Date: Thu, 18 Jul 2002 16:55:04 +0100
Reply-To: Clive Smith <clive.harman-smith@NTLWORLD.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Clive Smith <clive.harman-smith@NTLWORLD.COM>
Subject: Re: Running on Tap Water - attempt at de-confuscation
Content-Type: text/plain; charset="Windows-1252"
Todd, you just quoted an extract from someone:
>More air and fuel into the engine leads to more power. However by
compressing the inlet air the turbocharger also heats it. Higher air
temperatures lead to thinner >air and therefore an altered stoechiometric
ratio which can lead to a lean mixture and detonation. In high pressure
turbocharged engines the air/fuel mixture that >enters the cylinders can
explode prematurely (before the spark plug ignites, effect also known as
engine knock) due to the extreme engine environment conditions.
Most of this extract is obviously written by someone a little bit confused
about the actual thermodynamic and engineering realities, although they
obviously have some practical experience of water injection, or have seen a
few setups.
** Its not the turbocharger that heats up thats the problem, its that
compressing air (non ideally -adiabatically) that heats it up and the t/c
with it.
** The reference to a lean mixture is also misleading, this is not the
result in any way shape or form of supercharging . Also, despite weak
mixtures leading to hotter running (due to slower burning, risking exhaust
valve opening to the flame), its actually rich mixtures that are more likely
to lead to catastrophic detonation (we're talking detonation here not less
harmful pre-ignition) as they burn faster. Detonation is all about flame
fronts turning nasty, and a 'controlled burn' turning into an explosion,
which is not what an i.c. engine, Otto or Diesel is all about. The Diesel
tends to extract its power from the piston during a longer period of
constant pressure expansion, the Otto, a shorter one akin to constant volume
expansion. Picture the piston in a Diesel going down to make room for the
gas burning and expanding above it whereas there is no time for this in a
petrol engine - but we still want a nice controlled flame-front without any
pockets of high pressure gas being pushed towards their detonation
threshold - here's one way of helping...
...the simple fact of the matter is that unlesss the air is compressed
isothermally (impossible, requiring an adiabatic index of 1, the perefct
compressor), it gains heat as well as pressure. We don't want it to -
because it means that its pressure is partly by virtue of its temperature,
and also because the compression is then inefficient. We want to add the
heat in the engine, using fuel !!
The efficiency of all heat engines comes down to one thing - a function of
the difference in temperature between the start and end of the cycle.
At the beginning of the compression stroke we want absolutely as many oxygen
molecules as possible in the cylinder, as then we can introduce a larger
corresponding degree of fuel - which gives us the energy which produces
torque which translates to power when repeated over time. Also the lowest
temperature.
How do we ensure the max # of oxygen molecules? A dense charge - high
pressure at low temperature. If the temperature is already high (due to
non-ideal, partially adiabatic supercharging), it means there is less oxygen
and ALSO the compression BEGINS at a higher temperature. Remember that its
the DIFFERENCE between in temperature from the beginning of compression to
the final temperature reached after burning the fuel that will ultimately
determine the amount of energy potentially unleashed, and the efficiency of
the whole operation.
I think you can see that there's now accumulating MANY reasons why a low
high pressure cylinder fill gives benefits all round - the one I haven't
mentioned is that the final peak temperatures achieved are lower for a given
CR with a lower input temperature - this may seem obvious, but the facts are
that a reduced charge temperature makes much more difference than a
non-thermodynamicist (and I'm not one) could imagine - this is because its
so quick and the cylinder effectively insulated that heat hasn't time to
escape - thus the index of compression is approaching whats known as
adiabatic, about 1.4 in this case - and the heat adds to the pressure
resulting in a curve that increases its slope of pressure Vs temp slowly to
start but quickly steepens as the temperature rises. To round all that out,
start with a high temp in the cylinder and you can't do much compressing
before the max. temperatures and particularly the combination of pressure
and temp. approach levels where detonation is a danger.
Simply, we want cold, high pressure BEFORE we start the compression cycle,
giving the largest HEADROOM for high pressure combustion without detonation
of as much hydrocarbon as possible. The amount of heat that is realeased by
combusting a fuel in oxygen is very dependent upon the starting pressure,
hence all the aforesaid + high as CR's as this will allow, remembering again
that we're on a rather non-linear law here and that above about 12:1
compression gains are diminishing rapidly, and to a small extent, so is the
full cylinder volume that we can fill as the head volume contributes to it.
Since oxygen is the limiting factor, we want to burn it ALL and put excess
fuel in to ensure this happens with the added benefit that a degree of
charge cooling and exhaust gas cooling occurs - the few molecules taking up
space that oxygen might profitably use is a very small penalty - though fuel
consumption goes through the roof.
Getting the mixture right is nothing to do with supercharging and really
after all my woffle here, sounds the easy bit!
It has been suggested that water alone can add to the calorific value of the
fuel, by making it's hydrogen available at these sort of temperatures but I
have long been assured that dissassociation at these temperatures is
unlikely - however, other secondary and subtle effects than its ability to
cool the charge before entry into the cylinder via its latent heat of
vaporisation may come into play - obviously Methanol will release some
energy, but its main use (in both piston and gas turbine aircraft) was to
act as an anti-freeze and boost the latent heat of vaporisation.
The thermodynamic facts to take way here are:
1) An ideal compressor is Isothermal (no heat addition during compression)
2) An ideal Engine is Adiabatic (no heat loss during compression)
Clive Smith
'88 Syncro Transporter
> Higher air temperatures lead to thinner air
and therefore an altered stoechiometric ratio which can lead to a lean
mixture and detonation. In high pressure turbocharged engines the
air/fuel mixture that enters the cylinders can explode prematurely
(before the spark plug ignites, effect also known as engine knock) due
to the extreme engine environment conditions. This situation results in
severe engine damage (piston piercing). To avoid damage to the engine,
water is injected, along with fuel, in the combustion chambers in order
to provide a water/air/fuel mixture which not only burns more
efficiently and avoids spontaneous detonation but also provides
additional inlet air cooling and, hence, denser air.
>
----- Original Message -----
From: "Todd Last" <Rubatoguy@MINDSPRING.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Thursday, July 18, 2002 3:33 PM
Subject: Re: Running on Tap Water
> My understanding that water injection was a mix of water and methonal.
> Water injection was used in supercharged WWII fighters to cool the
> intake charge. It does not generate any additional power on its own.
>
> Here is a simple description:
>
> "A water injection system works similarly to a fuel injection system
> only it injects water instead of fuel.
> A turbocharger essentially compresses the air going into the engine in
> order to force more air than would be possible with the atmospheric
> pressure. More air into the engine means automatically more fuel has to
> be injected in order to maintain the appropriate stoechiometric value of
> the air/fuel ratio (around 14:1). More air and fuel into the engine
> leads to more power. However by compressing the inlet air the
> turbocharger also heats it. Higher air temperatures lead to thinner air
> and therefore an altered stoechiometric ratio which can lead to a lean
> mixture and detonation. In high pressure turbocharged engines the
> air/fuel mixture that enters the cylinders can explode prematurely
> (before the spark plug ignites, effect also known as engine knock) due
> to the extreme engine environment conditions. This situation results in
> severe engine damage (piston piercing). To avoid damage to the engine,
> water is injected, along with fuel, in the combustion chambers in order
> to provide a water/air/fuel mixture which not only burns more
> efficiently and avoids spontaneous detonation but also provides
> additional inlet air cooling and, hence, denser air. There are mainly
> three variations of water injection devices. They are dependent on the
> location of the water injectors. The first technique consists of
> injecting water at the entrance of the intake manifold. The second
> injects water at the exit pipe of the intercooler. The third technique
> injects water at the entry of the intercooler and is only used in
> competition vehicles. In this latter variation most of the in-cylinder
> detonation prevention is done by injecting additional fuel which is used
> as coolant (i.e. is not burned)."
>
> Todd
> '88 Westy
>
>
>
> Barry E. Muller wrote:
>
> >Some WWII fighters (Mustang, Hurricane, Spitfires mebbe) used water
> >injection to temporarily boost performance in extreme situations.
Obviously
> >they were not injecting pure water into the engine - just adding it to
the
> >mix. But hey, I read this 25 years ago, so don't start asking (me) any
> >details. As I recall they could run in this mode for only about 5
minutes
> >or so, before ruining the engine.
> >
> >bem
> >----- Original Message -----
> >From: "Clive Smith" <clive.harman-smith@NTLWORLD.COM>
> >To: <vanagon@GERRY.VANAGON.COM>
> >Sent: Wednesday, July 17, 2002 5:31 PM
> >Subject: Re: Running on Tap Water
> >
> >
> >
> >
> >>'I have noticed that most internal combustion engines seem to run more
> >>smoothly in very wet weather, assuming there are no wiring concerns and
> >>
> >>
> >that
> >
> >
> >>the engine is fully warmed up, but this could be another issue
> >>
> >>
> >altogether.'
> >
> >
> >>So have I, particularly in absolute downpours where the rain hitting the
> >>gound litterly sucks the temperature down by evaporation and the ater is
> >>
> >>
> >not
> >
> >
> >>necessarly held as vapour but as fine droplets. Just at this point they
> >>
> >>
> >seem
> >
> >
> >>to have the ability to radically alter the combustion process, as I have
a
> >>job believing that the whole effect is solely due to reduced inlet temps
> >>
> >>
> >and
> >
> >
> >>the consequent higher charge mass. Shall we synthesise our 'intuitive'
> >>experiences here? Simply injecting water into the inlet without thinking
a
> >>lot about exactly simulating the actual parameters that produce this
> >>
> >>
> >effect
> >
> >
> >>might be too simple.
> >>
> >>Clive
> >>'88 Syncro Transporter
> >>
> >>
> >>----- Original Message -----
> >>From: "Various" <AllStuff@HANS-WILLY.MYIP.ORG>
> >>To: <vanagon@GERRY.VANAGON.COM>
> >>Sent: Wednesday, July 17, 2002 7:58 PM
> >>Subject: Re: Running on Tap Water
> >>
> >>
> >>
> >>
> >>>Please let me preface my remarks by saying that I am skeptical to the
> >>>
> >>>
> >>point
> >>
> >>
> >>>of disbelief whenever someone claims to have invented a perpetual
motion
> >>>machine or broken the laws of thermo dynamics...
> >>>
> >>>A few tens of years ago I remember reading (in NEWSWEEK or TIME?) about
> >>>someone working on a concept about injecting a small amount of water
> >>>
> >>>
> >>(finely
> >>
> >>
> >>>atomized) into the hot combustion chamber, just after ignition. The
> >>>
> >>>
> >>theory,
> >>
> >>
> >>>as explained, was that the thermal expansion rate of the finely
atomized
> >>>water was greater than the expansion rate of the combustion gases,
> >>>
> >>>
> >mostly
> >
> >
> >>>due to the transition from liquid water to gaseous water, and therfore
> >>>
> >>>
> >>gave
> >>
> >>
> >>>an extra kick to the piston for "free". Exeptional gas milage was the
> >>>
> >>>
> >>quest,
> >>
> >>
> >>>the headline giving hope of a 100 mpg future.
> >>>
> >>>The story continued about the Oil companies' concerns and wanting to
buy
> >>>
> >>>
> >>him
> >>
> >>
> >>>out... The concept seemed to me somewhat possible, but I never heard
> >>>
> >>>
> >about
> >
> >
> >>>the concept since (maybe the conspiracy really does exist ;~) ).
> >>>
> >>>I say that this seems possible, not knowing much about the thermal
> >>>
> >>>
> >>expansion
> >>
> >>
> >>>curves of water (steam) and gasoline combustion gases.
> >>>
> >>>I have noticed that most internal combustion engines seem to run more
> >>>smoothly in very wet weather, assuming there are no wiring concerns and
> >>>
> >>>
> >>that
> >>
> >>
> >>>the engine is fully warmed up, but this could be another issue
> >>>
> >>>
> >altogether.
> >
> >
> >>>So let's see where this one goes.
> >>>
> >>>Alias Fred aka Bleu Schtroumpf
> >>>
> >>>
> >>>
> >>>-----Original Message-----
> >>>From: David Brodbeck [mailto:gull@CYBERSPACE.ORG]
> >>>Sent: 17 juillet, 2002 10:04
> >>>To: vanagon@GERRY.VANAGON.COM
> >>>Subject: Re: Running on Tap Water
> >>>
> >>>
> >>>On Wed, 17 Jul 2002, Timothy Crooks wrote:
> >>>
> >>>
> >>>
> >>>>I am no chemist, nor physicist, nor do I claim to be, but it has been
> >>>>demonstrated to, when I was about 14, by a chemist, that water can be
> >>>>
> >>>>
> >>used
> >>
> >>
> >>>>to make a fire burn hotter. He pointed out that there must be a fuel
> >>>>present, but when water as in the form of a steam, a true dry steam,
> >>>>
> >>>>
> >the
> >
> >
> >>>>caloric output is increased.
> >>>>
> >>>>
> >>>Is it increased by more than the caloric input needed to make the
steam?
> >>>
> >>> _ _
> >>> __ _ _ _| | | | David M. Brodbeck (N8SRE) Ypsilanti,
> >>>
> >>>
> >MI
> >
> >
> >>> / _` | | | | | |
> >>>
> >>>
> >+-----------------------------------------------------
> >
> >
> >>>| (_| | |_| | | | @ cyberspace.org
> >>> \__, |\__,_|_|_| "Geekdom is fantastic at being AGAINST something, and
> >>> |___/ it's hopeless at being FOR something."
> >>> -- Andrew Orlowski in The
> >>>
> >>>
> >Register.
> >
> >
> >
> >
> >
| 
