Exhaust Gas Recirculation System Description

EGR System Components:

EGR Flow Diagram:

PURPOSE
The Exhaust Gas Recirculation (EGR) system is used in automotive engines to decrease the emission levels of oxides of nitrogen (NOx).

DESCRIPTION
NOx defines a group of chemical compounds containing nitrogen and varying amounts of oxygen that can have harmful environmental effects in large quantities. NOx forms during the combustion process in amounts that are dependent on the concentration of oxygen in the combustion chamber and the duration that the combustion process temperatures exceed 1500°F. Decreased NOx levels are accomplished by reducing the peak combustion temperatures through dilution of the incoming fuel/air charge with exhaust gas. When combusted, exhaust gas (largely non-reactive carbon dioxide and water vapor) acts to absorb a portion of the combustion energy, resulting in lower temperatures throughout the combustion process and yielding lower amounts of NOx.

EGR DELIVERY RATE
Desired amounts of EGR depend upon the geometry of the combustion chamber and the operating condition of the engine. Extensive laboratory and vehicle tests are used to determine optimal EGR rates for all operating conditions. Too little EGR can yield high NOx, while too much EGR can disrupt combustion events. This engine uses a computer controlled valve to precisely regulate the amount of EGR delivered to the engine for all operating conditions.

EGR SOURCE
Exhaust gases are routed to the engine through the corrugated semi-flexible feed pipe which connects the crossover exhaust pipe to the crossover water pump housing.

EGR HEAT EXCHANGER
In the crossover water pump housing, as shown in the EGR Flow image, exhaust gases are precisely metered by the PCM controlled EGR Valve, then cooled by engine coolant and finally routed into the throttle body spacer through another corrugated semi-flexible feed pipe from the water pump crossover. A potential drawback with EGR is that for certain driving schedules, deposits can accumulate when hot exhaust gases are cooled. The system uses the crossover water pump housing as a cross-flow heat exchanger to cool exhaust gases in large easily cleaned passages to virtually eliminate any concern with deposit accumulation during the service life of the engine. This is done by having the cooling passage reduce EGR gasses below their deposit forming temperature prior to routing these gasses into the throttle body spacer.