Mercury Mariner 200, 225 Optimax Outboards Service Manual, 90-855348, Page 208Get this manual
STRATIFIED VS HOMOGENIZED CHARGE DFI engines use stratified charge inside the combustion chamber to aid in reducing emissionsAll other models use homogenized chargeThe difference between the two is:
Homogenized Charge
A homogenized charge has the fuelair particles mixed evenly throughout the cylinderThis mixing occurs inside the carburetor venturi, reed blocks and crankcaseAdditional mixing occurs as the fuel is forced through the transfer system into the cylinderThe homogenized charge is easy to ignite as the air fuel ratio is approximately 14.7: 1
Stratified Charge
A stratified charge engine only pulls air through the transfer systemThe fuel required for combustion is forced into the cylinder through an injector placed in the top of the cylinder (head)The injector sprays fuelair mixture in the form of bubble into the cylinderSurrounding this bubble is air supplied by the transfer systemAs the bubble is ignited and burns, the surrounding air provides almost complete combustion before the exhaust port opensA stratified charge is hard to ignite, the fuelair bubble is not evenly mixed at 14.7:1 and not easily ignited