• Version
• 143 Downloads
• 2.09 MB File Size
• 1 File Count
• November 30, 2016 Create Date
• November 30, 2016 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - The Effect of Piston Head Shape, Cylinder Head Shape, and Exhaust Restriction, on the Performance of a Piston Ported

A full—scale, three-dimensional, steady-flow mddei
of the two-stroke engine described in N.A.C.&. Technical
Note No. 674 (reference 1), was constructed for the pur-
pose of observing the scavenging—air flow obtained with
the various inletuport arrangements tested in the actual
engine. Based on experience gained from correlation of
the flow tests with engine tests, several pist6n~héad
shapes were developed, and the most promising were tested
in the engine. Several modifications of the_successful
,round—edge piston previously used, were also tested. Three
types of cylinder head: spherical, cylindrical, and.f1at
in cross section were tried, first in the_flow model and
then in the engine. The flat head was modified by milling
a portion of the surface away to form, Steps. The cylin—
drical and modified flat heads were run at va_rious angles
to the plane of symmetry.

Piston-and cylinder-head shapes were developed at
compression ratio of 7, purely from the. standpoint of
scavenging, and would not be suited to compreSSion-igni-
tion use without considerable modification. ..

A flat-top piston, with edge rounded to a 3/4—inch
radius was found best. The best cylinder-head shape tried
was spherical, with radius nearly the same as that of the
'cylinder bore.

An investigation was also made of the possibility of
producing a supercharging effect by restricting the ex-
haust ports while using normal piston and cylinder head.
A limited amount of supercharging was found possible by
this means, but the net gain was small owing to increased
pumping loss.

All tests were made over a range of scavenge ratios
of 0.8 to 1.6. Spark ignition was used in all engine
tests.

This investigation, conducted at the Massachusetts
Institute of Technology, was sponsored by, and conducted
with financial assistance from, the National Advisory
Committee for Aeronautics.