the reduction of pollutants from diesel engines (1)
TRANSCRIPT
The Reduction of Pollutants from Diesel Engines
By Sean McSweeney
How A Diesel Engine Works• Air is taken in and compressed by the piston.• As the pressure of the air rises, so does the
temperature. • When the temperature is over 200 C, fuel is
injected.• The fuel is ignited by the hot air, and the energy
released pushes the piston.• Exhaust is released, containg NOx and
particulate matter.
Diesel Engines vs. Petrol Engines
• Diesel engines are more efficient than petrol engines– It will give more torque at lower speeds– It energy content is 38.6 MJ/L – Lower auto ignition temperature
However, diesel engines produce higher levels of particulate matter.
Major Pollutants
• Soluble Organic Fraction (SOF)
• Particulate Matter (PM)
• NOx
Diesel Oxidation Catalysts
• Honeycomb Monolith Structure• Oxidation of CO, HC, SOF to less hazardous
components• Coated with precious metals to help reduce posionous
emissions
Diesel Particulate Filter (DPF)
Regenerating the DPF
• Catalysed DPFsCatalysing Washcoat on filter
• Fuel-Borne Catalysts• Hydrogen Trap• Hydrocarbon Dosing
Hydrogen trap• Traps HC’s at lower temperatures• Zeolites adsorb HC’s
Fuel Borne CatalystAdvantages-• Reduces combustion temperature• Regeneration is faster and more complete • FBC’s are more tolerant to high levels of fuel sulphur • Regeneration is independent of engine NOx/PM ratios • Do not produce additional NO2 emissions
Fuel – Borne Catalysts
Hydrocarbon Dosing
Reduction of NOx
Primary MethodsDelayed Injection, Miller Cycle
Secondary MethodsExhaust Gas Recirculation (EGR)Nitrogen Enriched Air (NEA)Selective Catalytic Reuction (SCR)Lean NOx Traps (LNT)
Exhaust Gas Recirculation
• Lowers temperature of fuel ignition
• Up to 50% NOx reduction
• NOx – PM trade off
Nitrogen-Enriched Air
• Some oxygen stripped from air.
• NOx reduction of up to 50%
• Less adverse effects than EGR
Selective Catalytic Reduction
• Ammonia used to convert NOx to N2 and water
• Usually using a V2O5 / TiO2 catalyst
• Can achieve an 80-90% reduction of NOx
• Problems with unburnt fuel, NH3 slippage
Selective Catalytic Reduction
Lean NOx Trap
• NO converted to NO2 using Pt oxidation catalyst
• Alkaline metal oxide in washcoat of catalyst traps NO2
• NO2 reduced by rhodium catalyst to N2
• Can reduce 60-70% NOx
• Problem with sulphur poisoning
Comparison of fossil fuel versus biodiesel
References
• Lamas, M.I. and Rodriguez, C.G. (2012) ‘Emissions from Marine Engines and NOx Reduction Methods’, Journal of Maritime Research, IX (1), 77-82• Heck, R., Farrauto, R.J., Gulati, S. T. (2009) Catalytic Air
Pollution Control: Commercial Technology, 3rd ed., USA: Wiley
• http://dieselnet.com/tech/dpf_cat.php• Biodiesel: A realistic fuel alternative for diesel engines.
Ayhan Demirbas. 2008