Stratified Vs Homogenized Charge; Homogenized Charge; Stratified Charge - Mercury 75 Service Manual

STRATIFIED VS HOMOGENIZED CHARGE

DFI engines use a stratified charge inside the combustion chamber to aid in reducing emissions. All other models
use a homogenized charge. The difference between the two is:

Homogenized Charge

A homogenized charge has the fuel/air particles
mixed evenly throughout the cylinder. This mixing
occurs inside the carburetor venturi, reed blocks and
crankcase. Additional mixing occurs as the fuel is
forced through the transfer system into the cylinder.
The homogenized charge is easy to ignite as the air/
fuel ratio is approximately 14.7:1.
90-830234R3 DECEMBER 1997

Stratified Charge

A stratified charge engine only pulls air through the
transfer system. The fuel required for combustion is
forced into the cylinder through an injector placed in
the top of the cylinder (head). The injector sprays a
fuel/air mixture in the form of a bubble into the cylin-
der. Surrounding this bubble is air supplied by the
transfer system. As the bubble is ignited and burns,
the surrounding air provides almost complete com-
bustion before the exhaust port opens.
A stratified charge is hard to ignite, the fuel/air bubble
is not evenly mixed at 14.7:1 and not easily ignited.
FUEL SYSTEM - 3D-3