F1technical.net

Again, my guesstimation above was based on F1T's number of TE to be 34% for a high-compression engine and as I have had a total efficiency of 25% in the back of my head for some time, that would translate to an ME of 74%.

Those 74% ME and a crank-power of 530 kW, it would mean internal-friction losses of 190 kW or 9% of the fuel-energy.

If you have a diferent number on the losses, please do not hesitate to share.

http://www.eng.auburn.edu/~jacksr7/SAE2002013355.pdf
http://www.federalmogul.com/NR/rdonlyre ... cript2.pdf
Figure 5 of:
http://www.badgersnowmobile.com/uploads ... r_2009.pdf

That Figure 5 was most interesting, though I have trouble with relating the friction-loss in kW to percentage of the output, 10%? But it's anyway obvious that losses increase more than proportionally to the Rpm, which was to be xpected of course.

I should be intrigued to learn about your own interpretation and xtrapolation of this to an 18k Rpm, 2.4 liter V8?

Check out Figure 13 of http://www.eng.auburn.edu/~jacksr7/SAE2002013355.pdf
(For the V10 at 18k rpm). This paper is more relevent than the snowmobile article.

At last, thanks Touring! Good Lord, I'm such a sucker for hard numbers, 65 kW for a three-liter V10 at 1800 Rpm, that's roughly 10% of the output for such an engine I guess.

Sticking to the 10%, it would mean this years 18k V8's would lose some 50-55 kW on internal friction. Case closed?

You're welcome! On reflection, 50-55kW doesn't seem like much, relatively, but then that doesn't include pumping losses. Thanks, I learned something, too.

I think you're right: case closed.

xpensive,

A BTE of 35% is probably somewhat high for an F1 engine. Brake Thermal Efficiency (BTE) is simply the ratio of the energy available at the crank versus the total (LHV) energy content of the fuel.

An F1 engine design has both good and bad points with regards to BTE. An F1 engine design naturally lends itself to good BTE because it is designed to operate mostly at Wide Open Throttle (WOT) conditions, which minimizes pumping losses. And also over a very narrow speed range, which means accessories and intake/exhaust tuning can be optimized for max efficiency rather than driveability. The high CR also helps produce a more efficient combustion cycle.

Unfortunately, an F1 engine is also designed for max power output. Which means that the bore/stroke dimensions are abnormally over-square. A large bore/short stroke engine naturally has high thermal losses, due to greater heat transfer with a large piston crown and combustion chamber surface area exposed to the max temp conditions at combustion TDC. A high RPM engine must also have early EOP valve timing to scavenge properly, which means less total work is extracted from the expansion of combustion gases.

I did a quick calculation, and by my math a modern F1 car uses about 5.3 lbs of fuel per minute at race speeds. At 720BHP and WOT, that would equate to a BSFC of around 0.44 lb/hp-hr, or a BTE of about 29.6% with a fuel having an LHV of 18,400 Btu/lb.

Can someone check my math?

Regards,
Terry

I'm sorry Terry, not in imperials, no way.

Anyway, if the internal friction losses of the 2.4 V8 at 18k Rpm is 55 kW, it means that ME is 90%.

If your TE of 29.6% is correct, we have a total efficiency of 26%. Not bad?

Can we have an explanation on the different interpretation of brake thermal efficiency (BTE). It is unclear to me if it includes the internal friction and ancillaries or not.

Based on definitions found on the web I think that the frictional losses up to the clutch are already considered in the BTE.

No argument there, it is indeed confusing, a 10% power-loss from friction is not xactly negligeable.

xpensive,

Brake Thermal Efficiency (BTE) takes into account all losses occurring within the engine, including accessory drive parasitic losses. The term "Brake" implies that the result is based on a power measured at the dyno "Brake". Mechanical friction losses mostly end up as heat rejected through the oil and coolant flows.

Engine performance is also commonly compared using Mean Effective Pressures (MEP), which is the equivalent mean pressure force acting on the piston throughout one cycle. Brake Mean Effective Pressure (BMEP) = Indicated Mean Effective Pressure (IMEP) - Friction Mean Effective Pressure (FMEP). These FMEP friction losses include accessory drive losses, crankcase windage losses, mechanical friction losses due to bearings, rings, pistons, valvetrain, etc., and intake/exhaust flow pumping losses.

BTE is a comparison of the engine work available at the crank versus the energy content of the fuel mass. BMEP is a comparison of the engine work available at the crank versus that being applied to the piston.

riff_raff

Thanks for that confirmation and explanation. We can safely assume that a figure of 29.3-29.6% is representative for the current V8 engines. The next generation of downsized tubo engines should improve this by 4% or more.

F1_eng wrote: I will put up a graph of FMEP for a 1600cc engine through its opperating range for some people to get some idea of frictional power losses, I won't tell you the engine.
If its straight-forward I will put it up if you want xpensive?

Hello F1 Eng,

It would be very appreciated if you put up that graph of FMEP of a 1.6lt F1 engine.
It's really relevant right now. [-o<

If it's from one of the old turbo engines, even a percentage value would be nice. Even though that is overly simplified.
Another favour you could give is if you give a power loss for each crank bearing, each piston, and each cam, oh yeah, a general pumping loss would be good.

I posted this on another thead some weeks ago, enjoy;

In a perfect world, there is never metal-to-metal contact in a piston-engine, but shearing of an ever so thin oil-film.
But that's nothing new in itself, certain roller-bearings operate with an oilfim less than one micron.

Anyway, shear-force on this film increases proportional with speed;

Force (N) = Dynamic viscosity (Ns/m^2) * Speed (m/s) * Area (m^2) / Film thickness (m)
Where; Dynamic viscosity = Kinematic viscosity (St) * Density (kg/m^3)

Xample, a 90 mm dia. piston, 30 mm long, at 20 m/s with 40 cSt and 875 kg/m^3 density lube, will generate a shear-force of 300 N if the oilfilm is 20 microns. When power is always Force times Speed, the powerloss will be 6 kW.

As piston- as well as all surface-speed will be proportional to Rpm, powerloss will be squared to Rpm.

A increase from 27 to 28, m/s or kRpm all the same, will result in an increase in friction-loss as (28/27)^2 -1 = 7.5%

First of all, hi to everybody in here as its my first post (after half a year of following this forum) ;D

I just wonder why is no one trying to use electromagnetic bearings on the engines.
It is definitively possible, even if not simple.
At Silesian University, from which i've graduaded lately, we had an opportunity to test magnetic bearing (MBC 500 http://www.launchpnt.com/magnetic-bearing/overview.html ). With manufacturers control (4 PD regulators) it can easily go with 4k rpm if my memory serves me well. We used minimal variance control on it and it was stable with 12k rpm. There was much more problems with shaft bending at such speeds, than with the bearing itself, actually. So it is useable, considering MBC 500 isn't state of the art in that matters. really...

So, question to more knowledgable and experienced members, what do U think of such option regarding sports engines?

Regards, Adam
PS sorry 4 my english, im Polish ;p