No Slide TitleAutomotive – Engine Performance
Types of Emissions
Emission Control Devices
Automotive – Engine Performance
Emission Types
Vehicles are responsible for producing emissions that are harmful to the atmosphere and the environment. Legislation has been introduced stating that emissions must be reduced. The major emissions produced by a vehicle are:
Hydrocarbons (HC) are created by unburnt fuel entering the atmosphere. They are either fuel that has not combusted properly or fuel vapour leaking from the fuel bowl, filler pipe etc. HCs are reactive and can cause illnesses.
Oxides of Nitrogen (NOX) are formed when nitrogen and oxygen mix under high pressure and high temperature 1400°C (2500°F).
NOX can cause eye and
respiratory problems.
* of 12
Automotive – Engine Performance
Emission Types
Carbon Monoxide (CO) is caused by the incomplete combustion of fuel. It is an invisible poisonous gas that can be fatal if large amounts are inhaled.
Particulates are soot particles caused by fuel additives. They are particularly prominent with diesel engines. 30% of the particles sink to the ground while the other 70% can be airborne for long periods of time.
* of 12
Automotive – Engine Performance
Emission Control Systems
Modern vehicles are fitted with emission control systems, designed to reduce emissions. These include:
A catalytic converter.
* of 12
Automotive – Engine Performance
Steel shell
Catalyst honeycomb
Reduction converter
Catalytic Converter
A catalytic converter removes the harmful gases that exit the exhaust.
Oxidization converter
The oxidization converter stores oxygen when the air/fuel mixture is lean. It converts hydrocarbons (HC) into water (H2O) and carbon monoxide (CO) into carbon dioxide (CO2).
A three-way converter contains honeycomb coated with platinum, palladium and rhodium to form oxidization and reduction converters.
The reduction converter converts oxides of nitrogen (NOX) into nitrogen (N2) and oxygen (O2).
The conversion process produces temperatures up
to 900°C (1600°F).
* of 12
Automotive – Engine Performance
Air Injection System
This system forces clean air into exhaust ports to ignite unburnt fuel (hydrocarbons), within the exhaust manifold. Some systems also force air into a catalytic converter to
aid the conversion process.
Air is forced into the exhaust ports by a vane type air pump, via an air injection manifold.
Vacuum operated diverter valve is used to stop air flow during deceleration, otherwise backfiring may occur within the exhaust.
A check valve is placed in the line to stop hot exhaust gases travelling back up the air hose.
* of 12
Automotive – Engine Performance
Exhaust Gas Recirculation (EGR) System
The system uses an EGR valve that can be either vacuum and/or electronically controlled.
The EGR system reduces NOX emissions. It feeds inert exhaust gases back into the inlet manifold, where they dilute the air/fuel mixture, without altering the air/fuel ratio. With less oxygen and fuel, combustion temperatures (and therefore NOx levels) are lower.
Early EGR valves were operated by ported vacuum. They did not function until engine was at operating temperature and above idle speed.
Exhaust gas flow
Automotive – Engine Performance
Electronic EGR Components
In an electronic system, the ECU uses data from sensors to control EGR valve operation.
Vehicles that conform to EOBD regulations must be fitted with feedback sensors (DPFE) to confirm valve operation.
The ECU calculates the ideal quantity of exhaust gas to recirculate (and timing). This provides optimum vehicle efficiency with the least amount of emissions.
Metering
orifice
Automotive – Engine Performance
Electronic Evaporative Emissions Control
In a modern vehicle, the fuel system is sealed and fuel vapours are stored and then burnt at an appropriate time, along with the normal air/fuel mixture.
Fuel produces vapours, if stored in a container that contains air. The rate at which fuel vapour is produced increases with air temperature increase. Older vehicles had vented fuel tanks and carburettors, allowing fuel vapours to enter the atmosphere.
The fuel tank has a sealed cap that may contain valves to relieve fuel pressure and allow air in. The tank contains an air dome that allows for fuel expansion and a vent line for vapour removal.
High pressure
release Cap
Air dome
Fuel outlet
Vent line
* of 12
Automotive – Engine Performance
Electronic Evaporative Emissions Control
The vent line is fitted with a roll over/vapour separator valve to stop liquid fuel entering the system (vehicle inversion). It connects to a charcoal canister that stores vapours when the engine is switched off.
A purge valve is used to control vapour removal from the canister. Vapours are drawn into the inlet manifold via a purge line. On older vehicles the valve is operated by ported vacuum (shown). On modern engines, the ECU controls valve operation for optimum engine efficiency.
Vacuum
Automotive – Engine Performance
Positive Crankshaft Ventilation (PCV)
Combustion produces high pressure in a cylinder. Some of the pressurized gas leaks past the piston rings into the crankcase, even on a new engine and is known as 'blowby'.
Modern vehicles are fitted with a PCV system. Vacuum is used to suck blowby out of the crankcase and into the inlet manifold to be burnt. Fresh air replaces the gases in the crankcase. System operation is regulated by a PCV valve.
Older vehicles had a breather tube that vented these gases into the atmosphere.
Fresh air enters through the air cleaner
Vapours pass into the inlet manifold
Air flow
Vapours pass through the
PCV valve and hose
Automotive – Engine Performance
PCV Valve
The PCV valve is a spring-loaded device, with an engine specific orifice size. The valve is sealed shut when an engine is stopped to prevent backfires.
At engine idle speed, maximum vacuum defeats spring pressure and the plunger moves to the other end of the valve, allowing minimal vapour flow.
At normal engine speeds, lower vacuum levels allow the plunger
to move to a central position and maximum vapour flow occurs.
To manifold