Emission Control Systems: Description and Operation

GENERAL DESCRIPTION

EMISSION CONTROL SYSTEM
The engine exhaust gases consist mainly of nitrogen (N2), however, they also contain carbon monoxide (CO), carbon dioxide (CO2), water vapor (H2O), oxygen (O2), nitrogen oxides (NOx), and hydrogen (H2), as well as various other unburned hydrocarbons (HC). Three of these exhaust gases, CO, NOx, and HC, are major air pollutants. Their emissions must be controlled.

The vehicle contains a sequential multiport fuel injection (SFI) system classified as a multi-point, pulse time, mass air flow, fuel injection system. This system supplies the engine with the air/fuel mixture necessary for combustion. An air induction system and fuel injection system work in conjunction with an electronic engine control system which consists of various sensors, switches, and the engine control module (ECM). All sensors and switches are connected to the ECM which interprets the data received from them and computes the timing and duration (pulse width) that the electrically operated injectors are energized.

The basic fuel requirement of the engine is detected from the data supplied to the ECM by the mass air flow (MAF) sensor. The ECM measures the amount of air drawn into the engine. Additional sensors and switches measure engine coolant temperature, engine speed, exhaust oxygen content, and number 1 cylinder top dead center.

The various sensors and switches detect any changes in the operating conditions and send signals to the ECM. This allows the ECM to control the injectors opening duration (pulse width) and maintain optimum exhaust emissions control and engine performance for all conditions.

The three way catalytic converter is mounted in-line between the header pipe and the muffler. The catalytic metals are thin-coated on a honeycomb-shaped, high temperature ceramic. The honeycomb is mounted inside the converter shell which is surrounded by a heat shield. It reacts with exhaust gases to convert them to less harmful products and therefore reduce the pollutant levels to within legally-prescribed limits. Refer to Exhaust System.