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 fuels Diesel Emissions CO not significant until smoke limit is reached Overall fuel lean higher CR favors oxidation HC not significant in terms of mass emission Crevice gas mostly air Significant effects Odor Toxics HC absorbed in fine PM Mechanisms Over mixing especially during light load Sag volume effect NOx very important No attractive lean NOx exhaust treatment yet PM very important submicron particles health effects Demonstration of over mixing effect Diesel 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 emissions NOx 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 is formed due to quenching of the formation of NO by mixing with the excess air NO HO2 NO2 OH NO2 O NO O2 Gets 10 20 of NO2 in NOx NOx 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 Injection at 27o BTC Note most of the NO is formed in the diffusion phase of burning NOx and NO emissions as a function of overall equivalence ratio Note that NO2 as a fraction of the NOx decreases with increase of 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 Partially oxidized fuel e g Polycyclic Aromatic Hydrocarbons PAH Lubrication 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 PM has effective absorption surface area of 200 m2 g Soluble Organic Fraction SOF 10 30 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 Dehydrogenation Oxidation Surface growth Dehydrogenation Oxidation Agglomeration Dehydrogenation Oxidation Adsorption condensation In cylinder Nucleation In atmosphere Time PM formation processes Diesel NOx PM regulation 1 US 1990 EU 1991 93 PM g bhp hr Euro II 1998 Euro III 2000 0 1 1994 1998 2004 Euro IV 2005 Euro V 2008 Euro VI proposed 2013 0 01 2007 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 Cooled for impact 4 Reduced oil consumption to reduce HC contribution to particulates 5 Exhaust treatment technology NOx PM 6 Cleaner fuels Effect 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 Regeneration needs 550oC Normal diesel exhaust under city driving 150 200oC Need oxidation catalyst CeO2 to lower light off temperature Image removed due to copyright restrictions Please see Fig 8 in Salvat O et al Control engine torque Passenger Car Serial Application of a Particulate Filter System on a Common Minimized fuel penalty Rail Direct Injection Diesel Engine SAE Journal of Fuels and Lubricants 109 March 2000 SP 1497 Peugeot SAE 2000 01 0473 Increase exhaust gas temperature by injection of additional fuel pulse late in cycle Diesel 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 0957 Clean Diesel Fuels 1 Lower sulfur levels 350 ppm 15 ppm 2 3 4 5 Lower percentage aromatics Oxygenated fuels Higher cetane number Narrower distillation range Diesel Emission Control Summary Emission regulations present substantial challenge to Diesel engine system Issues are performance and sfc penalty cost reliability infra structure support