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PICList Thread
'Water injection'
1998\06\14@234529 by Dennis Plunkett

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15/6/'98

Hello all
So is water injection a black art? It would seem that all the links that
Clyde Smith-Stubbs gave point to aircraft bobing around at 10000 feet
(Things are quite different up there), as for Diesels, this is to reduce the
emissions. Just form the users point of view, if you do an economy run
during the day and another at night which one is best and why (Its not
because your car can not see where its going at night either)?


Dennis



-=====================================================================-

Dennis Plunkett: Embedded Hardware, Software design
NEC Australia DRMASS
ph 03 9264-3867

-=====================================================================-

1998\06\15@031701 by Clyde Smith-Stubbs

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On Mon, Jun 15, 1998 at 01:46:22PM +1000, Dennis Plunkett wrote:
> 15/6/'98
>
> So is water injection a black art? It would seem that all the links that
> Clyde Smith-Stubbs gave point to aircraft bobing around at 10000 feet
> (Things are quite different up there), as for Diesels, this is to reduce the

Actually, often higher than 10,000. For example the P47C Thunderbolt had
an 18 cylinder Pratt and Whitney turbosupercharged engine which developed
2000 horsepower, but optional water injection allowed short-term boost
to 2300 horsepower at 27,000 feet.

The The use of water injection with petrol engines seems
to mainly be useful with turbo- or super-charging, and allows higher boost
ratios to be used without causing detonation. So it's a means of getting
more power, but it wouldn't help a normally-aspirated engine much, I suspect,
and I can't see it would do anything for fuel economy.

> emissions. Just form the users point of view, if you do an economy run
> during the day and another at night which one is best and why (Its not

I don't think it would make much difference. You might get slightly higher
power output at night because the air is cooler, but that wouldn't alter
the economy at all. Basically, for a given engine (or class of engine) you
get power out (driving the wheels) directly proportional to the power in
(as chemical energy from the fuel). The fuel economy of a car depends more
on such factors as how fast you drive (air resistance increases as a power of
the speed, I think it's the square theoretically, in practice it can be
higher), how much energy you lose through braking, etc.

Modern fuel-injection systems are very good at controlling the fuel-air
mixture across variations in air temperature, pressure etc. so these things
should have very little bearing on fuel economy. A carburetted engine
controls the mixure less accurately, so warmer (less dense) air would
result in a richer mixture, which might result in increased fuel consumption.


--
Clyde Smith-Stubbs               |            HI-TECH Software
Email: spam_OUTclydeTakeThisOuTspamhtsoft.com          |          Phone            Fax
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PGP:   finger .....clydeKILLspamspam@spam@htsoft.com   | AUS: +61 7 3354 2411 +61 7 3354 2422
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HI-TECH C: compiling the real world.

1998\06\15@085410 by Steve Baldwin

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> The The use of water injection with petrol engines seems
> to mainly be useful with turbo- or super-charging, and allows higher boost
> ratios to be used without causing detonation. So it's a means of getting
> more power, but it wouldn't help a normally-aspirated engine much, I suspect,
> and I can't see it would do anything for fuel economy.

The basic principle of water injection is to cool the air going into
the cylinder, making it denser and therefore having more oxygen to
support more fuel to make more power. When a mechanical supercharger
is used, it heats up the air in the act of compressing it, so water
injection is one method to get that loss back again.

With any engine (naturally aspirated or forced induction), maximum
power is made when the (dynamic) compression ratio, spark advance,
etc is just before the onset of detonation. One way to get that is to
have the engine right on the edge and then add a little water to cool
it back into the "keep engine intact" zone. (kinda like torqueing a
bolt by doing it up till it strips and then backing off half a turn).
In a new fangled car the same thing is done with a knock sensor and
ignition retard. These things are all to make more (or rather get the
most) power from the engine and to make power you are running it rich
anyway.

There is an alchemist form of water injection that claims to do
one of the things that exhaust gas recirculation does, which is to
take up some of the space in the cylinder with an inert gas (exhaust)
and effectively make the engine a bit smaller.

If you really want to cool an intake charge, Nitrous Oxide is a far
more fun way. :-)

Steve.

1998\06\15@213157 by Sean Breheny

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While on the subject of engines and cars, I would like to ask a slightly
related OT question that has been bugging me for a long time: How can a
car sit still on a hill with the engine holding it from rolling
backwards? The engine, of course, needs to keep its crankshaft turning in
order not to stall. However, the wheels are not turning in this case.
Somehow, the torque is being transferred from the engine to the wheels
while alowing them to move independently of the crankshaft. How is this
possible? What component in the drivetrain allows this?

Thanks,

Sean

1998\06\15@235855 by Dan Larson

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On Mon, 15 Jun 1998 18:00:21 -0400, Sean Breheny wrote:

>While on the subject of engines and cars, I would like to ask a slightly
>related OT question that has been bugging me for a long time: How can a
>car sit still on a hill with the engine holding it from rolling
>backwards? The engine, of course, needs to keep its crankshaft turning in
>order not to stall. However, the wheels are not turning in this case.
>Somehow, the torque is being transferred from the engine to the wheels
>while alowing them to move independently of the crankshaft. How is this
>possible? What component in the drivetrain allows this?

In a car with an automatic transmission,,, the :"torque converter" of course.

It is hard to explain, but it is an oil filled cavitiy in which two matched
turbines are attached to the input and output shafts.  Oils fills the voids
between the "vanes".  When the input shaft turns one turbine, the oil drags
the output turbine along.  It sort of takes the place of the clutch in a
manual transmission.

That's the best description I can give you as I am a non-mechanic!

>
>Thanks,
>
>Sean
>

Dan

1998\06\15@235904 by Dennis Plunkett

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At 06:00 PM 15/06/98 -0400, you wrote:
>While on the subject of engines and cars, I would like to ask a slightly
>related OT question that has been bugging me for a long time: How can a
>car sit still on a hill with the engine holding it from rolling
>backwards? The engine, of course, needs to keep its crankshaft turning in
>order not to stall. However, the wheels are not turning in this case.
>Somehow, the torque is being transferred from the engine to the wheels
>while alowing them to move independently of the crankshaft. How is this
>possible? What component in the drivetrain allows this?
>
>Thanks,
>
>Sean
>
>
The tourque converter in an automatic gearbox is the base point for engine
controlled non roll back. On some manual cars the brakes are used.

On card pre 1990 models, heal and toe prevented both roll back and roll
forward :-)


Dennis

-=====================================================================-

Dennis Plunkett: Embedded Hardware, Software design
NEC Australia DRMASS
ph 03 9264-3867

-=====================================================================-

1998\06\15@235914 by Mike Hamilton

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This only happens with an automatic transmission.  The crankshaft is
connected to what is known as a torque converter.  There is no physical
connection between the crankshaft and the wheels, instead there is a
"liquid" connection.  When the crankshaft hits a certain rpm, it causes the
liquid to spin.  The energy is transferred through the liquid to the other
side of the torque converter where the power is transferred to the wheels.
The car won't move until the gas pedal is pushed far enough to overcome the
friction and gravity holding the car back.
{Original Message removed}

1998\06\16@002329 by David Lions

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Not driving yet?  :)

The _neutral_ gear disconnects the engine from the rear axle.  So you
can use your brakes to stop the car without stalling the engine.  I only
know about manual gearboxes.


Sean Breheny wrote:
>
> While on the subject of engines and cars, I would like to ask a slightly
> related OT question that has been bugging me for a long time: How can
...
> possible? What component in the drivetrain allows this?
>
> Thanks,
>
> Sean

1998\06\16@093042 by paulb

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Dennis Plunkett wrote:

> Just from the users point of view, if you do an economy run during the
> day and another at night which one is best and why (Its not because
> your car can not see where its going at night either)?

 What about the extra 200W of lighting power divided by the efficiency
of the generator (alternator)?  If we're talking about an "economy run",
this could be significant.

 Cheers,
       Paul B.

1998\06\16@140328 by Barry Cooper

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At 12:05 PM 16.6.98 +1000, you wrote:
{Quote hidden}

 I used to hold my truck (ute if your are in Australia) with the clutch.
Mind you, I also thought clutch replacement was an annual event. (g)

       Barry

1998\06\16@213829 by Kolesnikoff, Paul

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Boy is this getting way OT. However, I couldn't resist this one. For 25
years I have been using my clutch to keep the car from rolling backwards
on a hill, and only now do I find out that I needed an automatic
transmission. The truth is that whether you have an automatic or a
standard transmission, to keep a car still on a hill, you need to get
the force that is applied to the wheels to match the force of gravity on
the car. With an automatic transmission, you do this by adjusting the
RPM of the motor as the slippage in the torque converter is fixed. With
a standard transmission, you have two means of controlling the force
applied to the wheels. The first is the gas, and the second is the
clutch. By holding the clutch partway in, you can get it to slip, so
that only a portion of the motors power is transferred to the wheels. To
keep from burning up the clutch, you give the motor just enough gas to
keep it from stalling.

Of course, servos could be put on both the gas and the clutch, along
with a motion, tilt, and stall sensor thus allowing a PIC to perform the
anti-rollback function automatically. Now let's talk about the
techniques needed to implement this scheme.

Hope this helps,
Paul Kolesnikoff


Date:    Mon, 15 Jun 1998 18:08:38 -0700
From:    Mike Hamilton <mikeh9spamKILLspamEARTHLINK.NET>
Subject: Re: Water injection

This only happens with an automatic transmission.  The crankshaft is
connected to what is known as a torque converter.  There is no physical
connection between the crankshaft and the wheels, instead there is a
"liquid" connection.  When the crankshaft hits a certain rpm, it causes
the
liquid to spin.  The energy is transferred through the liquid to the
other
side of the torque converter where the power is transferred to the
wheels.
The car won't move until the gas pedal is pushed far enough to overcome
the
friction and gravity holding the car back.
{Original Message removed}

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