Mercury 225 EFI, Service Manual

Page: 306 / 719

3
D
EMISSIONS
90-884294 OCTOBER 2001 Page 3D-1
FUEL SYSTEM
Section 3D – Emissions
Table of Contents
Exhaust Emissions Standards 3D-1 . . . . . . . . . . . . . . . . .
What Are Emissions? 3D-1 . . . . . . . . . . . . . . . . . . . . . .
Hydrocarbons – HC 3D-1 . . . . . . . . . . . . . . . . . . . . . . . .
Carbon Monoxide – CO 3D-1 . . . . . . . . . . . . . . . . . . . .
Oxides of Nitrogen - NOx 3D-2 . . . . . . . . . . . . . . . . . . .
Controlling Emissions 3D-2 . . . . . . . . . . . . . . . . . . . . . .
Stoichiometric (14.7:1) Air/Fuel Ratio 3D-2 . . . . . . . .
Outboard Hydrocarbon Emissions Reductions 3D-2 . . .
Stratified vs Homogenized Charge 3D-3 . . . . . . . . . . . . .
Homogenized Charge 3D-3 . . . . . . . . . . . . . . . . . . . . . .
Stratified Charge 3D-4 . . . . . . . . . . . . . . . . . . . . . . . . . .
Emissions Information 3D-4 . . . . . . . . . . . . . . . . . . . . . . . .
Manufacturer’s Responsibility: 3D-4 . . . . . . . . . . . . . .
Dealer Responsibility: 3D-5 . . . . . . . . . . . . . . . . . . . . . .
Owner Responsibility: 3D-5 . . . . . . . . . . . . . . . . . . . . . .
EPA Emission Regulations: 3D-5 . . . . . . . . . . . . . . . . .
Manufacturer’s Certification Label 3D-6 . . . . . . . . . . . . . .
Service Replacement Certification Label 3D-7 . . . . . . . .
Removal 3D-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Date Code Identification 3D-7 . . . . . . . . . . . . . . . . . . . .
Installation 3D-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Decal Location: 3D-7 . . . . . . . . . . . . . . . . . . . . . . . . . . .
Exhaust Emissions Standards
Through the Environmental Protection Agency (EPA), the federal government has estab-
lished exhaust emissions standards for all new marine engines sold in the United States.
What Are Emissions?
Emissions are what comes out of the exhaust system in the exhaust gas when the engine
is running. They are formed as a result of the process of combustion or incomplete com-
bustion. To understand exhaust gas emissions, remember that both air and fuel are made
of several elements. Air contains oxygen and nitrogen among other elements; gasoline
contains mainly hydrogen and carbon. These four elements combine chemically during
combustion. If combustion were complete, the mixture of air and gasoline would result in
these emissions: water, carbon dioxide and nitrogen, which are not harmful to the environ-
ment. However, combustion is not usually complete. Also, potentially harmful gases can
be formed during and after combustion.
All marine engines must reduce the emission of certain pollutants, or potentially harmful
gases, in the exhaust to conform with levels legislated by the EPA. Emissions standards
become more stringent each year. Standards are set primarily with regard to three emis-
sions: hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx).
Hydrocarbons – HC
Gasoline is a hydrocarbon fuel. The two elements of hydrogen and carbon are burned
during combustion in combination with oxygen. But they are not totally consumed. Some
pass through the combustion chamber and exit the exhaust system as unburned gases
known as hydrocarbons.
Carbon Monoxide – CO
Carbon is one of the elements that make up the fuel burned in the engine along with oxy-
gen during the combustion process. If the carbon in the gasoline could combine with
enough oxygen (one carbon atom with two oxygen atoms), it would come out of the en-
gine in the form of carbon dioxide (CO
2
). CO
2
is a harmless gas. However, carbon often
combines with insufficient oxygen (one carbon atom with one oxygen atom). This forms
carbon monoxide, CO. Carbon monoxide is the product of incomplete combustion and
is a dangerous, potentially lethal gas.