Eliminating the Throttle Using a Bleed Off Valve

[jeff88]

Was thinking, would it be possible to eliminate the throttle plate if the air intake had some sort of bleed off valve similar to a turbo or an adjustable pressure regulator? My original thought would be that as you step on the gas, less and less air gets bled off. By doing this, it would be as if you are at WOT at all times, but the "extra" air is released to atmosphere (or wherever), eliminating the need for the throttle, so the engine has one less thing to work against.

I'm thinking something like this transducer. It takes a signal input from 4-20 mA and provides an output of varying PSI of air. You could attach some sort of signal inducer to the accelerator pedal sensor which would put out the appropriate signal to the transducer which will allow the proper amount of air into the intake.

The other option would be a Variable Bleed Valve, which apparently is a popular part in the aerospace world. It would allow the necessary amount of air to be bled off, while limiting the restriction on airflow into the intake. This option would be different, because it would use all of the air coming in and divert it to the appropriate place, whereas the transducer would only put out the amount of air needed.

Would either of these work and if they did, would it improve efficiency at all? Would it require a turbo/super to pre-charge the air, or could it work at atmospheric pressure?

I attached a quick Paint sketch of the transducer option, because I am a visual person and to give everybody an idea of what I am thinking. I assume the VBV option would have a similar setup.

FYI, the links I included is just an idea of what I'm thinking about, not the ones I would use, unless it made sense.

[H-Man]

If you had this on forced induction, this would cost you efficiency. It wouldn't throttle with natural aspiration.

[Occasionally6]

To reduce the power output (at any given engine speed) from the maximum possible, you still have to be able to trap a reduced mass of air in the cylinder.

That is the purpose of throttling; it reduces P in P.V = m.R.T in the cylinder. When the P of the air that fills the cylinder is reduced, the equation balances by reducing m on the other side (T ~constant).

The inlet manifold is merely a reservoir of low pressure air from which the engine can draw. The throttle is the means used to maintain the desired pressure in that reservoir of air.

It is a variable sized orifice which allows just enough air to pass through it to match what is being drawn out of the reservoir by the engine. It's not possible to allow air into the reservoir at a higher rate without also increasing the air pressure in the reservoir.

The pumping work that costs fuel economy is due to the pressure difference between that within and that outside the cylinder.

If you don't (want to) reduce P in the cylinder, in order to reduce m and regulate power output you have to do something else; either reduce V or increase T. (Lets leave out combinations of all three).

Increasing T of the air in the cylinder, with the same pressure on each side of the piston, might work if it didn't causes issues with engine knock.

Reducing the V of the air in the cylinder is possible by varying the valve timing. Ideally you would shut the inlet valve immediately after the desired mass (volume) of air had entered the cylinder. There wouldn't have to be any work done until after the inlet valve shut. After that point the work done is recovered on the compression stroke, following the exactly the same line on a PV diagram as it does when throttled.

[jeff88]

OK, I was with you and then you lost me and then I was with you and then you lost me, I think I got the idea after a few reads (and a break between )...

Just to clarify: P.V = m.R.T where P=Pressure, V=Volume, m=mass, R=some constant, T=Temp. ???

I understand trapping a reduced amount of air in-cylinder, but why would my idea be any different in metering the amount of air into it, or the pressure into the manifold? My idea is to have a high(ish) pressure amount of air and only put in the right amount of low(ish) pressure into the manifold, bleeding off the rest.

You say you can't allow air into the reservoir at a higher rate without also increasing the air pressure and I get that, makes sense. If, by not using a throttle, the rate of air in is higher, then by using a bleed off valve, the pressure will be less than what the pressure would be in a throttled engine. Basically, increase speed and decrease pressure, thus equalizing the equation.

I assume, regarding your last paragraph, reducing the V into the cylinder would be similar to the way Toyota's Valvematic system works?

[Thenorm]

you wont be able to get less than atmospheric pressure in the intake unless you throttle it. a bleed valve or anything else wont work because there is no driving force to push the air out (no delta pressure). if you were turbo, the air would only bleed down to atmospheric.

[mort]

Originally Posted by jeff88

You say you can't allow air into the reservoir at a higher rate without also increasing the air pressure and I get that, makes sense. If, by not using a throttle, the rate of air in is higher, then by using a bleed off valve, the pressure will be less than what the pressure would be in a throttled engine. Basically, increase speed and decrease pressure, thus equalizing the equation.

Hi Jeff,
I'll take a stab... In this paragraph you suggest to bleed off the extra pressure, well I ask where are you bleeding it to? The pressure in the intake manifold is at best atmospheric. So you'd need to not just bleed it off, but actually suck it out and presumably throw it away, and also throw away the power used to do the sucking.
Throttling wastes power. In another thread I showed the formula to find the throttling power, it's never more than 5% of output power - maybe not really enough to get too worried about.
-mort

[jeff88]

Originally Posted by Thenorm

you wont be able to get less than atmospheric pressure in the intake unless you throttle it. a bleed valve or anything else wont work because there is no driving force to push the air out (no delta pressure). if you were turbo, the air would only bleed down to atmospheric.

I see what you're saying. I forgot to realize that at best, any bleed off will result in an equalization of pressures, i.e. atmospheric pressure, at best. No way to go lower than atm unless I somehow pulled the air out (assume a vacuum). It's basically like a balloon. It will expel air or helium out until the pressure of the inside and outside equalize. I imagine having a vacuum would be just as inefficient as a throttle (in the form of using electricity off the alternator or some device off of the drive belt, or something), so the improvement would be nullified.

Originally Posted by mort

I showed the formula to find the throttling power, it's never more than 5% of output power - maybe not really enough to get too worried about.
-mort

I think my response above applies to what you said. I tried to read your post, but will have to again after a good night's sleep. I would say that members here would gladly accept a 5% increase in power/efficiency. I know that's optimistic, but for my 30ish MPG car, that is 1.5MPG. I would take that!

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So a bleed valve won't work, but what about a device like the transducer in the first post, which is designed to only put out the appropriate amount of air, no more and no less. If the engine requires less than atmospheric pressure, than the transducer will be able to supply it. If it needs more, than it will supply that instead. Looking at the zero-based range transducer, the supply pressure needs to be at least 5PSI more than output (I assume for losses). If a turbo supplied all the air above atmosphere, than this could be relatively efficient (it uses milli-Amps). Less than atmospheric pressure and it can use "regular" air or turbo compressed air if the turbo is spooling.

This is just an idea, keep shooting me down if I'm wrong or forgot an important piece! I'm a little slow sometimes!

[mort]

Originally Posted by jeff88

I would say that members here would gladly accept a 5% increase in power/efficiency
...
So a bleed valve won't work, but what about a device like the transducer in the first post, which is designed to only put out the appropriate amount of air, no more and no less.

Hi Jeff,
I'll take any 5% improvements I can get.
Here is the cut away view of your transducer. That part: Supply Valve (at the bottom) is a throttle.

This is a miniature version with 1/4 inch air flow fittings, rated at something like 4.5 scfm at 25 psig. You might look into how much air an engine sucks in at cruise.
-mort

[Tesla]

Think you are missing the point of how gas engines operate, 90% of the time the intake manifold is at negative pressure, that's the nature of the beast, so there is nothing to bleed off and engine already controls how much fuel and air goes in, so any other restriction further back just results in the same outcome.

Pumping losses are a misnomer, the greatest loss is in the Induction stroke, so they should really be called sucking losses and this is the main reason why diesels are more efficient as they are designed to run with excess air, hence do not have a throttle, so minimal sucking losses.

[Thenorm]

Originally Posted by jeff88

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So a bleed valve won't work, but what about a device like the transducer in the first post, which is designed to only put out the appropriate amount of air, no more and no less. If the engine requires less than atmospheric pressure, than the transducer will be able to supply it. If it needs more, than it will supply that instead. Looking at the zero-based range transducer, the supply pressure needs to be at least 5PSI more than output (I assume for losses). If a turbo supplied all the air above atmosphere, than this could be relatively efficient (it uses milli-Amps). Less than atmospheric pressure and it can use "regular" air or turbo compressed air if the turbo is spooling.

This is just an idea, keep shooting me down if I'm wrong or forgot an important piece! I'm a little slow sometimes!

your transducer or any other device still wouldnt work. I'll lay out my assumptions clearly so this doesnt look like a wall of text.

-The cylinder on the intake stroke always moves a set distance and has a set volume, regardless of intake pressure.
-if you had a device to limit the amount of air particles entering the engine, lets say 50% of the particles. they would still occupy 100% of the volume in the cylinder, but now would be at half the pressure as governed by the equation PV=nRT . ie if n is 1/2 then P must be 1/2 to balance (all other factors stay same).
-lets also assume that the cylinder didn't fire and the air just went for a ride through the compression and power stroke. it would still be at half pressure when it comes time to the exhaust stroke, to get the air out of the cylinder, you would have to compress it back up from half pressure to atmospheric pressure to expell it into the exhaust, so it has the same pumping losses as if you had a throttle.

anyways, always keep thinking and generating ideas, even if they don;t work out, it is important to keep learning, which is my favourite thing in the world