TRANSIT BUS EMISSION STUDY COMPARISON OF EMISSIONS FROM DIESEL AND NATURAL GAS BUSES Nils-Olof Nylund & Kimmo Erkkilä 1
THE FINNISH NATIONAL BUS PROJECT 2002-2004 VTT performed more than 200 emission measurements with 34 different buses Some vehicles were subjected to a follow-up program to study emission stability and deterioration Variables in the study were, among others: vehicle certification class (Euro 1 to Euro 5/EEV) vehicle mileage fuel (diesel, natural gas) duty cycle (Braunschweig bus cycle, ECE, Orange Country) vehicle load 2
OBJECTIVES OF THE EXPANDED WORK ON CNG BUSES To provide unbiased emission data on current diesel and CNG vehicles extensive emission analysis Diesel buses Euro 3 without after-treatment Euro 3 with oxidation catalyst Euro 3 with OEM installed CRT Natural gas buses (catalyst equipped) Euro 3 lean-burn EEV lean-burn EEV lean-mix (combination of λ= 1 and lean-burn) EEV stoichiometric (λ= 1) 3
CHASSIS DYNAMOMETER TESTING 70 Braunschweig Bus Cycle 60 50 Speed (km/h) 40 30 20 10 70 Orange County Bus cycle 0 0 200 400 600 800 1000 1200 1400 1600 1800 Time (s) 60 50 Speed (km/h) 40 30 20 10 0 0 500 1000 1500 2000 Time (s) 4
NO x vs. PM FOR TOTAL BUS MATRIX NOx and PM emissions over the Braunschweig city bus -cycle 20 15 Brand A Brands A&B Brand A Brand B Diesel Euro 1 Diesel Euro 2 Diesel Euro 3 Diesel + CRT Euro 2 & 3 CNG Euro2 CNG Euro3 CNG EEV Euro limits (by factor 1.8) NOx g/km 10 Brand C Brand A Brand C 5 0 Brand A Brand B Brand C Euro 4 Brands D&E Euro 5 / EEV Euro 3 Euro 2 Euro 1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 PM g/km 5
NO x TREND 25 20 NOx emissions vs. Euro-levels in Braunschweig city bus -cycle Diesel Diesel + CRT CNG CNG EEV LB CNG EEV LM CNG EEV SM Euro limits (by factor 1.8) 15 g/km 10 5 0 Euro emission level 6
PM TREND PM emissions vs. Euro-levels in Braunschweig city bus -cycle 0.6 0.5 Diesel Diesel + CRT CNG CNG EEV LB CNG EEV LM CNG EEV SM Euro limits (by factor 1.8) 0.4 g/km 0.3 0.2 0.1 0.0 Euro emission level 7
PARTICLE NUMBERS 1.E+16 1.E+15 1.E+14 Particle size distribution over Br and Or test (ELPI) DI Euro III - Br DI Euro III - Or DI Euro III OC - Br DI Euro III OC - Or DI Euro III CRT - Br DI Euro III CRT - Or CNG Euro III OC - Br CNG Euro III OC - Or CNG1 EEV OC - Br CNG1 EEV OC rep. - Br CNG1 EEV OC - Or CNG2 EEV TW /OC - Br CNG2 EEV TW /OC - Or CNG EEV SM TW - Br dn/dlogdp [#/test] 1.E+13 1.E+12 DIESEL, DIESEL + OC 1.E+11 SM CNG 1.E+10 1.E+09 0.01 0.10 1.00 10.00 Aerodynamic Dp [µm] DIESEL + CRT CNG 8
DIESEL CRT vs LEAN-MIX CNG Relative emissions, worst result = 100% Brauschweig cycle PAH car. Euro 3 Diesel Items evaluated: NMHC 100 % FA Carcinogenic PAHs NMHC 50 % NO x NO 2 (tailpipe) PM# 0 % Ames CO 2 Ames mutagenicity Formaldehyde (FA) Particle mass (PM) Particle numbers (PM#) PM NO2 CO2 NOx 9
DIESEL CRT vs LEAN-MIX CNG Relative emissions, worst result = 100% Brauschweig cycle Euro 3 Diesel PAH car. Euro 3 Diesel +CRT Items evaluated: NMHC 100 % FA Carcinogenic PAHs NMHC 50 % NO x NO 2 (tailpipe) PM# 0 % Ames CO 2 Ames mutagenicity Formaldehyde (FA) Particle mass (PM) Particle numbers (PM#) PM NO2 CO2 NOx 10
DIESEL CRT vs LEAN-MIX CNG Relative emissions, worst result = 100% Brauschweig cycle PAH car. Euro 3 Diesel Items evaluated: Euro 3 Diesel +CRT NMHC 100 % CNG EEV LM FA Carcinogenic PAHs NMHC 50 % NO x NO 2 (tailpipe) PM# 0 % Ames CO 2 Ames mutagenicity Formaldehyde (FA) Particle mass (PM) Particle numbers (PM#) PM NO2 CO2 NOx 11
CONCLUSIONS On average, CNG delivers better emission performance than CRT equipped diesel Exhaust from advanced CNG vehicles was found less toxic than exhaust from CRT diesel Total numbers of particles and nanoparticles with CNG are similar to CRT diesel How will new diesel technology perform? 12