STATE PLANT BOARD
May 1947 ET-238
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
AN MHAUST AEROSML OGJULTOR FOR l-1/2-ORSEPOVWR MOTORS
By A. H. Yeomans and V. G. Bodenstein
Division of Control Investigations
Attachments using the exhaust of gasoline motors for
producing aerosols were used effectively on jeep and airplane
engines for mosquito and fly control work by the American military
forces during World War II. The particle size of aerosols pro-
duced by this method depends on the speed of the engine and on
the rate of flow, viscosity, and other physical characteristics
of the insecticide solution.
An exhaust aerosol generator has been constructed to be used
on a 1-1/2 horsepower, 4-cycle gasoline motor. The cost of
material and brazing, in addition to the motor, is estimated to be
less than $5. The apparatus can be modified slightly for use on
larger motors up to 20 horsepower. This method of producing an
aerosol is economical if the motor is already on hand.
This apparatus can be used for killing flies and any other
pests for which the aerosol bomb is used. The machine can be used
in barns, greenhouses, warehouses, and houses, and under canopies
in the field. It is not suitable for dispersing water suspensions
unless small quantities are used, but most oil solutions can be
used in the machine.
The carbon monoxide fusmes build up with extended use of the
machine in confined spaces, but for the usual time in applying
insecticides the carbon monoxide is not objectionable.
A Briggs and Straitton motor has been used with the governor
set for a speed of 2,500 r.p.a. The higher the speed the smaller
the particle size.
To break up the insecticide solution the oil is released into
the exhaust gas as the gas escapes between the 3/16-inch diameter
tube for the oil and the 1/4-inch diameter hole in the pipe cap.
This opening is 0.0214 square inch, which is sufficient to allow
the engine to be run with a back pressure of only about 3-1/2
pounds per square inch.
The flow of oil controls the particle size, and for ordinary
fly sprays the flov should be about 4 liters per hour. This flow
can be easily regulated by using a small opening in the oil line.
On this machine the opening is 0.035 inch in diameter, When
deodorized-kerosene standard fly sprays are used, this flow rate
gives an average particle diameter of about 15 microns.
The equipment required for this apparatus,in addition to the
motor,is as follows: Three 1/2-inoh ptpenipples one 2-1/2 inches,
one 3-1/2 inches, and one 5-1/2 inches long; two 1/2-inch pipe
caps; one 1/2-inch pipe tee; a piece of 3/16-inch (o.d.) copper
tubing about 3 inches long; one half.-union brakes coupling with a
1/2-inch tube flare at one end and a 1/8-inch pipe thread at the
other end; one 1/S-inch pipe valve; two 1/S-inch pipe fittings;
and a discarded aerosol bomb.
Figure 1 shows the complete assembly with the machine in
operation. Figure 2 shows a close-up of the nozzle. Figure 3
shows the cross section through the nozzle.
Construction of the apparatus (fig. 1) consists in attaching
the 2-1/2-inch pipe nipple (D) to the engine, the pipe tee (C) to
D with the tee upward, and then the 5-1/2-inch nipple (.) to the
top of C, with a pipe cap (F) on top. In a 3-l/2-inch nipple (B)
a hole 1 inch from one end ia bored with a 7/32-inch drill. One
end of a 3-inch length of 3-1/16-inch copper tubing (H), bent as
shown in figure 3, ise inserted into this hole so that it protrudes
slightly, and the other end extends 1 inch beyond B, In the center
of pipe cap (A) is drilled a l/4-inch diameter hole. As is further
illustrated in figure 3, a half-union brass coupling (M) with a
1/2-inch tube flare to a 1/S-inch thread, is put over the end of
H, with the thread at the top, and then brazed so that I is con-
nected to H and H to the pipe B. A brass disk (not shown) perforated
with a 0,035-inch diameter hole is placed on the 1/S-inch pipe
fitting (K), and a valve (G) is then attached. The cap A is then
tightened to the nipple B so that the tube R projects through the
hole. The tube is then marked, the cap removed, and the tube cut so
that it extends only to the inside edge of the 1/4l-inch hole. Cap
A is then replaced, completing the nozzle. With these fittings
completed, B is attached to pipe tee _. The discarded aerosol bomb
(J) is converted into the container by drilling a 1/2-inch diameter
hole in the base for filling, and a 1/4-inch diameter hole into the
tapered end, removing the tube, and brazing on a 1/S-inch pipe
fitting (L). The bomb is then attached to the valve G, and the
machine is ready for operation.
The motor should be run for 2 minutes to heat it up before
the insecticide solution is run through. The aerosol should appear
white, and in a closed room should remain air-borne for more than
30 minutes. If a bluish aerosol is produced, the machine is too
hot and the warm-up time should be cut down* If the liquid drips
from the nozzle excesseeively, the warm-up time may be too short,
the motor speed too slow, the liquid flow too great, or the oil
tube not centered in the 1/fwinoh hole in the pipe cap A.
Similar apparatus can be used on gasoline motors of various
sizes. The exhaust-outlet hole should be in proportion to the
horsepower of the motor, Sone recommended sizes when 3/16-inch o.d.
copper tubing is used for the oil line are as followed
Motor Horsepower Diameter of Outlet
Opening in Inches
1-1/2 0.250 (1/4)
3 -5 .266 (17/64)
5 -10 .29T (19/641
10-15 .313 (5/16)
15-20 14 (11/32)
Tor the larger motors the flow of oil should be increased in
proportion to the horsepower. bor motors larger than 1-1/2 horsepower,
an ordinary valve without the use of the capillary disk is sufficient
to control the oil flow. A flexible metal tubing can be used between
the oil tank and the outlet opening.
Figure l.-Assembly of 1-1/2-horsepower gasoline-engine exhaust aeroold
Figure 2.-Details of nosule of exhauet aerosol generator for use with
1-L/2-horeepower gasoline motor.
UNIVERSITY OF FLORIDA
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Figure 3.-Cross section through nozzle.