Throttle Plate Control

[robert dingli]

Sorry, I should have included this reply with my previous post.

> >I'm surprised that with an EFI system that people wouldn't consider 
> >cutting fuel rather than spark.  Of course hysteresis as mentioned above 
> >would be a must.  I would guess with too little or no hysteresis, that a 
> >really lean condidtion may occur as the computer would kind of half 
> >heartedly feed fuel right around the rev limit.
> 
> The most probable thing to get as a result is to increase the temperature in 
> the combustion chamber. The fuel actualy acts as a coolant.
> 
> >
> >Has anyone out there played with cutting fuel rather than spark?  If no 
> >one uses this method, why not?
> >
> 
> I think it is better to ignite later, than cutting off the fuel, in that way 
> the engine is not able to raise its r.p.m, while getting sufficient cooling 
> from the  incoming petrol
> 
> 
> /Georg Siotis/
> 

An important point to note is that the engine internals get hot mainly due to 
the combustion of fuel and air.  When the fuel stops, so does the combustion
(at worst a cycle later when the intake fuel puddle evaporates).  The air
circulating through the cylinder is more than enough to cool the system due
to heat generated by friction.  The lean mixture that may be experienced for
a single cycle is not significant.

I have heard of a recent US engine which can actually operate without any 
coolant by alternatively switching out half the cylinders and relying on the
throughput of air for cooling.

Igniting the mixture later (retarded far from MBT) will raise exhaust temps
dramatically, potentially melting the exhaust valves and exhaust system.

One problem with a smooth progressive rev limiter is that the user may not
realise that he/she is at the engine's limit.  I have struck this problem
driving deisels where the power is dropped very smoothly near max rpm.

Robert
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             Robert Dingli           r.dingli at ee.mu.oz.au

Power and Control Systems                 Thermodynamics Research Lab
Electrical Engineering                    Mechanical Engineering
   (+613) 344 7966                           (+613) 344 6728
  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA
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