believe iot or not

[Clare Snyder]

>
> Date: Thu, 20 Jan 2000 23:55:06 -0500
> From: "Bruce Plecan" <nacelp at bright.net>
> Subject: Re: Believe it or not... NOT
>
> This doesn't make sense to me.  Static CR would remain the same.
> The dynamic/effective CR should still be the same since nothing none
> compressable was added to the mix.  The VE should drop (less O2 to react),
> hence lower fuel amount needed, leaner mixture takes longer to burn hence
> more timing needed.
> Grumpy
>
He's got it down pretty close.
Addition of an inert gas allows more complete filling of the cyl with less
fuel, yet no leaning of the mixture. Lets say for argument's sake a full
charge is one litre. At low load, partial throttle, VE may be throttle
limitted to 20or 30%. The A/F mixture is 14:1. CR is 8:1.
With a 30% VE effective CR is  reduced somewhat - possibly as low as about
3:1.

Now, lets add 200cc of inert gas to the cyl.
We now have an effective VE of 40 or 50%, raising the effective compression
ratio at the same throttle opening, with the same A/F ratio, to closer to
5:1.

We get the same power out of the burning fuel - likely even a bit more due
to more squeeze. We also expand the inert gas charge due to heating, and a
portion of the heat that would normally go out the pipe is absorbed here.
This absorption of cyl heat by the inert charge also reduces the cyl
temperature to a point where less nitrogen is oxidized, thus reducing NOX
emissions.

A Miller Cycle engine takes this to extremes, with the engine running for
all practicle purposes at close to 100% VE for the majority of it's
operating regimen.
>
> | As the exhaust is 70% nitrogen and nearly 30% CO2 it is very nearly
> | inert gas. Adding this gas without any change in throttle position
> | increases the relative compression ratio.
> | The raised compression allows the engine mapper to
> | lower the amount of fuel  i.e. increase the A/F ratio to a greater
> | number prior to the onset of unstable combustion.
>


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