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The Automotive Industry:

The Automotive Industry:. Fuel Value Chain Light Duty Diesel Technology. 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

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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: delphi.com

  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

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