Emission Control System Fundamentals

When does the PCV system work best and why?

At idle because it operates on intake manifold vacuum. There is more blowby at idle because at higher speeds compression rings seal better, resulting in less bloby.

Are all orifices in the PCV Valve the same diameter?

No, the PCV Valves use a specific size orifice to match the engine displacement. Incorrect valves could lead to performance problems and oil leaks.

What are the three sources of emissions?

Crankcase, evaporation, and exhaust.

Where do Hydrocarbon vapors come form?

Fuel tank or vents in the fuel system.

What are blowby gasses?

HC's that leak past the piston rings. PCV helps to remove these.

What emissions come from the exhaust pipe?

Hydrocarbons (HC), CarbonMonoxide (CO, and Oxides of Nitrogen (NOx).

How is photochemical fog produced?

Hydrocarbons and oxides of nitrogen react with sunlight to form a dirty yellow brown haze.

How does spark, compression, and rich air-fuel mixture impact HC emissions?

Low compression results in unburned fuel, inadequate spark results in unburned fuel, and mixture that is too rich will all produce more HC emissions.

How does a PCV Valve operate?

Modulates a small amount of air leakage into the intake manifold that pulls the blowy gases from the crankcase.

What emissions come from the crankcase?

Mostly Hydrocarbons (HC).

What emission does the EGR reduce and how?

NOx, by recirculating up to 10% of the exhaust back into the combustion chamber lowering temperature up to 300F.

How do you test a PCV Valve?

Shake it - should rattle. Pull the valve from the mounting, with the engine running, cover the end of the valve with your thumb. Engine rpm should drop 50-80 rpm. (late model vehicles should have computer idle control disabled before running this test.) Check for vacuum should be present at the valve cover oil filler opening.

What emission is a result of incomplete combustion?

Carbon monoxide. an indication of a a rich mixture.

What is a two way Cat?

Oxidizes HC and CO, converting them into H2O and CO2.

What is a Reduction Cat?

Reduces harmful NOx into harmless nitrogen and O2

What two functions does an Air Injection system provide?

Reducing HCs and COs in the exhaust with a low pressure air supply. Heat up a cold Cat.

What is Positive Crankcase Ventilation?

Was the first emission control system to reduce HCs in blowy gasses by scavenging them from the crankcase and reintroducing them into the combustion chambers.

What is skin effect?

When burning fuel is quenched on the cylinder surfaces. HC emissions are higher when a combustion chamber has more surface area.

How is NOx produced?

When combustion temperatures are above 2,500F. High compression, carbon deposits, lean air-fuel mixtures, high intake temperatures, and excess cooling system temperatures.

What is a three-way dual bed cat?

has two different chambers for oxidizing and reducing.

How is blowby measured?

in cubic feet per minute (cf.). Normal blowby cf. can be estimated by diving maximum horsepower the engine can develop by 50. 250hp = 5cfm.

What is a three-way single bed Cat?

oxidizes and reduces in the same chamber