Fuel injector optimum location

[robert dingli]

Charlie Harris writes,

> Placement of the fuel injector always seems to generate a lot of
> "discussion".  Unfortunately, there isn't always an easy answer, even in
> similar conditions.  As an example, I'd like to point out the difference in
> injector location on two Indy car engines.  The Ford-Cosworth variety places
> the injector low in the port, just above the inlet valve.  This should enable
> more precise distribution between cylinders, though at some loss in  fuel
> evaporation due to the slightly shorter travel.  The Mercedes Benz-Ilmor (my
> job, BTW) places the injectors high above the trumpets.  This gives slightly
> more time for fuel vaporization, but gives slightly less control over where
> the fuel ends up.

Injector location can also affect throttle response.  Injectors closer to the
inlet valve provide a shorter path for the liquid film and better transient 
response.

An SAE paper detailing Mazda's 1993 (??) LeMans engine (the 26B quad rotor
that was mentioned a few weeks back) mentioned the benefits of at least a 
couple injector positions with respect to power and economy (they were
running in a fuel quantity restricted class).  I can't find the reference 
right now, but as Charles mentioned, injectors placed further up the inlet
stream result in better vapourisation and mixing.  There is also more time 
for the vapourising fuel to absorb heat from the air - cooling the inlet
charge.  The down side is an increase in response time.

One of my project cars (Toyota Celica RA23, 3SG 16v) has the injectors
mounted in the head which makes inlet manifold fabrication rather easy.

regards,
Robert

-- 
    Robert Dingli   r.dingli at ee.mu.oz.au
Power and Control Systems    (+613) 9344 7966
Thermodynamics Research Labs (+613) 9344 7712
     University of Melbourne, AUSTRALIA 
**  he who dies with the most toys, wins  **