Copy Link
Add to Bookmark
Report
Saxonia Issue 02 Part 050
The hot bulb engine
By Rumrunner/VOID
~~~~~~~~~~~~~~~~~~~
Before I get into the topic of the hot bulb engine, I want to tell a
little story to get everybody in the right mood. Here we go :
Having found a nice harbour, you sit in your boat with a nice cup of
coffee, freshly brewed. The wind is cool, and the air is fresh. You hear
seagulls calling out an internal message on the other side of the bay.
Then, something cathes your attention. You hear a sound from far away.
You almost don't notice that it is a sound, it's more like a feeling.
A majestic, calming, rythmic beat, finding it's way to your soul, giving
you impressions that will stay with you for as long as you live.
Some minutes later, a proud old wooden ship, about 38-44 feet long, comes
in sight. The sound increases. The boat comes even nearer. It's now only
a few shiplenghts away from you. The man on the rudder reaches for a
small handle. The sound slows down, before it picks up speed again in the
next second. The boat is now still, and the man lets an anchor go. Some
minutes later, the sound is gone.
What you have been witnessing in this situation is most certainly the
sound of an old hot bulb engine. A very special kind of engine which was,
as far as I know, mostly used in Norway, Sweden and Denmark for boats, but
used more commonly in the rest of the world for stationary purposes.
First a little about how such an engine is built. I will consentrate
mostly on the engines built in the nordic countries, but I don't think
that the differences will be too big on engines built elsewhere.
To start with, the common hot bulb engine is a one or two cylinder engine.
Nothing amazing about that, you might think. Many small engines are one
or two cylinders. Well, that's another case, but here, each cylinder is
much biggter than you would believe when you read the horsepower rating.
It's quite common to find engines with a size of 1830 cubic inches (30
litres) on each cylinder. If you look at the pistons, they could well be
used for buckets. Such size need to be supported with big a huge crankshaft
and huge bearings and, well, let's just say that the size in general is big.
Now, people not familiar with these kinds of engines may be thinking about
horsepower now. They will most likely be disappointed when reading the HP
rating on the engines. A huge engine will perhaps be rated at 40 HP. So
what's this? What one needs to know is how these engines work. When you take
a look at todays boat-engines, they are pretty much the same as in cars,
often they are regular car engines built up with water cooled exhaust
manifold, a heat exchanger (like a radiator in a car but cooled with sea
water), and perhaps tuned for better strenght at lower RPM (revolutions in
a minute). These new engines also use a gearbox, although not like in cars.
Most have free, ahead and back. Usually, they also incorporate some kind
of seawater cooling to prevent the oil in the gearbox from getting too hot.
Well, this is not how the hotbulb engines work. They are not meant for 4000
revolutions in a minute, they are hardly meant for 400 RPM, although some
might reach that high (yes, that's really fast) speed. They work mostly
in regions from 30-250 RPM, smaller engines might do a little more, perhaps
350 RPM. The huge volumes gives an extreme strenght from the slowest speed.
So what these engines lack in horsepower, they more than make up for in
torque (you know foot-pounds and similar). I have yet to hear about a
hotbulb engine using a gearbox, the propeller shaft is connected directly
to the crankshaft, so the propeller spins just as fast as the engine. Today
this is uncommon even in big ships. To be able to stand still with the
engine running and change from ahead to back direction, the propeller is
usually made so that you can turn the blades on it. And you need a huge
propeller, which really is a plus, as is doesn't give as much slip in the
water as a small, fast revving propeller does.
Now, consider this enormous strenght and that you get many such one
cylinder engines. How does this run? Simply, the sound is smooth and even,
you can count each stroke of the engine. Taking into account that most
hotbulbers were two-stroke engines, this means that a speed of 60 RPM in
a minute on the engines gives 60 ignition strokes in the same time. That's
one stroke every second. Listening to this relaxes you. Now, when you are
standing away from a boat equipped with such an engine, in addition to
hearing it, you can almost feel it, it's as if it becomes a part of you.
It's one of the very few things that human beeing ever has made that has
given me this feel.
The feel on the engine when you are on board, is perhaps a bit scary for
some. Imagine such an engine hammering away, it's not hard to understand
that you can certainly feel it. Standing with a cup of coffee on deck, you
can see rings in the coffee, as if you had thrown a small stone into it.
Looking at filmrecordings done on such a boat leaves you with the
impression that the man behind the camera was drunk, that is, until you
have read this. The boat really lives with the engine.
Now, I have a true example of what this can do to a young mind that does
not know what it is all about. A young couple with a kid had bought a boat
with such a hotbulb engine. When takig it home, the kid, 3-4 years old
suddenly disappeared. They found him in the engine room where he sat
listning to the engine. He's studying to become a music teacher now. And
music it is, forget about a loud noisy disco, listen to a hotbulber instead.
The steady, natural, warming, caressing sound is something that will live
with you for years.
I think that it's now time to tell a little more indepth how this engine
works. As said two-stroke engines were most common, although there were
some four-strokers too. Now, think of a diesel engine. Just like the
diesel, the hotbulber pumps the fuel directly into the cylinders. But the
engine needs some form of igniting help unlike the diesel. This is where
the name "how bulb" comes from. A part of the cylinder head is dedicated to
the purpose of igniting the fuel with red hot iron. To start the engine,
you need to heat up this part, either by the use of a blowtorch or simply
burning fuel in a little tray. When it's how enough, you start the engine
either by handpower on the smaller engines or with high airpressure on
the bigger ones. When the engine has started, you don't need to keep
heating the hotbulb anymore as the fuel burnt will keep it hot enough,
you even get a "free" form of ignition advance setting. The more fuel the
engine burns (which often implies higher RPM), the hotter the bulb will get
and the sooner the fuel will ignite, which is good. Otherwise, much fuel
would be wasted.
Although you need to keep the hotbulb hot enough, it should not get too
hot. This was a problem on some early engines, and you could find yourself
with a cracked hotbulb, which you had to change before you could continue
your voyage. This problem was solved in several ways. For example, the
nozzles which delivered the fuel to the cylinder could be turned around.
Upon starting the engine, the fuel stream went directly towards the hotbulb
but then the nozzle was turned downwards, towards the piston. Another way,
mostly found on the Swedish Bolinder engines (only on the smaller ones), was
letting a little stream of cold water into the cylinder. You know what would
happen if you get water in the fueltank of you car. It stops. However,
hotbulb engines didn't and you even got a little bonus as the water also
acted like a steam engine, giving extra power when it was warmed up. The
downside was that you had to have big water tanks to carry the freshwater,
as saltwater should not be used. Generally the problem of too hot bulbs
disappeared without taking special precautions on the latter engines.
The oiling system is special on hotbulb engines. Like most other two-stroke
engines, you could not have oil in the bottom pan of these, as it was used
as air-pump for the cylinders. So, oiling was accomplished by means of a
separate oilpump distributing right amounts to various parts. There are
also lot's of holes for oiling directly with an oil can on these engines,
which really is the best way of doing it if you want to know how the state
of the hardware is. But ofcourse it means more need for attention than,
let's say "automatic" engines.
Talking about oiling, I now got to think about a story I heard. Some
people had misunderstood what kind of engines these hotbulbers were, but
they were still impressed by them. After buying one, they filled the
bottom-pan with oil and started it up. What happened in most of these
cases? The hotbulber burns lubricating oil as well as kerosene, which they
were intended for (kerosene or diesel was most used, but also heavier
oils). So the engine ran faster and faster until the crackshaft broke.
Imagine a couple of hundreds of kilos of flywheel running about on the road
it's not something you want to block the road for. I guess they have gotten
some surprise when this happened.
Now, I think that this is enough for now, I will continue writing about
this engine in the next issue of the mag, hopefully with some sketches
and pictures. Among other things, I will discuss starting such an engine.
So, imagine this huge relaxed engine the next time you feel depressed or
stressed, it helps knowing that human beings at some point made something
worthy of existance.
