1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 143Get this manual

EMISSIONS
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:

• ATV
• Jet Ski
• Outboard Motors
• Personal Watercraft
• Snowmobiles
• Stern Drives