Institute for Internal Combustion Engines and Thermodynamics Analysis of options for a transfer function for emission correction between moderate and extended driving conditions Overview on the status of work at TU Graz (based on work plan proposed at 15.08.2015) 06.10.2015 S. Hausberger, S. Lipp, M. Grössing Based on the ppt file from 29.09.2015 here Analysis on 4 vehicles is shown to elaborate the design of a transfer function. EMROAD results not yet available for 3 of 4 vehicles. Stefan Hausberger RDE test procedure 1

Idea of a “Transfer Function” Working hypothesis: a “Transfer Function” in addition to the existing normalisation tools could reduce variabilities in emission results due to effects not covered yet. Several options for the method exist, below one of them is shown as schematic example. Since WLTP conditions are defined exactly, a function is elaborated, which shows changes compared to WLTP conditions. The function can be translated to any other centre point. “Severity” = function of: *95 percentile of v x apos, *Altitude to be overcome (m/km), *Weight of loading, *Ambient temperature, * Maximum velocity * Average velocity * Engine speed Parameters can be eliminated from the equation later easily.

Options for Transfer Functions The change of emissions (NOx at the moment) is analysed as function of change of the “severity parameters”. Change in the CF can be computed from the change in emissions on demand by dividing the result by the corresponding emission limit (e.g. 40mg/km effect on NOx means 40/80 = 0.5 change in CF).

Parameters to be considered in a transfer function Statistical analysis showed later gave same statistical quality for regression when differences or ratios are used as parameters. Differences are selected for all parameters since “difference” on x-axis remains the same for any new center point while the ratio depends on the denominator used (WLTP values versus corner values of “normal driving”). From physical point of view also differences are reasonable (e.g. [gNOx /kg loading)  transfer function looks as follows 𝐶 𝑡𝑓 = 𝑁𝑂𝑥 𝑡𝑟𝑖𝑝 − 𝑁𝑂𝑥 𝑊𝐿𝑇𝑃 = 1 𝑛 [ 𝐴 𝑖 × 𝑃 𝑖, 𝑡𝑟𝑖𝑝 − 𝑃 𝑖, 𝑊𝐿𝑇𝑃 𝑖 ] With Ai....Constant coefficients to be elaborated Pi....Value of severity parameter i in trip - Value of severity parameter i in WLTC Ctf... Emission value [g/km] in trip - Emission value [g/km] in WLTC Severity Parameters Pi relevant for NOx: “Severity” = function of: *95 percentile of v x apos, *Altitude to be overcome (m/km), *Weight of loading, *Ambient temperature, * Maximum velocity * Average velocity * Engine speed Parameters can be eliminated from the equation later easily.

Actual status (06.10.2015) Simulation: Raw exhaust gas map for NOx prepared Model for transient effects on raw NOx prepared (NOx change as function of O2 concentration which is simulated by boost pressure. Boost pressure simulated as function of dynamic load change) After-treatment model prepared with NOx conversion as function of space velocity and temperature. Available for SCR and SCR&NSC. Measurement: Analysis of 4 vehicles finalised (overview given on following slides) with exception of EMROAD results (EMROAD evaluation done for one vehicle only so far) PEMS data for one additional vehicle available, not yet included. Source # trips Vehicle NOx in WLTP [mg/km] Technology Emission class (tbd) TUG 28 C-segment 264 EGR + NSC EU 6 Audi 3 SUV 90 ? EU 6c Stage 1 Bosch 4 C segment 38 EU 6c Stage 2 VW 5 D segment n.a. Daimler   Analysis ongoing  Figures use a = (v(i+1) – v(i-1) )/(2x3.6) in all cases

Actual status (06.10.2015) Measurement: overview on dynamics in the trips from the 4 vehicles analysed later *….PEMS avg 18 vehicles is data shown March 2015 from data collection PEMS tests **..TNO data 95 percentiles read from a TNO diagram Figures use a = (v(i+1) – v(i-1) )/(2x3.6) in all cases

Results vehicle 1 (TUG) 28 trips with variability in all relevant severity parameters. Basic evaluation (Measured, CLEAR, EMROAD). Note: EMROAD evaluation shall be checked by JRC. In actual results EMROAD increases the standard deviation compared to direct measured values, CLEAR reduces standard deviation by 44% Measured CLEAR EMROAD Avg. NOx [mg/km] 455 357 525 Std dev. NOx [mg/km] 230 129 266 Ries route agg. in Winter, 95P( v*a pos) = 28, Ta = 4°C NEDC hot PEMS Graz standard route summer Ries route standard Summer 95P( v*a pos) = 12, Ta = 26°C WLTP hot

Example SPSS result, stepwise adding of most significant variables Transferfunction (TUG) Steps to set up transfer function: SPSS software used to run multiple regression. Dependent variable: difference or ratio of NOx in each trip vs. NOx in WLTP (1) SPSS looks for best fitting equation which explains dependent variable by function of other variables. (1)…. Any other trip can be used as reference if “differences” are analysed to get same slopes Example input data Example SPSS result, stepwise adding of most significant variables R²=0.64 R²=0.83 R²=0.87 R²=0.89

Results vehicle 1 (TUG) Transfer functions further reduce standard deviation between results if elaborated for differences in measured NOx and for differences in CLEAR-NOx. Parameters are statistically significant. Measured Measured + Ctf CLEAR + Ctf EMROAD + Ctf Avg. NOx [mg/km] 455 192 225 Std dev. NOx [mg/km] 230 76 58 200 Ries route agg. NEDC WLTC Note: function translates per definition to “WLTP” parameters. This is a reduction for most PEMS trips. Depending on the setting of the center point different levels can be adjusted later!

Results vehicle 1 (TUG) Transfer function does not work properly based on EMROAD results (JRC check of correct EMROAD handling by TUG open!) Measured Measured + Ctf CLEAR + Ctf EMROAD + Ctf Avg. NOx [mg/km] 455 192 225 Std dev. NOx [mg/km] 230 76 58 200 Ries route agg. NEDC WLTC Note: function translates per definition to “WLTP” parameters. This is a reduction for most PEMS trips. Depending on the setting of the center point different levels can be adjusted later!

Results vehicle 2 CLEAR reduces standard deviation compared to measured Nox emissions Transfer functions further reduce standard deviation for measured and for CLEAR NOx Measured CLEAR EMROAD Measured & Ctf CLEAR & Ctf EMROAD & Ctf Avg. NOx [mg/km] 145 137 Na 110 127 Std dev. NOx [mg/km] 68 25 na 12 20 WLTC

Results vehicle 3 CLEAR reduces standard deviation compared to measured NOx emissions No statistical significant function for measured Nox found. In general poor regression coefficients for this vehicle. Test with highest emissions has average dynamics and average temperature. Measurement error(s) or regeneration events? Measured CLEAR EMROAD Measured & Ctf CLEAR & Ctf EMROAD & Ctf Avg. NOx [mg/km] 90 82 na 75 Std dev. NOx [mg/km] 49 35 25 WLTC

Results vehicle 4 CLEAR reduces standard deviation compared to measured NOx emissions Transfer functions further reduce standard deviation for CLEAR Nox. No statistical significant function for measured NOx. In general poor regression coefficients for this vehicle Measured CLEAR EMROAD Measured & Ctf CLEAR & Ctf EMROAD & Ctf Avg. NOx [mg/km] 246 198  na 199 178 Std dev. NOx [mg/km] 82 35 50 26 No WLTC measured

No statistical significant transfer function Relevant severity parameters identified Note: only vehicle 1 has a sufficient number of trips and variability in the severity parameters to perform multiple regression with all parameters. Other vehicles allow only rough assessment of those parameters which varied in the tests. Analysis of EMROAD results open for vehicles 2, 3, 4. Parameters with statistical significant influence on NOx which thus may be included in transfer function ( X.. high influence, x… influence)   95P (v x apos) (+h/100km) Loading Amb. T [°C] rpm [s-1] v_avg [km/h] Veh 1   x Veh 2    x Veh 3 No statistical significant transfer function Veh 4 95Perc.(v*apos) is relevant Ambient temperature seems to be relevant but insufficient data available yet Loading and positive altitude gains less relevant if CLEAR is applied before but insufficient variability in these severity parameters for most vehicles.

Example on transfer function design Example for the case that 2 severity parameters (95 Percentile (v*apos)) and ambient temperature) are considered. Additional parameters can be added if data is available. Note: values are rough estimates from actual data and are shall be seen as placeholders! 𝐶 𝑡𝑓 = 𝐴 1 ×[95𝑃 𝑣∗ 𝑎 𝑝𝑜𝑠 −95𝑃 𝑣∗ 𝑎 𝑝𝑜𝑠 centre ] + 𝐴 2 × [𝑡𝑎𝑚𝑏−𝑡𝑐𝑒𝑛𝑡𝑒𝑟] “95𝑃(𝑣∗𝑎_𝑝𝑜𝑠 )centre ” … reference value where no correction due to transfer function occurs. Could be defined from existing data base, e.g. average of PEMS trip collection at TUG (see figure next slide). A1….Parameter for influence of 95Perc(v*apos). First estimates from data for “best technology”: Urban A1~10mgNOx/1m²/s³, Extra urban A1~5mgNOx/1m²/s³ A2….Parameter for influence of ambient temperature Example: if tcenter = 0°C, add 6 mg NOx/°C This parameter considers cool down effects of exhaust gas after-treatment, but also reduced EGR at low temperatures. To which extent EGR reduction shall be considered has to be discussed.

Example on transfer function design Example for the 95Perc(v*apos) “Threshold V2” adjusted to preliminary TNO results and TUG data Example with highest Diff: Diff 95Perc(v*apos) MW = 26 -20 = 6 Road = 26 -20 = 6 Urb = 16-13 = 3 Diff NOx [mg/km] MW = 6*5 = 30 Road = 6*5 = 30 Urb = 3*10 =30  weighted Diff NOx = 30 Diff CF = 30/80 = 0.38 Alternative: use trip average values (tbd) Work to do: Elaborate generic coefficients Ai for main influencing severity parameters. Elaborate centre line function (or value) for each parameter, e.g. “normal load = 120kg”, “normal t >0°C” Test if separate handling urban/road/MW is necessary. May be relevant for 95Perc(v*apos) to avoid loop holes

Summary Transfer function seems to be feasible “Differences” in emissions as function of differences in severity parameters seems to be best approach. CF changes can be directly calculated from such a function. Analysis on 4 vehicles shows 95perc(v*apos), Temp., loading and altitude gains as relevant parameters with highest effect of 95perc(v*apos). If the 95perc(v*apos) shall be used in a transfer function we suggest to add weighting function for trips with low time share with acceleration as suggested in last meeting (see “open to do’s”) If Temperature shall be included needs to be discussed (extended CF is defined already for T<0°C. Shall transfer function replace the actual step function?) Correct usage of EMROAD by TUG has to be verified by JRC Elaboration of a generic transfer function from measurement data would need a lot of tests (relevant parameters need to be varied or fixed) Test data shows behaviour of tested vehicle, not necessarily state of art Simulation will be applied to produce data set to elaborate proposal for parameters in transfer function

Open To do from Sept. presentations ToDo for Heinz Steven?: elaborate min share accel. From WLTP data base. Dynamics of the driving style (95 percentile of v x apos) + Good correlation with NOx for unbiased driving - Critical, for trips with short full load accelerations and long cruise control phases. Such trips would result in high 95 v*a+ percentiles and thus strong emission reductions by the transfer function.  misuse would be very attractive! Suggested solution: Define minimum “normal acceleration share” for urban, road, motorway. Correct 95 percentile of v*a+ with this share if acceleration time in the trip was lower. Example (acceleration time % values to be validated by Heinz?) Example Motorway: trip has only 60 seconds v*a with a above 0.1 m/s² and gives v*a+ = 30m²/s³ Correction with (157 – 60) = 97 seconds with v*a+ = 0: V*a+Corr = (30 * 60 + 97 * 0)/157 = 30 * 60/157 = 11.5 (alternative: calc. 95 percentile from 157s sample) Such a correction would be applied only if No. of seconds with a>0.1m/s² is below minimum value (e.g. 157 or 22% for MW). Thus the correction would not appear for “normal” driving.

Open To do from Sept. presentations Elaboration of mileage shares for combinations of severity parameters as matrix. (e.g. % share of 95P(v*apos) between 20 and 22 with temperature between -5° and 0°C with positive altitude gains 800-1000m and loading above 350 kg) Calculate overall effect of transfer function on EU average CF

Suggested rough timeline vs. status Topic Who until Collection of measured Emission data (PEMS and WLTP) > 3 vehicles “Step 2 like” > 3 vehicles “Step 1 like” ACEA 30.10.2015? Analysis of these data to validate feasibility of transfer function elaborate best design of transfer function (relevant parameters, diff or delta, etc. by checking significances and correlation coefficients) Status: Delayed due to missing data. Draft for one vehicle available. TUG finalised 06.10.2015 Set up PHEM models as shown before Status: Ongoing, first model results expected mid October TUG 15.10.2015 Analyse simulation results and elaborate preliminary transfer function. Status: open 30.10.2015 Further improvements, discussions etc. All ?