Can anyone give me a general explanation of how the modern emissions system works, I'm just curious. I understand how catalytic converters use a catalyst in a chemical reaction process to convert or capture? harmful emssions and chemical reactions work better at higher temperatures thus the hotter running engines? And I understand the old school PCV valves capturing gases from the crankcase.

But what about the newer stuff, the air injection? Where does it inject air, and why does that help emssions?

And the evaporitve emssions canister? how does this work?

what are the other parts of the emissions system?

thanks

 

Air pump forces air into the exaust system while the exaust pipes are cold in order to burn off fuel that has passed through the motor... Adding oxygen to the hot exaust fumes will cause left-over fuel to burn up...which helps the ozone...

Im not sure about the evap canister but i think its to take evaperated fuel out of the tank and forcing it through the intake to get rid of it... so that way when you open the gas cap it doesn't escape into the air... which eats the ozone... Infact i have seen stuff on TV that says to fill up at night when its cooler to help the ozone..

 

The Evap uses has a connection to the fuel tank, it uses vacuum to draw the fuel vapors through the charcoal canister... which is a lovely way to keep the garage smelling nice, but really.... who are we all kidding... big V8's that we all drive with the pedal to the floor and force fuel and air down its throat at levels that the maher never intended..... YAY!!

 

Oh yeah.. and the air pump.... can someone explain to me how this is not just a load of crap whereby you pump extra air into the exhaust to increase the air to emissions ratio in the exhaust in order to satifsy a test that measures PPM of emissions poo....

sorry gmax111.... not having a go at you....its just that I have been chatting to some cynical friends of mine about this very topic this week and the old air pump idea sound like a load of crap to me....

 

From what I have heard the air injection is there for 2 reasons. On the older cars they injected air in at the manifolds and in the middle of the cat. The air was injected in the middle of the cat so that the second stage of the convertor had oxygen to carry out the chemical reaction. It`s been a while since I looked at any smog info stuff, so I can`t remember what the second stage of the older style convertors does, possibly breaks down oxides of nitrogen. The chemical reaction to break down oxides of nitrogen requires oxygen so you must inject air because the first stage of the convertor is meant to burn off the hydrocarbons from unburnt fuel and in the process it uses all the oxygen that was in the exhaust gasses.

They inject air into the manifold to try and heat the convertor up. The air injection in the manifold is only supposed to run for a short time during warm up. I believe they are trying for a blast furnace effect with the air injection in front of the convertor. Rich warmup fuel mixture + oxygen = heat? At least thats my guess.

As far as I know I don`t think the LSx motors inject air into the convertor, I am not sure if they use convertors that break down oxides of nitrogen, I think they might be clean enough to run without them.

The EVAP charcoal canister is in the vent line for the gas tank. As the gas heats up and expands in the tank the vapors go through the vent line and get caught by the charcoal canister. When you start the car the engine sucks the vapors out of the canister and burns them.

The EGR valve dilutes the intake charge with exhaust gasses at part throttle. By diluting the intake charge there is less combustible material and the temperatures in the combustion chamber is lower. This reduces the amount of oxides of nitrogen that are formed since oxides of nitrogen are only formed at high temperatures.

 

great info, thanks all