Evening star., 1926-02-21
No. 138-"No-Knock" Fuels.

Stopping the engine from knocking.
even when 1t is choked with carbon.
Is one Of those hopes that even an
advanced motorist like Smith cannot
refrain from cherishing. Nowadays. as
a matter Of fact, he would be foolish
to do otherwise. for no-knock fuels arc
reality and not q myth.
For years carbon and knock re-
movers have been offered and car own.
ers have given them a trial. Many
OF these connections were OF color.
and as a consequence the ones that
really did tho work suffered. Nova
days. however. in addition to carbon
removers there are new fuels and fuel
dopes that enable one to get along
without knocks and without bother
ing to do away with the carbon. This
is the result Of intensive experimental
ton with fuels and refining processes.
as well as the discovery Of new things
in connection with the behavior Of
internal combustion engines
Many Causes Of Knocks.
The knock heard In the combustion
chambers Of an engine can occur in
several ways. II the compression ratio
is too high detonation Will occur on
sudden acceleration as well as in hill
climbing. II tho engine Is operated
will be what Is known as spark knock.
If the engine Is Allied with carbon the
harder particles soon will become in
candescent as the engine heats and
will act as miniature spark plugs SET
ting OF the gas too soon, causing an
other variety Of knock. Somewhat
the same thing will happen II the head
Of tho engine is faulty and II 1t has
'hot spots" in the form Of rough
y~k- Ayr> h@ g.
packed with carbon there is less space
in the cylinders for gas vapor. and
since the normal compression Of the
engine remains undiminished the car.
bon actually raises the compression
to the knocking, or detonation, point.
Finally, there Is the fuel itself. And
here Is where Smith was to learn some
thing new. He had a vague notion
that the no.knock fuel being offered
was highest gas. and knowing
through experience that he could not
use the latter in his engine. which
was designed for gas Of lower test,
he had been passing up the pumps
with the no-knock sign attached. This
was unfortunate, because he could have
been enjoying new thrills from his
engine.
Three Types Of Fuels.
Fuel Itself. regardless OF teSt or Spe-
cific gravity, varies in detonation
characteristics. At present there are
three kinds Of automobile fuels In com.
mon use:
straight-run gasoline. which u the
light portion Of crude oil taken out
and refined.
Cr-:ked gasoline, the product Of q
complicated process Of the hydro-car-
bons In crude, designed to obtain q
minimum of tho detonat1on qualities
and q maximum of tho no-knock quail.
ties.
Doped gasoline II straight run or
cracked gasoline mixed with chemicals
or hydrocarbons to increase tho non-
decorating qualities.
Smith reviewed the list and was ready
to give up the idea that no-knock
fuels were Imagination. Immediately
he wanted to know which was best
for use In an engine troubled with
knocking, ora loss of power through
the necessity of retarding the spark
when the knocks begin.
THAT is the simplest part OF all. -
told him. with straight-run gas
1t Is question Of where the crude
comes from. In the cracking process,
however. not 30 much depends upon
the crude itself. because tho no-knock
properties are the result Of selection.
Parafflns. naphthenes and benzenes all
arc found In crudes, and ref1ners try
to make their final product as rich
as possible In benzenes, which are best