[Rhodes22-list] Stupid people tricks

[Roger Pihlaja]

Richard,

There is no disputing the fact that 2-cycle engines produce more power per
unit weight than 4-cycle engines.  Their high specific power, relative
simplicity, low weight, & low cost are the reasons why they dominated the
marine engine market for so long.  But, those factors are not the issue
here.  The reasons why 2-cycle marine engines should be phased out ASAP are
that they consume almost 2X as much fuel & emit at least 10X more pollutants
in their exhaust as 4-cycle engines.  These pollutants are discharged
directly into the upper layer of the water, where they can cause dramatic
harm to the small organisms at the base of the food chain.

I would be interested in seeing a breakdown of how much of the heat in a
2-cycle engine is absorbed in vaporizing & heating up the incoming charge.
Given the low heat capacity & latent heat of vaporization of air & gasoline,
I wouldn't expect it to be very much.  If that's how the 2-cycle engine
cools itself, then it's a good thing they use almost twice as much fuel per
unit power than a 4-cycle engine because they would need to to reject the
heat.  Realize that the same sort of charge preheating occurs in a 4-cycle
engine, except not to as great an extent because the volumetric efficiency
of a 4-cycle engine is almost 2X that of a 2-cycle engine.

I'd be very surprised to see any 2-cycle outboard engine survive the torture
test my son put our Honda thru without seizing.

Roger Pihlaja
S/V Dynamic Equilibrium

----- Original Message -----
From: "Christine Allison" <sailnut at asan.com>
To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
Sent: Wednesday, July 16, 2003 4:50 PM
Subject: Re: [Rhodes22-list] Stupid people tricks


>
> <In effect, any 4-cycle engine is also partially "oil-cooled", a
> > property which 2-cycle engines do not have.>
>
>
> Quite a bit of study has been done in respect to this issue as it respects
> model aircraft engines.  It has been discovered that a good deal of
cooling
> occurs when the fresh fuel/oil mixture is inducted into the engine.  In
fact
> it is this cooling property that mandates the presence of a glow plug.  In
> the case of model aircraft purpose designed four stroke engines there is
no
> separate oil supply.  The oil is mixed with the combustible ingredients
> inducted and exhausted at the proper times in the cycle just like a 2
> stroke.
>
> The principal advantage to any 4 stroke engine (vs 2 stroke) is the fact
> that the cylinder is purged of the spent combustion products resulting
from
> the prior power stroke before inducting the fresh charge.  In other
respects
> a 2 stroke engine, operating at it's most efficient RPM will produce more
> power for it's displacement then an equivalent 4 stroke. Very simply a 2
> stroke has less internal friction and can burn more fuel per revolution of
> the crank all that equates to power.
>
> It is not unusual for a 2 stroke engine displacing 6./10 inch to produce
> more then 1 hp at its power peak.
>
> However it is true that the oil, acting as a sink,  in a 4-stroke outboard
> engine is responsible for a large percentage of the cooling.burden.
>
> Richard Smith
>
> __________________________________________________
> Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
>
>