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Workshop to Discuss Proposed Amendments to Motor Vehicle CNG Fuel Specifications

The California Environmental Protection Agency's Air Resources Board is holding a workshop to discuss proposed amendments to motor vehicle CNG fuel specifications. The objective is to increase flexibility for the industry to comply with regulations without significant impact on engine performance or emissions. The proposed amendments include the addition of an alternative statewide CNG fuel specification with a methane number (MN) of 80, as well as a limited use option with MN 73. The impacts of these specifications on fuel supply, composition, and engine emissions are also discussed.

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Workshop to Discuss Proposed Amendments to Motor Vehicle CNG Fuel Specifications

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  1. California Environmental Protection Agency Air Resources Board Workshop to Discuss Proposed Amendments to Motor Vehicle CNG Fuel Specifications February 2002

  2. Background & Issues Associated Gas Fuel Quality* Component SCC SSJV SC Standard Methane 88.2 86.2 86.2 88.0 min. Ethane 4.9 8.8 5.3 6.0 max. C3+ 3.7 2.5 4.8 3.0 max. Inerts 3.2 2.5 3.7 4.5 max. CO22.3 1.9 2.8 N20.9 0.6 0.9 BTU 1086 1100 1106 970 - 1150 * * * Volume Weighted Average * * So. Cal. Gas Co. Requirement

  3. Pipeline Map

  4. Proposed Amendments Long Term Solution • Collaborative industry agreement between gas producers and gas suppliers to provide complying CNG • Alternative Fuels Regulation that facilitates potential industry options

  5. Proposed Amendments Objectives of Proposed Amendments • No significant adverse impact on engine performance or emissions • Increase flexibility for industry to comply with the regulation

  6. Proposed Amendments Proposed Amendments to CNG • Add an alternative statewide CNG fuel specification • Methane Number (MN) of 80 • For SCC and SSJV add a limited use option CNG fuel specification • MN 73, if all three conditions are met • Station cannot economically provide MN80 fuel • Fleet vehicles can operate on MN73 fuel • Fueling stations have controls to prevent misfueling

  7. Proposed Amendments Methane Number Index • Calculated number based on hydrogen to carbon ratio of the hydrocarbon content of the fuel that predicts the likelihood of the fuel to cause engine knock • Similar to Motor Octane Number

  8. Proposed Amendments Methane Number Index (cont.) • Index used by engine manufacturers to design engines and evaluate performance • MN index allows hydrocarbon component content tradeoff • MN 80 applicable to existing and new engines • MN 73 applicable to LD vehicles and HD advanced technology engines

  9. Impacts Effect of Proposed CNG Specifications • Fuel Supply • Fuel Composition • Impact on Engines and Emissions

  10. Impacts Impact on Fuel Supply • Complying CNG under Existing Specification • SCC 11% • SSJV <1% • LAB 99% • Complying CNG under Proposal MN80 MN73 • SCC 21% 89% • SSJV 24% 99% • LAB 99% N/A

  11. Impacts Impact on Fuel Composition • Existing CNG specification equates to about MN 81 but limits ethane, propane, and higher hydrocarbons • Tradeoff could increase the content of ethane or C3+ • Small changes in reactivity • Existing Specification 0.1 MIR • Proposed Amendments 0.09 - 0.15 MIR

  12. Quality of CNG Entering SC Existing Specification Proposed MN 80 Specification

  13. Impacts CNG Motor Vehicle Emission Testing • Two studies conducted to evaluate CNG fuel quality affects • Driveability • Emissions • Fuel economy

  14. Impacts Light Duty Testing • 5 fuels tested • Methane content 82% - 94% • Ethane content 2% - 8% • C3+ content 0% - 10% • MN 63 - 103 • Wobbe Number 1245 - 1425 • 8 vehicles tested • Dedicated and Bi-fuel

  15. Impacts Light Duty Test Results • Emissions from all dedicated OEM vehicles • Below applicable ULEV standards • Slight variations in all emissions, both increases and decreases, but no correlation to fuel quality • No change in performance

  16. Impacts Heavy Duty Testing • 4 fuels tested • Methane content 82% - 95% • Ethane content 3% - 8% • C3+ content 0% -5% • MN 73 - 99 • Wobbe Number 1310 - 1363 • 7 vehicles tested • 3 advanced closed loop technology (ACL) • 2 first generation closed loop technology (1CL) • 2 open loop technology (OL)

  17. PM data for ACL Vehicles, UDDS Cycle

  18. NOx data for ACL Vehicles, UDDS Cycle

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