Evening star. [volume] (Washington, D.C.) 1854-1972, 1930-06-29
BLAME MOTORS
FOR GAS FAULTS
investigators Hold Gasoline
Temperatures Are Raised
by Car Construction.

A theory that "vapor lock-" causing
irregular operation Of an automobile en-
CINE, is largely attributable to vaporized
fuel and not to dissolved gases In the
fuel. as Is commonly assumed, is adj
vanced in Industrial and Engineering
Chemistry. journal Of the American
Chemical Society, by z. A. Clarke, Hal
B. Goats and George Granger Brown of
the University of Michigan. describing
investigations made under the research
program Of the Natural Gasoline Asso-
citation of America
Vapor difficulties in the operation of
the modern automobile may often be
laid directly at the door of the motor
manufacturer, the report declares.
Many fuel systems are so designed that
the T1fe NH; the supply tank lies close
to the muff1er and exhaust pipe of the
engine. Gasoline temperature is fur
ther raised in many cases by heat from
the crankcase, on which the mechan-
ical pump Is mounted. Again, when the
fuel enters the carburetor in encounters
heat by conduction from the exhaust Of
the not spot or convection from the ad-
Jacent exhaust manifold
The fuel systems of many motor cars
are so constructed that in warm weather
the temperature of the liquid gasoline
reaches 135 to 140 degrees F. and may
Al SOllIC SdSto tACecu LUU CeBTeeS, the
report points out. 1T is. of course, I'M
possible to prepare a fuel that will form
sufficient vapor to start the motor read
lily at 10 degrees and yet will not vaporize
In the fuel line and carburetor when
heated to temperature in excess of
$50 degrees. Yet this is one of the de-
mands made upon motor fuel by some
OF the modern passenger cars.
VapOr Will Limit Flow.
Formation of fuel vapor in those
passages designed to carry or meter
liquid fuel causes what is commonly
called 'vapor lock- Since the volume
OF gasoline vapor is approximately 1875
times that Of an equal weight of LIQUID
fuel. it is obviously impossible for the
small orif1ces and passages in the car
buretor to pass enough gasoline vapor
to maintain an explosive mixture.
"A relatively small amount of vapor,
usually not in excess of about four times
the liquid volume, will usually so limit
the How OF gasoline to the manifold that
the motor will not perform properly.
Any further vaporization of the fuel in
the liquid lines or jet Of the carburetor
restricts the flow of gasoline, so that
the mixture supplied to the motor be-
comes non-explosive"
Road tests showed that a fuel might
be heated to high temperatures without
vaporizing when under a greater pres
sure, as in the pressure-feed system.
Frequently the temperature of gasoline
FED by vacuum YVES also found to be
about IS degrees higher than that of
1uel delivered under pressure
The formation of bubbles in the let
passage is probably the most impor-
tant cause of vapor lock in the car
buretor." the report continues. THE
main fuel passage in the carburetor
81
fuel for satisfactory operation of the
motor, even when relatively large
volumes of vapor are flowing through
these passages with the LIQUID. The
small opening of the jet itself, how
ever, is usually inadequate to pass
sufficient weight of fuel If much more
than half the total volume of the
Iuel flowing through the jet is in
the vapor state.
VapOr Forms in Jet Passage.
"As the temperature of the air sup
piled to the carburetor is generally
higher than that of the fuel supplied
to the jet, fuel flowing through the
Jet passage Is usually heated to it's
maximum temperature just under the
Jet. This condition also makes the
jet passage the most likely place for
the formation of the greatest volume
Of vapor from the fuel
Small bubbles flowing through the
passages of the carburetor generally
expand in the jet passage owing TO
the heating effect of the hot air sup
piled to the curburetor and also owing
to the slight decrease in pressure exist
ing in the Jet passage This is en-
phasized in many carburetors by bleed
ing air into the jet passage, thereby
decreasing the partial pressure of gaso-
line vapor so that more gasoline tends
to vaporize, still further decreasing the
fuel flow
IF these expending bubbles in the
Jet passage become so large as to fill
the cross section of the passage, the
flow of liquid gasoline to the let is
interrupted. This irregular flow of
gasoline causes uneven operation of the
motor. AS long as the volume of bub-
pies does not exceed approximately
that Of the liquid gasoline, the motor
VIII operate in a satisfactory manner
with only negligible loss of power.
1t has generally been assumed that
the difficulty now known as vapor
lock is due to dissolved gases in the
motor fuel. In fact, the phenomenon
has frequently been termed gas lock-
If this we're true, the total vapor
pressure of the fuel and dissolved gases
would be direct indication of the
tendency of the fuel to cause vapor
lock. The fact that at least l per
cent of vaporized fuel was found neces-
sary to cause irregular operation of
the motor indicates that vapor lock
is due, not to dissolved gases, but
largely to vaporized fuel