unit of study types and sources of emissions vapor control systems improvement of combustion...

Unit of Study

Types and Sources of Emissions

Vapor Control Systems

Improvement of Combustion

Treating Exhaust Gas

Measuring Exhaust Emissions

Diagnostics

Three Major Pollutants

• Hydrocarbons (HC) un-burnt gasoline.

• Carbon monoxide (CO) partially burnt gasoline.

• Oxides of Nitrogen (NOx) air burns against itself.

• Evaporation from the fuel tank.• Blow-by gases which escape from the crankcase.• Tail pipe emissions.• Carburetor evaporation from the float bowl on old

cars.

Three Ways to Control Pollution

A. Improve combustion

B. Capture the vapors and re-burn them.

C. Treat the exhaust.

Positive Crankcase Ventilation(PCV)

Regulating the PCV Vapor Flow

AmountAmount

ConditionCondition

Manifold

Vacuum

Blow-by

Gases

Idle High

Vacuum

Small

Volume

High Speed Low Vacuum

Large

Volume

PCV Valve• The PCV valve has

two functions:

1. To regulate the

amount of vapor

entering the intake

manifold at various

engine speeds.

2. Prevent damage

from backfire.

PCV Valve at Idle Speed

Idle speedIdle speed

PCV Valve at Cruising Speed

PCV Valve during BACKFIREor when the Engine is OFF.

PCV Service

• Replace PCV valve every 30,000 miles. • Clean the breather filter if applicable. The valve

can be cleaned also if you don’t want to replace it.• Inspect hoses for proper routing and deterioration.• Check the air cleaner housing for oil build up.• Check PCV system function. 1) Use the PCV vacuum tester.

2) Use the tachometer and look for RPM drop.

PCV Trouble-Shooting Notes

• Defective PCV system can cause big time vacuum leaks. This can lead to a very fast idle speed or stalling.

• If the valve or hoses get clogged the vapors back-up into the air cleaner clogging it too and puts oil in the air cleaner housing.

• A strange problem is if a valve cover gasket starts leaking oil winds up in the air cleaner also.

Oil in Air Cleaner Housing

• Gasket leaks mess up the vacuum on a PCV system.

• Manifold sucks air though the leaking gasket and the blow-by backs-up into the air cleaner.

Fuel Tank Evaporative Controls

• Captures HC evaporation from the fuel tank.

• Seals the gas tank and store the vapors in a charcoal canister.

• Vapor are purged to the intake manifold when the engine is running.

Older Style Evap

1) Fresh air enters here

3) Fresh enters here mixes w/fuel vapor

2) Fuel vapor moves to canister

4) Intake vacuum draws vapor to manifold

5) PCM controls flow to manifold 6) Vapor burns in

cylinders

OBDII Evap 1

Fresh air vent controlled by the PCM.Closed when engine is off.Open while engine is running.

Vapor managementvalve.Closed when engine is off.Pulsed when engineis running.

PCM monitorspressure in fueltank. Can causeDTC.

OBDII Evap Test ModeSystem can be testedfor leaks.

VMV closed

CVV closed

Special device pumpsnitrogen into systemto check for leaks.

Evaporative Service

• Some charcoal canisters have a filter under them that needs to be replaced every 30,000 miles.

• Inspect the hoses for proper routing and deterioration.

• Check to gas cap.• 1996 and newer cars can be tested for leaks in the

system.• Use the scan tool to check the status of the purge

control solenoid or control valves.

Heated Air Intake Systems• Warms-up inlet air

around exhaust manifold.

• Enhances fuel evaporation for better combustion.

• Maintains a 120˚F air temp.

• 2 types: Vacuum operated and mechanical thermostat.

• Prevents throttle icing.

Engine COLDCOLD

Warm air

Engine WARMWARM

Cold airWarm air

Engine HOTHOT

Cold air only

Heated Air Intake Service

• Inspect system for proper hose routing, hose condition and connections.

• Check vacuum diaphragm for proper operation.

• Check blend door for proper movement.

• Check thermostat for proper operation.

Early Fuel Evaporation (EFE)

• Helps engine warm-up faster.• Uses exhaust gas to warm

intake manifold.• Uses a special passageway

under the intake manifold called a crossovercrossover.

• Use mostly on carbureted and throttle body Vee engines.

• A control valve forces the exhaust gas from one bank to the other.

• Only operates during the first 5 minutes or so of operation.

Heat Riser & EFE Valves

• Old Heat Riser valves used a bi-metal thermostatic spring to open and close the valve.

• EFE Valve was vacuum operated and was controlled by a TVS.

Heat Riser (EFE) Service

• Check exhaust valve for freedom of movement.

• Check vacuum diaphragm for proper operation.

• Check vacuum hoses for proper routing, condition and connections.

Exhaust Gas Recirculation (EGR)

System allows exhaustgas (water vapor) toflow from the exhaustmanifold to the intakemanifold. This coolsthe fuel mixture andreduces NOx emissions.

Intake manifold EGR valve

Transfer tube Exhaust manifold

3000º F 2500° F

Combustion Gases Water VaporCombustion Gases

Cooling the Air/Fuel Mixture

Cooling the combustion prevents formation of NOx emissions.

EGR Valve

• Convention vacuum diaphragm style.

• Back-pressure diaphragm type.

• Electronic (solenoid)

From exhaust

To intake manifold

EGR Controls

• EGR not necessary when the engine is cold or idling. Since NOx forms only from excessive combustion chamber temperatures.

EGR Service

• Checking valve for proper operation.

• Inspect hoses for proper routing, condition and connections.

TREATING EXHAUST GAS

• Air Injection Systems

• Catalytic Converters

Catalytic Converter

• Converts HC, CO, NOx into H²0, CO², O² & N²

• Uses rare metals to create a catalytic action.

• What is a catalyst?

• Single bed or two-way converters.

• Dual bed or three-way converters.

Most common construction Older GM style

Single bed

Three Types of Converters

• Two way converter. (Single bed)

• Three-way converter. (Dual bed)

• Three-way converter with/air.

Oxidation catalyst Reduction catalyst

Air injection tube

flow

Typical Three-Way Converter

Reduction CatalystNOx reduction

Oxidation CatalystBurns CO & HC

Testing Catalytic Converters

• Visual inspection on hoist. Check heat shields, air pipes pipe integrity.

• Mallet test for loose substrate.

• Exhaust back-pressure test.

• Temperature drop test using a pyrometerpyrometer.

• Cat test using the Gas AnalyzerGas Analyzer.

Air Pump or Air Injection Systems

• Pumps fresh air into the exhaust manifold to burn up any HC or CO still present in the exhaust.

• Acts as an after burner.

• Needs several control valves for the system to function properly.

Basic Parts

• Air Pump• Hoses• Diverter• Check

valves• Metal

injection tubing

Air Pump

• Belt driven vane pump.

• Pumps fresh air into the exhaust manifold or the catalytic converter.

Diverter Valve

• The engine will backfire on deceleration if air is pumped into the exhaust manifold.

• The diverter valve sends the air back into the atmosphere during decel.

Diverter Normal Driving

Diverter During Decel

One-Way Check Valve

• Prevents damage to system in case of a backfire.

• Allow air to flow into the exhaust manifold.

• Blocks exhaust from going back toward air pump.

Air Switching Valve

• Used on air management systems that integrate the air injection system and the catalytic converter.

• Simply changes air from being pumped into the exhaust manifold to the converter.

Air Management System

Air PumpEngine coldEngine cold

Air Management

Engine warmed-up

Measuring Exhaust Emissions

4 Gas Analyzer4 Gas Analyzer

HC, CO, CO2, O2HC, CO, CO2, O2

5 Gas Analyzer

HC, CO, CO2, O2, NOx

EPA EMISSION STANDARDS

• 1968-1971 HC 900 ppm CO 9.0%

• 1972-1974 HC 800 ppm CO 8.0%

• 1975-1979 HC 700 ppm CO 7.0%

• 1980 HC 300 ppm CO 3.0%

• 1981- on HC 220 ppm CO 1.2%

• I.M. 240 Test