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The Automotive Industry:

The Automotive Industry:

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The Automotive Industry:

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  1. The Automotive Industry: • Fuel Value ChainLight Duty Diesel Technology

  2. Section Overview • Air Pollutants from Light Duty Diesel Engines • Compression Ignition (CI) Engines • Benefits of Diesel Fueled Automobiles • PM Formation • Diesel Fuel Quality Issues • Sulfur • Aromatics • Cetane • Biodiesel (FAME) • Vehicle Emissions • Sulfur vs. Emissions • Conclusions

  3. Pollutants from Diesel LDV • Regional Pollutants • Carbon monoxide, a poisonous gas • Particulate Matter (PM) • Oxides of nitrogen (NOx), consisting of NO and NO2 • Hydrocarbons (HC or THC), from unburned or partly burned fuel • Carbon dioxide • Implies fuel efficiency (emerging regulations) • Targeted in Climate Change Actions • Diesel offers benefits

  4. Nature of Combustion • SI combustion is termed Homogenous because the fuel and air are fairly well mixed. The burn occurs as a flame front. • CI combustion is referred to as Heterogeneous because the fuel is distributed unevenly as droplets in the air. Burning occurs around droplets at many locations. • Some combustion types are now blurring this boundary • Low Temperature Combustion (not in production) • Homogenous Charge Compression Ignition (not in production) • Gasoline direct injection (in production)

  5. Compression Ignition (CI) Engines • Diesel-fueled engines are compression ignited • Only air is drawn in on the intake stroke • Fuel is injected at high pressure into the cylinder near the end of the compression stroke • Compression heats the air in the cylinder so that the fuel autoignites after a short ignition delay • High compression ratio is desirable • Power is controlled by managing the fuel quantity injected • Almost all automotive diesel engines are turbocharged for power density

  6. CI Engines Types • Indirect injection (IDI) diesel engines have a prechamber where combustion first occurs. They are becoming uncommon for automotive use. • Direct injection (DI) engines have a shaped piston of “bowl-in-piston” and inject into the “open chamber.” Efficiency is higher. • Combustion chamber shapes are still evolving • Four valves allow symmetrical, central injection

  7. Benefits of Diesel-Fueled Automobiles • Higher efficiency engines than spark-ignited (typically 30% better, no throttling losses) • Diesel fuel has higher energy density than gasoline • Lower engine speeds than with gasoline • Combustion time dictates upper limit • Traditionally low power density, but this is now remedied with advanced turbocharging • Auto makers are announcing high performance diesel cars • Variable geometry turbocharging reduces lag • Also broadens performance on a power map • “VVT” and “VGT” • Similar emissions issues to heavy-duty diesel: NOx and PM

  8. Diesel Engine Compression Ratio • Compression ratio is set as a compromise between cold starting and turbocharged operation • Variable compression schemes • Higher Cetane rating can encourage cold starting at a lower compression ratio • Higher Cetane rating can reduce combustion harshness • Sophisticated engine technology reduces cetane dependence

  9. PM Formation • In diesel engines, incomplete combustion causes elemental (black) carbon to form and be emitted • Unburned (PM “organic fraction”) fuel forms droplets or adsorbs onto the elemental carbon particles • Lubricating oil contributes heavy, condensed HC to the PM fraction • Wear particles and ash/metals in the oil are included • Sulfur in the fuel (and oil) forms some sulfuric acid which condenses and adds to PM • The remaining sulfur is emitted as sulfur dioxide and may form secondary PM in the atmosphere • Some of the PM mass forms beyond the tailpipe (air dilution)

  10. PM • Particulate matter (PM) is usually defined by a filter collection method • PM consists of small particles and condensed droplets • Composition varies widely • Mature atmospheric PM is usually large (300 nanometers) & is formed from many sources • PM is often classified by size • Both primary (tailpipe soot, brake dust) and secondary PM (from NOx) arise from engines and vehicles

  11. PM Size Distributions • Tailpipe PM is usually less than 100 nm in size • Small particles are considered to have higher health impacts • Traditionally less than 10 micron PM has been targeted for air quality regulation • In the US, less than 2.5 micron size particles are regulated for atmospheric quality • Most diesel PM is under 1 micron in size • Aftertreatment affects the nature of PM

  12. Description of PM Size Source: David Kittelson, Univ. of Minnesota, CRC Presentation

  13. Diesel Fuel Quality Issues

  14. Fuel Effects for Diesel Emissions • Some fuel properties intrinsically alter the diesel engine emissions • Some fuel properties are essential to enable advanced diesel engine technology • Some fuel properties benefit engine reliability and longevity

  15. Fuel Effects - Sulfur • Reducing diesel fuel sulfur level reduces acid formation in the exhaust and reduces PM mass • PM mass is decreased by reduction of sulfur in the fuel because less sulfuric acid is formed by oxidation of the fuel-bound sulfur • If a diesel oxidation catalyst is used, more acid is formed, and sulfur reduction has greater importance • The lubricating oil contributes 10 or 20 ppm of fuel sulfur equivalence

  16. Sulfur Content • Recent light-duty diesel engines have exhaust gas recirculation • High sulfur content precipitates acid in the EGR cooler and intercooler (aftercooler) • Lubricating oil life is impacted by high sulfur content • Diesel PM traps with catalytic action will be damaged by high sulfur levels Image:

  17. Sulfur and Diesel Aftertreatment • The US has performed extensive studies – eg. DECSE and EC-D programs • Sulfur in diesel poisons some catalyst sites • Some damage due to high sulfur fuel may be permanent • NOxadsorbers form sulfates that disable operation, and very high temperature regeneration is needed

  18. Example of Exhaust PM Filtration Technology Source: Johnson-Matthey

  19. Fuel Effects - Aromatics • Aromatic content and polyaromatic content of fuel are also reflected in organic PM makeup. Some species are known carcinogens • High aromatic content implies low cetane rating, which implies harder starting and harsher combustion (diesel knock) • Aromatic fuels generally produce higher PM mass

  20. Lubricants • Engine oil traditionally had high sulfur levels • Sulfur in anti-wear additives, such as ZDP • This could contribute to sulfur in the exhaust, perhaps at 10ppm fuel sulfur equivalent • Catalyst life concerns • Reducing sulfur in lubricants • Lubricants now require less basicity, since there is less sulfur in the fuel • Neutralizing acids in the pan/sump • The drive for extended oil change intervals

  21. Aromatics & Cetane; Final Boiling Point • Cetane rating indicates auto ignition capability • Cetanerating is strongly linked to the paraffin content (anticorrelated with aromatic content) • Poor cetane rating is associated with raised NOx • High boiling point products (High T90, for example) leads to poor combustion and higher PM • Aromatics are implicated in health issues (PAH, nitro-PAH)

  22. Fuel Effects - Cetane • Cetane index and Cetane number correspond reasonably well for conventional diesel fuel, and both measure auto ignition quality • A high Cetane number implies less premix burn, and reduced engine noise and NOx production • Effects of cetane and aromatic content are hard to separate

  23. FAME: Diesel Engine Deposits Source: Internal Injector Deposits 2011 Update,R Caprotti, Infineum,August 2011 at SAE PFL meeting

  24. Engine Requirements for Diesel Fuel Quality • Fuel must have sufficient lubricity for all diesel engines (Europe: 460-microns wear scar maximum limit via HFRR test) (ASTM D975 Lubricity, HFRR @60°C D6079 520 max microns) • Fuel must have sufficiently good autoignition properties (ASTM D975 index or number 50) • Drivers expect repeatable energy content

  25. Diesel Sulfur Content • Europe • 1994 2,000 ppm. (49 Cetane) • 1996: 500 ppm. • 2000: 350 ppm (51 Cetane) • 2005: 50 ppm maximum. “Sulfur-free” 10 ppm sulfur diesel also required. • 2009: 10 ppm • USA • 2006: 15 ppm for on-highway, ready for 2007 low PM standard

  26. Vehicle Emissions

  27. Light-Duty Diesel Emissions • Europe allows higher NOx from light-duty diesel engines, US does not • Technology is similar to Heavy-Duty • Reasonable targets can be met with fuel and air control, and with oxidation catalysts, and with EGR • Very low PM emissions require exhaust traps • Very low NOx requires SCR

  28. High Sulfur vs. Emissions • Recent light-duty diesel engines have exhaust gas recirculation • High sulfur content precipitates acid in the EGR cooler and intercooler (aftercooler) • Lubricating oil life is impacted by high sulfur content • Diesel PM traps with catalytic action will be damaged by high sulfur levels

  29. Measuring Emissions • Chassis dynamometer • Engine Dynamometer • On-Board Tools • Remote Sensing • On-Board Diagnostics • Inspection & Maintenance • Emissions Inventory • Superemitters (80/20 or 90/10 rules)

  30. Conclusions • Diesel quality affects engine performance and exhaust emissions • Advanced diesel engine has more benefits compared with gasoline engine • Sulfur content is the most important issue • Additives usage needs to be addressed carefully, taking into consideration engine performance and emissions