On Thu, 17 Jul 2003 22:29:44 +0100, Stewart
wrote:
From a point at sea, to the circles of your mind, this is Austin
Shackles:
I like the idea of using all that cold which is otherwise wasted when
running the engine.
Actually, you are (normally) using the heat which is otherwise wasted.
In this respect I suppose you are adding to nett efficiency.
If your plan will end up drawing the same amount of heat out of the
air, into which all waste heat from the engine is lost anyway, then
the overall system efficiency will not be affected. But if the
vapourised gas being drawn into the engine ends up being colder than
usual, then I guess you are going to be running your engine less
efficiently.
I would also guess that the quantities will be small, but just thought
I'd add some extra factors for you to calculate on the back of that
envelope.
It's a double edge sword.
The higher the inlet temp, the higher the peak temp the greater the
possible theoretical efficiency. Higher temps lead to engine damage
and melt down, good job the water has some additional cooling. But
the lower the inlet temp the denser the charge the greater the
volumetric efficiency. This is usually the winner, it's why even
injection LPG loses efficiency and uses more BTU/mile or KJ/Km
compared to petrol. Petrol vaporises in the inlet giving a slightly
better VE.
The best place to vaporise LPG is in the ENGINE! But so many people
only see LPG as a means to save money on slow gas guzzling
agricultural vehicles. They are quite happy with (nay their meaness
demands) low cost solutions comparable to the surface carburetor used
in Veteran cars. They don't demand the proper application of the fuel,
making use of it's greater inlet cooling and high octane rating to
allow use of High compression and/or HP turbo's with reduced/no need
for a flow restricting intercooler.
Then Toyota (New Prius) and others (Ford are on the bandwagon for gas
guzzling SUV's stateside) go and throw induction VE away by holding
the inlet valve open to half stroke so they only compress half the
full cylinder volume (at whatever pressure the throttle allows) into
an under sized combustion chamber giving 13.5:1 compression from BDC
to TDC. Appears high but moderate in geometric terms from inlet valve
closed point. As it has a high expansion ratio like a high comprssion
Diesel it gives Diesel like efficiency at part load. The downside is
that flat out they only fill the cyclinders to half volume so a 1500cc
Prius works like a poor 750 - 57bhp (+40bhp electric is 5bhp more than
the normal Paseo 1500's 92bhp). The Atkinson or Miller cycle. Now
all we need is someone to feed them LPG for low diesel fuel consumpion
rates on half price fuel!
http://www.pressroom.com.au/pressroo...s/priuskit.htm
If they where really green minded it would be LPG only to start with.
--
Peter Hill
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