Vacuum free 4-cycle?
Vacuum free 4-cycle?
(OP)
Does anybody here know if someone is working on an engine that has no manifold vacuum?
I have a few things i've gome up with that involve an IC engine with no manifold or chamber vacuum at part throttle. The engine basicly purges the charge from the cylinder again into the intake manifold(against a reed valve to create a bit of pressure to force exhaust out on overlap) until it reaches your 'throttle' point. My way of doing it is infinately variable and completely mechanical and to help with this I've developed a completely mechanical way to have variable compression ranging say from 8-12:1 and also thought of a low pressure direct injection system for it. I plan on building this for a Toyota 5M-GE I6 engine starting in a couple weeks.
I was just wondering what you guys thought about efficiency increases and if anyone is working on this kind of stuff. Sadly...I'm only 22 so most people don't take me seriously. Just wondering what you guy thought.
I have a few things i've gome up with that involve an IC engine with no manifold or chamber vacuum at part throttle. The engine basicly purges the charge from the cylinder again into the intake manifold(against a reed valve to create a bit of pressure to force exhaust out on overlap) until it reaches your 'throttle' point. My way of doing it is infinately variable and completely mechanical and to help with this I've developed a completely mechanical way to have variable compression ranging say from 8-12:1 and also thought of a low pressure direct injection system for it. I plan on building this for a Toyota 5M-GE I6 engine starting in a couple weeks.
I was just wondering what you guys thought about efficiency increases and if anyone is working on this kind of stuff. Sadly...I'm only 22 so most people don't take me seriously. Just wondering what you guy thought.





RE: Vacuum free 4-cycle?
No manifold vacuum? So what makes fresh air want to rush into the cylinder?
RE: Vacuum free 4-cycle?
BMW's Valvetronic system operates not entirely unlike what you are describing, except that they are shortening intake lift and duration at part load so that the air never goes into the cylinder in the first place, rather than sucking it in and then pushing it out again. It normally operates unthrottled (i.e. no significant intake vacuum), although there is a throttle only used as an emergency back-up in case the Valvetronic system fails.
Honda's upcoming A-VTEC system will also operate conceptually like this, albeit with a different mechanical arrangement.
These systems are reported to improve part-load fuel consumption about 10 - 15 percent.
Variable compression ratio is ordinarily extremely difficult to do in a way that doesn't create more problems than it solves (generally it screws up the shape of the combustion chamber when it is in low-compression mode) but if you have found some way around that, go nuts with it.
Direct injection systems ordinarily need to operate at a rather *high* pressure in order to get adequate atomization of the fuel. Gasoline-direct-injection systems use a higher pressure than normal outside-the-cylinder systems, but lower than common-rail diesel injection systems.
RE: Vacuum free 4-cycle?
I think the OP is talking about no change in restriction to airflow into the cylinder at all.
It is not clear to me how power delivery will be controlled.
There will of course be some vacuum at times as the system will not be 100% VE at all times.
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RE: Vacuum free 4-cycle?
These guys have been working on igniting lean mixtures for 30 years, and report they are now up (down) to 30-1 ratios.
http://www.leanburnignition.com/
RE: Vacuum free 4-cycle?
So instead of working against a strong vacuum at idle it pulls a full charge then purges most of it again til it gets to the 'displacement' it needs. It should not only save fuel but smooth out idle greatly on smaller 4 cylinder engines.
RE: Vacuum free 4-cycle?
Varying engine breathing with valve timing is not new. Using reed valves on 4-strokes is not new. So, what's new?
RE: Vacuum free 4-cycle?
Yes it is doable, no it is not practical yet.
RE: Vacuum free 4-cycle?
Hydrae
RE: Vacuum free 4-cycle?
Both over-expanded engines have idle speeds of around the same as that used in Otto engines of the same capacity.
Cheers
Greg Locock
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RE: Vacuum free 4-cycle?
And like also mentioned there is always going to be a vaccum, as long as you have a piston in a cylinder drawing in the air. Then add an airfilter etc. Of course unless you are boosting with positive inlet pressure.
RE: Vacuum free 4-cycle?
RE: Vacuum free 4-cycle?
I think I read something on some really early gas burning engines that did just that, I think they had separate valves for the air and gas. They used valve gear something like the Corliss steam engines and avoided the throttle loss in the same way as the Corliss, it takes work to push/pull a gas thru a restricted opening.
Of coarse at 50 RPM a short valve open close event is not all that short compared to what you need at 5000 RPM.
RE: Vacuum free 4-cycle?
RE: Vacuum free 4-cycle?
RE: Vacuum free 4-cycle?
Nowadays some truck calibrations use tricky fuel cutoff or decel fuel and throttle to enhance engine braking while keeping the cat lit but thats another story...
RE: Vacuum free 4-cycle?
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RE: Vacuum free 4-cycle?
Cheers
Greg Locock
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RE: Vacuum free 4-cycle?
Besides weight reduction possibly another reason why turbocharged engines are becoming increasingly popular.
Then again Toyota does use the atkinson/miller cycle engine on its Hybrids - so there's some benefit to it.
One could question why there is currently no miller cycle engine or very few engines with compressors on the market?
(I guess a turbo is small, few moving parts uses an inherently efficient compressor, where its rpm is not fixed to the rpm of the engine its actually not that surprising even considering its lag).
Regarding Diesel: Keep in mind Diesel-fuel is also 15% more dense than gasoline (also adding to the fuel economy of a diesel engine - a factor often forgotten when a Hybrid is compared to a Diesel).
Back to the topic, to what level does EGR and valve overlap reduce pumping losses on a modern engine?
RE: Vacuum free 4-cycle?
Have to agree with hemi on this one.
As mentioned before...block a fan or vacuum cleaner, and hear it immediatley speed up.
RE: Vacuum free 4-cycle?
From our testing the pumping losses from the engine taking in and expelling to 50% charge was less than the losses required to pull against a vacuum for an entire intake stroke and 'spring' back to full atmospheric at 90deg BTDC on the compression stroke (like where we closed the valve fully) before it started compressing the charge. In addition to that, when we added the reed valve in the intake for the engine to partially pump against it created a pressure on the back of the intake valve that worked great to expell any extra combustion gasses out the exhaust valve durring overlap which increased our part-throttle torque numbers alot. The reed valve's benefit, however, is only seen at mid/low rpm part-throttle engine use.
Two engines compared at full throttle there was a bit less power output on the engine with the new valvetrain but the losses are on par with the fact it's running an extra cam with extra valvespring.
RE: Vacuum free 4-cycle?
EGR, whether via external valve or internal, helps reduce pumping losses, reduces peak cylinder temps for Nox control, Helps increase available charge motion in cylinder and in the case of some higher compression engines helps reduce octane requirements.
RE: Vacuum free 4-cycle?
Fabrico, no offense, but you can't compare a centrifugal pump (vacuum cleaner) with a piston pump.
A piston driven vacuum cleaner would slow done and not speed up since it has to work against atmospheric pressure and a centrifugal pump simply has to move less air molecules.
RE: Vacuum free 4-cycle?
What you seem to be doing is trying to apply the Atkinson cycle technique to an engine with less than 4 cylinders or multiples thereof.
With a 4 cylinder engine when you have one piston on a compression stroke and with the intake valve remaining open to "exhaust" some of the charge back into the intake manifold you also have an "opposite" piston on an intake stroke that will, in effect, absorb the charge being "exhausted".
Results being a relatively constant vacuum within the LARGE VOLUME of the intake manifold.
So, with a 4-cylinder Atkinson cycle engine you still have intake throttling, vacuum in the intake manifold, and pumping losses (lowered) associated with same.
The problem you undoubtedly encountered in trying to apply this technique to a single cylinder engine is pulses of reverse airflow, A/F mixture, "spitting" out of the carburator. Made worse on a single cylinder engine by having virtually NO intake manifold VOLUME to act as a pressure vessel, accumulator.
Same as would happen with anything other than a 4 cylinder engine or multiples thereof, no synchronization of airflow into and out of the cylinders resulting in reverse flow "pulses" at the throttle valve.
Which is why Mazda went to the Miller Cycle for their V^ in the Mazda Millenia "S".
You arrived at the obvious solution, use a 2-cycle engine's reed valve at the carburator throat.
As you point out, pressure pulsing is then contained within the intake manifold itself and will actually help "fill" the combustion chamber on the next intake stroke....SuperCharging...??
The one thing you seemed to have missed is raising the mechanical compression ratio to ~13:1 but keeping the delayed closing of the intake valve so the effective compression ratio remains at 10:1.
Then at WOT the two engines would have equal HP/torque output capability.
RE: Vacuum free 4-cycle?
Not really. Pumping air twice is all lost work and “working against vacuum” is all conservative because you are getting it back in the very next cycle when that vacuum is “pulling” the piston up. Lost work comes just from vacuum decrease because of heating the gas.
RE: Vacuum free 4-cycle?
Take an old style bicycle tire air pump and cover up the inlet opening and now try to "prime" the pump by pulling the handle upward.
Pretty hard "travel" after about 50% distance, huh?
That's what it's like, "pumping loses" for a piston on an intake stroke with the throttle butterfly valve virtually closed.
RE: Vacuum free 4-cycle?
When you pull the pump up, try letting the handle go and see what happens on the compression stroke with the butterfly valve closed.
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RE: Vacuum free 4-cycle?
But just like the upcoming downhill "run" doesn't fully "cover" the energy you used to get to the top in the first place the "spring" doesn't fully return the input energy.
RE: Vacuum free 4-cycle?
Pumping losses in a typical engine are around 4% of the power output from memory, doubling that would be a bad thing.
Cheers
Greg Locock
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RE: Vacuum free 4-cycle?
Lets recover the loss.
Look at US Pat 3180079. Freeman in '61 was doing this mechanically with an air motor and roots type blowers.
Kawamura et al of Isuzu have several modern patents to this effect.
The general idea is to put a turbine in the intake. The part load pressure drop is made across the turbine which is coupled to a generator to recover the pumping loss as electrical power.
When extra power is desired from the engine, the generator can be switched to become a motor which turns the turbine wheel to supercharge the engine.
RE: Vacuum free 4-cycle?
RE: Vacuum free 4-cycle?
At full throttle I can see a 4% loss because it doesn't work against much as there is no vacuum or anything. At part-throttle you have a big vacuum, and while there might be a spring back it's not near as much pull as when the valve was open because the cylinder now has air/fuel in it. You lose usable springback at about 45-60 deg crank angle.
RE: Vacuum free 4-cycle?
Figure is from memory, it is in Heywood
Cheers
Greg Locock
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RE: Vacuum free 4-cycle?
Recovery of pumping loss is most effective at low engine outputs hence automotive applications are good candidates. This same device can also recover pumping loss but there is less pumping loss power than there is exhaust power to be recovered.
DKJones and GregL:
It is hard to determine what they are talking about when pumping loss is expressed as a percent. I assume that the stated percentage is percent of full power. However pumping loss is zero at full power. So the stated 4% would be 4% of full power but this would be available only at some significantly reduced power level.
If we describe pumping loss as the percentage of power output at the condition producing maximum pumping loss, i.e. Pumping Loss/Output Power
This can go over 100% since operating conditions can be chosen where there is more pumping loss than power out of the engine.
RE: Vacuum free 4-cycle?
RE: Vacuum free 4-cycle?
Autos run at variable loads most of the time.
RE: Vacuum free 4-cycle?
if you think an engine at WOT has no pumping losses then you are sadly mistaken.
And the concept of a pumping loss as an important parameter in an engine that is not at WOT is a bit of a puzzle.
Cheers
Greg Locock
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RE: Vacuum free 4-cycle?
We always ran our T210 at ~75% power level, hour after hour, in level cruise.
300HP x .75 = 225HP
My 911/996 C4 in "level cruise" at 70MPH uses about 40-50HP. 20-25% of WOT.
Pumping losses...
WOT...As the piston moves downward from TDC on an intake cycle it creates a vacuum at the top of the piston. As we all know, are certainly should know, mother nature HATES a vacuum so air immediately begins to rush into the cylinder bore to fill the area just previously displaced by the piston.
Ideally the cylinder area vacated by the piston would be filled fully, all the way up to local atmospheric pressure.
BUT, and this is where K&N makes their money.
If the outside of the intake valve were truly open, fully open, NO RESTRICTIONS, to the atmosphere then the filling of the cylinder bore would be much easier and quicker.
Just like everything else, air molecules have inertia, so it takes a "moment" to get them moving, and at 5000RPM there are not many "moments" available.
So even at WOT "Otto" engines are not exactly "free-breathing"
Now, fully close that WOT and only rely on the IACV for intake airflow.
The pumping losses quickly become huemongus.
The reason an airplane wing "wants" to move upward, WILL move upward, is to fill the vacuum above. For that same reason the piston "wants" to move upward against the "demands" of the connecting rod/crankshaft.
RE: Vacuum free 4-cycle?
But look at this from energy efficiency. Any heat rejected by the intercooler is a dead loss. No way in most practical situations of any recovery. However, if you compress it in one step in the cylinder, it does take more work but the work, or most of it at hopefully, is recovered in the subsequent expansion.
Turbocohen: Way back when I was flying, cruising speed was considered 67% of full power. This is over three times the 20% or so that the average auto engine runs at cruising. The point is that aircraft engines work harder hence are better candidates for turbocompounding.
GregL: OK We all realize that there is pumping loss at WOT. Wwest makes a good point (prev. Post), thanks wwest.
Si engines are controlled by making them inefficient.
At WOT any attempt to recover pumping loss with a turbine wheel mounted in the intake will result in reduced power. Yet at low power levels there is significant pumping loss available and it is ok to recover this power since the reduced power level is desired.
RE: Vacuum free 4-cycle?
Got data to back that up? Using an intercooler reduces the net exhaust backpressure for a given mass of compressed air. More dense airat a lower pressure is easier to pump into a manifold than hot lower density air. i.e, If boosting to 10 psi without an intercooler vs boosting to 7 psi with an intercooler (aiming for the same mass flow) then the 7psi system will require less work from the turbine and less backpressure will be working against the piston during the exhaust stroke. Additionally there will be less residual spent gas in the combustion chamber. There are other factors as well.
Just my 0.02 dinars, Turbo
RE: Vacuum free 4-cycle?
Why are pumping losses all that different at closed throttle or WOT.
At closed throttle, you have more suction against the piston on the induction stroke, but you have less pressure against it on the compression stroke. +1-1=0
At WOT you have less suction against the piston on the induction stroke, but more pressure against it on the compression stroke. -1+1=0
I agree with turbocohen, there is energy lost to the intercooler, but less manifold pressure is necessary to move the same mass of air into the engine.
If people think that the deceleration felt when lifting off the throttle is proof of increased pumping losses, they certainly need to think through all the other things that are happening, like inertia, friction etc
This engine braking goes away at light throttle not because of a change in pumping losses, but because the engine starts making power by burning enough fuel to overcome pumping and inertia and friction losses in the engine, drive train and chassis.
Regards
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RE: Vacuum free 4-cycle?
Cheers
Greg Locock
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RE: Vacuum free 4-cycle?
Regarding pumping loses, I think that there is no point to evaluate it on part throttle because that’s only way Otto engine is regulated. If, by any miracle, we succeed to lower them, we would need to introduce more of them immediately in order to lower the power output.
Way to lower them under WOT is to reduce resistance and utilize resonance.
Supercharging just increase those losses because there is more flow trough same configuration.
RE: Vacuum free 4-cycle?
RE: Vacuum free 4-cycle?
A mechatronic piston driving a linear generator seems like a good idea but a fuel cell is even better until you have to deploy it under all of the conditions that the ole crankshaft does everyday.