Why turbo engine have EGR

[modeler]

EGR exhaust gas recirculation, I read up some stuff and the main idea is use exhaust gas to reduce temperature of burning, reduce NOx emission, and prevent knocking. But why?
Ideally a turbo engine want to inhale air as cold as possible, as more oxygen as possible, that's the whole point of turbo it, correct. so why EGR.

If you worry about knocking or high temperature, you just compress less air into the engine, I still can't turn my head around why introduce hot burnt waste air into cylinder.

Sponsored

 

[Carolina Jeeper]

It's an emissions lowering system. The EGR system has been around a while and it's not going away.

As far as i know the EGR valve is mostly open at idle and mostly or completely closed during acceleration. So it doesn’t affect higher RPM performance much.

There are many that install EGR block off or delete kits on some engines. I'm not sure if there is a kit for the 2.0 4 cylinder yet.

 

[jeepoch]

EGR exhaust gas recirculation, I read up some stuff and the main idea is use exhaust gas to reduce temperature of burning, reduce NOx emission, and prevent knocking. But why?
Ideally a turbo engine want to inhale air as cold as possible, as more oxygen as possible, that's the whole point of turbo it, correct. so why EGR.

If you worry about knocking or high temperature, you just compress less air into the engine, I still can't turn my head around why introduce hot burnt waste air into cylinder.

@modeler,

I used to work for Chrysler as a Powertrain Software Engineer who actually implemented the EGR Valve functionality on all Small Car, Large Car and Jeep/Truck programs for the 2002 through 2010 model years. I have since moved to Colorado and away from the rat race they call the automotive industry. However, I can give you a quick summary of why EGR has been implemented.

Essentially it's primary purpose is to reduce Nitrous Oxide (NOx) emissions. NOx is one of the primary pollutants (among others) that cause smog. NOx is produced from incomplete combustion of the fuel air mixture during the piston's power stroke.

In the past with carbureted engines, it was very difficult to obtain an optimal fuel/air proportion (called the stoichiometric ratio), which produces the best possible conditions for optimal combustion. With the advent of the Engine Control computer as well as fuel injection and a way more precise spark timing control, unfavorable emissions were greatly reduced.

Yet with ever stricter emission standards being legislated for each successive model year, even conditions close to stoichiometry were just not perfect enough. Low Emission Vehicles (LEV), Ultra Low (ULEV), Super Low (SULEV) and practically zero (PZEV) standards could simply not be met without even more emission reduction sophistication.

Exhaust Gas Recirculation (EGR) was introduced to help achieve these ever stricter regulations. It works by recycling some amount of exhaust gas back into the fresh air intake stream. The primary benefit is that exhaust gas contains a very high percentage of already combusted material which is now practically inert (can't effectively be combusted yet again). The proportions of recombustable material is extremely small and almost insignificant.

So this recycled gas displaces the amount of fresh air (combustable) O2 entering into the piston. Now instead of a normal O2 volume, the intake with EGR is some fraction of both combustible (O2) and non-combustible gas. With less O2 available, the amount of the resultant NOx is reduced proportionally. Hence it's exhaust emission benefit.

Unfortunately as it should be obvious, engine output power will also be reduced proportionally. Therefore, the volume of exhaust gas that is recycled must be dynamically managed in order to prevent the degradation of the overall engine output power. Especially when maximum torque demand is requested by the driver (during acceleration). At constant speed, reducing the potential of applying maximum power is way less important. It takes a lot less energy (force) to maintain constant motion. This follows Newton's first law, "objects in motion tend to stay in motion". So recycled gases are only introduced when practical, where maximum performance is not essential.

The EGR Valve is the mechanism that provides this dynamic control of the volume of exhaust gas recycled at any instant in time based on various operating conditions (where acceleration is but one of many factors). The valve is typically controlled by a Pulse Width Modulated (PWM) actuator or as a very high-count stepper motor.

The recycled gas temperatures are managed by manifold design and recycled gas volume. However, this is much less influential than the displacement of free O2 from the input manifold (or turbo).

Hope this helps with an overall elementary understanding. Under the covers the EGR system is rather sophisticated and very math (calculus and matrix algebra) intensive.

Best regards,
Jay

 

[DaltonGang]

@modeler,

I used to work for Chrysler as a Powertrain Software Engineer who actually implemented the EGR Valve functionality on all Small Car, Large Car and Jeep/Truck programs for the 2002 through 2010 model years. I have since moved to Colorado and away from the rat race they call the automotive industry. However, I can give you a quick summary of why EGR has been implemented.

Essentially it's primary purpose is to reduce Nitrous Oxide (NOx) emissions. NOx is one of the primary pollutants (among others) that cause smog. NOx is produced from incomplete combustion of the fuel air mixture during the piston's power stroke.

In the past with carbureted engines, it was very difficult to obtain an optimal fuel/air proportion (called the stoichiometric ratio), which produces the best possible conditions for optimal combustion. With the advent of the Engine Control computer as well as fuel injection and a way more precise spark timing control, unfavorable emissions were greatly reduced.

Yet with ever stricter emission standards being legislated for each successive model year, even conditions close to stoichiometry were just not perfect enough. Low Emission Vehicles (LEV), Ultra Low (ULEV), Super Low (SULEV) and practically zero (PZEV) standards could simply not be met without even more emission reduction sophistication.

Exhaust Gas Recirculation (EGR) was introduced to help achieve these ever stricter regulations. It works by recycling some amount of exhaust gas back into the fresh air intake stream. The primary benefit is that exhaust gas contains a very high percentage of already combusted material which is now practically inert (can't effectively be combusted yet again). The proportions of recombustable material is extremely small and almost insignificant.

So this recycled gas displaces the amount of fresh air (combustable) O2 entering into the piston. Now instead of a normal O2 volume, the intake with EGR is some fraction of both combustible (O2) and non-combustible gas. With less O2 available, the amount of the resultant NOx is reduced proportionally. Hence it's exhaust emission benefit.

Unfortunately as it should be obvious, engine output power will also be reduced proportionally. Therefore, the volume of exhaust gas that is recycled must be dynamically managed in order to prevent the degradation of the overall engine output power. Especially when maximum torque demand is requested by the driver (during acceleration). At constant speed, reducing the potential of applying maximum power is way less important. It takes a lot less energy (force) to maintain constant motion. This follows Newton's first law, "objects in motion tend to stay in motion". So recycled gases are only introduced when practical, where maximum performance is not essential.

The EGR Valve is the mechanism that provides this dynamic control of the volume of exhaust gas recycled at any instant in time based on various operating conditions (where acceleration is but one of many factors). The valve is typically controlled by a Pulse Width Modulated (PWM) actuator or as a very high-count stepper motor.

The recycled gas temperatures are managed by manifold design and recycled gas volume. However, this is much less influential than the displacement of free O2 from the input manifold (or turbo).

Hope this helps with an overall elementary understanding. Under the covers the EGR system is rather sophisticated and very math (calculus and matrix algebra) intensive.

Best regards,
Jay

So, what you just said, in a nutshell: EGR sucks for the engine, mileage, and performance.

 

[jeepoch]

So, what you just said, in a nutshell: EGR sucks for the engine, mileage, and performance.

Yep. Thank you Mr. EPA. Likely would never have happened otherwise.

 

[modeler]

Unfortunately as it should be obvious, engine output power will also be reduced proportionally. Therefore, the volume of exhaust gas that is recycled must be dynamically managed in order to prevent the degradation of the overall engine output power.

so why they have to do this?
Why not just do a valve to let compressed air just go out so intake air get back to original temperature when depressurized. That means "turbo the engine only when needed" (at acceleration), otherwise the engine will be exact as NA 2.0 engine

 

[DaltonGang]

so why they have to do this?
Why not just do a valve to let compressed air just go out so intake air get back to original temperature when depressurized. That means "turbo the engine only when needed" (at acceleration), otherwise the engine will be exact as NA 2.0 engine

Because Ralph Nader sucks. Remember, "55 saves lives"??

 

[modeler]

Because Ralph Nader sucks. Remember, "55 saves lives"??

ok, ok, thanks for the post

 

[Dyslexican]

Yep. Thank you Mr. EPA. Likely would never have happened otherwise.

Thanks for sharing this and breaking it down .

 

[Dyslexican]

Yep. Thank you Mr. EPA. Likely would never have happened otherwise.

Thanks for sharing this and breaking it down .

 

[cs2k]

I heard EGR actually increases MPG by "reducing pumping loss" in gasoline engines. Not sure how true this is.

I know there are a lot of EGR delete kits for diesel engines pre crackdown by EPA. Has anyone experimented with this on gas engines? The pentastar V6 has an EGR valve as well.

 

[At Risk Ute]

I heard EGR actually increases MPG by "reducing pumping loss" in gasoline engines. Not sure how true this is.

I know there are a lot of EGR delete kits for diesel engines pre crackdown by EPA. Has anyone experimented with this on gas engines? The pentastar V6 has an EGR valve as well.

I deleted the EGR on my 2008 Mazdaspeed 3 which is similar to our engine (2.3L direct injection turbo). Also deleted the balance shaft and a bunch of other crazy mods. My advice is to let it be. Dumb emissions thing, but the juice ain’t worth the squeeze.

Sponsored