DIY_EFI Digest V5 #718 - knock sensor / Autospeed articles / water injection / dynos etc

[Hugh Keir]

Just read the Autospeed articles by Tim White which are based on his
Bachelor of Engineering thesis presented in November 1999 to the University
of New South Wales School of Mechanical and Manufacturing Engineering.

Any one know if copies are available from Tim or the University or are in
the public domain so we can speak about them?

The title of his thesis is:- "The Effect of Spark-Knock on the Performance
of a Modern Spark-Ignition Engine'.

The first page of each of the three parts of the article can be found at the
following links. To see the remainder of each part you have to subscribe to
Autospeed.

http://www.autospeed.com/A_0587/page1.html

http://www.autospeed.com/A_0594/page1.html

http://www.autospeed.com/A_0601/page1.html

The article talks about the types of sensors used in his tests. Conclusions
are drawn in a number of areas including whether power is still rising in
high compression engines at the onset of knock.

The article also presents a table that shows amongst other things the number
of °C effect of intake temperature etc that = 1 octane of fuel, allowing you
to estimate the cost of reducing the various temperatures etc versus higher
octane fuel and the cost of the modifications ( intercooler, water inj etc )
to your car.

On a turbocharged car ( well mine anyway ) where you are tuning for more
power you will at some point want to increase the boost and optimise the
ignition and fuel. This will have obvious consequences on inlet temperature
and the dreaded " knock ".

The site http://www.aquamist.co.uk/dc/technic/technic.html shows a graph
that backs up many of the results found by Tim White in the Autospeed
article. The lines on the graph show cylinder pressure against crankshaft
angle. It caught my eye that the area under the curve for the water injected
( blue line ) setup was significantly greater than the detonating ( red and
yellow ) and the non detonating ( green line), which must mean significantly
more power from a water injection setup.

Water injection has now become a must have on my shopping list.

The following articles show a DIY water injection kit:-

http://www.autospeed.com/A_0527/page1.html  part 1

http://www.autospeed.com/A_0534/P_1/article.html  part 2

http://www.autospeed.com/A_0574/P_1/article.html part 3

http://www.autospeed.com/A_0578/P_1/article.html part 4

http://www.autospeed.com/A_0589/P_1/article.html part 5

http://www.autospeed.com/site/autospeed/images/0574_00.jpg shows a picture
of the board

http://www.autospeed.com/cgi-bin/browse.cgi?category=705&product=1280 - buy
the kit for AU$ 107.25 = US $58

The DIY-WB has given me and I am sure others ( as soon as the boards and
group buy parts are ready ) a fantastic opportunity to have a real go at
optimising the performance ( don't know if my soldering is good enough yet
but I'm sure gonna find out ) of our vehicles in a way that was previously
never possible.

Mix in a little of one of the following pieces of dyno ( sorry but I just
don't want to do it on a rolling road, I want to do it myself )  software or
possibly a datalog from my as yet unpurchased ECU.

On Track Dyno       http://www.ontrackdigital.com/generic.html?pid=4
Road Dyno            http://www.charm.net/~mchaney/roaddyno/dyno.htm
Revtrigger             http://www.students.tut.fi/~eppu/bin/rev.html#Updates

I have also found this self build datalogger
http://www.geocities.com/93notch/EMS/ , though not sure how useful it might
be.

Only one thing missing in my life , ( well that I can admit to )  a
.......... DIY KNOCK SENSOR .......... any thoughts possibly a modified
version of the SAAB unit http://www.geocities.com/tv41mxa/tweakyourapc.html
or
http://web.inter.nl.net/users/turbo-team-europe/apc.htm or
http://www.users.qwest.net/~qed/volvoapc/index.html

With all the individuals that want to spoil the party and seem unable to say
thanks to the DIY_WB team and abide by their rules,  its hard to believe
that there would be enough enthusiasm to do a DIY knock sensor, but maybe
just maybe.

This is a long post to get to the point that I am passionately interested in
tuning my vehicle not because I race or want to show off or have any
commercial interest, but because I care about how well I have made it run
with tools available to me.

Bruce and the team I take my hat of to you for your selfless efforts to
bring the DIY-WB project to it's conclusion.

I hope that I can do you justice by building the boards myself and reporting
on how I have improved things on my vehicle.

I also hope I may have some skill that you will find useful in the future.

Hugh


----- Original Message -----
From: "Mark Agnello" <m_agnello at yahoo.com>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, August 29, 2001 8:57 PM
Subject: Re: DIY_EFI Digest V5 #718 - knock sensor


>
> > > TVS wrote:
> > > >
> > > > I assume the frequency has some dependence on
> > variables
> > > > like bore diameter and combustion chamber shape,
> > but is the knock detection
> > > > circuitry likely to 'listen' for a wide range of
> > frequency's or just a
> > > > narrow band?
> > >
>
> These are just educated guesses, but I suspect they
> apply.  Detonation is closely coupled to the pressure
> wave in the combustion chamber.  The pressure wave is
> an acoustic event.  As such, it should be influenced
> by the geometry of the combustion chamber at the
> instant of the event.  The dominant mode's wavelength
> will probably be proportional to the cylinder bore.
>
> If the event timespan is too short to propagate
> laterally, then the dominant mode will probably be
> related to the combustion chamber height at the time
> of the event.  Even if there is a lateral mode, I
> wonder if the high frequency content in a knock signal
> is due to the vertical mode(s)?
>
> WRT the cylinder head and/or block structure
> influencing the dominant frequencies, I agree there
> will be some interaction.  Unlike the 10 Hz bell
> analogy, I don't believe there will be a dominant
> vibrational mode of the engine structure.  These
> structures are too complex to have a primary mode and
> I'll bet auto manufacturers spend a lot of time
> designing engine structures that don't have
> significant vibrational modes.  I know aircraft engine
> manufacturers do this.  If they didn't, the life of
> the engine mounted fuel pumps, actuators, sensors, and
> accessories would be severely shortened.
>
> What do y'all think?  Remember, I'm just a lonely old
> EE that likes to read SF.;)
>
> Autospeed published an article based on an Aussie grad
> student's research into engine knock earlier this
> year.  Does anyone have a copy and does it shed light
> on this issue?
>
>
> =====
> Mark Agnello
> Washington Crossing, PA (USA)
> 88 Toyota Celica All Trac Turbo (restoration project)
> 92 Toyota Celica All Trac Turbo
> 96 Honda VFR
> 89 Honda Hawk GT (restoration project)
>
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