Atomization vs Vaporization

[Greg Hermann]

At 10:03 AM 12/11/01, Steve.Flanagan at VerizonWireless.com wrote:
>Robert,
>
>Good info,
>
>But what can we do as engine tuners to  control Atomization vs Vaporization?
>
>I am asking specifically for a turbo application.
>
>The only things I can play with are Intercooler Temp (which I want as cold
>as possible), Boost (which I also want as high as possible),  Fuel Pressure,
>and Injector Pulse width.

A cooler inlet tract retards vaporization, generally a good thing. For one
thing, both fuel and water reach their saturation partial vapor pressure at
a much lower level in cooler air.
>
>Are you better off with a Harder - Shorter spray or a Softer - Longer spray
>(High fuel pressure vs Low Fuel pressure?)

High fuel pressure and smaller injectors tend to produce better (finer)
atomization. Pintle type injectors (Bosch design) tend to produce better
atomization than ball or disc type injectors ( Rochester or Lucas designs,
respectively). Unfortunately, the ball and disc design injectors offer a
wide dynamic range than the pintle type do. (More compromises here.)
Kinsler Fuel Injection has some pretty good info on the various injector
designs.

To me these facts present a pretty good argument in favor of staged injectors.
>
>Here is a question I asked a week or two ago:
>
>Does the temp of the Air coming out of the intercooler effect the
>atomization process?  Can too cold of an air charge hurt atomization????????

Not much effect on atomization from charge air temp. As mentioned above,
there is an effect on vaporization.
>
>One last thing, what effect does a temp change on air do the requirement for
>the fuel?  Lets say you can get the air charge to go from 130 deg C to say
>100 deg C,  how much fuel should be added.  Can you simply use the PV=nrT
>(converting to Deg K) formula and consider it a linear function.

Yep. Fuel mass flow requirement is going to depend very strongly on inlet
tract air density. (Don't expect a perfectly direct relationship, though:
VE drops somewhat as inlet tract air density increases because pressure
losses in the ports, etc. increase with air density.)
>
>Thanks
>
>Steve

Greg


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