Why is exhaust valve smaller than intake valve ?
Joe McGuckin
that of the two valves, the exhaust valve was the smaller.
Why is this? I would have expected that the larger valve would be the
exhaust valve.
Thanks,
joe
Terry Hollis
It is normal for the exhaust valves to be smaller than the intake
valves.
The intake is more difficult to fill because of the low intake pressure
compared to the exhaust which can have the pressure as high as required
simply by opening the exhaust valve a bit ealier.
Regards - Terry Hollis
Todd Fitch
converted into energy that drives the piston down. After that there's
less to be expelled. Instead of a carefully metered mixture of liquid
and gas you have only spent gasses which are easier to evacuate. Every
engine I've been into has the capacity for greater intake volume than
exhaust.
You'll probably get a more scientific explanation but hope this helps.
Todd
Chip Stein
The exhaust gasses are under pressure when exiting so the valve does
not need to be as large. the intake is under vaccuum and needs the
larger valve to let in the right amount of fuel/air mix.
Chip
Dave Baker
>From: tgf...@adelphia.net (Todd Fitch)
>Date: 14/04/02 17:06 GMT Daylight Time
>Message-id: <1fa0c146.02041...@posting.google.com>
>
>I'm not an engineer but when the combustion mix explodes, it is
>converted into energy that drives the piston down. After that there's
>less to be expelled.
You're confusing the internal combustion engine with an atomic bomb which
actually does convert a tiny amount of matter into energy. If matter were
actually to disappear in normal chemical reactions this would be a very strange
and dangerous planet. I hope your physics teacher isn't reading this.
Dave Baker
Puma Race Engines (www.pumaracing.co.uk)
Dean Dardwin
It is you who were asleep in physics class...
"... the exhaust valve size needs to be somewhat smaller than the intake valve area, simply because the "leftovers" of combustion (especially in a modern, clean-burning engine) take up less space than the incoming fuel-air mixture."
Dean
Robert Hancock
produces energy, there is a small amount of mass lost by E=mc2, just like in
a nuclear reaction. However, given the limited amount of energy produced,
the corresponding amount of mass lost would likely be unmeasurable in
practice..
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamshaw.ca
Home Page: http://www.roberthancock.com/
"Dave Baker" <pumar...@aol.com> wrote in message
news:20020414123642...@mb-fl.aol.com...
Dave Baker
>Date: 14/04/02 20:51 GMT Daylight Time
>Message-id: <d5lu8.31265$Kq4.1...@news2.calgary.shaw.ca>
>
>Actually, I believe that in fact when you set off a chemical reaction that
>produces energy, there is a small amount of mass lost by E=mc2, just like in
>a nuclear reaction. However, given the limited amount of energy produced,
>the corresponding amount of mass lost would likely be unmeasurable in
>practice..
Fraid not. The law of conservation of mass in chemical reactions precludes that
completely. Any energy "released" is not created as such but comes from the
potential energy stored in the molecular bonds of the reactants. In a similar
way to how the potential energy of water at the top of a hill can be converted
into kinetic energy and hence power in a turbine at the bottom of the hill.
Mass is neither created nor destroyed and energy is neither created or
dissipated in any normal chemical reaction. The system simply changes state
with effects that vary depending on whether the reaction is endothermic,
exothermic or whatever.
Science hasn't been unclear on this subject since Lavoisier disproved the
phlogiston theory and demonstrated the Law of Conversation of Mass in the
1700s. I suspect Einstein would be horrified to think that his equation, which
has a very specific and limited application, had so entered the common parlance
or become so misunderstood that the energy released from common reactions was
being attributed to it.
Edgar Montrose
Great question and this thread has true potential! Gonna be some great readin'!
LOL!
Robert Hancock
neither mass or energy must necessarily be conserved by themselves. There is
nothing magic about a nuclear reaction in this respect vs. a chemical one.
See here:
http://www.launc.tased.edu.au/online/sciences/physics/massener.html
"Mass interchangeability with energy stems from Einstein's Special
Relativity. This is incorporated into quantum mechanics. Simply, whereever
an emission of energy takes place no matter what format, some mass must be
lost. A chemical exothermic reaction emits such a tiny amount of energy, the
mass loss is negligible but for nuclear reactions, it certainly is not."
Also here:
http://dbhs.wvusd.k12.ca.us/Equations/Conserv-of-Mass.html
And here:
http://physics.pdx.edu/~egertonr/ph311-12/relativ.htm
"The conversion of energy into mass leads to the concept that mass and
energy are somewhat equivalent, and that it is actually the total which is
conserved. The conservation of mass-energy therefore replaces our previous
idea of the separate conservation of these two quantities. The reverse
process, conversion of mass into energy, is also possible. For example, a
star like our sun converts hydrogen into helium and heavier elements within
its core, via a nuclear reaction. The products of this reaction have
slightly less mass than the original hydrogen and this difference in mass
(Dm) accounts for the radiant energy (E = Dm c^2 = 4.0E16 J/s) liberated.
The same principle applies to nuclear reactors and nuclear weapons, and even
to the energy liberated in chemical reactions (where the change in mass is
too small to be measured)."
Anyway, this is, of course, totally irrelevant to the question at hand, but
technically there is some mass lost in the process.
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamshaw.ca
Home Page: http://www.roberthancock.com/
"Dave Baker" <pumar...@aol.com> wrote in message
news:20020414171403...@mb-fg.aol.com...
Chuck Bremer
purely a guess: maybe the exhaust valve is smaller to increase the velocity
of the escaping gases? Similar to placing your thumb over the end of a
water hose when you wash your car... same volume of matter, but moving
faster.
???
Chuck
"Robert Hancock" <hanc...@nospamshaw.ca> wrote in message
news:6Hsu8.37182$ir6.1...@news1.calgary.shaw.ca...
Dave Baker
>From: "Robert Hancock" hanc...@nospamshaw.ca
>Message-id: <6Hsu8.37182$ir6.1...@news1.calgary.shaw.ca>
>
>No, I'm pretty sure I'm right on that. It's mass-energy that's conserved -
>neither mass or energy must necessarily be conserved by themselves. There is
>nothing magic about a nuclear reaction in this respect vs. a chemical one.
>See here:
>
>http://www.launc.tased.edu.au/online/sciences/physics/massener.html
>
>"Mass interchangeability with energy stems from Einstein's Special
>Relativity. This is incorporated into quantum mechanics. Simply, whereever
>an emission of energy takes place no matter what format, some mass must be
>lost. A chemical exothermic reaction emits such a tiny amount of energy, the
>mass loss is negligible but for nuclear reactions, it certainly is not."
>
<snip>
This is an area of science where the tiniest imprecision in the definition or
understanding of the terms can lead to problems with the conclusions drawn.
Debating it based on web articles is probably also not definitive. However I
have to submit that all of your links are incorrect or at best not quite
precise in their definitions.
To genuinely lose mass in a reaction of any sort a fundamental particle
containing mass (proton, electron, neutrino etc) must be lost. By lost I mean
disappear from our known universe. Losing such a particle from the measureable
bounds of the experiment (such as radioactive decay) does not fulfil this
definition and nor even does splitting such a particle into its constituent
quarks.
Even in a nuclear explosion this does not exactly happen. The energy released
comes from the energy stored in the atoms which binds the electrons and nuclei
together or from the Strong Nuclear Force which binds protons to neutrons. All
of the original constituent particles of the atoms which took part in the
explosion still exist but are no longer bound together in the same way.
One of the problems of definition and which I think is responsible for the
error relating to the quote about solar energy:
>The products of this reaction have
>slightly less mass than the original hydrogen and this difference in mass
>(Dm) accounts for the radiant energy (E = Dm c^2 = 4.0E16 J/s) liberated.
is in the definition of the rest mass of atoms or particles. In a reaction
where elements are split or combined into lighter or heavier elements it is
certainly true that the rest mass of the products can be different from that of
the reactants. The difference, however, is always contained in elementary
particles (electrons usually) released or combined during the reaction. The
change in rest mass still does not mean that particles containing mass
disappeared from the universe. It is a problem with definition or measurement
of the bounds of the experiment.
Notwithstanding my comment about web articles above and FWIW try this.
http://www.circlon.com/HTML/EmcFallacies.html
Dave Baker
>From: j...@via.net (Joe McGuckin)
>Date: 14/04/02 08:40 GMT Daylight Time
>Message-id: <248eb73d.02041...@posting.google.com>
Just out of interest why would you assume this?
UserEddie214
>I honestly have no idea, and I am not a physicist or
>engineer, so this is purely a guess: maybe the exhaust
>valve is smaller to increase the velocity of the escaping
>gases? Similar to placing your thumb over the end of a
>water hose when you wash your car... same volume of
>matter, but moving faster.
>
>???
There may also be some thermal considerations.
????
s.z.
>Chuck
Mike Graham
<cbremer@*hotmail*.com> wrote:
>I honestly have no idea, and I am not a physicist or engineer, so this is
>purely a guess: maybe the exhaust valve is smaller to increase the velocity
>of the escaping gases? Similar to placing your thumb over the end of a
>water hose when you wash your car... same volume of matter, but moving
>faster.
That's not a bad idea. You want the exhaust gasses to be moving
quickly so that their inertia, if you will, helps to produce a partial
vacuum to help suck in intake air.
Don't know if it's true, but it sounds good. 8-)
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Mike Graham | Fighting the good fight against porosity,
mi...@metalmangler.com | lack of fusion, and people who constantly
<http://www.metalmangler.com>| try to correct the spelling of 'weldor'.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Mike Graham
>One of the problems of definition and which I think is responsible for the
>error relating to the quote about solar energy:
It's emitting photons, and photons have some mass of sorts... at
least, enough to make solar sails work.
Mike Graham
>Just out of interest why would you assume this?
I would have assumed it as well, because the intake air is cold
(small) and the exhaust air is hot (big).
However, the intake air comes in under partial vacuum, wheras the
exhaust air is pushed out by direct compression - a much much more
powerful force.
Brian Evans
Discusses how cams work, and included a paragraph on the relative flow
requirements of intake vs exhaust ports. He doesn't actually say why. I'm
going to guess that its more related to the balance to intake flow capacity
and the fact that the intake cycle is power by atmospheric pressure, while
the exhaust cycle is powered by the combustion pressure.
Brian
"Joe McGuckin" <j...@via.net> wrote in message
news:248eb73d.02041...@posting.google.com...
Dave Baker
>From: Mike Graham mi...@metalmangler.com
>Date: 15/04/02 11:32 GMT Daylight Time
>Message-id: <ovalbu0bt2a23elkn...@4ax.com>
>
>On 15 Apr 2002 07:58:52 GMT, pumar...@aol.com (Dave Baker) wrote:
>
>>One of the problems of definition and which I think is responsible for the
>>error relating to the quote about solar energy:
>
> It's emitting photons, and photons have some mass of sorts... at
>least, enough to make solar sails work.
Which is at the heart of the definitions problem. If photons have mass (which
they do under some theories but not others) then the sun is just emitting
massive particles rather than turning mass into energy and if you shone those
photons back into the sun with a mirror then the mass would return.
The problem with a human understanding of all this is that we tend to think of
mass as solid bits we can see and energy as things we can't. But on a quantum
level where mass and energy are equivalent the distinction becomes blurred and
measurements of mass consist largely of measurements of energy potentials.
Consider a proton. It consists (on current theory) of 3 quarks. Two "up" quarks
and one "down" quark. The rest mass of all of these can be measured
independantly in a particle accelerator. The rest mass of the proton is much
greater than the rest mass of the three quarks that make it up and the balance
consists of kinetic and potential energy inside the proton.
If a proton is split up it looks like mass is lost and turned into energy but
if the three quarks recombine, the mass of the proton is the same as it was
before. What that says about mass and energy I'm not sure.
As far as normal chemical reactions are concerned, which is where this all
started, I see no need to postulate any requirement for mass turning into
energy. No atoms are lost because the equation balances on both sides. The
established theories of ionic and covalent bonding show where the energy
released has come from.
Here's a simple thought experiment. Assume it's possible to contain and bring
together just two atoms that can combine exothermically into a molecule. Say
for example Na and Cl to form a molecule of salt although which atoms and
molecules we choose makes no difference here. (I don't know if NaCl is an
exothermic reaction but it doesn't affect the thought experiment)
If the energy released comes from mass then which mass gets lost? If either of
the atoms lose a fundamental particle (electron or proton for example) then
they are no longer Na or Cl and so we can't end up with a molecule of salt. But
we know we must get salt because that's how it happens. Multiply this reaction
trillions of times into something inside a test tube and the problem remains.
Does one atom of Na or Cl out of trillions give itself up and turn into energy
to allow the rest to combine and if so how do the atoms decide which one?
What ionic and covalent bonding theory says is that the energy level of the
electron shells or clouds changes as the reaction proceeds and in some
reactions is reversible. This involves no loss of any fundamental particles
from the reactants. But if we predetermine that mass and energy are equivalent
and that all energy is carried in the form of photons which have mass then the
release of energy is also a release of mass by definition.
Get even deeper down into string theory and nothing has mass anyway. Everything
that we call a fundamental massive particle consists of "strings" vibrating in
a multi-dimensional manifold of which we observe only the three dimensions of
space. Mass is only the observed property of attraction that matter or energy
has for each other due to gravity but how gravity works is still not explained
and the graviton, although postulated, has not yet been found.
I'm heading for being well out of my depth here so I'll call it a day :)
Ken
engine, all you have pushing air into the cylinder is atmospheric pressure.
The exhaust valve can be smaller because you actually have to pistons
upstroke pushing exhaust gasses out.
Terry Hollis wrote:
--
Ken B.......ö¿ö
Email: mailto:kb...@iprimus.com.au
ICQ: 697292
** Diplomacy is the art of saying "nice doggy" until you can
find a rock **
Robert Hancock
either of
> the atoms lose a fundamental particle (electron or proton for example)
then
> they are no longer Na or Cl and so we can't end up with a molecule of
salt. But
> we know we must get salt because that's how it happens. Multiply this
reaction
> trillions of times into something inside a test tube and the problem
remains.
> Does one atom of Na or Cl out of trillions give itself up and turn into
energy
> to allow the rest to combine and if so how do the atoms decide which one?
I think you answered your own question earlier in your post here. You're
presuming that for mass to be lost, there have to be fundamental particles
that disappear. If you take the weight of an atom that undergoes fission,
for example, and compare it to the weight of all the various shrapnel
afterwards, you'll find that the remainder weighs a bit less, even though no
particles have been lost - and the energy released by the kinetic energy of
the particles accounts for this lost mass. Strange, yes, but that's just the
way this binding energy business works. Same with a chemical reaction, it
predicts that strangely enough the reaction products end up weighing
slightly less, even though all the original particles are still there.
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamshaw.ca
Home Page: http://www.roberthancock.com/
"Dave Baker" <pumar...@aol.com> wrote in message
news:20020415132400...@mb-fm.aol.com...
Geoff
Dave's spot on here. It's the energy in the bonds between atoms that is
released during an exothermic (heat-shedding) reaction. Any mass to energy
conversions would be releasing far, far more energy.
Joe McGuckin
that you'd want a larger valve in order exhaust the gas quickly.
joe
pumar...@aol.com (Dave Baker) wrote in message news:<20020415040547...@mb-dd.aol.com>...
Dave Baker
>From: j...@via.net (Joe McGuckin)
>Date: 16/04/02 07:38 GMT Daylight Time
>Message-id: <248eb73d.0204...@posting.google.com>
>
>The gas resulting from combustion would be under pressure. I guessed
>that you'd want a larger valve in order exhaust the gas quickly.
>
>joe
The fact that it's under pressure means it flows through a given size opening
quicker anyway. The very reason it can be smaller than the intake valve.
Dave Baker
>Date: 16/04/02 01:23 GMT Daylight Time
>Message-id: <Y9Ku8.41533$de1.1...@news3.calgary.shaw.ca>
>
>> If the energy released comes from mass then which mass gets lost? If
>either of
>> the atoms lose a fundamental particle (electron or proton for example)
>then
>> they are no longer Na or Cl and so we can't end up with a molecule of
>salt. But
>> we know we must get salt because that's how it happens. Multiply this
>reaction
>> trillions of times into something inside a test tube and the problem
>remains.
>> Does one atom of Na or Cl out of trillions give itself up and turn into
>energy
>> to allow the rest to combine and if so how do the atoms decide which one?
>
>I think you answered your own question earlier in your post here. You're
>presuming that for mass to be lost, there have to be fundamental particles
>that disappear. If you take the weight of an atom that undergoes fission,
>for example, and compare it to the weight of all the various shrapnel
>afterwards, you'll find that the remainder weighs a bit less, even though no
>particles have been lost - and the energy released by the kinetic energy of
>the particles accounts for this lost mass. Strange, yes, but that's just the
>way this binding energy business works. Same with a chemical reaction, it
>predicts that strangely enough the reaction products end up weighing
>slightly less, even though all the original particles are still there.
I'm going to try and be really precise with definitions here. An exothermic
reaction is carried out by combining two elements in equal masses (A and B)
that react to form a molecule C. The reaction is carried out inside a totally
sealed environment - imagine we are in the future if necessary to make the
technology possible. The container, forcefield or whatever, is a perfect
insulator and does not allow the passage of heat, light or any other radiation
and is inert to the reaction. However we can measure the temperature inside the
container and weigh its contents with perfect precision (Heisenberg
notwithstanding).
We introduce into this container exactly 1 gram of A and 1 gram of B both at 20
degrees C. They combine to form C and we observe the temperature of the product
has risen to 40 degrees C due to the exothermic reaction. This temperature
cannot now change of course until the container is opened because it is a
perfect insulator.
1) Is the mass of C, immediately after the reaction is completed, more than,
less than or exactly 2 grams?
After you've thought about and answered this I'll continue as necessary
depending on what your answer is.
Mike Graham
>The fact that it's under pressure means it flows through a given size opening
>quicker anyway. The very reason it can be smaller than the intake valve.
So the bottom line is that the exhaust valve is smaller so that the
intake valve can be larger, yes?
J. Todd Wasson
>opening
>>quicker anyway. The very reason it can be smaller than the intake valve.
>
> So the bottom line is that the exhaust valve is smaller so that the
>intake valve can be larger, yes?
>
>
>
Right :-)
Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com
My little car sim screenshots:
http://performancesimulations.com/scnshot4.htm
Dave Baker
>Date: 16/04/02 11:48 GMT Daylight Time
>Message-id: <ma0obuc835ghesfsp...@4ax.com>
>
>On 16 Apr 2002 09:38:17 GMT, pumar...@aol.com (Dave Baker) wrote:
>
>
>>The fact that it's under pressure means it flows through a given size
>opening
>>quicker anyway. The very reason it can be smaller than the intake valve.
>
> So the bottom line is that the exhaust valve is smaller so that the
>intake valve can be larger, yes?
>
Pretty much yes. The intake valve relies on the pressure difference across it
to generate flow - at most 15 psi in a normally aspirated engine. Any loss of
intake valve area and hence flow leads to a directly related fall in volumetric
efficiency and power.
The exhaust stroke benefits both from the higher cylinder pressure after
combustion and also positive displacement from the piston. A reduction in valve
area leads primarily just to a pumping loss which acts as a parasite power loss
at the crank. There will also be a minor loss in VE because the chamber has not
been scavenged so completely and can not therefore fill with quite so much
fresh charge. These effects are minor in relation to loss of intake flow
capability though.
Obviously there has to be a break even point. If there was no exhaust valve at
all then the engine can't run. As the exhaust valve is made smaller and the
intake valve made larger the pumping loss increases until it finally balances
out any extra power from more intake flow. This point on most engines is when
the exhaust valve area is around 70% of the intake valve area. Production
engines aren't designed to maximise power. Intake valves are generally smaller
than optimum to improve turbulence, gas speed and hence low rpm torque and fuel
efficiency. Exhaust valves are larger than optimum to reduce pumping loss.
Modify a production engine for race use and the valve area ratio generally
needs to change.
This is pretty trivial engine theory though and not nearly so interesting as
quantum mechanics and relativity. Of slightly more interest is the optimum
valve area ratio in a forced induction engine. Most people never get past the
point of "thinking" (for want of a better word) that because the intake side is
now positively displaced too then the exhaust valve needs to be made larger and
the intake smaller. All this serves to demonstrate is that very few people know
how to think. The solution to the optimum valve area ratio in a forced
induction engine ought also to be easily deducible from a consideration of
pressure differences across the engine but that's another story.
Dean Dardwin
Rather than simply state the obvious, I went through the trouble of searching the 'Net and found this quote from a Mercedes-Benz engineer:
"... the exhaust valve size needs to be somewhat smaller than the intake valve area, simply because the "leftovers" of combustion (especially in a modern, clean-burning engine) take up less space than the incoming fuel-air mixture."
Dean
Dave Baker
>Date: 16/04/02 13:08 GMT Daylight Time
>Message-id: <3CBC1422...@dxd.com>
>
>
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>
>Wrong. It's common knowledge that the exhaust charge is less dense than
>the intake charge, hence the requirement for the intake valve to be larger.
>
>Rather than simply state the obvious, I went through the trouble of
>searching the 'Net and found this quote from a Mercedes-Benz engineer:
>
>"... the exhaust valve size needs to be somewhat smaller than the intake
>valve area, simply because the "leftovers" of combustion (especially in
>a modern, clean-burning engine) take up less space than the incoming
>fuel-air mixture."
>
>Dean
If I had a penny for every supposedly authoritative web site that was wrong I'd
be a rich man. If you think you can answer technical questions by relying on
the dubious thought processes of others then you are wrong too. The phrase
"takes up less space" is meaningless in relation to a gas which takes up
whatever space is available for it in the container. The proper terms to use to
accurately quantity gases are mass or pressure/density/temperature
relationships etc.
As for the phrase "leftovers of combustion" - the mass of outgoing charge is
IDENTICAL to the mass of incoming charge (quantum physics notwithstanding). If
this were not the case then an engine would get steadily heavier or lighter
over time which is clearly absurd. If the mass is the same and the volume is
the same then the density is the same by definition. All that has changed as a
result of the combustion process is the temperature and pressure in accordance
with the Universal Gas Laws. If the pressure has increased and the density
stayed the same then the flow rate through a given orifice goes up. By how much
you can go away and research if you want the slightest chance of redeeming
yourself.
Being a Mercedes Benz engineer doesn't guarantee knowing sod all about
anything. Relying on the opinion of one without even being able to work through
the basic physics errors contained therein doesn't say much for you either -
especially as you accused me of sleeping through physics at school.
There's an old Russian saying - "an empty barrel makes the greatest sound". You
might do well to ponder on that before revealing your lack of education in your
critique of others again.
As for "common knowledge" and "state the obvious" - the world somehow survives
despite most people being wrong about most things they thought they knew. A
small minority have the capability to deduce things correctly based on
education and brain power. Which category do you believe you fit into I wonder?
Dean Dardwin
The original poster, Joe, was seeking knowledge. Maybe he's not as knowledgeable about the subject as you THINK you are...
but your comment "All this serves to demonstrate is that very few people know how to think" proves that you are a dumbass pseudo intellectual snob. Do mankind a favor a stick your head in a black hole... a place you obviously understand much better than a combustion chamber.
Dean
Dave Baker wrote:
the intake smaller All this serves to demonstrate is that very few people know
Dean Dardwin
You really are stupid!
Dean
Mike Graham
>As for the phrase "leftovers of combustion" - the mass of outgoing charge is
>IDENTICAL to the mass of incoming charge (quantum physics notwithstanding).
And blow-by notwithstanding... 8-)
Dave Baker
>Message-id: <3CBC1E0C...@dxd.com>
>
>
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>
>You really are stupid!
>
Oooow - ouch - is that the best comeback you can offer? Run out of primary
school physics to throw into the debate now have you?
Stephen Bigelow
Dave Baker <pumar...@aol.com> wrote in message
> >Wrong. It's common knowledge that the exhaust charge is less dense than
> >the intake charge, hence the requirement for the intake valve to be
larger.
Nonsense.
> >Rather than simply state the obvious, I went through the trouble of
> >searching the 'Net and found this quote from a Mercedes-Benz engineer:
> >
> >"... the exhaust valve size needs to be somewhat smaller than the intake
> >valve area, simply because the "leftovers" of combustion (especially in
> >a modern, clean-burning engine) take up less space than the incoming
> >fuel-air mixture."
Nonsense.
> >Dean
Ahh.
All is revealed
> As for "common knowledge" and "state the obvious" - the world somehow
survives
> despite most people being wrong about most things they thought they knew.
A
> small minority have the capability to deduce things correctly based on
> education and brain power. Which category do you believe you fit into I
wonder?
>
>
> Dave Baker
> Puma Race Engines (www.pumaracing.co.uk)
Well stated, Dave, as usual.
The intake, (I believe) needs to be larger because the intake charge relies
on atmospheric pressure for filling, at least in NA engines.
Near complete exhausting of the cylinder is comparatively easy because that
quickly rising piston tends to push things out of its way quite well!
It's not that they purposely make the exhaust valve small, it's that they
purposely make the intake large. There is only so much real estate in the
head.
Steve
Dave Baker
>Date: 16/04/02 13:46 GMT Daylight Time
>Message-id: <3CBC1D4...@dxd.com>
>
>
>--------------040604030802050400010701
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>
>
>The original poster, Joe, was seeking knowledge. Maybe he's not as
>knowledgeable about the subject as you THINK you are...
>
>but your comment "All this serves to demonstrate is that very few people
>know how to think" proves that you are a dumbass pseudo intellectual
>snob.
The intellectual snob bit I'll concede. The pseudo bit is clearly not
applicable as I apparently really do understand at least some physics. The
dumbass bit I'll ignore because it's more a reflection on your debating
capabilities than on my intellect. Try these ones on for size:
Debating physics with you Dean is like having an arse kicking contest with a
paraplegic - a cast iron win but not very sporting. And to plagiarise the words
of the wonderful, and sadly missed, Douglas Adams - " It gives me a headache
just trying to think down to your level".
Enjoy.
Joel Frahm
<sbige...@sprint.ca> wrote:
>The intake, (I believe) needs to be larger because the intake charge relies
>on atmospheric pressure for filling, at least in NA engines.
>
>Near complete exhausting of the cylinder is comparatively easy because that
>quickly rising piston tends to push things out of its way quite well!
>
I would suppose that even after the gas mix has burned and the piston
is at the bottom, the cyl pressure is still well above atmospheric
pressure, so the exhaust pops out when the valve opens. I also
suppose that the very hot exhaust is much larger in volume than the
very cool, dense intake charge but, this is still not a big deal given
the force that the exhaust has left over. There is a good deal of
energy to be had there, that's why turbochargers work so well I think.
>It's not that they purposely make the exhaust valve small, it's that they
>purposely make the intake large. There is only so much real estate in the
>head.
>
Exactly. The intake charge has to be dragged kicking and screaming
into the engine with only the downward moving piston to get it there
(in a NA engine with no ram air setup.) The exhaust goes blasting out
of there and all the piston has to do is sweep out the dregs.
-Joel. Frahm
These opinions are mine and not those of my employer or anyone else.
Robert Hancock
increase in the kinetic/heat energy of the C molecules compared to the A and
B.
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamshaw.ca
Home Page: http://www.roberthancock.com/
"Dave Baker" <pumar...@aol.com> wrote in message
news:20020416055851...@mb-fv.aol.com...
Blue
"Mike Graham" <mi...@metalmangler.com> wrote in message
news:5qalbus373au8t845...@4ax.com...
> On Mon, 15 Apr 2002 07:06:46 GMT, "Chuck Bremer"
> <cbremer@*hotmail*.com> wrote:
>
> >I honestly have no idea, and I am not a physicist or engineer, so this is
> >purely a guess: maybe the exhaust valve is smaller to increase the
velocity
> >of the escaping gases? Similar to placing your thumb over the end of a
> >water hose when you wash your car... same volume of matter, but moving
> >faster.
>
> That's not a bad idea. You want the exhaust gasses to be moving
> quickly so that their inertia, if you will, helps to produce a partial
> vacuum to help suck in intake air.
> Don't know if it's true, but it sounds good. 8-)
It may also be a consideration that getting gas into the cylinder is more of
a problem than getting it out. Getting it in efficiently has a large effect
on power and the necessarily larger valve is more tolerable. Getting it out
is easy and positive with engine momentum.
Blue
J. Todd Wasson
>>>>
>>>opening
>>>
>>>>quicker anyway. The very reason it can be smaller than the intake valve.
>>>>
>>> So the bottom line is that the exhaust valve is smaller so that the
>>>intake valve can be larger, yes?
>>>
>>>
>>>
>>
>> Right :-)
>>
>>
>Wrong. It's common knowledge that the exhaust charge is less dense than
>the intake charge, hence the requirement for the intake valve to be larger.
Dave Baker covered this better than I could possibly have done, but I'll echo
a bit of it anyway. This "common knowledge" is probably better labeled as
"common misunderstanding of the relationships between temperature, pressure,
and density".
Density is mass/volume. At xx crank angle (BC or TC for example), neither the
gas mass nor the cylinder volume changes (by definition), therefore the density
doesn't change either. The pressure is much higher though with the burned
gases, but pressure and density are not the same thing.
You could say that the higher pressure burned gases are less dense *if you
allowed them to expand to a volume at which the pressures between the before
and after case were identical*, because then you'd have identical mass in a
larger volume, but this isn't happening in an engine.
>Rather than simply state the obvious, I went through the trouble of
>searching the 'Net and found this quote from a Mercedes-Benz engineer:
>
>"... the exhaust valve size needs to be somewhat smaller than the intake
>valve area, simply because the "leftovers" of combustion (especially in
>a modern, clean-burning engine) take up less space than the incoming
>fuel-air mixture."
An unfortunate choice of words from this engineer seeing that the amount of
space taken up matches the space available at all times. Unburned intake gases
at 14.7 psi in a 40 cubic inch volume cylinder will take up the same space that
the gases will after they're burned. The pressure might increase by a factor
of four or five, but the gases will certainly take up the very same 40 cubic
inch space. They won't simply leave the cylinder walls and clump together in a
"smaller space" in the middle of the cylinder and leave a vacuum around them.
Consequently, if you were to open the exhaust valve, you now have four or five
times as much pressure available to propel the exhaust out of the cylinder.
With this high pressure available, it makes sense to sacrifice exhaust valve
size for greater intake valve size. How much space is taken up by the gases is
irrelevant.
J. Todd Wasson
>on atmospheric pressure for filling, at least in NA engines.
>
>Near complete exhausting of the cylinder is comparatively easy because that
>quickly rising piston tends to push things out of its way quite well!
>
Exactly. Not to mention that the high pressure exhaust gases will have a
tendency to expel themselves from the cylinder to a large degree (or at least
aid the process). During the blow down phase, where the exhaust valve begins
to open before BC, the gases are under high pressure (it seems to me I read
from 3 to 5 atmospheres or more depending on the crank angle you're looking
at... not sure though). With that high pressure, they'll begin rapidly
accelerating out of the exhaust valve even before the piston reaches BC. At
that point, yes, the rising piston tends to push things out quite well :-)
>It's not that they purposely make the exhaust valve small, it's that they
>purposely make the intake large. There is only so much real estate in the
>head.
This is how I currently understand it too.
J. Todd Wasson
>Dave,
>
>The original poster, Joe, was seeking knowledge. Maybe he's not as
>knowledgeable about the subject as you THINK you are...
>
>but your comment "All this serves to demonstrate is that very few people
>know how to think" proves that you are a dumbass pseudo intellectual
>snob. Do mankind a favor a stick your head in a black hole... a place
>you obviously understand much better than a combustion chamber.
>
>Dean
Geeze. I don't understand your view here at all, Dean. I go over to Dave
Baker's website and this is the first thing I read on his racing engine
company's successes:
"MGB - 4 new UK track records in 6 races for Phillip Conn's 1950cc engine we
built in 1993.
Ford CVH - our engines have won the Fiesta XR2 Challenge for 3 years and set
many new circuit records. We have also built successful engines for the Stock
Hatch and Hot Hatch series and done cylinder head work for the XR2i
championship.
VW Golf - our advanced flow developed cylinder head work led to engine power
that enabled Paul Rose to win the Slick 50 championship in 1997, 1998 and 1999.
Ford Pinto - Our F2000 stock car engines enabled Graham Kelly to win the
scottish Crimmond championship in 1998, 1999 and 2000.
Hillclimb - Andy Bougourd's Suzuki GSX1100 engined Mallock set numerous track
records and FTDs in 2000. We engineered the big valve cylinder head, overbored
block and throttle body system for him leading to an increase in power from 120
bhp to 200 bhp. Nick Ferbrache's Chevy V8 engined car has set several new track
records and FTD at the Brighton Speed Trials in 2000 after we reworked the
cylinder heads.
"
This has some more stuff too, which to me demonstrates that Dave has a very
good grasp of the subject:
http://www.pumaracing.co.uk/mainmenu.htm
Looks to me like Dave understands combustion chambers a lot better than any of
us probably could ever hope to. I sure hope Dave doesn't stick his head in a
black hole, as there's plenty to be learned from him. What am I missing, Dean?
Dave Baker
>From: "Robert Hancock" hanc...@nospamshaw.ca
>Message-id: <DI2v8.48105$Kq4.1...@news2.calgary.shaw.ca>
>> I'm going to try and be really precise with definitions here. An
>exothermic
>> reaction is carried out by combining two elements in equal masses (A and
>B)
>> that react to form a molecule C. The reaction is carried out inside a
>totally
>> sealed environment - imagine we are in the future if necessary to make the
>> technology possible. The container, forcefield or whatever, is a perfect
>> insulator and does not allow the passage of heat, light or any other
>radiation
>> and is inert to the reaction. However we can measure the temperature
>inside the
>> container and weigh its contents with perfect precision (Heisenberg
>> notwithstanding).
>>
>> We introduce into this container exactly 1 gram of A and 1 gram of B both
>at 20
>> degrees C. They combine to form C and we observe the temperature of the
>product
>> has risen to 40 degrees C due to the exothermic reaction. This temperature
>> cannot now change of course until the container is opened because it is a
>> perfect insulator.
>>
>> 1) Is the mass of C, immediately after the reaction is completed, more
>than,
>> less than or exactly 2 grams?
>
>In this case, I think you'll get a tiny decrease in mass - equivalent to the
>increase in the kinetic/heat energy of the C molecules compared to the A and
>B.
Ok, I thought this was what your viewpoint had been but I wanted to carefully
set out the conditions of the experiment to be sure. The easiest to think about
this, rather than worry about the quantum aspects to start with, is to look at
the thermodynamics. The experiment is sealed; nothing has got in or out even
down to the photon level. In effect it's a perfect Lavoisier experiment which
even now we can't create because no container is a perfect insulator.
This means that the weight inside the container must be the same i.e. exactly 2
grams because nothing, neither mass nor energy, has got in or out. The higher
temperature is the red herring that seems to be at the root of most of the
erroneous views in web pages I've come across over the past couple of days.
Remember that energy also has mass in accordance with Einstein's formula and
while that energy is contained in C as higher temperature it also makes up part
of the 2 grams mass.
What has happened is that potential energy stored in the bonds of A and B has
turned into lower bond energy but higher temperature in C. Bond energy has its
mass equivalent just as heat energy does and as already mentioned in a previous
posting, most of the mass equivalence we measure in fundamental particles is
contained in bond energy inside them. It isn't until we break the sealed
conditions of the experiment and allow the heat to escape into the surroundings
that the mass of C can change. But we still haven't turned mass into energy.
This is just a transfer of energy as happens anytime something is heated or
cooled.
Consider a metal bar situated close enough to a similar hotter metal bar to
pick up heat via either radiation or convection. They aren't touching and no
particles get transferred but as one bar cools and the other heats up there is
a transfer of energy which has an equivalent mass in accordance with E=mc^2.
But no atoms or fundamental particles have altered or been destroyed any more
than they have in the Lavoisier experiment. The molecules have gained kinetic
energy which is how heat manifests in matter and mass changes at the same time
due to the energy equivalence. Whether we postulate that photons with mass have
been transferred or massless photons have created an increase in kinetic energy
that has a mass equivalent makes little difference.
And so we come full circle to how this part of the thread started. Before
Einstein's time scientists understood Lavoisier's conservation of mass theory
because there was nothing else to interfere with or corrupt their understanding
of it. After Einstein it became all too easy to trot out E=mc^2 anytime a
transfer of energy took place and conclude that mass had been destroyed. Sadly
most of the web pages you come across doing a web search for E=mc^2 have an edu
in the title and at least half of them claim that mass gets destroyed in a
normal chemical reaction. This apparently means that many graduates and post
graduates don't really understand the quantum theory they have just been
studying.
God knows it certainly is a tricky subject, especially compared to engines, and
accordingly hard to explain. I hope I've done it some justice and that we are
now in agreement.
This is still only really scratching the surface of quantum theory though and
when the boundaries between mass and energy are so blurred it is easy to
postulate opposing views. For example it is certainly correct that 1 gram of A
plus 1 gram B of at 20 degrees C have more mass than the product of reaction C
if allowed to cool to the same temperature. What happens though if you cool
everything to absolute zero? The mass changes as the temperature drops but as
the elemental particles that make up both A, B and C are the same then the
masses should be the same. What is different is that the specific heat capacity
of C is different from the combined specific heat capacities of A and B. The
specific heat capacity is part of the equation that balances the temperature
rise of the products of a reaction with the bond energies of the products and
reactants.
This means that ones view about whether mass is destroyed and turned into
energy could vary with the temperature at which a reaction is carried out.
Hairy stuff but interesting to think about :)
Jim
because it's difficult to keep it cool. A larger valve would absorbe more
of the heat from the passing exhaust and be less able to dissapate that heat
when seated. I believe warping is a problem (well, I'm kinda old, maybe
they fixed that problem). The intake valve is not subject to this issue for
obvious reasons.
Or did someone say this in one of the hundreds of messages and I missed
it...
Jim
Edgar Montrose
Blue
"Jim" <jimi...@rochester.rr.com> wrote in message
news:sU5v8.146795$GF1.19...@typhoon.nyroc.rr.com...
> I'd like to throw my guess into the mix. I think the exhaust valve is
small
> because it's difficult to keep it cool. A
A better question is: Why should the exhaust and intake valves be the same
size?
Altogether different considerations for each and as someone down the line
stated - "Its a problem of shortage of real estate in the head.." For
volumetric efficiency the intake valve must be as large as possible (sort
of - G).
Robert Hancock
has
> turned into lower bond energy but higher temperature in C. Bond energy has
its
> mass equivalent just as heat energy does and as already mentioned in a
previous
> posting, most of the mass equivalence we measure in fundamental particles
is
> contained in bond energy inside them. It isn't until we break the sealed
> conditions of the experiment and allow the heat to escape into the
surroundings
> that the mass of C can change. But we still haven't turned mass into
energy.
> This is just a transfer of energy as happens anytime something is heated
or
> cooled.
I'm not entirely sure about that - I'm thinking that as long as the
temperature remains above what it was before the reaction, you're still
going to have that drop of mass.
However, I think it's safe to say that a more authoritative source would be
needed to resolve that particular question with more certainty :-)
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamshaw.ca
Home Page: http://www.roberthancock.com/
"Dave Baker" <pumar...@aol.com> wrote in message
news:20020416230951...@mb-bk.aol.com...
Christopher Warren
snip
So, if we simply heat up an object, it gets lighter?
--
The opinions expressed here are my personal opinions and in no way
reflect
those of my employer.
Good data is Good data. Bad data is JUST an opinion.
Robert Hancock
it's a closed system which undergoes a reaction internally. You're just
adding energy, there's no mass being converted.
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamshaw.ca
Home Page: http://www.roberthancock.com/
"Christopher Warren" <@ford.com> wrote in message
news:3CBEBBDC...@ford.com...
JazzMan
>
<snip>
> So, if we simply heat up an object, it gets lighter?
>
Not that can be measured. A heated object expands, and
since the mass stays the same, it becomes less dense.
This is only really significant when dealing with gasses
that are free to expand as they are heated, such as hot
air balloons and such. Heat up a brick and it still flattens
your foot. Heat up a balloon, and it will rise.
My opinion on the valve question? Intake gasses can only
enter through the intake valve at 14 psi (atmoshperic).
Exhaust gasses on the other hand can be pushed out at much
greater pressure because of the piston. Since cylinder head
space is limited. it's a good compromise to increase the
intake valve area at the cost of exhaust valve area. Some
energy is lost in the form of exhaust gas resisting being
pushed through a smaller valve, but is made up for with
the easier filling of the intake charge. A supercharged
engine would probably get away with smaller intake valves,
but don't know if anyone has actually tried that.
JazzMan
--
***************************************
In memory of Pincushion
http://www.captured.com/underground/memories/patrick_magee.html
***************************************
Please reply to jsavage"at"airmail.net.
Curse those darned bulk e-mailers!
***************************************
Mike Graham
wrote:
>your foot. Heat up a balloon, and it will rise.
It's important to drive home the point, here, that the ballon
doesn't get lighter in the sense of it having less mass, it simply
gets lighter than the air around it, so it is lifted. I realize,
jazzman, that you are aware of this, but I thought the point needed a
bit more hammering. 8-) In a vacuum, the balloon weighs the same hot
and cold.
>pushed through a smaller valve, but is made up for with
>the easier filling of the intake charge. A supercharged
>engine would probably get away with smaller intake valves,
>but don't know if anyone has actually tried that.
I think the same issues would apply, anyway. The compression in the
cylinder (without combustion) is over 100psi with the valves closed.
(yeah, I know it varies a LOT depending on age and type of engine,
etc... diesels can hit 400psi or more). Now, I don't know
superchargers.. I know basically how they work, but I don't know how
*well* they work. Do they hit anything like 100psi input pressure? I
think turbos run something like 20-ish psi... at least, I hear murmurs
of 'boost' and 'waste-gates' and whatnot, and apparently there is some
kind of limit as to how hard you can pump the input air without
causing problems? Anyway, as long as the input air is supplied at a
lower rate than the waste in the cylinder can be exhausted, then it
will make sense to have a smaller exhaust valve. I can see the ratio
changing as boost pressures rise, though...
Stephen Bigelow
> On Thu, 18 Apr 2002 23:35:13 -0500, JazzMan <No_...@airmail.net>
> wrote:
>
> >your foot. Heat up a balloon, and it will rise.
>
> It's important to drive home the point, here, that the ballon
> doesn't get lighter in the sense of it having less mass, it simply
> gets lighter than the air around it, so it is lifted. I realize,
> jazzman, that you are aware of this, but I thought the point needed a
> bit more hammering. 8-) In a vacuum, the balloon weighs the same hot
> and cold.
It weighs the same at atmo, too.
It gets *larger*, without gaining mass, i.e. less dense, than it was at its
previous lower temperature.
Steve
Ottawa
Mike Graham
<sbige...@sprint.ca> wrote:
>It weighs the same at atmo, too.
'Weighs' is a wretchedly imprecise term, because in standard usage
it basically refers to the force applied to a spring scale. This is
why they say 'we weigh less on the moon' because the force of gravity
is less. Mass is absolute, weight is... not.
You can't weigh a helium-filled balloon in our atmosphere.