In-Use Evaluation of Regulated, Ammonia and Nitrous Oxide Emissions from Heavy-Duty CNG Transit Buses Using a Portable FTIR and PEMS

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1 In-Use Evaluation of Regulated, Ammonia and Nitrous Oxide Emissions from Heavy-Duty CNG Transit Buses Using a Portable FTIR and PEMS Xu Wang 1, Saroj Pradhan 2, Arvind Thiruvengadam 2, Marc Besch 2, PragalathThiruvengadam 2, David C. Quiros 1, Shaohua Hu 1, Tao Huai 1 1 Monitoring & Laboratory Division, California Air Resources Board 2 Center for Alternative Fuels, Engines & Emissions, West Virginia University PEMS International Conference & Workshop March 26 & 27, 215

2 Background Compressed natural gas (CNG) is a widely used fuel by urban transit buses, initially with lean-burn engines and later oxidization catalysts (OxC) Since 28, the majority of CNG engines are stoichiometric and use a three-way catalyst (TWC) to meet stringent NOx (.2 g/bhp-hr) and PM (.1 g/bhp-hr) standards CNG engines accounted for ~5% of heavy-duty engine sales in California over past decade Existing emission measurements from TWC-equipped CNG identified elevated ammonia (NH 3 ) emissions relative to OxC-equipped CNG and diesel heavy-duty engines 2

3 Objectives 1. Evaluate the performance of a portable FTIR (MKS 23 HS) for measuring criteria gaseous pollutants relative to a laboratory-grade gaseous analyzer 2. Use the portable FTIR to report non-criteria gaseous pollutant emissions for ammonia (NH 3 ) and nitrous oxide (N 2 O) during chassis dynamometer test cycles and realworld bus routes 3. Report final emission factors from CNG urban transit buses for criteria gaseous pollutants measured using a chassis dynamometer (UDDS, OCTA) and selected real-world bus routes (Sacramento Regional Transit) 3

4 Test Vehicles and Instrumentation Bus A Bus B Bus C UDDS 3 3 OCTA 3 3 Route A 2 2 Route B 2 2 Chassis Dyno Instruments: CVS: Horiba MEXA-72d Partial Flow: MKS 23 HS FTIR On-Road Instruments (Partial Flow): PEMS: Horiba OBS-22 FTIR: MKS 23 HS Cummins Westport ISL-G 28 MY 28, Stoichiometric + TWC Odometer [mi]: ~23, GVWR [lbs]: 42,54 HORIBA OBS MKS FTIR 4

5 Chassis Dynamometer Test Cycles Urban Dynamometer Driving Schedule (UDDS) Time: 16 sec Distance: 5.6 mi Average: 18.9 mph Max: 58 mph Speed (mph) OCTA UDDS Time (s) Orange County Bus Cycle (OCTA) Time: 195 sec Distance: 6.5 mi Average: 12. mph Max: 41 mph 5

6 Chassis Testing for Criteria Gases: TEMS (CVS) and FTIR Emissions Factor [g/bhp-hr] TEMS FTIR OCTA CH4 CO/1 CO2/1 THC NOx TEMS FTIR UDDS CH4 CO/1 CO2/1 THC NOx Horiba MEXA 72 and MKS FTIR agree within 2-27% 6

7 Two Real-World Urban Transit Bus Routes Route A Local Only Sacramento RT #51 Route B Local + Highway Sacramento RT #7 B Distance: 11 mi Time: ~28 sec 14 mph Distance: 1 mi Time: ~16 sec 23 mph MKS 23 HS FTIR: CO, CO 2, NO x, NMHC, NH 3, N 2 O, CH 4 Horiba OBS: CO, CO 2, NO x, THC 7

8 On-Road Testing for Criteria Gases: PEMS and FTIR Emissions Factor [g/bhp-hr] Route A (Local Only) OBS FTIR CO/1 CO2/1 THC NOx Route B (Local + Highway) OBS FTIR CO/1 CO2/1 THC NOx PEMS and FTIR agree within 6 to 28% (excluding CO) 8

9 Emission Rate [mg/sec] On-Road Real-time FTIR and PEMS (Horiba OBS-22) Generally Agree OBS NOx FTIR NOx Vehicle Speed OBS THC FTIR THC Vehicle Speed Speed [mph] NO X measurements are within within 15-25% THC measurements are within within 6-1% Time (s) 9

10 Elevated NH 3 Emissions are Generally Associated With Acceleration Events NH3 Emission Rate [mg/se Segment 1: Pickup 18 mph 8 mg/s Segment 2: Hwy 42 mph 13 mg/s Segment 3: Drop-off 16 mph 8 mg/s Time (s) Speed [mph]

11 Elevated N 2 O Emissions are Generally Associated with Vehicle Speed Route B: Local + HWY Bus B, Run #1 Vehicle Speed mph bus 2 route B N2O mg/sec Bus B, Run #2 Vehicle Speed mph bus 2 route B N2O mg/sec Bus C, Run #1 Vehicle Speed mph bus 3 route B N2O mg/sec Vehicle Speed mph bus 3 route B N2O mg/sec Bus C, Run #

12 Average Gaseous Emissions from Heavy-Duty CNG Transit Buses by Cycle and Route g/bhp-hr OCTA 5.7 bhp-hr/mi UDDS 4.5 bhp-hr/mi On-Road Local (A) 4.4 bhp-hr/mi On-Road Hwy (B) 2.9 bhp-hr/mi Average 4.4 bhp-hr//mi CH N 2 O x NH NO x THC CO CO 2 / Reported values as measured by MKS 23 FTIR 12

13 Emission Factors from Selected CNG Pollutants Compared to Other Heavy-Duty Vehicles Vehicle This Study Heavy-Duty Stoich CNG+TWC.2 gnox THC g/bhp-hr NO x g/bhp-hr CO g/bhp-hr NH 3 mg/bhp-hr N 2 O mg/bhp-hr Heavy-Duty Lean CNG+OxC (A) (A) (A) 7 (B) Heavy-Duty Lean CNG (A) (A) (A) Heavy-Duty Diesel (DPF+SCR).2 gnox ~. (C) (C) (C) (C) (C) (A) Yoon et al. (213). JAWMA Vol 63 Issue 8. CBD, UDDS, and SS cycles, converted from distance-based emission factors assuming 4 bhp-hr/mi. (B) Johnson, et al. (211). Emissions from In-Use NG, Propane, and Diesel Fueled HD Vehicles. DEER Conference 211. (C) Quiros, et al. (215). Gaseous and Particulate Emissions from Heavy-Duty and Natural Gas Trucks. 215 CE-CERT PEMS Conference. Congested Highway Driving. 13

14 Conclusions The portable MKS 23 HS FTIR agreed within 2-27% to laboratorygrade CVS measurements for criteria gases Real-time FTIR emissions showed: NH 3 emissions occurred predominately during vehicle acceleration events rather than vehicle speed N 2 O emissions were elevated during highway driving conditions, but with some vehicle-to-vehicle dependence Emissions during dynamometer cycles (OCTA or UDDS) generally bound on-road emissions for most pollutants measured, except NO X was ~1.4 times higher (.26 g/bhp-hr), and N 2 O was ~3 times higher (26.3 mg/bhp-hr) on-road (Highway Route B) compared to UDDS dynamometer cycle for the CNG Transit Buses measured 14

15 Questions Contact Information Xu Wang, Ph.D. P.E. Staff Lead, On-Road CNG Testing Phone: (916)