Effect of Air- Fuel Ratio on Engine- Out Exhaust Hydrocarbon Species from a Direct Injected Gasoline Engine April 6, 2016 Stani Bohac, Jason Gaudet, John Hoard University of Michigan 2016 DOE- Crosscut Lean/Low- Temperature Exhaust Emissions Reduction Simulation (CLEERS) Workshop April 6-8, 2016 Ann Arbor, Michigan 1
Why Bother with Hydrocarbon Speciation? Low volatility HC and particulates nucleate to form ultra-fine particles (<100 nm) condense (dew point) or adsorb (van der Walls forces) onto existing particles Particulate properties EGR cooler fouling filtration efficiency and regeneration of a GPF performance of exhaust particle sensors (conductivity, collection efficiency, etc.) Olefins and acetylenes high concentrations relative to oxygen displace oxygen and can temporarily deactivate a Pt-based catalyst at low temperatures C 3 H 6 can reduce NO x conversion on an Fe-zeolite SCR catalyst cycled between reducing and oxidizing (LNT-SCR or TWC-SCR) Paraffins slightly higher oxidation catalyst light-off temperature Methane not included in NMOG but is a greenhouse gas 2
Methane Properties of Hydrocarbon Classes Very stable and difficult to oxidize in a catalyst or atmosphere (10 yr in atm) Extremely low SMOG impact (0.01 go 3 /ghc) and not included in NMOG Significant greenhouse gas (methane GWP 25X CO 2 ) Paraffins (e.g., 2,3,3-trimethylpentane) Relatively stable & not the easiest to oxidize in a catalyst or atm (4 days in atm) Low SMOG impact (1.2 go 3 /ghc for 2,3,3-trimethylpentane) Olefins and acetylenes (e.g., propene) Easy to oxidize in a catalyst or atmosphere (15 hr in atm) Can deactivate a catalyst High SMOG impact (12 go 3 /ghc) Aromatics (e.g., m-xylene) Most are easy to oxidize in a catalyst or atmosphere (15 hr in atm) High SMOG impact (11 go 3 /ghc) Oxygenates (e.g., formaldehyde) Easy to oxidize in catalyst and atmosphere (3 hr in atm) Moderate/High SMOG impact (9 go 3 /ghc) 3
Prior Investigations PFI engines Papa (SAE 670494) Pioneering work Kaiser et al. (J of High Res Chomatography, v17, p264, 1994) effect of engine operating condition HCCI engines Kaiser et al. (SAE 2005-01-3749) effect of A/F ratio Lean stratified GDI engines Cole et al. (SAE 982605) Asian market Mitsubishi Legnum Kaiser et al. (SAE 2000-01-0254) effect of start of injection timing (i.e., mixing) Stoichiometric GDI engines May et al. (Atm Env, v88, p247, 2014) median of 64 vehicles but only 2 are GDI Hasan et al. (Atm Env, v129, p210, 2016) 8 hydrocarbon species from wall-guided GDI Ø only 8 species Ø Didn t vary λ 4
Objective Speciate engine-out gaseous hydrocarbons from a GDI engine operated rich, stoichiometric, and lean to provide information for other studies on the effects HC species on particulates, EGR cooler fouling, aftertreatment, and sensors. 5
Experimental Setup Engine Test engine GM Ecotec LNF 2.0L DISI turbocharged I4 engine (MY2010) Bore x Stroke x Con Rod x Wrist Pin Offset: 86 mm x 86 mm x 145.5 mm x 0.8 mm CR: 9.2:1 Performance: 260 bhp @ 5300 rpm 260 lb-ft @ 2500-5250 rpm (22 bar BMEP) Fuel injection: side mounted injector wall guided spray Bosch HDEV5 injectors, 22.5 cc/s n-heptane @ 100 bar 52-155 bar Boosting: Borg Warner twin scroll K04 turbocharger maximum turbine-in T= 980 C maximum boost = 20 psig Valve timing: dual VVT with 50 CA phasing authority 10.3 mm intake and exhaust valve lift Fuel/oil: 93 octane E10 premium unleaded 5W-30 Mobile 1 synthetic lubricating oil 6
Experimental Setup Fuel Premium Unleaded E10 Pump Gas supplied by Corrigan Oil, analysis by Paragon Laboratories (Livonia, MI) Octane: 99.4 RON, 91.3 MON, 95.4 AKI, 8.1 sensitivity LHV: Density: HC type (FIA): Elemental analysis: Oxygenates by GC: Vapor pressure: Distillation: 42.254 MJ/kg 0.7113 g/ml 83.0% saturates, 0.9% olefins, 6.0% aromatics (% v/v) 80.89% carbon, 15.05% hydrogen, 4.06% oxygen (% m/m) 10.02 ethanol (% v/v) 12.34 psi DVPE (ASTM) 10% at 47.9 C, 50% at 96.7 C, 90% at 144.6 C (Class E winter fuel) 7
Experimental Setup Emissions Horiba Mexa-One THC by FID Shimadzu GC-17A HC speciation by capillary column and FID MKS 2030HS FTIR Oxygenated and low molecular weight HC speciation by FTIR 8
130 Species Library, C 1 C 10 methane t-2-pentene c-2-hexene 3-ethyl-c-2-pentene c-2-octene ethene 3,3-dimethyl-1-butene 2-methyl-c-2-pentene 2,4,4-trimethyl-1-pentene 2,3,5-trimethylhexane acetylene c-2-pentene 2,2-dimethylpentane 2,3-dimethyl-2-pentene 2,4-dimethylheptane ethane 2-methyl-2-butene methylcyclopentane c-2-heptene c-1,2-dimethylcyclohexane propene cyclopentadiene 2,4-dimethylpentane methylcyclohexane ethylcyclohexane propane 2,2-dimethylbutane 2,2,3-trimethylbutane 2,2-dimethylhexane 3,5-dimethylheptane propadiene cyclopentene 3,4-dimethyl-1-pentene 2,4,4-trimethyl-2-pentene ethylbenzene 2,5-dimethylhexane & propyne 4-methyl-1-pentene benzene ethylcyclopentane 2,3-dimethylheptane 2-methylpropane 3-methyl-1-pentene 3-methyl-1-hexene 2,4-dimethylhexane m&p-xylene 2-methylpropene cyclopentane 3,3-dimethylpentane 3,3-dimethylhexane 2-methyloctane & 4- methyloctane 1-butene 2,3-dimethylbutane cyclohexane 2,3,4-trimethylpentane 3-methyloctane 1,3-butadiene MTBE (C5H12O) 2-methylhexane toluene styrene n-butane 4-methyl-c-2-pentene 2,3-dimethylpentane 2,3,3-trimethylpentane o-xylene methanol 2-methylpentane cyclohexene 2,3-dimethylhexane 1-nonene t-2-butene 4-methyl-t-2-pentene 3-methylhexane 2-methylheptane n-nonane 2,2-dimethylpropane biacetyl 3-pentanone 4-methylheptane i-propylbenzene 1-butyne 3-methylpentane c-1,3- dimethylcyclopentane 3-methylheptane 2,2-dimethyloctane c-2-butene 2-methyl-1-pentene 3-ethylpentane 1-c,2-t,3- trimethylcyclopentane benzaldehyde 3-methyl-1-butene 1-hexene t-1,2-dimethylcyclopentanec-1,3-dimethylcyclohexane2,4-dimethyloctane 2-methylbutane n-hexane 1-heptene t-1,4-dimethylcyclohexane n-propylbenzene ethanol t-3-hexene 2,2,4-trimethylpentane 2,2,5-trimethylhexane 1-methyl-3-ethylbenzene 2-butyne c-3-hexene t-3-heptene 1-octene 1-methyl-4-ethylbenzene 1-pentene t-2-hexene n-heptane t-4-octene 1,3,5-trimethylbenzene 2-methyl-1-butene 3-methyl-t-2-pentene 2-methyl-2-hexene n-octane 1-methyl-2-ethylbenzene n-pentane 2-methyl-2-pentene 3-methly-t-3-hexene t-2-octene 1,2,4-trimethylbenzene 2-methyl-1,3-butadiene 3-methylcyclopentene t-2-heptene t-1,3-dimethylcyclohexane n-decane Methane in gray;; Paraffins in black;; Olefins in red;; Aromatics in blue;; Oxygenates in green 9
Test Conditions λ (-) 0.90 1.00 1.10 Speed (rpm) 1600 1600 1600 BMEP (bar) 8.0 8.0 8.0 Spark ( BTDC) 20 24 26 CA of P max ( ATDC) 16 16 16 SOI ( BTDC firing) 285 288 285 P rail (bar) 60 61 62 EVC * ( ATDC) 26 26 26 IVO * ( BTDC) 35 35 34 BSFC (g/kwh) 275 251 244 T cyl.1-exh ( C) 641 664 644 T turb-out ( C) 578 598 580 * at 0.25 mm lift 10
Energy Balance and Standard Exhaust Species 11
Energy Balance 100 20 90 18 Combustion Efficiency (%) 80 70 60 50 40 30 20 Comb. Eff. (%) % fuel energy in CO % fuel energy in HC (from GC) 16 14 12 10 8 6 4 Fuel Energy in CO and HC (%) 10 2 0 0 0.85 0.90 0.95 1.00 1.05 1.10 1.15 Lambda (- ) Combustion efficiency best with λ=1.10 For λ=0.90 more energy in CO than HC. For λ=1.10 more energy in HC than CO. 12
Temperature and Standard Exhaust Species Turbine- Out T ( C) NOx and THC (ppm, ppmc1) 600 595 590 585 580 575 570 565 560 555 550 3000 2500 2000 1500 1000 500 0.85 0.90 0.95 1.00 1.05 1.10 1.15 NOx (ppm) GC THC (ppmc1) CO (%) 13 turbine- out T ( C) O2 (%) 0 0.85 0.90 0.95 1.00 1.05 1.10 1.15 Lambda (- ) 5.00 4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 5.00 4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 O2 (%) CO (%)
Speciation Results (GC+FTIR) 14
Hydrocarbon Speciation for λ = 0.90 Peak Result ppmc1 mghc/s mghc/gfuel Confidence 60unidentified 514.95 5.389 3.327 unidentified 1methane 144.45 1.816 1.121 High Probability 2ethene 114.89 1.263 0.779 High Probability 3acetylene 105.25 1.074 0.663 High Probability 322,3,3- trimethylpentane 92.14 1.031 0.636 High Probability 5propene 84.6 0.93 0.574 High Probability 282,2,4- trimethylpentane 81.07 0.907 0.56 High Probability 92- methylpropene 64.29 0.707 0.436 High Probability 44m&p- xylene 61.88 0.644 0.397 High Probability 312,3,4- trimethylpentane 54.61 0.611 0.377 High Probability 56unidentified 51.7 0.541 0.334 unidentified 39unidentified 41.69 0.466 0.287 unidentified FTIRethanol (C2H6O) 36 0.655 0.404 11n- butane 33.7 0.384 0.237 High Probability 362,2,5- trimethylhexane 31.48 0.352 0.217 High Probability FTIRacetaldehyde (C2H4O) 30 0.522 0.322 FTIRMTBE (C5H12O) 30 0.418 0.258 591,2,4- trimethylbenzene 28.94 0.303 0.187 Low Probability 531- methyl- 4- ethylbenzene 28.62 0.299 0.185 Low Probability 57unidentified 28.57 0.299 0.185 unidentified 142- methylbutane 26.58 0.301 0.186 High Probability 151- pentene 26.32 0.289 0.179 High Probability 46unidentified 24.46 0.254 0.157 unidentified 61n- decane 23.74 0.265 0.163 High Probability 272,3- dimethylpentane 21.37 0.24 0.148 High Probability 4ethane 18.22 0.215 0.132 High Probability 54unidentified 17.24 0.18 0.111 unidentified 42unidentified 16.74 0.174 0.107 unidentified 58unidentified 16.21 0.17 0.105 unidentified 332,3- dimethylhexane 16.07 0.18 0.111 High Probability 302,4- dimethylhexane 15.61 0.175 0.108 High Probability 263- methyl- 1- hexene 15.47 0.17 0.105 Low Probability 15
Hydrocarbon Speciation for λ = 0.90 continued Peak Result ppmc1 mghc/s mghc/gfuel Confidence 55 unidentified 14.17 0.148 0.092 unidentified 29 2,5- dimethylhexane & ethylcyclopentane 13.6 0.152 0.094 High Probability 25 2,4- dimethylpentane 13.13 0.147 0.091 High Probability 45 unidentified 12.19 0.124 0.077 unidentified FTIRformaldehyde (CH2O) 12 0.285 0.176 10 1,3- butadiene 9.07 0.096 0.059 High Probability 19 2- methyl- 2- butene 8.8 0.097 0.06 High Probability 12 t- 2- butene 8.36 0.092 0.057 High Probability 52 n- propylbenzene 7.94 0.083 0.051 High Probability 21 2,3- dimethylbutane 7.65 0.086 0.053 High Probability 22 2- methylpentane 7.37 0.083 0.051 High Probability 8 propyne 6.88 0.072 0.044 High Probability 40 2,4- dimethylheptane 6.8 0.076 0.047 High Probability 34 unidentified 6.71 0.075 0.046 unidentified 38 2,3,5- trimethylhexane 6.62 0.074 0.046 Low Probability 47 1- nonene 6.45 0.071 0.044 High Probability 51 unidentified 5.61 0.059 0.036 unidentified 37 n- octane 5.32 0.06 0.037 High Probability 18 2- methyl- 1,3- butadiene 5.26 0.056 0.035 Low Probability 49 2,2- dimethyloctane 5.09 0.057 0.035 High Probability 13 c- 2- butene 4.75 0.052 0.032 High Probability 7 propadiene 4.41 0.046 0.028 High Probability 16 2- methyl- 1- butene 4.39 0.048 0.03 Low Probability 23 3- methylpentane 4.22 0.047 0.029 High Probability 48 unidentified 3.94 0.044 0.027 unidentified 35 3- methylheptane 2.77 0.031 0.019 High Probability 41 unidentified 2.43 0.027 0.017 unidentified 17 n- pentane 2.27 0.026 0.016 Low Probability 24 methylcyclopentane 2.07 0.023 0.014 High Probability 43 2,3- dimethylheptane 2.07 0.023 0.014 High Probability FTIRmethanol (CH4O) 2 0.051 0.031 50 unidentified 1.77 0.02 0.012 unidentified 20 cyclopentadiene 1.62 0.017 0.01 Low Probability 6 propane 16 0 0 0 High Probability
Hydrocarbon Speciation for λ = 1.00 Peak Result ppmc1 mghc/s mghc/gfuel Confidence 53 unidentified 198.39 2.033 1.383 unidentified 5 propene 100.22 1.079 0.734 High Probability 2 ethene 92.12 0.991 0.674 High Probability 9 2- methylpropene 75.77 0.816 0.555 High Probability 31 2,3,3- trimethylpentane 59.59 0.653 0.444 High Probability 1 methane 50.45 0.621 0.422 High Probability 26 2,2,4- trimethylpentane 49.77 0.545 0.371 High Probability 35 unidentified 47.88 0.524 0.356 unidentified 54 n- decane 45.55 0.497 0.338 High Probability 37 m&p- xylene 41.14 0.419 0.285 High Probability FTIRMTBE (C5H12O) 35 0.477 0.324 FTIRacetaldehyde (C2H4O) 32 0.545 0.371 30 2,3,4- trimethylpentane 31.17 0.342 0.232 High Probability FTIRformaldehyde (CH2O) 30 0.696 0.474 3 acetylene 29.23 0.292 0.199 High Probability 49 unidentified 23.85 0.244 0.166 unidentified 11 n- butane 22.82 0.254 0.173 High Probability FTIRethanol (C2H6O) 22 0.392 0.266 46 1- methyl- 4- ethylbenzene 20.59 0.211 0.144 High Probability 4 ethane 19.21 0.222 0.151 High Probability 15 1- pentene 18.25 0.196 0.134 Low Probability 14 2- methylbutane 18.07 0.2 0.136 Low Probability 33 2,2,5- trimethylhexane 16.4 0.179 0.122 High Probability 39 unidentified 15.91 0.162 0.11 unidentified 10 1,3- butadiene 13.21 0.137 0.093 High Probability 47 unidentified 13.19 0.135 0.092 unidentified 25 2,3- dimethylpentane 12.49 0.137 0.093 High Probability 36 unidentified 12.47 0.127 0.086 unidentified 50 unidentified 12.17 0.125 0.085 unidentified 53 unidentified 198.39 2.033 1.383 unidentified 5 propene 100.22 1.079 0.734 High Probability 2 ethene 92.12 0.991 0.674 High Probability 17
Hydrocarbon Speciation for λ = 1.00 continued Peak Result ppmc1 mghc/s mghc/gfuel Confidence 41n- nonane 11.22 0.123 0.083 High Probability 521,2,4- trimethylbenzene 10.94 0.112 0.076 Low Probability 182- methyl- 2- butene 10.39 0.112 0.076 High Probability 34n- octane 10.04 0.11 0.075 High Probability 172- methyl- 1,3- butadiene 9.68 0.101 0.069 Low Probability 12t- 2- butene 9.49 0.102 0.069 High Probability 292,4- dimethylhexane 8.84 0.097 0.066 High Probability 322,3- dimethylhexane 8.59 0.094 0.064 High Probability 48unidentified 8.45 0.087 0.059 unidentified 38unidentified 8.42 0.084 0.057 unidentified 8propyne 7.87 0.081 0.055 High Probability 243- methyl- 1- hexene 7.64 0.082 0.056 Low Probability 192,3- dimethylbutane 7.43 0.082 0.056 High Probability 232,4- dimethylpentane 7.28 0.08 0.054 Low Probability 282,5- dimethylhexane & ethylcyclopentane 7.14 0.078 0.053 High Probability 44unidentified 7.13 0.073 0.05 unidentified 7propadiene 6.93 0.071 0.048 High Probability 212- methylpentane 6.29 0.069 0.047 Low Probability 13c- 2- butene 5.93 0.064 0.043 Low Probability 51unidentified 5.8 0.059 0.04 unidentified 45n- propylbenzene 5.24 0.054 0.037 High Probability 162- methyl- 1- butene 5 0.054 0.037 Low Probability 20MTBE (C5H12O) 4.08 0.047 0.032 High Probability FTIRmethanol (CH4O) 4 0.099 0.067 27n- heptane 3.3 0.036 0.025 High Probability 401- nonene 2.9 0.031 0.021 High Probability 432,2- dimethyloctane 2.64 0.029 0.02 High Probability 42unidentified 2.39 0.026 0.018 unidentified 223- methylpentane 2.03 0.022 0.015 High Probability 6propane 0 0 0 High Probability 18
Hydrocarbon Speciation for λ = 1.10 Peak Result ppmc1 mghc/s mghc/gfuel Confidence 50 unidentified 185.99 2.044 1.419 unidentified 5 propene 93.18 1.076 0.747 High Probability 2 ethene 73.78 0.851 0.591 High Probability 9 2- methylpropene 65.35 0.754 0.524 High Probability 51 n- decane 61.27 0.717 0.498 High Probability FTIRformaldehyde (CH2O) 56 1.391 0.996 33 unidentified 49.01 0.575 0.399 unidentified 29 2,3,3- trimethylpentane 45.12 0.53 0.368 High Probability FTIRMTBE (C5H12O) 45 0.656 0.456 24 2,2,4- trimethylpentane 36.45 0.428 0.297 High Probability FTIRacetaldehyde (C2H4O) 36 0.656 0.455 35 m&p- xylene 29.6 0.323 0.225 High Probability 28 2,3,4- trimethylpentane 24.18 0.284 0.197 High Probability FTIRethanol (C2H6O) 24 0.457 0.317 11 n- butane 20.13 0.241 0.167 High Probability 39 n- nonane 19.17 0.225 0.156 High Probability 15 unidentified 18.42 0.213 0.148 unidentified 3 acetylene 17.88 0.192 0.133 High Probability 1 methane 16.69 0.22 0.153 High Probability 46 unidentified 16.49 0.181 0.126 unidentified 32 n- octane 13.99 0.164 0.114 High Probability 14 2- methylbutane 13.53 0.161 0.112 Low Probability 43 1- methyl- 4- ethylbenzene 13.35 0.147 0.102 Low Probability 37 unidentified 12.11 0.132 0.092 unidentified 10 1,3- butadiene 11.47 0.128 0.089 High Probability 31 2,2,5- trimethylhexane 10.45 0.123 0.085 High Probability 18 2- methyl- 2- butene 10.35 0.119 0.083 High Probability 41 unidentified 9.78 0.108 0.075 unidentified 19
Hydrocarbon Speciation for λ = 1.10 continued Peak Result ppmc1 mghc/s mghc/gfuel Confidence 44 unidentified 9.4 0.103 0.072 unidentified 17 2- methyl- 1,3- butadiene 9.13 0.102 0.071 Low Probability 12 t- 2- butene 8.94 0.103 0.072 High Probability 23 2,3- dimethylpentane 8.77 0.103 0.072 High Probability 34 unidentified 8.3 0.091 0.063 unidentified 47 unidentified 7.79 0.086 0.059 unidentified 49 1,2,4- trimethylbenzene 7.61 0.084 0.058 Low Probability 19 2,3- dimethylbutane 7.39 0.087 0.061 Low Probability 25 n- heptane 7.19 0.085 0.059 High Probability 30 2,3- dimethylhexane 6.38 0.075 0.052 High Probability 27 2,4- dimethylhexane 6.28 0.074 0.051 High Probability 4 ethane 6.08 0.075 0.052 High Probability 36 unidentified 5.98 0.064 0.044 unidentified 45 unidentified 5.81 0.064 0.044 unidentified 21 2,4- dimethylpentane 5.4 0.064 0.044 Low Probability 8 propyne 5.37 0.059 0.041 High Probability 16 2- methyl- 1- butene 5.24 0.06 0.042 Low Probability 13 c- 2- butene 5.07 0.059 0.041 Low Probability 7 propadiene 4.61 0.051 0.035 High Probability 48 unidentified 3.9 0.043 0.03 unidentified 26 2,5- dimethylhexane & ethylcyclopentane 3.87 0.046 0.032 High Probability 42 n- propylbenzene 3.79 0.042 0.029 High Probability 20 2- methylpentane 3.68 0.043 0.03 High Probability 22 3- methyl- 1- hexene 3.41 0.039 0.027 Low Probability FTIRmethanol (CH4O) 3 0.079 0.055 38 1- nonene 2.02 0.023 0.016 High Probability 40 unidentified 1.91 0.022 0.016 unidentified 6 propane 0 0 0 High Probability 20
Hydrocarbon Speciation: Top 5 Identified Species 0.90 1.00 1.10 Methane Propene Propene 144 ppmc 1 100 ppmc 1 93 ppmc 1 Ethene Ethene Ethene 115 ppm C 1 92 ppmc 1 74 ppmc 1 Acetylene 2-Methylpropene 2-Methylpropene 105 ppmc 1 76 ppmc 1 65 ppmc 1 2,3,3-trimethylpentane 2,3,3-trimethylpentane n-decane 92 ppmc 1 60 ppmc 1 61 ppmc 1 Propene Methane Formaldehyde (CH 2 O) 85 ppmc 1 50 ppmc 1 56 ppmc 1 Top identified species: Methane for λ=0.90 (oxidation process runs out of oxygen) Propene for λ=1.00 and 1.10 (temperature quenching of crevice HC reactions) 21
Prominent Fuel HC Appear Prominently in Exhaust HC Top 6 fuel species (ppmc 1 basis) are: 2,2,4-trimethylpentane 2,3,4-trimethylpentane 2,3,3-trimethylpentane n-butane 2-methylbutane ethanol They account for 54% of the fuel by weight. These 6 HC species are among the highest concentration exhaust species (ppmc 1 ) for λ=0.90, 1.00, and 1.10 22
Hydrocarbon Classes Total Concentrations of Identified HC Concentration (ppmc 1 ) 700 600 500 400 300 200 paraffins olefins aromatics oxygenates 100 0 0.90 1.00 1.10 Lambda (- ) Leaner operation reduces paraffins, olefins, and aromatics Leaner operation increases oxygenates (greater abundance of O 2 ) At each lambda, paraffins and olefins dominate aromatics and oxygenates 23
Hydrocarbon Classes Fraction of Total Identified HC Fraction of Total Identified HC (%C1) 50 45 40 35 30 25 20 15 10 5 0 paraffins olefins aromatics oxygenates 0.90 1.00 1.10 Lambda (- ) Fractions of paraffins and aromatics decrease as mixture becomes leaner. Fraction of oxygenates increases as mixture becomes leaner (greater abundance of O 2 ). 24
Exhaust Gas Hydrocarbon Composition (Molar Average) λ=0.90 λ=1.00 λ=1.10 C:H:O CH 2.20 O 0.0392 CH 2.15 O 0.0684 CH 2.11 O 0.115 molecular weight (g/mol) 43.2 47.8 50.0 molecular composition C 2.91 H 6.41 O 0.114 C 3.13 H 6.74 O 0.214 C 3.13 H 6.60 O 0.360 During rich combustion, many exhaust HC come from oxidation that was halted by oxygen deficiency. Ø low MW (high fraction of methane) Ø H:C ratio same as the fuel Ø O:C ratio same as the fuel Fuel C:H:O is CH 2.22 O 0.0377 Very close to rich exhaust C:H:O During lean combustion, many exhaust HC come from crevice HC oxidation that was halted by low temperature during expansion. Ø higher MW (low fraction of methane;; larger partial oxidation products) Ø H:C ratio slightly lower than the fuel (lower fraction of paraffins) Ø O:C ratio significantly higher than the fuel (higher fraction of oxygenates) 25
Low Volatility Hydrocarbons 26
Effect of Lambda on High, Medium, and Low Volatility HC* Concentration (ppm HC) 350 300 250 200 150 100 high volatility HC (C1- C4) medium volatility HC (C5- C8) low volatility HC (C9- C10) 50 0 0.90 1.00 1.10 Lambda (- ) Leaner operation reduces concentrations of high, medium, and low volatility HC The majority of exhaust HC molecules are high volatility HC * HC only (no oxygenates) 27
Effect of Lambda on Exhaust Hydrocarbon Vapor Pressure* 0.6 THC Vapor Pressure (mbar) 0.5 0.4 0.3 0.2 C9- C10 0.1 0 0.90 1.00 1.10 Lambda (- ) Leaner operation reduces vapor pressure of THC and low volatility HC (C 9 -C 10 ) * HC only (no oxygenates) 28
HC Condensation and Adsorption* 0.6 Psat of n- decane (mbar) 0.5 0.4 0.3 0.2 0.1 λ=1.10 λ=1.00 λ=0.90 0.0-30 - 20-10 0 10 Temperature ( C) Even if all HC were n-decane, HC condensation/nucleation will not occur above 4 C for λ=0.90. HC adsorption onto existing particulates is possible (van der Waals forces). Recommend quantifying C 9 -C 10 HC found on particulates. * HC only (no oxygenates) 29
Summary and Conclusions Energy balance and standard exhaust gases Combustion efficiency reached 99.0% at λ=1.10 At λ=0.90, more energy in CO than in HC. At λ=1.00 and 1.10, more energy in HC than in CO. Hydrocarbon Speciation Highest concentration species: λ=0.90: methane (oxidation runs out of oxygen) λ=1.00 and 1.10: propene (quenching of crevice HC oxidation reactions) Exhaust hydrocarbon composition: At λ=0.90: CH 2.20 O 0.0392 MW=43.2 g/mol At λ=1.00: CH 2.15 O 0.0684 MW=47.8 g/mol At λ=1.10: CH 2.11 O 0.115 MW=50.0 g/mol Paraffins, olefins and aromatics decrease with leaner mixture Oxygenates increase with leaner mixture Low volatility hydrocarbons At the conditions tested, HC condensation/nucleation will not occur above 4 C HC adsorption is possible 30