AIR POLLUTION & EVAPORATIVE EMISSIONS

Hydrocarbons Unburned fuel vapors When exposed to sunlight, chemical reaction occurs that produces ground-level ozone O3. Harmful to all living things Vehicle emissions create 50% of this ozone

Carbon Monoxide Colorless, odorless, toxic gas Product of incomplete combustion Displaces oxygen which reduces oxygen in bloodstream Vehicles produce 2/3’s of co in atmosphere

Carbon Dioxide Product of proper combustion Does not directly impair human health Greenhouse gas –Traps heat –Helping to increase global warming

Just What is Ozone? Ozone is a form of oxygen with a different chemical property Ozone differs from oxygen: –Has a distinctive odor –Contains 3 oxygen atoms –Absorbs damaging ultraviolet (UV) radiation In large concentrations ozone is hazardous

Earth’s Atmosphere Troposphere start on the surface and extends 5 – 9 miles –Air most dense –All weather occurs is this region Stratosphere extends for 31 miles –Contains the Ozone layer

Good Ozone Blocks or absorbs most of the suns ultraviolet rays Approx. 3,000 million tons of ozone in atmosphere If concentrated at sea level, would measure only 3 mm thick

Bad Ozone (Smog) Brown haze seen on hot summer days Result from burning fossil fuels – chemical reaction from heat & sun light Health problems –Aggravates heart, lung ailments –Can lower immune system –Eye & nose irritations Environmental problems –Inhibits plant growth, weakens plants –Reduce yields –Deteriorates man-made materials –Acid rain

Evaporative Emissions Hydrocarbons escaping through fuel evaporation. Diurnal – gas evaporation as daytime temps increase Running Loss – vaporization from hot engine & exhaust parts Hot Soak – hot engines (off), vaporization can continue Refueling – Vapors forced out of tank as liquid fuel enters

Evap. Emission Control Systems Sealed fuel tank – domed to allow for vapor expansion Liquid-vapor separator – when tank is full fuel can enter vent lines Vent lines – routes vapor to canister & engine Activated charcoal canister – absorbs fuel vapors, releases vapors with fresh air Non venting gas cap – pressure/vacuum relief valve

Carbon Canister Holds vapors when engine not running Engine fully warm & off idle, canister is “purged” allowing fresh air in, fuel vapors routed to engine & burned

Canister Operation

Purge Valve Normally closed Vacuum or electric solenoid Engine off or idling valve is closed Engine running valve opens allowing purge of canister Solenoids either on/off or PWM

Basic Purge Operation

Thermostatic Vacuum Switch (TVS) Installed in intake manifold coolant passage Valve 115 F, allows vacuum to flow

Canister Venting Open bottom – When purging fresh air enters from bottom of canister Closed bottom – fresh air enters for clean side of air filter Electric vent solenoid – PCM controlled, allows fresh air in when commanded, seals system when closed.