Andrea Jungers

William McCary

Hydrocarbon Traps

Professor Ahmet SelametME 5530

Overview

• Background of hydrocarbons• Hydrocarbons and pollution• Automotive sources of

hydrocarbons• Hydrocarbon traps of automobiles

Intake – EVAP systems Exhaust – TWC

Types of HydrocarbonsAlkyl CompoundsSaturated Alkanes (Paraffins) single bond

Unsaturated Alkenes (Olefins) double bond

Cyclanes (Napthenes) single bond ringAlkynes (Acetylene) triple bond

Aromatics Benzene, Toluene, Xylene

Alcohols Methanol, Ethanol

Ethers Methyl Ether

PollutionVOCs• Volatile organic compounds• Chemicals containing hydrogen, carbon

and possibly other elements • Evaporate easily• VOCs increase the amount of nitric oxide

in the air, which in turn combines with oxygen to produce nitrogen and ozone

• Ozone is otherwise known as smog at ground level

• VOCs in the air prevent ozone from breaking down

• Ozone can react with lung tissue causing inflammation, changes in breathing passages and coughing

http://www.epa.ohio.gov/dapc/echeck/whyecheck/healthef.aspxTransportation

• Transportation is the largest source of air pollution in the United States (http://www.ucsusa.org/clean_vehicles/why-clean-cars/air-pollution-and-health/cars-trucks-air-pollution.html)

• In the early 20th blow-by gases were allowed to be exhausted into the atmosphere

• Positive crankcase ventilation (PCV) was first installed on new cars in the 1960s and it marked the beginnings of the Evaporative Emissions Control Systems (EVAP)

Intake Evaporative Emission Control Systems (EVAP)• Approximately 20-40% of all HC emissions originate from

evaporative sources• First form of emission control on a vehicle and often the least

expensive• Five ways evaporative emissions are produced:1) Diurnal Evaporation2) Running losses – Positive Crankcase Ventilation3) Hot soak4) Re-fueling5) Permeation

• The function of the EVAP system is to block/capture HCs produced from these five sources and prevent their release into the atmosphere

• PZEV – Partial Zero Emission Vehicle near zero evaporative emissions

Positive Crankcase Ventilation (PCV)

Fixed Orifice PCV System

• Meters blowby from crankcase into intake manifold

• Provides ventilation based on size of orifice valves and intake manifold vacuum

• Two orifice valves balance strength of vacuum applied to crankcase

Variable –Flow PCV Valve

• Variable-flow PCV valve more accurately matches ventilation flow with blowby production

• Blowby is typically greatest during high loads

• A small amount of gases in the combustion chamber escapes past the piston during a compression stroke

• These gases are called “blowby” gases – unburned HCs make up approximately 70%

• Closed crankcase ventilation routes blowby gases back into the engine airtake system

Evaporative Emission Control Systems (EVAP)

http://www.visteon.com/company/features/media/050103index.html

• First examples of this system used in application is the 2000 Nissan Sentra CA

• Two HC Trap Catalysts, one under the oil pan and the other under the floor.

• Process:

• The first HC Trap begins to capture HC within the exhaust gas until the Close-Coupled TWC is warmed up.

• The first HC Trap then releases HC and begins conversion.

• Any HC that were not converted by the first HC Trap will then be caught by the second HC Trap.

• The second HC Trap finally releases HC and completes conversion.

Exhaust Gas Hydrocarbon Trap Systems

Three Way Catalyst (TWC)Chemical Reactions

• Oxidation

• Reduction

Catalyst Structure & Layering

Zeolite vs. Hydrocarbon Molecules

Zeolite Washcoat Substrate

• The substrate is generally a monolith, or honeycomb, structure which creates support for the bottom coat.

• The bottom coat is often zeolite, a porous alumino-sillicate.

• silicon tetra-oxide (SiO4)

• aluminum tetra-oxide (AlO4)

• The HC molecules found in exhaust gas range from 0.4-0.7nm while the zeolite molecular size is between 0.5-0.8nm.

• The top coat, the washcoat, consists of a catalyst from converting HC that released from the zeolite.

Hydrocarbon Capture

Calculating Efficiency Measuring HC Emissions

• Area Under the Curves

• Area A: Amount of HC Trapped by Catalyst

• Area B: Unconverted HC emitted from the HC Trap Catalyst

• Area C: Difference between HC at the Inlet and Outlet of HC Trap

• Efficiency Equations

Trapping & Conversion Performance

Active vs. Passive System Control

Bypass Loop Valve Timing & Positions

  Valve 1

Valve 2

Valve 3

Engine Starting

Closed Open Open

Switch: 60 sec

Open Closed Closed

Fully Heated

Open Open Open

• Active Control: Valve System• The valve timing is very fast

and the bypass loop switches within 60 sec of starting the engine.

• The first HC trap is heated, and then the valves switch to heat the secondary HC Trap.

• Passive Control: Hole Drilled in Absorber• A small hole increases

trapping efficiency of the first HC Trap but increases the light-off time of the second

• A large hole decreases trapping efficiency of the first HC Trap but decreases the light-off time of the second.

Supelcarb® HC Trap Supelpure ® HC Trap• S-Trap: 19 cm × 13

mm• Bed Length: 50.2 cm

• Company: Sigma-Aldrich• St. Louis, MO

• Two Size Options• 750 cc : 41.9 cm ×

59 mm• 120 cc : 28.2 cm ×

35 mm

• Price Range: $100.00 to $500.00

Purchasing Hydrocarbon Traps

• “Mobile Emissions Catalysts.” BASF.com. http://www.catalysts.basf.com/p02/USWeb-Internet/catalysts/en/content/microsites/catalysts/prods-inds/mobile-

emissions/AISHC). 10 Oct 2013.

• Heck, Ronald M. and Farrauto, Robert J. “Automobile exhaust catalysts.” Elsevier Science B.B. 2001. 443-449. Web. <http://data.obitet.net/makale/makale/internalcombustionengines/056.pdf>

• Nishizawa, Kimiyoshi. "The Hydrocarbon Trap." Technologies for Near-Zero-Emission Gasoline-Powered Vehicles. Ed. Fuquan (Frank) Zhao. Warrendale, PA: SAE

International, 2007. 269-282. Print.

• Schager, Martin. “Automotive Evaporative Emissions Systems.” The Technology Interface. Winter 2003. Vol 5. Web. <http://technologyinterface.nmsu.edu/5_1/5_1e/5_1e.html>

• Sullivan, Kevin R. “Emissions Sub System – Evaporative Emission Control System.” http://www.autoshop101.com/. Web. 1998-2013.

• "Feature Stories." Visteon.com. http://www.visteon.com/company/features/050103.html. Visteon Corporation. 10 Oct. 2013.

• http://www.ucsusa.org/clean_vehicles/why-clean-cars/air-pollution-and-health/cars-trucks-air-pollution.html

• http://www.epa.ohio.gov/dapc/echeck/whyecheck/healthef.aspx

• http://www.sigmaaldrich.com/catalog/product/supelco/22446?lang=en&region=US

References