September 9th, 2012, 10:52 AM
Join Date: Dec 2011
Location: Ava, MO
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Here's my input on the EGR:
Exhaust Gas Recirculation (EGR) - Explained
Posted 02-15-2012 at 03:53 PM by Seattle FSB
To increase performance, modern engine design incorporates a leaner Air/Fuel Ratio with advanced ignition timing. These performance increases promote increased combustion temperatures which support an edothermic reaction between Nitrogen and Oxygen, producing mono-Nitrogen Oxides (NOx). High levels of NOx can corrosively damage internal engine components and also react in the environment to cause smog, acid rain, ozone depletion and respiratory health effects.
Exhaust Gas Recirculation (EGR) is designed to reduce combustion chamber temperatures which promote NOx formation. It does this by reintroducing inert exhaust gas back into the intake. As we know, the EGR does not operate all of the time. The EGR is typically not employed at idle (low-speed, zero load) because it would cause unstable combustion, resulting in rough idle. EGR is also omitted at high loads and WOT because it would reduce peak power output by reducing the intake charge density. When properly operating under light cruise conditions, the EGR valve reduces NOx emissions, reduces the chance of detonation and cools the exhaust valves which give them a much longer service life (all very important benefits). The EGR is now exploited by manufacturers to support performance changes in modern engine design.
A properly operating EGR can increase the efficiency of gasoline engines through several mechanisms:
Reduced throttling losses. The addition of inert exhaust gas into the intake system means that for a given power output, the throttle plate must be opened further, resulting in increased inlet manifold pressure and reduced throttling losses.
Reduced heat rejection. Lowered peak combustion temperatures not only reduce NOx formation, it also reduces the loss of thermal energy to combustion chamber surfaces, leaving more available for conversion to mechanical work during the expansion stroke. Additionally, lower cylinder temperatures reduce engine octane requirements which lessens the danger of detonation.
Reduced chemical dissociation. The lower peak temperatures result in more of the released energy remaining as sensible energy near TDC, rather than being bound up (early in the expansion stroke) in the dissociation of combustion products. This effect is minor compared to the first two.
The EGR can decrease the efficiency of gasoline engines by at least one more mechanism:
Reduced specific heat ratio. A lean intake charge has a higher specific heat ratio than an EGR mixture. A reduction of specific heat ratio reduces the amount of energy that can be extracted by the piston.
Keep in mind that the EGR is just one of several Emissions Systems in your Bronco:
Secondary Air Injection. This is used to support the catalytic converter's oxidation reaction, and to reduce emissions when an engine is started from cold.
Exhaust Gas Recirculation. This system routes a metered amount of exhaust into the intake tract under particular operating conditions which dilutes the air/fuel charge to reduce peak combustion chamber temperatures.
Catalytic Converter. This converts hydrocarbons, carbon monoxide, and NOx into less harmful gases by using a combination of platinum, palladium and rhodium as catalysts.
Evaporative Emissions Control. This system collects vapors from the fuel tank in a canister containing activated carbon. During certain engine operational modes, the vapors are introduced into the engine to be burned.
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