43 replies to this topic

[AdamLarnachJr]

Anyone know if any of the teams dyno test their engines with a large blower blowing air into the intake? At 200mph, I'd assume there would be about 7lbs of pressure rammed into the intake, could this increase the power?

I figure it would lead to a more accurate measurement of the vehicles actual power at certain speeds, you could perhaps accomplish this by taking a large blower and direct it toward the airbox. The only reason I thought of this, is becaus I saw the TF cars running a fuel tank vent that produces 14psi at top speed into the fuel cell so the power doesn't drop off at the end of a run.

[desmo]

Yes, in fact some of the manufacturers have built small windtunnels atop their transient dyno test beds to simulate the actual pressures and distributions of airflow into the intake trumpets. In lieu of this a less accurate alternative is simply to pressurize the airbox to values measured during track testing.

[Wolf]

But isn't this pressure increse some 4%? Why would they bother with all that for simulating measly 4%? Waste of money, if you ask me...

[MRC]

Adam, I don't quite get how you get 7psi pressure increase. Maybe 0.7psi? A 7psi increase would give you about a 1.5 pressure ratio. That's forced induction territory. Going by a simple isentropic (stagnation) pressure ratio chart, you would have to be going somewhere above, about Mach 0.75, to get that kind of pressure ratio. I did my own quick calculation, for 200mph

Delta Pressure = 1/2 (rho)*(Velocity_1 - Velocity_2)^2

Assume: Isentropic compression, V_2=0 (not correct, I know, but close enough), STP

200mph=89.41 m/s

I get a delta P of 4815 Pa. That's 0.6984 psi. So that's a 1.0475 pressure ratio (ie- a 4.75% increase). While there quite a few things not taken into account, this will get us close. So assume some fudge factor, and say 3% increase, to be a bit pessimistic. So, Wolf, your estimate seems quite good. However, I would say that these guys would sell their dear old grandmother into third world slavery for a 4% increase in pressure ratio. For 10% they'd probably be willing to start whoring out their ma. If I was in charge of dyno operations (for an F1 engine), and some underling told me that he couldn't be bothered to figure out something to simluate this, his ass would be out the door. Feel free to point out any corrections to my calculations.

[Wolf]

MRC- but how hard would it be to figure it out sans windtunnel-dyno? I don't think one would be way off mark superimposing speed related pressure increase (one could callculate flow disturbances in that pressure increase) on the real data acquired on 'normal' dyno...

[AdamLarnachJr]

Then how at 300mph are the TF cars making 14psi? It's a very small scoop as well, and I would figure you could have some sort of ram air effect. If a Camaro equipped with a hood scoop has an increase of over 15hp at a relativley low speed over the non equipped Camaro, I'm sure a "standard" dyno test of an F1 car would be less than one simulating speed. And the Camaro's gain isn't factory doubletalk, its an actual chassis dyno test where a large fan blew air at x mph at the Camaro with a hood scoop, and without it.

[desmo]

I think that likely the point of using a windtunnel to feed the airbox on the dyno is more to get a picture of the distribution of airflow into the intakes than an averaged pressure ratio. This would give insights into potential future airbox development as well as to get more optimal individual cylinder fuel mappings for the ECU.

I understand that airbox designs have been developed more by experimental trial and error than by a feeling of actually understanding the aero goings-on inside. Of course CFD simulations have been done, but the intermittant nature of the intake process as well as the resultant resonances, harmonics and standing waves all dependant on both vehicle speed and engine rpm makes modeling of the behavior of the flows within near impossible.

Don't forget as well that there is a neccessary tension between the aero boys doing the chassis trying to get the shape of the airbox optimised for external aero, and the engine crew trying to optimise there for feeding the engine. One can imagine that at times these aims run at cross purposes to each other.

As an example of how poorly understood airbox aero is here's a snippet from John Judd's Engine Developments Ltd. General Manager Stan Hall on the subject: "Even now I don't think people really understand what makes a good airbox; there are wide variations around. I know that Renault spent a vast amount of money trying to analyse the problem, but as I understand it they didn't get a good answer as to what makes a good engine airbox design.

"There are all sorts of strange things going on. It tends to be more of a problem at places where there are high speeds, such as Hockenheim. You can get a situation where on one particular lap on one particular straight, the driver shifts up normally but once he hits sixth the car just won't go on accelerating, it might even slow down. The problem doesn't occur on the next lap. The other car doesn't do it. Bring the car in and change the airbox for one nominally the same and the problem goes away...

"Inside the airbox are maybe little sharp edges here or there, or maybe it's the driver's head position on a certain lap. It is a weird thing. It is all to do with resonances and harmonics. I think it is to do with the natural frequency of the airbox itself, the pressure and volume of air inside it- all things that are very difficult to simulate."

My father, who is currently writing a book on the physics of musical sound, suggests that insights into the behavior of F1 airboxes might be gained by viewing the airbox as a 40-reeded musical instrument!

[Jezztor]

Yes, desmo is correct in everything he has said. To my understanding, because of the venturi effect (small opening, widening out into a flat wide tray), a few nodal lines, resonance / sound nodal waves (which in theory are area's where the sound waves, being in wave form, cancel eachother out where the trough of one wave fuses with the rise of another). Its funny how, even in road cars, companies like Oettinger who make airdams etc for cars, don't really know what they're doing. they think that a big inlet trumpet funneling into a small filter is the best option.

anyone got any info on teams design's & work?

jezz

[FordFan]

A couple of years ago Jaguar had that sort of problem (at Hockenheim, I think). Irvine was down a couple of horsepower on the straight from Herbert - and they couldn't for the life of them figure out why.

[DOHC]

Really interesting post desmo! And yes, there's a big difference in external fluid dynamics and internal (better known as "channel flow") fluid dynamics. This is well-known in the aerospace industry, where they usually have people who specialize in channel flow and only do air intakes on jet airplanes. Other teams do the external aero, which is often considered a lot simpler, in spite of the typically complex geometry. Surely they must have some air intake experts in the F1 industry?

[BRIAN GLOVER]

Howdy Desmo, no wonder you're so smart, Its in the genes. You have to go really fast before you can increase the pressure beyond that of ambient. Much easier to decrease it. I know Mooney aircraft with their M237P (The designation 237 came from the true airspeed in MPH at 10000' on a standard day.) The indicated airspeed was 167kts. They tried air scoops into the intake which only increased drag and did nothing for power gain. If you run a Mooney at that speed, it will over heat. (Baffling in an aircooled engine is also a vague science.)
Scoops on car hoods just look nice, but dont do anything. Compressibility factors in airplane external design only arrive at near .75 mach. WWII airplanes never had this taken into account in their airfoil design. Intake design for supersonic aircraft take compression gain(super sonic) into account to slow air to sub sonic velocities before entering the compressor, so those'Barge boards' or splitters are there for very different reasons than on a F1 car. The max speed of a F1 car is the speed that these airplanes fall out the sky, so their aerodynamic considerations are vastly different. Even Lears have Vref speeds at over 140kts at full gross.
I often wonder why they have that airbox on top at all. Surely the increase in drag offsets any power gains. When i first read about Renaults wide V, it stated that one of the main reasons was to illiminate yhe overhad airbox and to get denser air down the sidepods as the inlets were between the cams and the exhaust would be less restrictive coming out the top.
I remember the 61 Ferrari F1 (shark nose)car and the LM Ferraris of the same year had identicle engines except the LM car was detuned so as to run for 24 hours. Turns out, by having no intake scoop or airbox, and a different exhaust system, the detuned engine produced more HP. Maybe the airbox is there for traffic reasoms. I know NASCAR cars loose HP if they draught too close. The base of the windshield is the highest pressure. Educate me.

[QUOTE]Originally posted by desmo
[modeling the of the behavior of the flows within near impossible.

Don't forget as well that there is a neccessary tension between the aero boys doing the chassis trying to get the shape of the airbox optimised for external aero, and the engine crew trying to optimise there for feeding the engine. One can imagine that at times these aims run at cross purposes to each other.

[MRC]

Adam, there is just no way that anyone is getting a 14psi boost in pressure at 300mph. That's roughly Mach 0.39 @STP. So just looking up in a comp. fluid flow book (Saad), you would get a pressure that is 111% of your original pressure (if you compressed it adiabatically & reversibly). Is the 14psig after the supercharger? Maybe we are talking two different places, here.

Desmo, I imagine that the transient modeling of the airbox is much more difficult than steady state performance modeling. With a transient there are residual waves, that are harder to predict, and their timing of when they hit the valve, will depend somewhat on how fast the engine's rpm is changing. One of the other problems that I am aware of is modeling large and complex volumes like this, in engine simulation packages, like wave or gtpower. More subvolumes are required to accurately predict wave travel. Even, with more subvolumes, they don't handle spherical wave travel very well. These subvolumes don't work well with bigger volumes, thus some models are linked to a CFD package, where the CFD and engine simulation package hand off data to each other. That way the airbox can be done in CFD. This can get isanely time consuming, though. Then you have mixed gas flows, from the fuel vapor, and flows around all kinds of things, so I can see how it gets unmanageable real quick.

On a side note, the new Renault engine's airbox has a kind of ridge or hump in the middle of the bottom of the airbox. Seems like they are dealing with keeping the volume in spec along with the increase in width, maybe?

BG, I'll have to take issue with the generalization that there are no compressibilty effects below 0.75 Mach. What pressure rise (and thus performance rise) is of concern to you? Is a 1% increase in performance at 100MPH not signifigant? I'm sorry but I always hear people saying that compressibilty is not a factor under x.xx Mach or whatever. Sure, but how much is important? If the reports of an F1 engines horsepower is reasonable at 850bhp, then at 200MPH (and @850bhp), the stationary power would be around 825bhp. 25bhp more horsepower sounds worthwhile to me.

While there are likely some cylinder air balance issues to be looked into, with a pressure rise, I would still want to adjust my fuel properly, to take into the account the pressure rise. Even if there were no balance issues.

[BRIAN GLOVER]

Hello Mick, This is a much quieter place than that 'other' place isn't it?. There are a few riots taking place right now.

I think that I would be more concerned about drag than the small gains in engine power. I think the air box is there for traffic considerations IE turbulent air rather than any increase in pressure. But since it is there, they might as well experiment with it. If the air goes in thru a small hole and the airbox gets wider as it gets to the trumpets, i dont think compression is a factor in the design but rather to give better control to the active stacks to perform their optimisation of intake velocities at the valves. I also think that air density plays the biggest role in engine performance. When the density drops, so does the intake velocity at the valve and the stacks extend to the appropriate place in the airbox. Fuel is adjusted. obviously The HP difference in Malaysia and England with the potential atmospheric extremes, can be as much as 50hp. A multi valve inlet is more sensitive to atmospheric changes than a two valve set up.
How often does a F1 car get to 200mph? But the drag is significant at 100mph. Also, if a 25hp gain was achieved at 200mph, it is not sufficient to overcome the increase in drag that the airbox sticking in the wind offers at that speed.
( compression gain in the airforce refers to the transition to mach1)
The downforce variations are more drastic, but that is another story.

Originally posted by MRC
BG, I'll have to take issue with the generalization that there are no compressibilty effects below 0.75 Mach. What pressure rise (and thus performance rise) is of concern to you? Is a 1% increase in performance at 100MPH not signifigant? I'm sorry but I always hear people saying that compressibilty is not a factor under x.xx Mach or whatever. Sure, but how much is important? If the reports of an F1 engines horsepower is reasonable at 850bhp, then at 200MPH (and @850bhp), the stationary power would be around 825bhp. 25bhp more horsepower sounds worthwhile to me.

While there are likely some cylinder air balance issues to be looked into, with a pressure rise, I would still want to adjust my fuel properly, to take into the account the pressure rise. Even if there were no balance issues.

[Pioneer]

They put the air intake up there because the regs already require the rather large roll bar up there. So they're going to pay the drag penalty regardless.

[remmosffej]

In my (intro) aero text, they treat all flows less than 0.3 mach as incompressible and all above as compressible. The criterion is change in density. Less than 0.3 mach the change in density of air is less than 5%. According to my aero prof, that was a fairly standard value.

[BRIAN GLOVER]

Thanks Remmo, dont know what i was thinking. I saw .75 mach some where in a airplane magazine. Above that airfoil designs change drastically. WWII airplanes had blowers, so 'ram air' was not a factor for the engine. We are talking about speeds below 200mph and mostly in the summer.i.

Originally posted by remmosffej
In my (intro) aero text, they treat all flows less than 0.3 mach as incompressible and all above as compressible. The criterion is change in density. Less than 0.3 mach the change in density of air is less than 5%. According to my aero prof, that was a fairly standard value.

[AdamLarnachJr]

I didn't come up with the calculations, the TF aero guys did.

Why wouldn't a team simply use two air intakes located in the sidepod and use a roll hoop like those found on some LMP's? You'd get a straighter shot at the wing, less surface and frontal area, less drag, and no "packed" air that forms a barrier around the intake.

I would like to thank all of you for your comments as well, it is much appreciated.

[imaginesix]

Li'l Adam:
FIA Technical Regulations downloads


The relevant section is:
3.16 Upper bodywork :
3.16.1) With the exception of the opening described in Article 3.16.3, when viewed from the side, the car must have bodywork in the triangle formed by three lines, one vertical passing 1330mm forward of the rear wheel centre line, one horizontal 550mm above the reference plane and one diagonal which intersects the vertical at a point 940mm above the reference plane and the horizontal 330mm forward of the rear wheel centre line.
The bodywork over the whole of this area must be arranged symmetrically about the car centre line and must be at least 200mm wide when measured at any point along a second diagonal line parallel to and 200mm vertically below the first.
Furthermore, over the whole area between the two diagonal lines, the bodywork must be wider than a vertical isosceles triangle lying on a lateral plane which has a base 200mm wide lying on the second diagonal line.
3.16.2) When viewed from the side, the car must have no bodywork in the triangle formed by three lines, one vertical 330mm forward of the rear wheel centre line, one horizontal 950mm above the reference plane, and one diagonal which intersects the vertical at a point 600mm above the reference plane and the horizontal at a point 1030mm forward of the rear wheel centre line.
3.16.3) In order that a car may be lifted quickly in the event of it stopping on the circuit, the principal rollover structure must incorporate a clearly visible unobstructed opening designed to permit a strap, whose section measures 60mm x 30mm, to pass through it.

[WPT]

I think it interesting to compare the pressure rise in a ram-air (sub-sonic diffuser) at 200 mph, about 0.7 psi, to that of a super-sonic aircraft. In the Concorde the sub-sonic diffusers supply about 70% of the required thrust at cruise (the engine only supplies about 8%). This is because of the divergent nature of its' design. The Concorde cruises at about Mach 2.2.
WPT

[AdamLarnachJr]

Originally posted by imaginesix
Li'l Adam:
FIA Technical Regulations downloads


The relevant section is:
3.16 Upper bodywork :
3.16.1) With the exception of the opening described in Article 3.16.3, when viewed from the side, the car must have bodywork in the triangle formed by three lines, one vertical passing 1330mm forward of the rear wheel centre line, one horizontal 550mm above the reference plane and one diagonal which intersects the vertical at a point 940mm above the reference plane and the horizontal 330mm forward of the rear wheel centre line.
The bodywork over the whole of this area must be arranged symmetrically about the car centre line and must be at least 200mm wide when measured at any point along a second diagonal line parallel to and 200mm vertically below the first.
Furthermore, over the whole area between the two diagonal lines, the bodywork must be wider than a vertical isosceles triangle lying on a lateral plane which has a base 200mm wide lying on the second diagonal line.
3.16.2) When viewed from the side, the car must have no bodywork in the triangle formed by three lines, one vertical 330mm forward of the rear wheel centre line, one horizontal 950mm above the reference plane, and one diagonal which intersects the vertical at a point 600mm above the reference plane and the horizontal at a point 1030mm forward of the rear wheel centre line.
3.16.3) In order that a car may be lifted quickly in the event of it stopping on the circuit, the principal rollover structure must incorporate a clearly visible unobstructed opening designed to permit a strap, whose section measures 60mm x 30mm, to pass through it.

Yes, I have a binder filled with the 2001 Tech Regs and Illustrations. Is 3.16.1-2 the literature you are refering to preventing this? I don't see anything in the regs preventing the structure from being a hoop, what I mean precisely is a roll over hoop like a Champ car, what exact part of the regulations prohibits a rollover hoop like this?

[imaginesix]

Originally posted by AdamLarnachJr
Yes, I have a binder filled with the 2001 Tech Regs and Illustrations. Is 3.16.1-2 the literature you are refering to preventing this? I don't see anything in the regs preventing the structure from being a hoop, what I mean precisely is a roll over hoop like a Champ car, what exact part of the regulations prohibits a rollover hoop like this?

The regulation that prevents the Champcar rollover hoop look is 3.16.1. "...when viewed from the side, the car must have bodywork in the triangle formed by three lines...".
I call it the 'billboard rule'.;)

[AdamLarnachJr]

Oh duh

Thanks for clearing that up.

Thats a stupid rule btw, very freaking stupid, "billboard" rule is right

[Ursus]

Weren't teams required to cut an opening in the rear of the airbox in an effort to limit hp after Sennas death? Anyone remember if it had any effect?

AS for the 'billboard' reg. From what I can make of it, it should be easy to make low drag solution if one really didn't think the airbox offered any advantage.

[Ben]

They did, but when taken to the limit of it's letter you had the McLaren MP4-10 and the Benetton B195 that really lost nothing from it. I can't believe anyone bought the idea that the midwing was for useful downforce - try a big high pressure area to prevent airbox leakage.

The rule was recinded mid 95 I think.

Ben

[imaginesix]

Originally posted by Ursus
AS for the 'billboard' reg. From what I can make of it, it should be easy to make low drag solution if one really didn't think the airbox offered any advantage.

I agree.

The regulations specifying an airbox as currently seen aren't 'airtight' (pun intended). There is some scope for running an intake elsewhere, without incurring the drag penalty of the 'billboard' area.

My theory as to why such an intake has not been developed is simply that the FIA would ban it before it had a chance to race. The 'intent' of the rule is pretty obvious, and any divergence from the standard interpretaion would make for a strange-looking car with a big performance advantage. The FIA isn't into 'strange' or 'performance'.

[Pioneer]

I dunno... I mean... that are is big viewed from the side, but thats not what counts. Looking at it from the front, consider the area covered by the drivers helmet combined with the necessary roll bar is not much smaller than the whole box.

I don't think it would make much of a difference really.

[AdamLarnachJr]

It does hoever have a relatively large increase in surface area over a standard roll hoop, but I like the idea of having a non airtight box so any air that builds up and forms a sort of boundary around the intake hole, would "simply" be exhausted through crevices or some other device.

[moog101]

The ram air issue..

A Yamaha R6 makes 108 bhp at the crank static, but at a given speed can make up to 120 bhp. This is purely thanks to the ram air intake in the nose of the bike pressurising the air box, and 12 bhp is not a bad increase for free..

[AdamLarnachJr]

Hate to beat a dead horse but the turbocharged R8 picks up a little over 15hp at 150mph.

[MRC]

I've heard the 108/120 bhp thing from Yamaha on the R6, too. However I still think it is a bunch of BS.

[DOHC]

Thought I'd kick this thread alive again.

About the ram air issue, I think that it's clear from calculations above that isentropic compression does not make for a very large effect. However, an effect that hasn't been discussed is the air flow resistance of the intake trumpets and channels. The faster the engine revs, the higher is the gas velocity, and flow resistance increases.

The work needed to suck air into the cylinders is tapped from the engine output. But with a ram air intake, the small pressure increase and freely available ram air velocity means the engine has to generate less of the necessary intake manifold velocity. So the power loss caused by the intake stroke is reduced.

The theory, or rather thought, as I have no expertise in this area, is that the increased engine power output is due to a reduced flow resistance and not to a "supercharging effect" due to the somewhat higher air pressure.

My guess is also that if an engine is equipped with a supercharger or turbocharger, then a significant part of the increased power comes from reducing (or even eliminating) power loss during the intake stroke -- it's the blower that takes care of putting the gas in the cylinders, not the pistons. The other part, of course, is that the total charge can be increased.

Any comments?

[12.9:1]

Good observation DOHC !
The CART 2.65L V8, is trbo-boosted only .151bar - 2.195psi over atmospheric !
As the engineers continue to find more and more hp, the regulators continue to turn down the boost, despite all this the 2.65L produces over 800hp!

.

[AdamLarnachJr]

Speaking of CART, a new engine formula will be announced soon, hopefully this may keep CART alive through next season, if not they are going to die out very soon:(

[MRC]

DOHC, I would have to agree with you that there is likely more to ram air effects, than merely the pressure rise. I think it has more to do with losses at the inlet than friction reduction later on down the pipe. High velocity will give rise to boundary layer losses. Whenever you increase the density of a fluid you are going to decrease the work required to raise the pressure. This will account for a small amount of any pressure rise gain. I think the main benefit to ram air is a reduction in pressure recovery time, ie- better throttle response.

Even in a naturally aspirated engine, the pistons do not bring in the air into the cylinders. May seem like semantics, but the difference in pressure brings the air into the cylinders. Many people have the opinion on pressure charged engines, that they don't have to worry much about pressure losses in the intake path. This is not a good approach or attitude for obtaining maximum power. Both a pressure charged engine and a naturally aspirated one are relying on a pressure gradient to fill the cylinders. What is nice about pressure charging is that you can do some of the compression then after cooling then do the rest of the compression work in the cylinder. The aftercooling not only drops air temperature (ie - likelyhood of knock), but also reduces total compression work.


I still think 120 bhp for the R6 is a bunch of crap.

[DOHC]

Originally posted by MRC
Even in a naturally aspirated engine, the pistons do not bring in the air into the cylinders. May seem like semantics, but the difference in pressure brings the air into the cylinders. Many people have the opinion on pressure charged engines, that they don't have to worry much about pressure losses in the intake path.

MRC, I find your points very interesting but have some minor problems with the quote above.

I think it's clearly the pistons in a naturally aspirated (NA) engine that bring the air into the cylinders. First, you're of course right that without a pressure gradient, there wouldn't be any flow at all. But my point is that this pressure gradient is in the NA engine created solely by pulling the piston down during the intake stroke. The required energy is taken directly from from the crank. (And then indirectly from other cylinder's combustion stroke, and/or from the flywheel.) In addition, the faster the engine revs, the greater is the flow resistance in the intake path. The resistance and work needed to bring the air into the cylinder presents a load on the available power at the crankshaft.

For a supercharged engine with a high enough boost pressure, this is not so, the pressure gradient is then created by the blower. Likewise, any ram device is going to supply a little bit of the pressure gradient, and also a good amount of gas velocity. This implies that the pistons during the intake stroke will present a smaller load, or none at all, on the crank, thereby reducing internal losses in the engine.

You are of course right that in the supercharged engine you have additional benefits, such as to have an increased charge, a pre-compression that again reduces the load on the crank presented by the compression stroke, and then an intercooler will both increase density and efficiency.

[MRC]

The power to drive a blower or a turbo is not free, if that is what you are implying. If you want to say that the pistons have to deal with the pumping losses created by drawing in the charge that's fine. Where does that power loss get transmitted to? The crank. A blower absorbs horsepower to do pumping work. This pumping work is related by it's volumetric flow and pressure rise. The pistons still do some pumping work, even with a blower. There is never a case where there will be no piston pumping work. With a turbo, the work is done at the expense of backpressure. A turbo is not free power, as almost everyone touts it to be. Watson's book does a good job of delving into this.


My main point here is that one has to be very careful to make comparions between pressure charged and naturally aspirated engine. Flow losses through duct work are not going to be much lower in a NA setup vs a pressure charged one, given the same duct work. Total pumping losses (on a percentage basis) will likely be lower, however. From what you were saying, I'm getting the jist that you were thinking that there might be lower flow losses with the pressure charged setup. The flow losses will not really be any lower. The velocity of the air is mostly dictated by the demands of the engine rather than the pressure charging device. The pressure charging device really is using work to raise the pressure.

My other point is that attention must be paid to all the intake and exhaust parameters that were deemed inportant design decisions with a naturally aspirated engine, as pressure charged engines. Many times I have seen modified engines to run some pressure device where no thought was given to runner length, for example. Just becuase something is pressure charged doesn't mean everything else can be disregarded.

[Wolf]

OK, seeing some new faces since I posted Intake Scoops...Crazy Idea Alert Thread, I thought to post the link... I'm fairly sure it could work at lower speeds.

[DOHC]

Originally posted by MRC
The power to drive a blower or a turbo is not free, if that is what you are implying.

Of course not, that is all very clear, the engine "produces" the power to drive the supercharger or turbocharger. What is free, however, is the ram effect (small). As for the turbocharger, I suppose you could say that a certain amount comes "for free," since the turbine recovers some energy that would otherwise be lost in the exhaust.

A little bit aside, think of a gas turbine (let's say a turbojet engine). The turbine saps some energy to drive the compressor. Remove the turbine (and hence the compressor) and that engine becomes pretty lame -- a ramjet, which won't be very good unless the speed and ram effect really produces compression. But then we essentially have to be in the transsonic to supersonic regime. For lower speeds, there's a huge payoff in tapping exhaust energy with a turbine, and feeding it back to a compressor. If I understand the idea behind blown piston engines, the same conditions apply there (although in piston engined airplanes you also need a compressor to compensate for low air density/pressure at altitude).

Originally posted by MRC
From what you were saying, I'm getting the jist that you were thinking that there might be lower flow losses with the pressure charged setup. The flow losses will not really be any lower.

Yes, that was my thought. I'm aware that the flow losses in the intake pipes will be pretty much the same, but there is also a loss in creating the pressure gradient. Doesn't it make a difference whether these losses will be covered by the piston, or by the blower? In an NA engine, it's the pistons, although ram effect my cover some of those losses. (Unlike in the ramjet, in an ICE the ram effect doesn't have to provide any compression, flow is enough.)

So in the NA engine, the piston has to be pulled down to generate the pressure gradient, and take the necessary force and energy from the crank. The force isn't that small. Suppose piston area is 40 cm^2, and you need to maintain a 0.2 bar pressure difference, then that equates to an 80 N force. Assume you have to move that piston 25 m/s; then we need to tap 2 kW power, or roughly 3 hp, for that single cylinder's intake stroke. (These figures aren't actual data, they're just guesstimates; I took the figure 0.2 bar because if you'd be down to 0.1 bar it's really hopeless to create a 100 m/s gas transport in the intake pipes.)

But if it's a turbocharged engine, the high pressure boost is generated by tapping exhaust energy that would not have done mechanical work on the crank. (Thermal losses alone are about twice as large as mechanical work on the crank!) And because the hot high pressure exhausts still expand down the exhaust manifold on the way to the turbine, this energy comes if not for free at least at a very low cost -- the back pressure increase implies that the pistons may have to help pushing out the exhausts a little bit, but I think it will cause a very marginal loss of power.

What I don't quite understand is the statement that there are no cases without piston pumping work. There are, of course, although I'm not sure if this is of any relevance to ICEs in general and high revving ones in particular. The case I'm thinking of is piston steam engines. There, high pressure steam pushes the pistons. Why exactly wouldn't the blower provide a pushing effect if you can build a really high boost pressure, say 2 - 5 bar? A pushing effect would more than eliminate piston pump work losses.

Ok, this has been a little bit aside from the ram effect, but I think one can suspect from physiscs alone that the ram effect can help reduce flow losses in the intake, losses that certainly cost a good number of hp.

Again, I'd like to emphasize that all I'm using here is physics, I'm not an ICE expert, so take it with a pinch of salt, read it critically, and correct me where I'm wrong.

[Billy Gunn]

Hi All,

Airbox design is critical to the F1 engine. I'm sure a lot of time is spent with internal splitters and such to get cylinder by cylinder distribution as even as possible. There is also an air filter in there as well! (an ingested stone is terminal for the engine ~ and with all those gravel traps.......) But the one thing all these posts have forgotten is that engine crankcase venting has to be discharged into the airbox!!! Now think that one through! And further you just might want to get some cooling air to the ignition driver / hydraulics / actuator manifold.....?

Just noticed the Monaco close -ups ..... whats that on the back of the air box for the Arrows???????

Billy G

hangyerganzieontneckiesneck

[desmo]

While I am not sure exactly how the plumbing for the venting of the compartmentalized crankcase chambers is arranged, I've often thought that a pulsed pressure output (or outputs) phased with the crank's rotation into the airbox might be of potential use in some fashion.

The Arrows photo with the aluminum-looking valve body or junction block feeding into the rear of the airbox, does raise some interesting questions. Some of the vent hoses one sees in photos terminating in the airbox look to be of a pretty large diameter. As if quite a lot of air might be moving through them at times.

Also, although I can't post them here or share them, I've seen some interesting shots of the Cossie Arrows is running and the heads look very strange, almost as if there is only enough metal in them to support a single cam per bank. The photos don't show the timing drive end though, so it is really hard to say.

[H. Eckener]

DOHC,

I think the performance gain you are touting do to a reduction in pumping work because super/turbocharging is some what offset by the need to throttle an SI engine. If you get the air in there to push the piston down you are going to have to do something with it. A CI engine is fairly tolerant of excess air and you can use fuel to throttle an CI (some don't use butterfly valves) engine to a certain extent, but I can't think of any example where an SI engine used fuel control to throttle an engine as the main instrument of load control. Hell a diesel never really run rich, most are lucky if they get to stoic. SI's just don't like excess air.

You've got the air in there now what do you do? You can't open the intake valve longer to pump it back out and you can't add any fuel through the valve either, so you just have to open the exhuast valve with some VVT and pump it out.
Now you add DI, you can add fuel and ignite that off late or open the exhuast valve early to reduce power, although combustion in the manifold may keep the turbo spooled up and exhuast valve metalurgists probably won't like you too much.
Now add DI and some crazy EVA lsolenoid or ultra crazy camshaft VVT lobes and you can let lots of air into a cylinder then open the exhuast valve early around BDC, then close it, add fuel, ignite as usual, then open the exhuast valve again in the usual manner. No need for an AIR pump.

A wastegate or boost valve would be indirect examples of engine throttles.

[just me again]

I have just looked trough Autosports Le Mans suplement, and it look like all turbocars have some sort of airbox before the air restrictors ( small or big ), but nearly all NA engines have the air restrictors before the airbox.
I don´t know what it means, but i think it is an interresting difference.
Bjørn

[AdamLarnachJr]

Yes thats a good point. Most if not all of the LMP turbo cars run a reverse Ferrari'ish exhaust intake to the turbo then spit the forced air into the restrictors and finally the airbox. Or, actually I think the turbo's may have the restrictors mounted on them but Im too lazy to go through my ACO regulations to find out for sure:)

All of the GT/GTS cars run a similiar method before the restrictor whereas most of the NA LMP's dont. I have a few pictures of them at the following URL.

http://home.off-road...ajlarnach/ALMS/

[AdamLarnachJr]

This is an image of the MG Lola's insides, notice the intake structure before the turbocharger.


This is an image of the Panoz/Mugen, notice the two K&N air filters that lead into a "coveted" airbox, I have no idea where the restrictors are located in that airbox. The intake in the bodywork is a small NACA duct.