An experimental investigation of rectangular exhaust-gas ejectors applicable for engine cooling Page: 1 of 19
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REPORT No. 818
AN EXPERIMENTAL INVESTIGATION OF RECTANGULAR EXHAUST-GAS EJECTORS
APPLICABLE FOR ENGINE COOLING
By EUGENE- J. MANGANIELLO and DONALD BOGATKYSUMMARY
An experimental investigation of rectangular exhaust-gas
ejector pumps was conducted to provide data that would serve
as a guide to the design of ejector applications for aircraft
engines with marginal cooling. The pumping characteristics
of rectangular ejectors actuated by the exhaust of a single-
cylinder aircraft engine were determined for a range of ejector
mixing-section area from 20 to 50 square inches, over-all length
from 12 to 42 inches, aspect ratio from I to 6, diffusing exit
area from 20 to 81 square inches, and exhaust-nozzle aspect
ratio from I to 42. A few tests were conducted with a multi-
stage ejector, a divided ejector, and a-n ejector incorporating
bends along its length.
With a decrease in the quantity of air pumped and an in-
crease in the length of ejector, the ejector pressure rise increases
to optimum values. Optimum values of ejector area were
found to depend upon mass-flow ratio of air to exhaust gas for
given engine operating conditions. Diffuser-exit sections con-
siderably improved the performance of the ejectors. An
arrangement of a straight mixing section with a diffusing exit
and a flattened exhaust nozzle proided the most favorable
ejector performance. An ejector composed of a straight mixing
section of 4-inch length and 25-square-inch area with a diffus-
ing exit of 1-inch length and 1.87 exit-area-entrance-area ratio
provided a pressure rise of 6 inches of water for a mass flow
of air representative of cooling requirements (six times the mass
flow of exhaust gas) for the engine when operated at a cruise
power of 85 indicated horsepower.
A simplified analysis, which considers the effect of pertinent
ejector variables and indicates the performance in terms of
known engine quantities, was made. The agreement between
theory and experiment was fair over the range of ejector con-
figurations tested, except that a serious discrepancy existed in
that the optimum ejector areas prescribed by theory were smaller
and the values of peak pressure rise predicted at the small
optimum areas were higher than indicated by the tests.
INTRODUCTION
The cooling problem has been one of the main obstacles
to the attainment of high power outputs with modern air-
cooled aircraft engines. Adequate cooling on the ground,
in climb, and in long-range cruise has been difficult to obtain
in most submerged and pusher-type installations, and in
some high-performance tractor installations. The possi-bility of the use of ejector pumps actuated by the engine
exhaust has been suggested as a means of providing the
additional cooling-air pressure drop required in installations
with marginal cooling.
Some experimental investigations of the ejector principle
have been made in connection with aircraft problems. Ref-
erences 1 and 2 present results of ejector tests with regard
to jet-thrust augmentation. The tests were conducted, for
the most part, with small-scale models actuated by com-
pressed air under steady-flow conditions. An investigation
of the design and operating conditions of small-scale com-
pressed-air ejectors, the results of which are pertinent to
their pumping as well as to their thrust-augmentation charac-
teristics, has been conducted at the United Aircraft Corpora-
tion. In reference 3 results are presented of a preliminary
investigation made to determine the suitability of ejectors
actuated by the exhaust of a radial aircraft engine for pro-
viding engine cooling air at the ground condition. The
pressure drops realized with some of the ejector combinations
investigated in reference 3 were of significant magnitude for
cooling. Tests made at the Northrop Aircraft, Inc. of a
number of exhaust-ejector systems for cooling aircraft engines
showed that appreciable improvement in cooling could be
obtained by the use of ejectors.
In view of the results presented in references 1 to 3 and of
the general interest in ejector cooling augmentation, the
present investigation was conducted at Langley Field, Va.,
in the fall of 1942 to obtain additional quantitative informa-
tion on the performance of exhaust-gas ejector pumps and
to provide design data for the application of ejectors to
aircraft-engine installations. The publication of the results
was delayed by the transfer of the staff and equipment to
Cleveland, Ohio.
The experimental work was performed on ejectors of rec-
tangular cross section actuated by the exhaust from a single-
cylinder aircraft engine. The pumping characteristics of
ejectors of various area were determined for a range of length,
aspect ratio, diffusing exit, and shape of exhaust nozzle
Ejectors of rectangular cross section were tested because if
was felt that this approximate shape would readily lend itselt
to installation on engine cowls of conventional configuration.
Engine power was limited to about the cruise value (70
percent rated). A simplified theoretical analysis was made
that indicates ejector performance in terms of known engine
and exhaust-gas quantities.
161
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Manganiello, Eugene J. & Bogatsky, Donald. An experimental investigation of rectangular exhaust-gas ejectors applicable for engine cooling, report, May 1, 1944; (https://digital.library.unt.edu/ark:/67531/metadc60100/m1/1/: accessed May 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.