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National Advisory Committee for Aeronautics, Technical Notes - The Effect of Inlet Valve Design, Size, and Lift on the Air Capacity and Output of a Four Stroke Engine

The factors which affect the volumetric efficieaty
of an internal combustion engine may be classified into
two categories

Operating conditions, such as revolutions per i _H” in
minute, inlet and exhaust pressures, Operating tempera—Wm;r ‘ .j
tures, and so forth.

Design factors, including—deeign of Cylinder, .—
valves, inlet and exhaust manifolds, valv e timing, and
SO forth.

This investigation was carried out to determine the ef—
fec_t of inlethv-alve. dles.ign size,‘ and'lift on volumetric "
efficiency at several engine speeds. In order to accom~
modate valves of d1fferentisizesa th-e cylinder end of the
inlet port had a different diameter for each size of va.lvo
tested. All other_operating conditions and design ratios
were held constant.

In references 1 and 2 reports were made of previous
investigations at Massachusetts Institute of Technology
On the relative importance of inertia of the air columns,
fluid frictiOn, and heat transfer upon volumetric effi—
ciency. In these reports it Was_ sho_wn that-. at low air
velocities, the ValYe:-and por_t affect the volumetric éf—._
fic.iency chiefly by- increasin-g the temperature of the
charge in th.e cylinder-J At higher ve-lpcities the volu—
metric efiiciency-may also be-reduced by a lowering oi
the pressure in the cylinder at the time of inlet closing.

Methods have been deveiopedrfor experimentally deter~
mining the resistance offered to steady air chw by dif~
ferent designs of port and valve. (See refs as: see 3, 4,
5. and 6.) The measuT-e of this Iesisoance Is embodied in
the curve of _steady~flow coeffi'cient a-glainsJ liit— diameter
ratio obtain.ed- by static— flow. test-s. :This_type of tost~
ing is described in appendix A.

Resistance to. flow-' can be reduced by the following "
means- (1) increasing  the valve- area (2) increasing' the
Valve lift and (3) improving the Valve and port design.