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Chapter 33 Emission Control Systems Pollutants • Emissions of most concern are HC, CO, NOx, CO2, and O2 • O2 content indicates combustion efficiency • The allowable amounts of emissions are regulated by the government • All vehicles for the last 40 years have been equipped with devices to reduce emissions Hydrocarbons (HC) • Evaporative fuel emissions also a source • Other causes of HC emissions – Unburned fuel in sheltered areas of combustion chamber – Fuel is absorbed into oil on cylinder walls – Fuel is not adequately mixed with air – Misfires – Very rich or lean mixtures Carbon Monoxide (CO) • Formed when there is not enough oxygen to combine with carbon during combustion • Caused by a lack of air or too much fuel • CO will not occur without combustion • As the mixture gets richer, CO increases Nitrogen Oxides (NOx) • As combustion reaches more than 2300ºF (1261ºC) N and O2 combine • NOx formation controlled by controlling combustion temperature • A rich mixture reduces NOx but increases CO and HC Carbon Dioxide (CO2) • Byproduct of ideal combustion • CO2 production directly related to the amount of fuel consumed • Levels are highest with a slightly lean mixture • CO2 also produced by manufacturing processes Oxygen (O2) • Too much O2 in exhaust indicates an improper air/fuel ratio • Very low O2 readings indicate a rich mixture • High O2 readings indicate a lean mixture • O2 levels are not affected by the catalytic converter Diesel Emissions • Diesels are most efficient of internal combustion engines • Typical diesel emissions include: – – – – Carbon (soot) and various carbon compounds NOx Sulphur dioxide Water Various HC compounds CO2 Inspection and Maintenance (I/M) Programs • Purpose is to identify and repair vehicles that are emitting excessive emissions • The Federal Test Procedure (FTP) samples pre-production vehicles for the next model year • If the emissions are lower, the vehicle is certified for use I/M Programs (cont’d) • After the 1990 Clean Air Act, more precise testing started, called the I/M240 test • A vehicle is operated on a dyno and tested for 240 seconds under differing load conditions • Also tests the EVAP system Air Injection Systems • Pumps fresh air into the exhaust • Caused combustion of exhaust gases • Older systems pumped air into exhaust manifolds • Later systems pumped air into catalytic converters Pulse (Non-Pump) Systems • Instead of using an air pump, some systems used the natural exhaust pressure pulses to pull air from the air cleaner Diesel Emission Controls • Modern diesels have emission levels similar to gasoline engines • Particulate filters and new fuel injection systems reduce soot emissions • Diesels emit less HC, CO, and CO2 Low-Sulfur Fuel • Eighty percent of all diesel fuel sold must be low-sulfur • Reduced sulfur from 500 PPM to 15 PPM • Allows use of particulate filters and NOx catalysts Diesel Fuel Injection • When injection begins at precisely the right time, emissions are minimized • Many diesels use common rail injection: – Uses high-pressure to provide better atomization of the fuel – Engine runs cleaner and quieter – Many systems fire the injectors several times Glow Plugs • Diesels can be hart to start when cold • Most diesels use small electric heaters to heat the intake air • Driver is alerted to wait when starting to allow warm up PCV System • Diesels produce very little vacuum so traditional PCV systems not work • A multi-stage filter may be used to collect, coalesce, and return crankcase oils to sump • Other systems work with the turbocharger to draw crankcase gases out and back into the intake Crankcase Depression Regulator (CDR) • • • • • Similar to a PCV valve Designed to work with very low vacuum Minimizes crankcase pressures Used on turbo and non-turbo engines Must be calibrated to the engine EGR Systems • Very similar to those on gas engines • Most diesel EGR applications cool the incoming gases before the cylinders • Most EGR coolers use engine coolant that passes through a separate circuit to cool the gases Catalytic Converters • Most common on diesel engines is an oxidation catalyst • Uses the O2 to oxidize CO to form CO2 and HC to H2O and CO2 • Also reduces soot emissions • May have a NOx adsorber built in or separate Particulate Matter (PM) Filter • Placed after the catalytic converter • Early filters needed regular cleaning • Newer designs periodically burn the collected PM • Use of regular diesel fuel in place of lowsulfur fuel will destroy the PM filter Selective Catalyst Reduction (SCR) Systems • Used to reduce NOx emissions • A reductant is injected into the exhaust stream and then absorbed onto a catalyst • The reductant removes oxygen from a substance and combines another substance with oxygen to form another compound • Ammonia and urea water are commonly used SCR Systems (cont’d) • Work well only if exhaust is within a specific temperature range • The PCM controls exhaust temperature and reductant injection • Reductant supply tanks must be refilled Urea • Organic compound made of carbon, oxygen, and hydrogen • Helps eliminate over 90% of nitrogen oxides in exhaust gases • Urea systems are low cost and not affect engine performance ... system Vehicle Emission Control Information (VECI) • All vehicles have a VECI decal • Normally on the underside of the hood Classifications of Emission Control Devices • All emission control devices... three categories – Evaporative control – Pre-combustion control – Post-combustion control Evaporative Emissions System Enhanced EVAP System • Similar to previous EVAP systems but can detect small... Pre-Combustion Systems • Better sealing pistons • Intake manifold designs • Combustion chamber • Improved cooling designs systems • Lower compression • Spark control • Decreased friction systems PCV Systems