Air box design

[Flatjack]

Simple Question

What are the considerations with the design of the airbox related to getting maximum power? This does not have to realte to F1 cars

Hope you can halp

[pabs]

In general terms, any time you have an air breathing engine, you want to get an optimum amount and quality of air to mix with the fuel during the combustion process. It is, therefore, the function of the air box to provide the air needed for the combustion. Some factors that affect your design are how "clean" is the airflow, what is your required mass flow rate, what is your required pressure, etc. All these factors will affect the shape, location, and maybe even materials that you use to build your airbox. But always, what you are looking for is to get the right mixture of air and fuel to drive the combustion.

[woodyracing]

you also want to keep the air as cool as possible too
( see "rookie question" thread http://tentenths.com/forum/showthrea...threadid=17211 )

[UnclePeto]

Why is there 'cleanliness' of the air important? I assume your talking about the flow of the air and not actually literally how clean the air is! why does that effect performance??

[woodyracing]

im not sure how cleanliness of air affects performance, but you want the air as clean as possible, so that dirt doesn't build up in the throttle bodies or whatever (i was told that this increases ware on some of the internal components).

[pabs]

Well, I didn't mean literally that the air needs to be clean in term of physical impurities, although now that we talk about it, woodyracing is right. In terms of physical impurities, you don't want a whole lot of dirt cloggin up anything as this tends to increase the losses of the system. What I meant in terms of "clean air" was more in terms of how homogeneous your flow is. For example usually you don't want turbulent air as it tends to be rather messy, so part of the function of the air box is to straighten out the flow. This is also why the air box and in general anything that needs air flow (for say cooling purposes) is located somewhere where they can get "clean" air. This tends to increase the efficiency of the combustion, cooling, etc.

[pabs]

As to why this affects effiency, well think about it this way:
Turbulent flow is in general very messy right? This means there are swirls and eddies and what have you present in the flow. So imagine this, your No. 1 cylinder happens to get its air from a region of the flow that had high concentrations of fluid while your No. 2 cylinder gets it from a region of the flow that was very thin. Your fuel-to-air ratio in each case will be different and will have different power outputs. Neither case will be optimal and your overall efficiency will be lower. As a general rule, you always want laminar, "clean" flow. I can show you some instances in aerodynamics where turbulent flow is preferred, but they are rather few and do not apply to what we are talking about. As always, these are just my general comments, based on what I have learned and studied. I am not an expert in combustion so if anyone has a different idea, I always enjoy learning from those who do know what they are talking about.

[racealign]

one of the guys in under 2 litre sports sedans used to pack ice around the air box and around the ducting. He found that in an 8 lap race the power was dropping by 20odd horsepower by about lap 5 due to the under bonnet temperature build up. He tried other ways to get air out of the engine bays....but the ice keep it going for the whole race...worked really well.

[pabs]

Right...as someone explained, cold air is more dense so you get more air in there. As an example, if you know someone who flies airplanes, asked them about temperature/altitude restrictions. If the temperature is too high (air less dense) the engines do not produce as much power. The best place to fly in that regard is Alaska...cold and at sea level. That is also the reason that your car will run better at say Miami (low altitude) than Denver (mile high city). MORE AIR I TELL YA!!!!

[KC]

Using dry ice in the air cleaner can or airbox of sportsman drag racers is a common practice. Cold air is dense and requires less time to get more into the engine and creates more power.

I would imagine that aero effeciency, intake pressure, intake and intake turbulence all are critical to the designer. The airbox must draw in air without increasing drag and reducing rear downforce. It must maintain proper air feed to the engine from 30 mph to 215 mph. I would imagine that the shape and size of the opening and the shape of the airbox is one of the most explored sections of the monocoque. I would also hazard to guess that the airbox design also works as a pressure drop just after the opening to draw in more air and cool it to produce more power as well.

[UnclePeto]

So lets say if u stuck a 'freezer' on the air ontake into a normal car ur gonna get better performance....mmm let me think???

[pabs]

Well, by "freezer" I assume you mean some way of cooling the flow a lot. In general terms, and assuming you have no pressure losses, then you are right. Bear in mind that when we say cool air, we are referring at the change in density with temperature. Air, like most fluids, decreases volume as it is cooled, thus increasing density; by contrast water increases volume as it changes from liquid to solid phase. Then, consider that mass flow rate varies with density as well as velocity of the flow and cross-sectional area. Then, for a given velocity and area, increased density will give you a higher mass flow rate, provided you enough pressure to push the fluid. So if you have your fuel-to-air mixture right, you will get improved performance. Your fuel comsumption might also increase, but that's a different issue. Again, if anyone has a different opinion, please post it so we all can learn a bit more.

[woodyracing]

what about cars without air boxes?

I removed my air box and fitted a PiperCross free flow induction (cone shaped) filter. These are unrestictive and allow the air intake to suck up much more air, and the shape is designed to have a large surface area and promote, even increase air flow speed.
The problem with these type though, is that they suck up the hot heat from the engine bay. This can partly be fixed by adding an air induction pipe (like a brake duct) from the front of the car.
I had an idea to make an air box, covered in heat shield material, and have a cold air induction pipe which would feed my cone filter with cold air, and keep the air cool in the air box.
Seems K&N are addressing the heat problem in their new 57i kits, with a plastic heat shield - i think a fully covered box with intake tube would have been better.

anyway these are more design ideas.

[Dino IV]

Those are common problems, woodyracing. Mostly people try to seperate there filter with sheet metal, which probably is the best way to go.

A seperate water\air cooler system would be interesting as well, only the additional pump needs to be judged on power consumption. Using the normal cooling system is of no use as the temperature difference is of no use, as it only works when the intake air is really hot, like when turbocharged.

In F1 however fairly reasonable amounts of pressurizing is realised with the airboxes. Because of the much larger variety in circumstances, such a design on roadcars could prove of little use, but perhaps a swicthable or adaptable system would be of some attraction. If the designs would keep up.