MIT OpenCourseWare http://ocw.mit.edu 2.61 Internal Combustion Engines Spring 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.Diesel Emissions and Control • Diesel emissions • Regulatory requirements • Diesel emissions reduction • Diesel exhaust gas after-treatment systems • Clean diesel fuelsDiesel Emissions • CO – not significant until smoke-limit is reached ¾ Overall fuel lean ¾ higher CR favors oxidation • HC – not significant in terms of mass emission ¾ Crevice gas mostly air – Significant effects: ¾ Odor ¾ Toxics (HC absorbed in fine PM) – Mechanisms: ¾ Over-mixing, especially during light load ¾ Sag volume effect • NOx – very important ¾ No attractive lean NOx exhaust treatment yet • PM – very important ¾ submicron particles health effectsDemonstration of over-mixing effectDiesel HC emission mechanisms Images removed due to copyright restrictions. Please see: Fig. 11-35 and 11-36 in Heywood, John B. Internal Combustion Engine Fundamentals. New York, NY: McGraw-Hill, 1988. Effect of nozzle sac vol. on HC emissionsNOx mechanisms • NO: Extended Zeldovich mechanism N2 + O ↔ NO + N N + O2 ↔ NO + O N + OH↔ NO + H – Very temperature sensitive: favored at high temperature – Diffusion flame: locally high temperature – More severe than SI case because of higher CR •NO2 : high temperature equilibrium favors NO, but NO2 isformed due to quenching of the formation of NO by mixingwith the excess air NO + HO2 ↔ NO2 + OH NO2 + O ↔ NO + O2 – Gets 10-20% of NO2 in NOxNOx formation in Diesel engines Images removed due to copyright restrictions. Please see: Fig. 11-15 and 11-16 in Heywood, John B. Internal Combustion Engine Fundamentals. New York, NY: McGraw-Hill, 1988. Normalized NO concentration from cylinder dumping experiment. NOx and NO emissions as a function of Injection at 27o BTC. Note most of the overall equivalence ratio Φ. Note that NO2 NO is formed in the diffusion phase of as a fraction of the NOx decreases with burning increase of Φ.Diesel combustion Image removed due to copyright restrictions. Please see: Flynn, Patrick F., et al. "Diesel Combustion: An Integrated View Combining Laser Diagnostics, Chemical Knetics, and Empirical Validation." SAE Journal of Engines 108 (March 1991): SP-1444.Particulate Matter (PM) • As exhaust emission: – visible smoke – collector of organic and inorganic materials from engine ¾Partially oxidized fuel; e.g. Polycyclic Aromatic Hydrocarbons (PAH) ¾Lubrication oil (has Zn, P, Cu etc. in it) – Sulfates (fuel sulfur oxidized to SO2, and then in atmosphere to SO3 which hydrates to sulfuric acid (acid rain)Particulate Matter • In the combustion process, PM formed initially as soot (mostly carbon) – partially oxidized fuel and lub oil condense on the particulates in the expansion, exhaust processes and outside the engine ¾PM has effective absorption surface area of 200 m2/g – Soluble Organic Fraction (SOF) 10-30% ¾(use dichloromethane as solvent)Elementary soot particle structure Image removed due to copyright restrictions. Please see: Fig. 11-41 in Heywood, John B. Internal Combustion Engine Fundamentals. New York, NY: McGraw-Hill, 1988.Source: Environmental Protection Agency, www.epa.gov.PM formation processes Nucleation Surface growth Agglomeration Adsorption, condensation Dehydrogenation Oxidation Dehydrogenation OxidationTime Dehydrogenation Oxidation In-cylinderIn atmosphereDiesel NOx/PM regulation 0.01 0.1 1 2007 1991-93 1990 PM(g/bhp-hr)1994 1998 2004 US Euro II (1998) Euro III(2000) Euro IV(2005) Euro V(2008) Euro VI (proposed-2013) EU 0.1 1 10 NOx (g/bhp-hr) (Note: Other countries regulations are originally in terms of g/KW-hr)Diesel Emissions Reduction 1. Fuel injection: higher injection pressure; multiple pulses per cycle, injection rate shaping; improved injection timing control 2. Combustion chamber geometry and air motion optimization well matched to fuel injection system 3. Exhaust Gas Recycle (EGR) for NOx control ¾ Cooled for impact 4. Reduced oil consumption to reduce HC contribution to particulates 5. Exhaust treatment technology: NOx, PM 6. Cleaner fuelsEffect of EGR 1.35 L single cylinder engine, Direct Injection, 4-stroke Images removed due to copyright restrictions. Please see: Uchida, Noboru, et al. "Combined Effects of EGR and Supercharging on Diesel Combustion and Emissions." SAE Journal of Engines 102 (March 1993): 930601.Split Injection Images removed due to copyright restrictions. Please see: Nehmer, D. A., and Reitz, R. D. "Measurement of the Effect of Injection Rate and Split Injections on Diesel Engine Soot and NOx Emissions." SAE Journal of Engines 103 (February 1994): 940668.PM Control Images removed due to copyright restrictions. Please see: Zelenka, P., et al. "Ways Toward the Clean Heavy-duty Diesel." SAE Journal of Engines 99 (February 1990): 900602.Post injection filter regeneration Image removed due to copyright restrictions. Please see: Fig. 8 in Salvat, O., et al. "Passenger Car Serial Application of a Particulate Filter System on a Common Rail Direct Injection Diesel Engine." SAE Journal of Fuels and Lubricants 109 (March 2000): SP-1497. Increase exhaust gas temperature by injection of additional fuel pulse late in cycle. • Regeneration needs ~550oC • Normal diesel exhaust under city driving ~150-200oC • Need oxidation catalyst (CeO2) to lower light off temperature • Control engine torque • Minimized fuel penalty Peugeot SAE 2000-01-0473Diesel particulate filters use porous ceramics and catalyst to collect and burn the soot Please see slide 9 in Johnson, Tim. "Diesel Exhaust Emission Control." Environmental Monitoring, Evaluation, and Protection in New York: Linking Science and Policy, 2003.State-of-the Art SCR system has NO2 generation and oxidation catalyst to eliminate ammonia slip Image removed due to copyright restrictions. Please see p. 9 in "Recent Developments in Integrated Exhaust Emission Control Technologies Including Retrofit of Off-Road Diesel Vehicles."Manufacturers of Emissions Controls Association, February 3, 2000.Integrated DPF and NOx trap Image removed due to copyright restrictions. Please see: Fig. 3 in Nakatani, Koichiro, et al. "Simultaneous PM and NOx Reduction System for Diesel Engines." SAE Journal of Fuels and Lubricants 111 (March 2002): SP-1674. From Toyota SAE Paper 2002-01-0957Clean Diesel Fuels 1. Lower