<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content="text/html; charset=iso-8859-1" http-equiv=Content-Type>
<META name=GENERATOR content="MSHTML 8.00.6001.19046">
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT size=2 face=Arial>Somewhere the efficiency ratio changes because,
although Vancouver had the misfortune of the fast ferry fiasco, the jet drive
system is a popular marine propulsion engine in certain size ships.There seem to
be a definite limit to the efficiency as per power to weight
ratio.</FONT></DIV>
<DIV><FONT size=2 face=Arial>H.</FONT></DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=dmc@danielchisholm.com href="mailto:dmc@danielchisholm.com">Daniel
Chisholm</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=gasification@lists.bioenergylists.org
href="mailto:gasification@lists.bioenergylists.org">Discussion of biomass
pyrolysis and gasification</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, May 26, 2011 12:52
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [Gasification] Underwater
gasification?</DIV>
<DIV><BR></DIV>A Humphrey is a low-compression ratio, low pressure piston
engine. As such it will have a lower thermal efficiency than a higher
compression ratio engine, though that does not necessarily mean it is a bad
solution. The elegance of a Humphrey comes from the fact that its piston
and its workload happen to be one and the same thing (a column of water),
which allows it to avoid high speed machinery, reduction gearboxes, rotary
pumps etc, all of which have a dollar and efficiency cost. (and a side
comment for what it's worth - the combustion process in a Humphrey engine
would be a lot closer to being a constant volume rather than a constant
pressure one).
<DIV><BR></DIV>
<DIV>With a reaction engine, the lower the speed of the vehicle, the more
strongly its propulsive efficiency depends on accelerating a large mass a
small amount. Marine applications are very slow speed, which is why
efficient marine propulsion systems use very large propellers, which
accelerate enormous columns of water a very small amount.</DIV>
<DIV><BR></DIV>
<DIV>This is why a container ship uses large propellers rather than a jet boat
type of propulsion.</DIV>
<DIV><BR></DIV>
<DIV>Propelling a ship by means of a steam jet would be an even bigger
mismatch (an exhaust velocity of hundreds of meters per second, versus a
vessel speed of only ten or so m/s), the efficiency would be miniscule.</DIV>
<DIV><BR></DIV>
<DIV>Perhaps this might help to understand why a reaction engine's
exhaust speed affects its propulsive efficiency:</DIV>
<DIV>
<UL>
<LI>The energy that it takes to accelerate a mass jet is proportional to the
mass flow rate, times the square of the jet velocity (which is to say - to
the kinetic energy that you are delivering to the jet).
<LI>The thrust that that mass jet produces is proportional to the mass flow
rate times the jet velocity (which is to say - to the momentum that you are
delivering to the jet)</LI></UL></DIV>
<DIV>If you look to optimize the problem (reduce the amount of energy it takes
to produce a given level of thrust), you will see that propulsive efficiency
is improved by accelerating a larger amount of mass by a smaller
delta-V.</DIV>
<DIV><BR></DIV>
<DIV>
<DIV>
<DIV><BR>-- <BR>- Daniel<BR>Fredericton, NB Canada<BR></DIV></DIV></DIV>
<P>
<HR>
<P></P>_______________________________________________<BR>Gasification mailing
list<BR><BR>to Send a Message to the list, use the email
address<BR>Gasification@bioenergylists.org<BR><BR>to UNSUBSCRIBE or Change
your List Settings use the web
page<BR>http://lists.bioenergylists.org/mailman/listinfo/gasification_lists.bioenergylists.org<BR><BR>for
more Gasifiers, News and Information see our web
site:<BR>http://gasifiers.bioenergylists.org/<BR><BR><BR><BR>__________
Information from ESET NOD32 Antivirus, version of virus signature database
6156 (20110526) __________<BR><BR>The message was checked by ESET NOD32
Antivirus.<BR><BR>http://www.eset.com<BR><BR></BLOCKQUOTE></BODY></HTML>