Document ID: EPA-HQ-OAR-2014-0827-0712
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2015-07-13T04:00Z

July 8, 2015

MEMORANDUM

SUBJECT:	Numerical Standards for Tractors, Trailers, and Vocational Vehicles Based on the GEM Executable Code; and Derivation of the Numerical Engine Standards 

FROM:	Angela Cullen, Engineer, Assessment and Standards Division
		Jessica Brakora, Engineer, Assessment and Standards Division
		Lauren Steele, Engineer, Assessment and Standards Division

TO:	Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles - Phase 2 - Docket EPA-HQ-OAR-2014-0827

Numerical Standards for Tractors, Trailers, and Vocational Vehicles 
      
      The agencies established the proposed standards by evaluating specific vehicle technology packages using a prepublication version of the Phase 2 GEM.  This prepublication version was an intermediate version of the GEM source code, rather than the executable file version of GEM, which is being docketed for this proposal and is available on EPA's GEM Webpage.  Both the GEM source code and the GEM executable file are generally functionally equivalent.
      
      Formal external peer review and expert external user review was then conducted on the version of the GEM source code that was used to calculate the numerical values of the proposed standards.  It was discovered via these external review processes that the GEM source code contained some minor software "bugs."  These bugs were then corrected by EPA and the Phase 2 proposed GEM executable file was derived from this corrected version of the GEM source code.  Moreover, we expect to also receive technical comments during the comment period that could potentially identify additional GEM software bugs, which would lead EPA to make additional changes to GEM before the Final Rule.
      
      Thus, even without the agencies making any changes in our projections of technology effectiveness or market adoption rates, it is likely that further revisions to GEM could result in us finalizing different numerical values for the standards.  It is important to note that the agencies would not necessarily consider such GEM-based numerical changes by themselves to be changes in the stringency of the standards.  Rather, we believe that stringency is more appropriately evaluated in technological terms; namely, by evaluating technology effectiveness and the market adoption rates of technologies.
      
      The tables below compare results from the prepublication GEM source code with results from the proposed GEM executable for combination tractors, vocational vehicles, and trailers.  The combination tractor results are directly from each version of GEM.  The vocational vehicle GEM results underwent post-processing to recognize idle reduction technologies as well as to make some adjustments as described below.  The trailer results are based on equations developed from both the prepublication and proposed GEM versions.  Note that NHTSA fuel consumption values are not shown in the tables below.  These values have been calculated using a conversion factor of 10,180 grams CO2 per gallon of diesel fuel, or 8,887 grams CO2 per gallon of gasoline, and are presented in the supporting documentation for GEM.  It should also be noted that the version of the GEM executable code that was used for developing the stringencies uses unrounded inputs, which is different than the compliance version of the GEM executable, which will round the inputs.
      
         Table 1:  Comparison of GEM Results for Combination Tractors
 
                                    Class 7
                                    Class 8
                                     Heavy
                                     Haul
 
                                    Day Cab
                                    Day Cab
                                  Sleeper Cab
                                       
 
                                      Low
                                     Roof
                                      Mid
                                     Roof
                                     High
                                     Roof
                                      Low
                                     Roof
                                      Mid
                                     Roof
                                     High
                                     Roof
                                      Low
                                     Roof
                                      Mid
                                     Roof
                                     High
                                     Roof
                                       
Baseline
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
Pre-Publication Source Code
                                      107
                                      118
                                      121
                                      86
                                      93
                                      95
                                      79
                                      87
                                      88
                                      57
Proposed GEM Executable
                                      106
                                      117
                                      120
                                      85
                                      92
                                      94
                                      79
                                      87
                                      88
                                      57
2021
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
Pre-Publication Source Code
                                      97
                                      107
                                      109
                                      78
                                      84
                                      86
                                      70
                                      78
                                      77
                                      54
Proposed GEM Executable
                                      96
                                      107
                                      109
                                      77
                                      84
                                      86
                                      70
                                      78
                                      77
                                      54
2024
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
Pre-Publication Source Code
                                      90
                                      100
                                      101
                                      72
                                      78
                                      79
                                      64
                                      71
                                      70
                                      52
Proposed GEM Executable
                                      89
                                      99
                                      100
                                      72
                                      78
                                      78
                                      64
                                      71
                                      70
                                      51
2027
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
Pre-Publication Source Code
                                      87
                                      96
                                      96
                                      70
                                      76
                                      76
                                      62
                                      69
                                      67
                                      51
Proposed GEM Executable
                                      86
                                      96
                                      96
                                      70
                                      76
                                      76
                                      62
                                      69
                                      67
                                      51
      
Table 2:  Comparison of Coefficients for GEM-Based Trailer Compliance Equations
Subcategory
GEM
Version
                         GEM-Based Equation Constants
                                       
                                                                               
                                   Intercept
                                     Aero
                                      CRR
                                      WR
Long Dry Van
Pre-Publication Source Code
                                     77.4
                                     -6.1
                                      1.7
                                    -0.001

Proposed GEM Executable
                                     77.1
                                     -6.1
                                      1.7
                                    -0.0011
Long Refrigerated Van
Pre-Publication Source Code
                                     78.3
                                     -6.0
                                      1.8
                                    -0.001

Proposed GEM Executable
                                     78.0
                                     -6.0
                                      1.8
                                    -0.0011
Short Dry Van
Pre-Publication Source Code
                                     134.0
                                     -10.5
                                      2.2
                                    -0.003

Proposed GEM Executable
                                     133.4
                                     -10.2
                                      2.2
                                    -0.0031
Short Refrigerated Van
Pre-Publication Source Code
                                     136.3
                                     -10.3
                                      2.4
                                    -0.003

Proposed GEM Executable
                                      136
                                     -10.1
                                      2.4
                                    -0.0031

        Table 3:  Comparison of GEM-Based Equation Results for Trailers

                                    Dry Van
                               Refrigerated Van

                                     Long
                                     Short
                                     Long
                                     Short
Baseline
                                       
                                       
                                       
                                       
Pre-Publication Source Code
                                      85
                                      147
                                      86
                                      151
Proposed GEM Executable
                                      84
                                      147
                                      86
                                      150
2018
                                       
                                       
                                       
                                       
Pre-Publication Source Code
                                      83
                                      144
                                      84
                                      147
Proposed GEM Executable
                                      82
                                      143
                                      84
                                      147
2021
                                       
                                       
                                       
                                       
Pre-Publication Source Code
                                      81
                                      142
                                      82
                                      146
Proposed GEM Executable
                                      81
                                      142
                                      82
                                      145
2024
                                       
                                       
                                       
                                       
Pre-Publication Source Code
                                      79
                                      141
                                      81
                                      144
Proposed GEM Executable
                                      79
                                      140
                                      80
                                      144
2027
                                       
                                       
                                       
                                       
Pre-Publication Source Code
                                      77
                                      140
                                      80
                                      144
Proposed GEM Executable
                                      77
                                      139
                                      79
                                      143
      
  Table 4:  Comparison of Post-Processed GEM Results for Vocational Vehicles
                                       
                                      LHD
                                      MHD
                                      HHD
                                       
                          Pre-Publication Source Code
                            Proposed GEM Executable
                          Pre-Publication Source Code
                            Proposed GEM Executable
                          Pre-Publication Source Code
                            Proposed GEM Executable
CI Baseline
                                     U[a]
                                      316
                                      315
                                      201
                                      200
                                      212
                                      224
                                       M
                                      325
                                      324
                                      203
                                      203
                                      214
                                      228
                                       R
                                      339
                                      338
                                      199
                                      199
                                      203
                                      221
                                       E
                                      318
                                      317
                                      200
                                      200
                                      223
                                      236
SI Baseline
                                       U
                                      334
                                      333
                                      213
                                      212
                                      224
                                      237
                                       M
                                      344
                                      343
                                      215
                                      215
                                      226
                                      241
                                       R
                                      358
                                      358
                                      211
                                      210
                                      214
                                      234
CI 2021
                                       U
                                      296
                                      295
                                      188
                                      187
                                      198
                                      209
                                       M
                                      305
                                      304
                                      190
                                      189
                                      200
                                      213
                                       R
                                      318
                                      317
                                      186
                                      186
                                      189
                                      207
                                       E
                                      312
                                      311
                                      195
                                      196
                                      215
                                      231
SI 2021
                                       U
                                      320
                                      319
                                      203
                                      202
                                      214
                                      226
                                       M
                                      329
                                      329
                                      205
                                      205
                                      216
                                      230
                                       R
                                      343
                                      342
                                      201
                                      201
                                      204
                                      223
CI 2024
                                       U
                                      284
                                      282
                                      179
                                      179
                                      190
                                      199
                                       M
                                      292
                                      291
                                      181
                                      181
                                      192
                                      203
                                       R
                                      304
                                      303
                                      178
                                      177
                                      182
                                      197
SI 2024
                                       U
                                      312
                                      310
                                      197
                                      197
                                      208
                                      219
                                       M
                                      321
                                      320
                                      199
                                      199
                                      210
                                      223
                                       R
                                      334
                                      333
                                      196
                                      195
                                      199
                                      217
CI 2027
                                       U
                                      272
                                      265
                                      172
                                      168
                                      182
                                      188
                                       M
                                      280
                                      273
                                      174
                                      170
                                      183
                                      192
                                       R
                                      292
                                      285
                                      170
                                      166
                                      174
                                      186
SI 2027
                                       U
                                      299
                                      292
                                      189
                                      185
                                      196
                                      207
                                       M
                                      308
                                      301
                                      191
                                      187
                                      198
                                      211
                                       R
                                      321
                                      314
                                      187
                                      183
                                      188
                                      205
Note:
[a]  U = Urban, M = Multipurpose, R = Regional, E = Emergency

Derivation of Vocational Vehicle Standards

      The agencies developed a method to normalize the standards so that vehicles certified over the Regional composite cycle would have similar stringency as vehicles certified over the Multi-Purpose or Urban cycles.  The reason for this is that the agencies expect each vehicle to be tested with an appropriate duty cycle for its intended application and want to minimize unintended incentives to place a vehicle in a less appropriate subcategory to receive a benefit of a less stringent standard. A summary of the normalizing process can be found in the draft RIA Chapter 2.9.2.1.

      Characteristics of the baseline vehicles that were used for each subcategory can be found in the draft RIA: Predefined modeling parameters are presented in Table 4-8, 4-9 and 4-10 of the draft RIA Chapter 4; and User-enterable modeling parameters are presented in Table 2-43, 2-44, and 2-45 of draft RIA Chapter 2.9.2.    

      As described in draft RIA Chapter 2.9.2.1, the agencies identified a "best baseline vehicle" with which to normalize the performance of the defined baseline vehicles of the three duty cycles within each weight class. Table 5 lists some characteristics of the vehicles that the agencies chose as the "best baseline vehicles" for each weight class.  For the HHD weight class, these are the vehicles intended to be certified over the Regional cycle, while for the MHD and LHD weight classes, these are the vehicles intended to be certified over the Multi-Purpose cycles. In the draft RIA at 2.9.2.1, it is stated that the best vehicle for LHD and MHD was the Urban vehicle, however that statement was an error.  In the LHD weight class, the Multi-Purpose vehicle is identical to the Urban vehicle, and in the MHD weight class, the Multi-Purpose vehicle is nearly identical to the Urban vehicle, with a slightly different tire radius.

                  Table 5:  Best Vocational Baseline Vehicles
                                Weight Category
                                    Engine
                                 Transmission
                                Tire Radius (m)
                               Drive Axle Ratio
                               Steer CRR (kg/t)
                               Drive CRR (kg/t)
                                      HHD
                                    455 hp
                                   10 spd MT
                                     0.483
                                     3.76
                                      7.7
                                      7.7
                                      MHD
                                    270 hp
                                  5 spd MH AT
                                     0.462
                                     4.88
                                      7.7
                                      7.7
                                      LHD
                                    200 hp
                                  5 spd MH AT
                                     0.378
                                     4.56
                                      7.7
                                      7.7

      GEM was used to simulate each of the vehicles over its intended duty cycle as well as over the other two composite cycles.  Following the process described in the draft RIA 2.9.2.1, the normalization process using the proposed GEM executable yields values presented in Table 6, which can be compared with the results obtained using the pre-publication source code, as presented in Table 2-46 of the draft RIA.

                   Table 6: Vocational Baseline Normalizing
                                  Class 2b-5
                                   Class 6-7
                                    Class 8
                                     Urban
                                 Multi-Purpose
                                   Regional
                                     Urban
                                 Multi-Purpose
                                   Regional
                                     Urban
                                 Multi-Purpose
                                   Regional
                       Straight GEM Baseline Performance
                                      317
                                      327
                                      331
                                      200
                                      204
                                      197
                                      236
                                      233
                                      200
                             Normalization Factor
                                     0.97
                                     1.00
                                     1.04
                                     1.00
                                     1.01
                                     0.99
                                     0.99
                                     1.01
                                     0.98
                    Population Weighted Best Vehicle Result
                                     328.8
                                     202.4
                                     193.9
                      Population Weighted Baseline Result
                                     325.5
                                     201.1
                                     225.3
                              Normalized Baseline
                                      315
                                      324
                                      338
                                      200
                                      203
                                      199
                                      224
                                      228
                                      221

      The numerical stringencies of the proposed standards were determined by applying technology effectiveness and adoption rates as described in the proposal (see draft RIA 2.9.5), then averaging the subcategory-specific percent improvements within each weight class, then calculating the numerical value of the standard by applying this averaged percent improvement to the normalized baseline. For example, for MY 2027 in the HHD weight class, the technology package as specified in the proposal for the Regional subcategory would achieve 11.6% improvement, the Multi-purpose technology package would achieve 17.4% improvement, and the Urban technology package would achieve 18.9% improvement. These average to 16%, so the HHD 2027 standards were calculated by reducing each of the HHD normalized baseline values by 16%.
      
Derivation of the Proposed Engine Standards
      
      As described in Section II.D(a) of the HD Phase 2 Notice of Proposed Rulemaking, the agencies derived the proposed engine standards based on our projections of the effectiveness of various technologies over the proposed engine test cycles (i.e., percent reduction) and the extent to which such technologies could be adopted by industry by 2021, 2024, and 2027.  The values used for tractor engines are shown in Table 7 below.
      
         Table 7:  Projected Tractor Engine Technologies and Reduction
                                       
                     SET-weighted reduction (%)  2020-2027
                           Market penetration (2021)
                           Market penetration (2024)
                           Market penetration (2027)
                          Turbo compound with clutch
                                     1.8%
                                      5%
                                      10%
                                      10%
                              WHR (Rankine cycle)
                                     3.6%
                                      1%
                                      5%
                                      15%
            Parasitic/Friction (Cyl Kits,  pumps, FIE), lubrication
                                     1.4%
                                      45%
                                      95%
                                     100%
                           Aftertreatment (lower dP)
                                     0.6%
                                      45%
                                      95%
                                     100%
              EGR/Intake & exhaust manifolds/Turbo /VVT/Ports
                                     1.1%
                                      45%
                                      95%
                                     100%
                             Combustion/FI/Control
                                     1.1%
                                      45%
                                      95%
                                     100%
                                  Downsizing
                                     0.3%
                                      10%
                                      20%
                                      30%
                              Dis-Synergy Factor
                                       
                                      75%
                                      85%
                                      85%
                                       
                                       
                                       
                                       
                                       
                 Weighted Reduction for Engines w/o TC or WHR
                                       
                                     1.45%
                                     3.44%
                                     3.64
                    Weighted Reduction for Engines with TC
                                       
                                     2.79%
                                     4.92%
                                     5.12%
                    Weighted Reduction for Engines with WHR
                                       
                                     4.08%
                                     6.36%
                                     6.56%
                                       
                                       
                                       
                                       
                                       
                                Total Weighted 
                                 Reduction (%)
                                       
                                     1.5%
                                     3.7%
                                     4.2%
      
      The proposed standards were derived from the weighted reductions which combined all these technologies by multiplying together an effectiveness factor for each technology (equal to 100% minus the SET weighted percent reduction times the market penetration) and applying a dis-synergy factor that reflects the degree to which combining multiple technologies reduces slightly the effectiveness of each individual technology.  The assumed dis-synergy factors are also shown in Table 7.  Because turbo compound and Rankine cycle waste heat recovery are mutually exclusive technologies, we calculated intermediate values for engines without either turbo compound or Rankine cycle waste heat recovery, and for engines with either turbo compound or Rankine cycle waste heat recovery.  These intermediate values are also shown in Table 7.  For example, the average percent reduction in 2021 for engines without either turbo compound or Rankine cycle waste heat recovery would be:
      
      [100% - (100%-(45% x1.4%))x(100%-(45% x0.6%))x(100%-(45% x1.1%))x(100%-(10% x0.3%))]x75% = 1.45%
      
For each change in the standards (in 2021, 2024, and 2027) these intermediate values were combined based on the projected penetrations for turbo compound or Rankine cycle waste heat recovery.  For example, the total weighted reduction for 2021 was calculated as:
      
      1.45% x (100% - 5% - 1%) + 2.79% x 5% + 4.08% x 1% = 1.543%
      
      This same approach was used to calculate the proposed vocational engine standards, although it was not necessary to calculate intermediate values.  Table 8 below summarizes the derivation of the vocational engine standards.
      
        Table 8: Projected Vocational Engine Technologies and Reduction
                                       
                          FTP Weighted Reduction (%)
                                   2021-2027
                              Market Penetration
                                     2021
                              Market Penetration
                                     2024
                              Market Penetration
                                     2027
                              Model based control
                                     2.0%
                                      25%
                                      30%
                                      40%
                              Parasitic /Friction
                                     1.5%
                                      60%
                                      90%
                                     100%
                              EGR/Air/VVT /Turbo
                                     1.0%
                                      50%
                                      90%
                                     100%
                                  Improved AT
                                     0.5%
                                      50%
                                      90%
                                     100%
                            Combustion Optimization
                                     1.0%
                                      50%
                                      90%
                                     100%
                              Dis-Synergy Factor
                                       
                                      75%
                                      85%
                                      85%
                                       
                                       
                                       
                                       
                                       
                         Total Weighted reduction (%)
                                       
                                     2.0%
                                     3.5%
                                     4.0%
      
      
      The numerical tractor and vocational engine standards for Alternatives 2, 4, and 5 were also calculated in the same manner as the proposed engine standards.