Atomisation

[Dave Williams]

-> Interesting...I must admit that I had thought that, under part
-> throttle, as the runner velocity was low it was better to inject at
-> the narrowest point. I hadn't thought about whether the poorer
-> atomisation would countermand this.

 The TBIs inject as far away from the valve as possible, into the
low-pressure (15-19 inches of vacuum) intake tract.  There's plenty of
*time* for vaporization to occur, plus the sonic flow across the
butterfly goes a good job of breaking the fuel up to start with.  The
port injectors are like pissing into a urinal; the fancy spray patterns
the books show only exist for a small part of the injector's duty cycle
if you look at one with a strobe.


-> I guess we are assuming here that a TBI system will have a larger ID
-> than the carb as it will not need a venturi?

 They run slightly larger butterfly sizes than carburetors on the
average, and without the venturis the flow is typically higher.  Some
TBIs mount the injector in such a way as to restrict air flow, though.

 Ford's second-generation injection for their DOHC Indy motors went from
conventional injection nozzles to injecting into venturis to help
atomization.  It helped mid-range torque a lot, and dramatically
improved fuel consumption; enough to let them eliminate one fuel stop.
                                                           
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