SOMETIMES THE CAR SMOKES
The officer will get you if you don’t watch out, if you leave a trail
of smoke behind you; then it will be:
“Good morning, Jedge, your Honor.”
“Guilty? Two dollars, please.”
“Cheap,” you say. Yes, if it were only the two dollars; but there is
the time lost in appearing in court and then, really, you know, to make
that smoke you were burning money.
Such smoke comes from two sources: Burning too much gasoline and using
too much lubricating oil; usually the latter. Excessive use of gasoline
comes from faulty carburetor adjustment, or poor design of carburetor
or intake manifold, or keeping the engine cylinder at too low a
temperature, because of the water being too cold in the cooling system.
In the latter case the carburetor may vaporize the gasoline properly,
but it condenses in the cylinder and does not burn well and the part
which is not consumed passes off as black smoke, which issues from the
exhaust pipe.
We must have a certain amount of oxygen to consume the gasoline
entirely. The size of the cylinder limits the amount of air (from which
the oxygen is taken) which may be taken in and if the carburetor is
adjusted to feed too much gasoline, there may not be enough oxygen
present to consume it all. Practically speaking, what is not consumed
forms carbon or smoke.
The obvious remedy is to adjust the carburetor so that no more gasoline
will be fed to the engine than is required for running. In cold weather
it is necessary, usually, to supply heat to the ingoing air at the
mixing chamber of the carburetor, so that the vaporization will be
complete.
A light blue smoke coming from the exhaust pipe indicates too much
lubricating oil. This may be due to feeding too much oil or to running
the engine a great deal with the throttle nearly closed. In order to
draw a charge of gas into the cylinder the piston travels partly out
of the cylinder and forms a vacuum. With the throttle wide open a high
vacuum is not obtained because a large amount of gasoline and air is
allowed to come in and fill the cylinder. When the engine is throttled
down by closing the throttle, the air cannot enter in such a large
quantity, and in consequence there is a decided vacuum in the cylinder
on each intake stroke of the piston. This vacuum has a tendency to draw
oil up past the piston into the combustion chamber, where it burns and
forms smoke. This is why, when the machine is left at the curb with the
engine running for any length of time, it will often be found to start
away with clouds of smoke issuing from the exhaust.
In the same way, when the engine is running slowly, air passes through
the carburetor so slowly that the gasoline is not broken up into very
fine particles, consequently it does not fully vaporize and is very
easily condensed. It forms liquid gasoline in the intake pipe or
cylinder. This is called “loading up” and is responsible for black
smoke when the machine is started.
One way of overcoming this is to supply a larger amount of heat than
usual to the mixing chamber. Most carburetors are not designed to take
care of this condition and the only remedy would be to stop the engine
instead of allowing it to run while standing at the curb.
To overcome smoke from the oil which is drawn up past the piston, it is
customary to have a groove turned in the piston under the lower piston
ring, with five or six holes drilled in the groove through the piston.
The piston ring then scrapes the oil from the cylinder wall into the
groove and it is led back into the crank case through the piston walls.
This prevents it from working up into the combustion chamber. Many
manufacturers have this scheme on the very new models and repair men
are using it on older models which were not turned out with it.
Sometimes the oil level will be found too high. This may be corrected
often by lowering the oil troughs, or by filing off the dip on the
bottom of the connecting rod so that it touches the oil with a narrowed
surface.
In addition to the smoke resulting from too much gasoline or oil there
is a large amount of carbon deposited in the cylinder which takes up
space in the combustion chamber and raises the compression so high
that pre-ignition occurs and the engine knocks. The car must then be
taken to a repair shop to have the carbon burned or scraped out. This
is expensive work and besides the car is laid up and one loses its use
while the scraping is being done. The owner will see that he has been
spending a lot of money to supply gasoline and oil that he didn’t need
to use just to make smoke and carbon and expense and that he has lost
from every point of view.
Smoke should not be confused with steam which issues from the exhaust
pipe in cold weather. One of the products of combustion in the gas
engine is water, a natural result of the breaking up of a hydro-carbon.
This usually passes off at a high temperature as an invisible vapor. In
cold weather it condenses immediately it strikes the air and is visible
in the form that we call steam. Really it is a fog that we create.
Therefore do not let the policeman summons you for having a smoking
engine, when it is only steam issuing from the exhaust pipe. If he
doesn’t know which it is you probably can convince him, by the color.
If it is white it is steam, if it is black it is gasoline smoke, and if
it is light blue it is the smoke from the lubricating oil. Therefore
watch your exhaust for there are many eyes watching you just now in
parks and city streets.