EGR makes a difference Bill
Posting Guru
Joined: Aug 2000
Posts: 1,127
Likes: 3
From: (near) Denver USA
On modern spark-ignition engines, EGR systems coexist reasonably well with both high power output and good fuel economy (depending on the engine application). To do that, modern EGR systems produce variable EGR rates (the amount of exhaust gas introduced into the cylinder) that are controlled by the ECM/PCM, based on engine load, speed, and temp, and based on external conditions (ambient air temp, barometric pressure, etc.).
Instead of using rudimentary vacuum signals actuate the EGR valve, some newer EGR valves are operated by servo motors, and some systems use multiple valves with various orifice sizes to control the EGR rate even more precisely.
EGR systems for compression-ignition (diesel) engines have been a huge and somewhat controversial topic in the automotive industry over the last year, so there is now a huge volume of readily available information on that subject.
On an older engine design like the 351C/351M/400, with its primitive EGR controls and a vacuum operated valve, the EGR system compromises driveability, power, and economy in the pursuit of NOx emissions control. With the NOx reduction mandates of the early '70s, EGR was obviously the most cost-effective option for vehicle manufacturers.
Here's an interesting SAE article from back in 2001 about an experimental Saab engine that uses up to a 70% EGR rate without disrupting the stoichiometric 14.6:1 mixture.
http://www.sae.org/automag/techbrief...001/techb3.htm
Europe and Japan are starting to mandate EGR and catalytic converters in their own domestic automotive markets, but they have been very slow to adopt even the emissions control standards that the US had in place 20+ years ago, which is more than a little ironic, considering their adamant support of the "Kyoto Protocol."
Instead of using rudimentary vacuum signals actuate the EGR valve, some newer EGR valves are operated by servo motors, and some systems use multiple valves with various orifice sizes to control the EGR rate even more precisely.
EGR systems for compression-ignition (diesel) engines have been a huge and somewhat controversial topic in the automotive industry over the last year, so there is now a huge volume of readily available information on that subject.
On an older engine design like the 351C/351M/400, with its primitive EGR controls and a vacuum operated valve, the EGR system compromises driveability, power, and economy in the pursuit of NOx emissions control. With the NOx reduction mandates of the early '70s, EGR was obviously the most cost-effective option for vehicle manufacturers.
Here's an interesting SAE article from back in 2001 about an experimental Saab engine that uses up to a 70% EGR rate without disrupting the stoichiometric 14.6:1 mixture.
http://www.sae.org/automag/techbrief...001/techb3.htm
Europe and Japan are starting to mandate EGR and catalytic converters in their own domestic automotive markets, but they have been very slow to adopt even the emissions control standards that the US had in place 20+ years ago, which is more than a little ironic, considering their adamant support of the "Kyoto Protocol."
