Quote:
Originally Posted by olds
okay, then this is directed toward all of you because I'm guessing you don't understand how chemistry or physics work
Let me introduce or refresh a new concept to you all. You can boil water without heat, you use pressure. The two are directly related but not interchangeable.
Now, if you have a valve that controls vacuum - pressure - of exhaust gasses you are not varying temperature in any way. When the valve opens as more fuel is being put into the engine (and coming out), the pressure of exhaust gases decreases and it has a similar effect as lowering temp. BUT there is no temperature regulation or change.
It has NO direct effect on exhaust gas temperatures. There is no possible way that a vacuum which controls pressures can be regulated by temperature. Because the properties are directly related, it has the same effect and it's easier for people who can't explain it to say --- oh it lowers exhaust temperatures.
So before you all start saying I don't know my stuff, you better think about it for a while.
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@ Olds
Cut and pasted this from an article in EGR systems... there is much more detail about the systems for later vehicles etc - but for now - this states quite clearly what the EGR system does... regardless of whether or not the valve itself operates by vacuum doesn't really matter for purposes of this "argument":
Understanding Exhaust Gas Recirculation Systems
Posted 11/5/1997
By Henry Guzman
Exhaust gas recirculation (EGR) systems were introduced in the early '70s to reduce an exhaust emission that was not being cleaned by the other smog controls. Oxides of nitrogen (NOx) are formed when temperatures in the combustion chamber get too hot. At 2500 degrees Fahrenheit or hotter, the nitrogen and oxygen in the combustion chamber can chemically combine to form nitrous oxides, which, when combined with hydrocarbons (HCs) and the presence of sunlight, produces an ugly haze in our skies known commonly as smog.
How to reduce NOx NOx formation can be reduced by:
Enriching the air fuel (A/F) mixture to reduce combustion temperatures. However, this increases HC and carbon monoxide (CO) emissions.
Lowering the compression ratio and retarding ignition timing; but this leads to reduced performance and fuel economy.
Recirculating some exhaust gases.
How EGR systems work The EGR valve recirculates exhaust into the intake stream. Exhaust gases have already combusted, so they do not burn again when they are recirculated. These gases displace some of the normal intake charge. This chemically slows and cools the combustion process by several hundred degrees, thus reducing NOx formation.
The design challenge The EGR system of today must precisely control the flow of recirculated exhaust. Too much flow will retard engine performance and cause a hesitation on acceleration. Too little flow will increase NOx and cause engine ping. A well-designed system will actually increase engine performance and economy. Why? As the combustion chamber temperature is reduced, engine detonation potential is also reduced.