Turbo Lag

[RAGHBIR SIAN]

>Hello all,
>
>An idea which we have been discussing is injecting fuel into the exhaust
>manifold during periods of closed throttle in order to keep the turbine
speed up >and reduce turbo lag.
>Has anyone tried something like this? Would the burning fuel damage the
>turbine blades? What type of injector would be suitable? (maybe a Diesel
>injector.)
>
>All ideas appreciated!
>Chris Howard

>What you are looking for is called an Anti-Lag System (ALS).  It is
>used in many rally-race cars that compete in the WRC.

>This system actually causes an intentional mis-fire by not firing one
>of the cylinders.  The air/fuel mixture is still injected, and ends up
>getting pumped out the exhaust. 
>The system is currently used on several Rally cars in the US.  It is
>supposed to keep the boost always running atleast 10-12 lbs.
>The biggest draw backs to this are the noise and the flames that shoot
>out the exhaust.  (I wonder how a Catalytic converter would react to
>this.)

Hi Chris,

I have worked on Anti lag systems (Um-Luft for Germans) for quite a while
(about 4 Years). Most of what people have said is partially correct hence i
have decided to reinforce what they have said and also clarify the issue.

         ANTI LAG.
What you basically do is as soon as you come of the throttle pedal and the
ECU senses the throttle is shut you retard the ignition timing to about 30
degrees after TDC YES that is correct and at the same time dump some fuel
and also open the idle speed valve to fully open(You cannot burn fuel
without air (somebody is going to try and prove me wrong)). This does two
things lets the fuel and air into the cylinder (remember the amount of air
in a cylinder is quite small during periods of shut throttle) which carry on
combusting until after the exhaust valve is opened, and any residual fuel
shall burn close to the turbine, hence increasing its speed and hence the
boost pressure at shut throttles.
You can only do this for periods of no more than 5 seconds because the
pumping losses of the engine become fairly high and the advantage of anti
lag becomes somewhat of a disadvantage.

We have used air and fuel injectors in the exhaust and also elecris motors
with a centrifugal clutch which disables the shaft at a predetermined speed
hence freeing the wheel to spin with the exhaust gases.

Clint mentioned Ford motorsport in the U.K used an ALS system. well all i
can say about that is they were very late in introducing the system and
secondly did not have a clue of how to implement the control hence the
spitting of turbo charger turbines through the exhaust. 

I hope this helps.
If you have any more questions please mail me direct as i think would be
cluttering up the bandwidth. I would be happy to carry on if nobody minds.

ciao
R.S.Sian

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                     Raghbir Sian    
  Engine Control and Combustion Analyst

"As Always A ***CONTROL*** Freak"
A committee is a group of the unwilling, chosen from the unfit, to do the
unnecessary....   Anonymous
Life is just one damned thing after another...  Joseph Heller
Time spent on any item of the agenda will be in inverse proportion to the sum 
involved.

E-mail: sian at mail.bogo.co.uk
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