EFI stuff, (so I don't get kicked off the list)

[Bill Bradley]

> I propose that, (and I won't even mention Occam), oop's, it slipped out,
> that there is a fundamental assumption being made, that one part of the
> problem, ie. fuel delivery, mixture, & burn, is being addressed the same
> way, focussing on the fuel side.
> Why is the "air" charge not being highly compressed into the fuel
> charge, (like Coke, a fizzy thing), and then delivered during the power
> stroke, resulting in "cooled" burn, more precise air/fuel ratio

	1) Because the stociometric ration of air to gasoline is 14.7:1
by mass.  Trying to cram 14.7grams of air into one gram of gas would
be quite a trick
	2) Because compressing the air takes work and energy.  No matter
how or where you do it.  A cylinder is actualy pretty efficient at it.
	3) Telling the fuel and air expand loses energy.  The amount of
energy you get out depends on the ratio of the maximum cylinder volume
to minimum cylinder volume (also known as the compression ratio), the
higher the ratio, the better (why diesels at 20-30:1 are much more
efficient than gasoline engines at 7-12:1)  This extracts the heat energy
(good ol' PV=nRT), that's why diesels don't put out nearly as much waste
heat either.


	Ideally for maximum efficiency you want as high a compression
ratio as possible.  The problems that come up are pressure (how much can
the head, block, etc take), heat (the more you cool the engine, the more
energy you lose), and compression ignition (the heat of compression
igniting the fuel).  Diesels use compression ignition (look ma, no
spark plugs!) gasoline engines try to avoid it (where it's called knocking
and pinging)
	The best diesel designs control the fuel-air mix by injecting the
fuel right into the cylinder (see VW and Audi TDI(turbo direct injection)
diesels) which get incredible mileage, good power, and don't sound like
diesels (since the fuel is injected in stages its much smoother power).
	Unfortunately you can't get them in the US (AFAIK) despote Europe
getting 58mpg Golf TDIs, and 40+mpg Audis and Volvo 850s using the TDI
6 cylinder.  Similar technolgoy exists for direct cylinder gasoline
injection, but there still seem to be technical problems since I've seen
papers for systems going into production "Real Soon Now" for at least
25 years (The oldest I have a copy of is a Texaco design for injecting the
fuel directly at the spark plug at the top of the compression stroke to
give a locally rich burning condition and be able to use a very high
compression ratio without premature ignition problems.  Neat idea...wonder
whatever happened to it)

	Another route is lean-burn engines.  Inject less fuel than would
burn completely in the cylinder.  This produces higher termperatures inside
the chamber and extracts more of the energy due to more complete combustion
of the gasoline (less CO and HCs in the exhaust too).  The Honda CVCC 
3-valve per cylinder was a lean burn design, as have some of their other 
engines.  The drawbacks are that lean mixtures are hard to keep lit to
burn completely, they burn very hot(nasty to engine components), and 
produce more Nitrogen Oxides than a conventional design.


	Bill