On Sat, Jul 23, 2011 at 08:10:24PM -0700, Kevin Shepherd wrote:
>
> Seams we are waiting for the production of a micro deisel. 4 cyl. Fresh water
> cooled. Common rail injection. Bio fuel compatable. Thimble sized cylenders.
> 3hp. With 2kw perm mag gen. Comes in sound enclosure. And under 80 lbs.
Well, small diesels do exist; at least one company makes a 4HP diesel
outboard, and there's a number of diesel motorcycles. But these are all
one-lungers, and *heavy*. The problem is that this approach focuses on
precisely the area where diesels don't do well rather than using their
strengths, and so is ultimately unproductive.
Diesels are fundamentally different from gasoline engines; we tend to
forget that, because the mechanical details are so similar. The latter
convert pressure to work, and the less heat generated, the better; the
former are all about converting _heat_ to work (Rudolf Diesel's patent
was actually titled "Method of and Apparatus for Converting Heat into
Work".) Diesels need thermal mass to run well - which means lots of
heavy, solid chunks of metal. High efficiency in diesels is a product of
being able to conserve that heat; this is why the most efficient diesels
are *huge*, massive machines. The low-speed versions in ships, for
example, exceed 50% thermal efficiency (as contrasted against 24% or so
for the average gasoline engine.)
Better alternatives for this kind of application do exist, but are
unfortunately not well supported (i.e., getting parts for your Stirling
engine would be rather difficult in Borabora. :) Although the whole
micro-CHP approach may change that in the next few years... stay tuned.
--
Ben Okopnik
-=-=-=-=-=-
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