expert

[Richard]

The key is enabling the likes of Cosworth & Sauber to have a viable business.

As for road relevance, its not a direct relationship, but equally F1 shouldn't become a dinosaur by ignoring the way the rest of the world is going.

If you want to see what F1 will be like if it ignores modern engine development then have a look at IRL with their push rod single spec engines.

[xpensive]

I'm at a bit of a loss here, while I can appreciate, though kicking and screaming, WBs arguments that a lmited cylinder turbo-formula makes sense engineering-wise, why did it take BMW so long to tag along, apart from their short attempt in the early 70s, and how many turbo-Mercedes cars are there on the streets as we speak?

[WhiteBlue]

Why did it take BMW so long to tag along, apart from their short attempt in the early 70s, and how many turbo-Mercedes cars are there on the streets as we speak?

You probably have half the last years Mercs with turbo engines if you consider the diesels as well. The problem is you were getting variable vane high temp turbos for petrol mainly from Borg-Warner. So it really is an issue of competitive pricing through competition. When Honeywell (Garrett) start pumping those things out things will probably improve.

[ringo]

It would make a lot more sense to spend some of the available development money on things like hybrid turbo chargers than wasting it on double diffusors and other meaningless aero configurations that will never do anybody any good but the team that first introduces them. They get copied within one season where the teams collectively spend 100 mil $ on them and then they get banned and the games starts from scratch again. If you attach competitive advantages to efficiency technologies like hybrid turbo charging, turbo assisted downsizing and direct fuel injection everybody profits in the end even the automotive end customer.

KERS isn't such a bad example. Initially when F1 KERS came out the first test samples had a specific weight of 2.5 kg/MJ over one race. Now we are down to 0.88 kg/MJ. If the restrictions would be lifted they would be at 0.33 kg/MJ pretty soon and that would be a point where such systems start being quite attractive to the real world. KERS will never make any sense from a weight to energy ratio point of view if you compare this to a naked thermal working engine but it would be silly IMO to look at it that way.

If you compare KERS with the engine and the fuel weight it will never get anywhere near that in a time frame of a formula. The engine weights 95 kg without ancillaries and probably 145 kg effectively with the gear box, exhaust, radiators, fuel tank and all ancillary sub systems. You add 75 kg of average fuel weight during a race and get a total of 225 kg. The engine provides 2.02 GJ mechanical work during the race. We end up with 0.11 kg/MJ specific weight of the primary drive system. If we would do KERS just to provide mechanical work during a race it would be pretty stupid considering that a good system is still three times heavier than our primary source of mechanical energy. The development will probably have to run another ten years from 2013 to 2023 to get close to the V8 engine that we have now in 2010.

The rational behind it as you said is the promotional effect it has by reducing the fuel consumption and giving a competitive advantage of having additional power in acceleration phases that is not available to cars without it. The reduction of fuel consumption makes no sense in an ivory tower F1 but is a massive point for road cars which are subject to penal taxes for exceeding fuel consumption limits. The FiA just plays the same game with F1 as the tax man plays with the automotive manufacturers. If you want to be successful in automotive you have to have class best fuel efficiency in the real world.

Automotive manufacturers promoting their cars through F1 should be subject to similar mechanisms to prevent them using false advertising. If F1 and GP racing was a game of non automotive sponsored teams I would agree with your view but it isn't and it has never been in more than 100 years of history. From 1960 to 1990 F1 was lined up with the most important marketing trend in the automotive world, getting ever higher power to weight ratio from the engine. Already in 1990 that wasn't true any more for the real world. As a replacement F1 started to play aerodynamic games that had no relevance to the realm world. If F1 is to become relevant again to automotive technology is has to drop the silly aero game and deal with issues that are relevant to the industry. The FiA certainly has been committed to achieve that for the last decade. It would be marvelous if all those efforts would be rewarded from 2013. So read my lips:

"F1 has to be relevant to the real world to be exciting, meaningful and have a chance to survive politically."

When you use the word "specific" in engineering, it is used to represent a unit per kg. For example specific volume, specif consumption. So you should say MJ/kg instead.
The "Aero game" that F1 plays is very relevant to fuel consumption when translated to road cars. This is even more important for US market, where highway driving is the focus. Ferrari aso directly applies some F1 technologies to it's cars which affect performance and drag, directly affecting fuel efficiency.
BMW efficiency dynamics is another philosophy that uses some aero tricks to save fuel.

[Richard]

how many turbo-Mercedes cars are there on the streets as we speak?

They do have a number of forced aspiration models, but they use super rather than turbo charging.

In case someone asks, the Mercedes "Kompressor" uses the engine pulley to drive the fan forcing the air flow, whereas a turbo uses the exhaust gases to drive the fan.

[WhiteBlue]

When you use the word "specific" in engineering, it is used to represent a unit per kg. For example specific volume, specif consumption. So you should say MJ/kg instead.
The "Aero game" that F1 plays is very relevant to fuel consumption when translated to road cars. This is even more important for US market, where highway driving is the focus. Ferrari aso directly applies some F1 technologies to it's cars which affect performance and drag, directly affecting fuel efficiency.
BMW efficiency dynamics is another philosophy that uses some aero tricks to save fuel.

I wasn't looking for specific energy but for specific weight of regenerative and primary equipment for producing mechanical energy. Kg/MJ is a very suitable SI unit to compare this kind of equipment as you would appreciate if you had reflected on my figures.

Quite contrary to your thoughts most of the F1 aero games are completely irrelevant to road cars. Road car aerodynamics are 99.9% aimed at minimizing drag without substantial considerations of downforce. You obviously try to avoid lift and you need a bit of downforce for the 2% of sportier cars but that is a pretty small segment. F1 aerodynamics are primarily concerned with maximizing downforce at a given power surplus with configurations that have vastly more drag than any road car will ever have.

[Tim.Wright]

Actually, for the auto industry, most of the wind tunnel time is spent evaluating acoustics.

Tim

[autogyro]

Actually, for the auto industry, most of the wind tunnel time is spent evaluating acoustics.

Tim

Extremely important point that Tim.
It shows that road car aero is pretty much a fully sorted discipline and fine tuning for side issues is the only real application.

[...]

[WhiteBlue]

Back to the turbo issue and the 2013 formula. I would try to understand the energy potential of the exhaust gas.

• assume a AFR of 14 and 115 kg of race fuel
• gives me a total of 15*115kg of exhaust mass in 80 min=0.36 kg/s
• assumed entry temp to turbine 900°C (Garret interview)
• assumed exit temp from turbine 40°C
• average heat capacity of exhaust gas cp = 1.07 kJ/kg K?
• thermal power of exhaust gas stream 330 kW
• energy potential over the race time 1.584 GJ

So even with a very crude calculation it is clear that I have a very substantial potential which I can tap with my exhaust turbine. The question is: How much of that potential is available to a turbine with reasonable cost and weight?

[ringo]

Your exhaust temperature is very low, infact too low.
You would be a billionaire if you developed a turbine like that.

[WhiteBlue]

Your exhaust temperature is very low, infact too low.
You would be a billionaire if you developed a turbine like that.

So what would you suggest as a an achievable exhaust temp and what would be the design criteria for the best possible extraction.?

[ringo]

Remember that your turbine is operating between 2 pressures, the engine exhaust pressure (idealy) and atmospheric or turbine exit nozzle pressure.
The gas will expand till it reaches the turbine exit pressure and that determines the temperature.
If you want to get the egt down to 40*, don't expect to extract that work from the turbine. You need other means of doing that. The exhaust gas simply wont expand and slow down that much (the turbine wont slow down as much either).
There is something called energy quality. Low temperature energy tends to have poor quality and is not very useful for doing work, (it's usually low velocity energy). This is why most of the cogeneration applications have water heaters or process steam at the end instead of machines to extract work. Poor quality energy is best used for heating than doing work.

Roughly you can expect a temperature drop of 400 degrees or so from a turbine.

[WhiteBlue]

We obviously need some basic figures here. While ambient temperature seems to be the wrong approach we may have more luck with 1000°C to 400°C as a Delta T. What would be a reasonable assumption for turbine pressure differential and what would be the extractable energy in kJ/kg K with affordable turbine technology? I mean we could probably even use multi spool turbines if the energy potential makes it justifiable.

[ringo]

That equation is only one side of the story. Even a turbocharger on Mitsubshi evolution can take 80 horsepower. That is because a gas turbine uses heat as the primary power source. The mechanical contribution from the gasses is not as large as the heat contribution. You can capture both contribution using thermodynamic calculations:

The turbine has an isentropic efficiency. Radial turbine are about 70%.
The compressor has an efficiency too.

Finding the power required to compress atmospheric air to 2.5 bars to feed a 700hp enigne. (A lot of details left out couldn't type them in..)

At 2.5 bars the compressor outlet temperature, assumg the inlet temp is 300Kelvin is going to be 429 Kelvin. (Use pressure ratio calculation)

Power required by the compressor, (heat rate) Q dot = change in enthalpy across the compressor x the mass flow rate of the gas.

= mass flow of air x (difference in (specific heat of air at constant pressure, Cp x temperature change))

After Quick calculations a 700hp car is going to need around 0.48 kg/s flow of air.
Air Cp at 300k = 1006.92 kj/kg
Air Cp at 429K = 1019.2 kj/kg

Hence Compressor power = 0.48kg/s * (429*1019.2-300*1006.92) = 64.9 KW

You have to divide this by the turbine efficinecy of 70% to see how much power the exhaust gas has to loose to compress this air. You get 92 KW. So the exhaust from a 700hp turbocharged car at 2.5 bars has to give up 92KW of power.

Just to put this into perspective a top fuel car's supercharger requires 900hp to to compress the air to around 4 bar.
http://en.wikipedia.org/wiki/Top_Fuel

For white blue, this is smikle's calculation a while back in the engine thread. You really need charts or a program to find enthalpies.

First you deal with the compressor work. This comes off the turbine.
After doing all smikle has done, you can look at the quality of the exhuast that's left back to figure out how much load the turbine can take.
This is all limited to the exhaust energy, you can't get more than that, and you can't take it all.
I will try and do a whole calculation, engine and turbine, but it's going to take some time, since i have to refresh my memory.

[WhiteBlue]

For white blue, this is smikle's calculation a while back in the engine thread. You really need charts or a program to find enthalpies.

First you deal with the compressor work. This comes off the turbine.
After doing all smikle has done, you can look at the quality of the exhuast that's left back to figure out how much load the turbine can take.
This is all limited to the exhaust energy, you can't get more than that, and you can't take it all.
I will try and do a whole calculation, engine and turbine, but it's going to take some time, since i have to refresh my memory.

That calculation applies to the compressor side which I assume needs less power compared to the potential in the exhaust gas. The reason I make this basic assumption is the history of super efficient piston aero engines after WWII and serially turbo charged plus turbo compounded commercial truck engines you find today.





Both types of piston engines are extracting a lot more power from the exhaust gas than their turbo charging requires. The turbines that were used on the Wright R-3350-972TC-18 of the Super Constellations were said to have turbine efficiency of 82%.



Unless I'm badly mistaken the R-3350 used a set of three single spool axial turbines and not radials. So let's assume that we would also use a one or two stage axial turbine.

If we forget the weight penalty of electric turbo compounding and charging for a moment we can focus on finding out what kind of power an electric turbo compounder can really extract under sensible conditions from a 2013 formula one engine.

The R-3350 recovered 22% of the primary engine power from the exhaust which we can probably increase to say 26% due to more modern methods achieved in the last 55 years of turbine construction. So assuming 650 bhp engine power our target is 169 bhp turbo compounded mechanical power yielding 119.8 kW electric battery power after applying the generator efficiency.

If I use n smikle's calculation but use my own mass flow assumption of the engine which reflects the higher efficiency of the 2013 engine and I apply electric motor efficiency of 95% I come to a compressor requirement of 72.6 kW battery power. The net difference of 47.2 kW would be permanently available for electric propulsion. If I consider that the engine will run on average at 80% effective peak power and I loose 5% for battery to mechanical power again I end up with another 0.215 GJ of race energy.

To put that into perspective the whole KERS system was supposed to generate 0.132GJ of race energy if we achieve a recovery target figure of 2.2 MJ/lap. I am convinced that installing a reduced KERS system and using the saved weight for an electric turbo compounder and charger would be more efficient.

Alternatively to a hybrid turbo charging system I would also look at a twin spool turbine that would drive the charger on one spool and the compounder via a reduction gear on the crank shaft by the second spool. The first spool would be designed with variable vane to avoid the use of a waste gate and eliminate turbo lag. That combined turbo charger/compounder would be potentially more efficient than the hybrid design due to weight advantages and no conversion losses. It would be a sophisticated piece of kit with some cost but it would meet the objectives of bringing efficiency technologies to the automotive market.