Accelerated aging procedures for pollution control devices Giorgio Martini, JRC

Introduction Ideally an accelerated aging procedure for pollution control devices should have the following basic features: Should reproduce as close as possible the deterioration mechanisms occurring in the real world Should be applicable to all current and future technologies Should not lead to excessive testing burden The time needed to age the devices should be drastically reduced compared to the useful life

Challenges: Different technologies (and their combination) to be addressed: DPF (passive or active regeneration), DOC, SCR (vanadia or copper-zeolite systems), LNT Different applications These lead to different thermal loads and oil consumption – In principle different aging procedures should be developed for each application

Other issues : A full exhaust system should be aged – the presence of a device upstream to another device will strongly influence the deterioration mechanisms Additional thermal aging to compensate for chemical poisoning (as prescribed in light duty legislation) is a very rough approximation – it affects mainly NOx, while light-off, CO and HC are much less affected Maximum temperature to which the systems should be exposed depends on the technology considered Validation of accelerated aging procedures is difficult

Procedure for RPCD The procedure for RPCD was developed taking inspiration from the DAAAC consortium work The original DAAAC protocol wasmodified in order to make it suitable for regulatory purposes More specifically the data collection phase was “standardized” by prescribing the use of the WHTC cycle instead of collecting data in the field for a specific application as required by the original version Also the stationary aging cycle to be used is now fixed as a result of the use of the WHTC for the data collection phase

DAAAC ProtocolTM The DAAAC consortium (SwRI+industrial partners) has developed a protocol to generate accelerated aging procedures starting from field data with the following objectives: Closely reproduce the deterioration mechanism observed in the field for different applications and for different technologies Reduce the aging time to approximately 10% of the full useful life field operation The work started in 2008 and the protocol so far developed has been also validated (at least to a certain extent) by comparing devices “field” aged with identical systems artificially aged

Step 1- Collection of field data Engine with intended after-treatment system installed in its intended configuration Original DAAAC version: Engine to be operated as it would be operated in the real application for a period of time needed to obtain all the relevant data Modified version: Engine to be operated as follows: Engine test bed (WHTC) or chassis dynamometer (WHVC with gradients – see UNECE proposal for HD hybrids) 10 cycles to be repeated (1 cold +9 hot) Data to be collected Engine speed/load (this is known) Exh. after-treatment temperatures Oil/additive consumption (either measured or typical values)

Step 2- Processing field data Temperature data processing (same as in the original protocol): Experimental temperature data are processed into bins of 10 ºC or smaller The time in each bin is calculated and then extrapolated to the full useful life given in Table 1 of the proposed procedure (in this case 500,000 km) Temperature data are then reduced to a single arbitrary temperature and the effective aging time at that temperature is determined by using the Arrhenius equation

Step 2- Processing field data

Example of application Euro V HD engine with a SCR Temperature recorded at the inlet of the SCR over the WHTC cycle

Example of application

Example of application Temperatures recorded have been binned in bins of 10 °C width The cumulative thermal load on the pollution control device over the useful life of the vehicle (500000 km in this case), can be reproduced by exposing it at 800 K for about 24 hours

Step 3- Bench aging time calculation The aging engine is operated at the aging modes and the measured temperatures are then processed to determine the effective aging time for each data point. In such way it is possible to calculate the number of times the aging cycle has to be repeated in order to make the effective aging time match the aging time at the arbitrary single temperature Aging time strongly depends on aging temperature.

Step 3- Bench aging time calculation

Definition of the stationary aging cycle from the WHTC As a first step, the k-means algorithm has been applied to the WHTC speed and load distribution k-means clustering is a method to partition n observations into k clusters in which each observation belongs to the cluster with the nearest mean, serving as a prototype of the cluster. The speed and load conditions of the WHTC have been binned (blue circles in the plots) and then a number of modes (red dashed circles) have been identified as representative of the various bins A 10 mode or 11 mode stationary cycle seems to be the best compromise between the representativeness of the WHTC and the practicality of the execution of the cycle (e.g. in the 15 modes there are too many modes that are very similar to each other and that are not very relevant to aging)

9 modes 10 modes 11 modes 15 modes

11 modes Mode % Speed % Load Normalized to 1hr 1 2.92 0.58 626 2 45.72 1.58 418 3 38.87 3.37 300 4 20.23 11.36 102 5 11.37 14.90 62 6 32.78 18.52 370 7 53.12 20.19 410 8 59.53 34.73 780 9 78.24 54.38 132 10 39.07 62.85 212 11 47.82 62.94 188

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Step 4 – Active regenerations An additional aging mode is added in case of DPF with active regeneration The filter regeneration will be triggered during this mode and the corresponding thermal load will be taken into account to calculate the duration of the thermal aging The number of active regenerations in the accelerated aging procedure shall never be less than 50% of active regenerations to which the RPCD is subjected during its useful life

Step 5 – Chemical poisoning/deposit formation The oil consumption rate of the engine is measured over 24 hours performing consecutive WHTC – Alternatively a default value (30 g/h) or a value requested by the manufacturer based on sound information and data can be used The oil consumption rate of aging engine is measured under the aging cycle conditions over a minimum of 24 hours (24 cycles) The number of aging cycles required to reach full useful life total oil consumption can be then calculated If the bench engine oil consumption rate is not sufficient to achieve the desired total oil consumption in the same time (cycles) as needed to achieve the thermal aging target, the addition of an “oil consumption mode” is permitted The “oil consumption mode” speed and load are selected in such a way that the lubricant consumption is maximized and effective thermal aging is minimized

Step 5 – Chemical poisoning/deposit formation In the original test protocol developed by DAAAC, in order to further decrease the time needed to reach the calculated lubricant consumption over the useful life, the increase of lubricant consumption was also permitted Among the several possible ways to increase fuel consumption (oil in fuel, intake manifold injection, high additive package oil, exhaust manifold injection, in- exhaust-injection, piston ring modification) the piston ring modification was considered the least artificial This method has been validated by comparing the structure of the deposits in the field aged and artificially aged pollution control devices The other methods have been not investigated

Adaptation of the HD procedure to LD? Issues: Lower mileage/ shorter useful life Lower impact of chemical poisoning? Different applications/technologies Speed based cycle (not normalized as for HD) …

Adaptation of the HD procedure to LD? Vehicle 1, gasoline, PFI, 3-way cat, SRC hot

Adaptation of the HD procedure to LD? Vehicle 2, GDI-stoich, 3-way cat, SRC hot

Adaptation of the HD procedure to LD? Vehicle 3, DOC, LNT, DPF, SRC cold

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