I had often read that one should avoid running a diesel engine unloaded
(i.e. without the prop turning) as this will result in glazing of the
bores. This is usually mentioned relative to the idea of running the
engine for electrical needs.
However, it seems to me that narrowboat engines are usually only
lightly loaded. In the old days, only one horse (one horsepower) was
needed to propel the boat, though nowadays we prefer a little quicker
get up and go. I read somewhere recently that on a normal canal run,
only about 5hp are needed. However, boats may have 20-45 hp engines
installed. Clearly such engines are not heavily loaded, a so perhaps
bore glazing is to be expected with ordinary usage?
The wikipedia page on Diesel Generators says, with respect to bore
glazing, that "Ideally diesel engines should run at least around 60-75%
of their maximum rated load, and at around 75% of their maximum speed."
(An interesting sidelight to this page is that diesel gennies that are
lightly loaded also can get bore glazing).
My understanding is that the extra engine power is needed for quick
stopping and river cruising, so engines should not be smaller.
However, I remember that some automobile company had an engine that
would turn off some cylinders when less power was needed. I don't know
enough about diesel engines to know if that would help deal with the
problem - if there in fact is one.
Of course, maybe it takes so long to develop significant bore glazing
that most boatowners would never see it.
Anyway, suppose one had an alternator on their engine capable of
producing 3.75 kilowatts, and a way of using that (washer, vacuum,
etc.)
Then since 1 hp is roughly .75 kw, such an arrangement would appear to
use 5 hp, just the same as normal cruising, and so would be no more
harmful to the engine.
Tell me where I've gone wrong. A little knowledge is a dangerous
thing.
- george
www.canals.com [still down]
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