1 Pump-to-Wheels Methane Emissions from the Heavy-Duty Transportation SectorNigel N. Clark, David L. McKain, Derek R. Johnson, W. Scott Wayne, Hailin Li, Vyacheslav Akkerman, Cesar Sandoval, April N. Covington, Ronald A. Mongold, John T. Hailer, Orlando J. Ugarte The WVU pump-to-wheels study is the first end-use paper in a collaborative scientific research series designed to measure and better understand the sources and amount of greenhouse-gas methane that is emitted across the natural gas supply chain.
2 Sponsors
3 Study Bounds
4 Necessary Measuring & Modeling of Methane EmissionsVehicle tailpipe Vehicle crankcase Dynamic venting CNG station compressor CNG station plumbing CNG station nozzle (refueling) LNG station delivery LNG station boil-off LNG station plumbing LNG station nozzle (refueling) Vehicle tank losses Manual venting
5 LNG Station and Vehicle TanksTwo-long term LNG station audits Pressure rise monitoring Refueling activity SI and HPDI Vehicle Tanks Ambient heat gain and pressure rise Mass emissions from venting
6 Measuring Non-Exhaust EmissionsFull Flow Sampling System (FFS) Capture entire leak plus dilution air Leaks, losses, vents, nozzle emissions, crankcase emissions for chassis testing, key on/off emissions ±4.4% Accuracy Explosion proof blower Calibrated mass air flow sensor Ultraportable Greenhouse Gas Analyzer – methane, CO2, and H2O
7 Modeling LNG Station PRV EmissionsLNG station boil-off emissions could not be measured experimentally Frequency of PRV events unpredictable Vented volumes too large for measurement equipment PRVs difficult to access Developed thermodynamic and heat transfer Model to predict LNG tank pressure rise and PRV emissions. Predict heat addition to stored LNG in Station Tank Heat transfer through storage tank walls Heat transfer into dispense and offload piping Dispenser heat transfer Account for environmental conditions Two Thermodynamic Approaches Homogeneous two zone (liquid/vapor) model Stratified temperature model Results compared with vehicle tank pressure rise experiments and long term audits at two LNG fueling stations.
8 Comparison Model and Experimental ResultsAudit 2 Segment 4 Simulation Pressure Comparison Heat Transfer by Source over All Audit 1 Segments Audit 1 Pressure Rise Rate Comparison
9 Vehicle Tailpipe Emissions9 L – Transit 9 L – Refuse 9 L – OTR 12 L – OTR 15 L – OTR Retrofits (12 L OTR, SI, CNG, On-road) (9 L Refuse, SI, CNG, Chassis) (15 L OTR, HPDI, LNG, On-road) (9 L Transit, SI, CNG, In-use)
10 Vehicle Crankcase EmissionsCrankcase Emissions Modeling – 9 liter SI Engines Linear regression model using boost pressure to predict crankcase methane from 9 liter SI natural gas engines Used to when direct crankcase methane measurements not available Model prediction error range from 16% under prediction to 22% over prediction
11 Vehicle Tailpipe and Crankcase EmissionsChassis dynamometer and on-road (PEMS) measurements used Fuel specific methane emissions (tailpipe + crankcase).
12 Data across vehicle and engine typesActivity-averaged tailpipe, crankcase vent, and HPDI fueling system vent methane emissions as a percentage of natural gas fuel consumed.
13 Stasis Scenario-Tailpipe and Crankcase EmissionsA distribution of vehicle, fuel (CNG / LNG), and engine types was adopted based on an extensive review of future natural gas vehicle adoption. Average Tailpipe FSME for Each Activity for Each Vehicle Type (g/kg fuel) Vehicle Type Idle City Arterial Highway g/kg fuel Refuse Trucks 0.67 2.99 5.39 2.20 Transit Buses 3.85 10.23 9.00 8.24 9L SI OTR Tractor 2.32 10.02 5.61 4.23 12L SI OTR Tractor 0.55 3.61 3.32 2.33 15L HPDI OTR Tractor 14.14 7.33 6.51 4.50 Average Crankcase (Dynamic Vent for HPDI)FSME for Each Activity for Each Vehicle Type (g/kg fuel) Vehicle Type Idle City Arterial Highway g/kg fuel Refuse Trucks 16.62 9.06 7.39 5.56 Transit Buses 12.81 10.38 8.00 6.63 9L SI OTR Tractor 18.46 9.97 6.25 4.91 12L SI OTR Tractor 21.52 7.77 6.47 5.01 15L HPDI OTR Tractor (Dynamic Vent) 0.00 22.10 10.15 4.81
14 Stasis Scenario-CNG/LNG Station EmissionsNumber of fueling stations was linked to fleet size Average FSME from CNG Station Vehicle Type Compressor Continuous Nozzle Emissions g/kg fuel g/day g/event Transit Bus 0.70 816 3.61 Refuse Truck* 1.12 9L OTR Tractor 0.68 12L OTR Tractor 0.49 Average 0.75 Average FSME from LNG Station Vehicle Type Refueled at LNG Station Nozzle Emissions Continuous Manual Vehicle Tank Venting Station Fuel Tank BOG Delivery g/event g/day % Total Fuel 9L SI OTR Tractor 17.7 12.8 0.250 0.100 0.128 12L SI OTR Tractor 15L HPDI OTR Tractor Average
15 Emissions Distribution for One Specific ScenarioAbsolute and relative contribution of methane emissions by component for the base case scenario. Numbers represent the average methane loss per unit of fuel used (g/kg). The percentage values reflect the contribution of each source to the total PTW emissions.
16 Acknowledgements and InformationSupport was provided by the Environmental Defense Fund, Cummins, Cummins Westport, Royal Dutch Shell, the American Gas Association, Chart Industries, Clean Energy, the International Council on Clean Transportation, PepsiCo, Volvo Group, Waste Management, and Westport Innovations. Funding for EDF’s methane research series, including the West Virginia University study, is provided for by Fiona and Stan Druckenmiller, Heising-Simons Foundation, Bill and Susan Oberndorf, Betsy and Sam Reeves, Robertson Foundation, Alfred P. Sloan Foundation, TomKat Charitable Trust, and the Walton Family Foundation. Support was also provided by West Virginia University’s George Berry Chair endowment. The authors also acknowledge the support provided by the WVU Transportable Chassis Testing Laboratory personnel including Drs. Arvind Thiruvengadam and Marc Besch. TAP Members – Name (Association) Joe Rudek (EDF) James Saunders (Westport Innovations) Greg Arney (Sempra Energy) Scott Baize (Cummins) Roxanne Bromiley (Shell) Dave Dixon (Clean Energy/NorthStar LNG) Roe East (Cummins) Ron Eikelman (Agility) Tony Greszler (Volvo) Steve Hanson (PepsiCo) Derek Johnson (WVU) John Lemmons (Waste Management) David McKain (WVU) Rachel Muncrief (ICCT) Shawn Murphy (Shell) Peter Murray (Chart Industries) Susan Robinson (Waste Management) James Saunders (Westport) Ralph Wagner (AGA) Chip Wertz (Waste Management) Eric Woods (Waste Management) SC Members – Name (Association) Drew Nelson (EDF) Barry Caldwell (Waste Management) Fanta Kamakate (ICCT) Tony Greszler (Volvo) Al Halvorsen (PespsiCo) Ian Craig (Shell) Paul McWhirter (Shell) Kathryn Clay (AGA) Todd R. Campbell (Clean Energy) Nigel Clark (WVU) Susan Robinson (Waste Management) Roe East (Cummins) Steven Hamburg (EDF) Peter Murray (Chart Industries) Scott Baker (Westport Innovations) SAP Members – Name (Association) Dave Allen (University of Texas) Brent Bailey (Coordinating Research Council) David Kittelson (University of Minnesota) Charles Powars (St. Croix Research) Bob Sawyer (University of California-Berkeley)
17 Websites http://pubs.acs.org/doi/abs/10.1021/acs.est.5b06059