emissions

Emissions and Emission systems
           components and descriptions

           Table of Contents
     section 1 .........emission descriptions
                              1. NOX(Oxides of nitrogen)
                               2.C.O.(carbon monoxide)
                               3.H.C.(hydrocarbon)
      section 2 .........emission control systems and components
                              1.PCV
                              2.Evaporative emissions system
                              3.Catalytic converters
                              4.EGR

section 1

NOX, or nitrogen oxide,is formed when combustion chamber temperatures reach or exede 2,500 degrees f. when that temperature is reached,the nitrogen and oxygen in the air-fuel mixture combine.NOX is also formed at cooler temperatures,but in very minimal amounts.
the best way to reduce NOX is to reduce combustion chamber temperatures.

C.O.,or carbon monoxide,is caused by a rich fuel mixture.When the air-fuel mixture burns, hydrocarbons combine with oxygen and form CO2. if the fuel mixture is to rich(to much fuel and not enough air)there is not enough oxygen to go around, so each carbon combines with only one oxygen,forming C.O.

H.C,or hydrocarbon,is a chemical compound made up of hydrogen and carbon.Gasoline itself is a hydrocarbon.(humans,animals and dinosaurs are made partly of carbon,hence the phrase fossil fuel) hydrocarbon emissions are caused in three main ways=
1.fuel system evaporation=fuel is a hydrocarbon,when it evaporates it realeases hydrocarbons into the atmoshpere.
2.Crankcase vapors=blowby gases that enter the crankcase,and if not reburnt,will enter the atmosphere.
3.engine exhaust= the largest emitter of hydrocarbons.when gasoline is not burnt completely,it passes from the combustion chamber,through the exhaust and to the atmosphere.some unburnt gas is normal,but a poorly tuned motor or misfire will greatly increase H.C.

section 2

PCV,
or positive crankcase ventilation,is used to control crankcase hydrocarbons.It is a very basic system.fresh air is drawn from the air cleaner housing through a closure hose to the valve cover.the fresh air is pulled through the crankcase,mixing it with any vapors.it is than pulled through the pcv valve,and run into the upstream of the combustion chambers to be burnt.
   PCV VALVE is a one way spring operated plunger valve.when manifold vacume is high,the vacume forces the valve closed.When vacume is low,the spring pressure overcomes the vacume and allows the valve to open.

EVAPORATIVE EMISSIONS SYSTEMS
   there are many different versions of this system, so I will just give the basics.
the purpose of this system is to eliminate evaporated gasoline from entering the atmosphere.It does this by burning the vapors instead of venting them to the atmosphere.A basic system consists of a fuel tank vent valve(with hose connecting it to the canister),charcoal canister,purge valve and hoses.
The way it works is any fuel that evaporates in the tank is routed to the charcoal canister,where it is stored.when the purge valve opens(can be vacume valve on old cars,electric on newer)it allows vacume to draw fresh air through the canister,pulling vapors and air into the intake manifold,and on to the combustion chamber where it is burned.The purge valve only opens during cruise and light acceleration as the canister usually does not contain a large amount of fuel vapor,therefor it is more or less a controlled vacume leak.under cruise and light throttle a leaner mixture is desired,making for a good time to create a vacume leak.
modern systems incorporate a vapor management valve,fuel tank pressure sensor,canister vent valve,purge flow sensor,and powertrain control module.

CATALYTIC CONVERTERS
cat. converters are used to help reduce hydrocarbons in the exhaust.even a finely tuned good running engine will emit hydrocabon emissions out the exhaust.older cars had a COC or conventional oxidation catalyst type converter.these converters are used to convert HC's and CO's to enviromentaly safe gases and water.newer cars use a TWC or three way catalyst. It is used to convert HC's CO's and NOX into safe gases and water.
these conversions are accomplished by heating metals such as platinum,palladium, rhodium and ceria.When heated these metals will have chemical reactions with the emission gasses.

EGR
or exhaust gas recirculation,is used to control NOX emissions.It does this by routing small amounts of exhaust gas into the intake manifold.Since exhaust gas contains little or no oxygen it does not burn.This dilutes the fuel-air mixture and results in a less powerfull combustion,therefor the combustion temperature will not be as great.Remember,NOX is formed at temps above 2500 degrees,so cooler temps are the key to controlling it.It is only used at cruise and light throttle, when high power is not needed.
older cars did not use a monitor system,but modern cars use a position sensor witch is mounted on the egr, or a pressure feedback system, which measures exhaust backpressure over a meatered orifice.