Annex 4 Evaluation of test measurement procedures for PM ... · UNCLASSIFIED Low Emission Diesel Research – Phase 3 Report AEAT/ENV/R/1873 Issue 1 Annex 4 – Measurement techniques

Annex 4 Evaluation of test measurement procedures for PM for light-duty vehicles

CONTENTS

A4.1 Introduction and objectives of Task 4 .......2

A4.2 Feedback from SI project and steering group ........................................................3

A4.2.1 CONCLUSIONS AND RECOMMENDATIONS FROM SI PHASE 2 STUDY ............................................................................... 3

A4.2.2 STEERING GROUP PRIORITISATION OF POSSIBLE TEST PROCEDURES ..................................................................... 3

A4.2.2.1 On-the-road driving...................................................... 5 A4.2.2.2 Dynamometer testing ................................................... 5 A4.2.2.3 Unloaded testing.......................................................... 6

A4.3 Experimental investigations......................7 A4.3.1 SENSITIVITY OF FAS RESULTS TO PARAMETERS FOR LIGHT-DUTY

VEHICLES .......................................................................... 7 A4.3.1.1 Rate of accelerator pedal depression............................... 9 A4.3.1.2 Extent of accelerator pedal depression ...........................11 A4.3.1.3 Effects of ambient temperature.....................................14 A4.3.1.4 The influence of vehicle preconditioning .........................15

A4.3.2 CORRELATION BETWEEN PM EMISSIONS OVER DRIVE CYCLES AND PEAK SMOKE DENSITY FROM FAS TEST FOR MODERN DIESELS. ..........................................................................17

A4.3.3 CORRELATION BETWEEN PM EMISSIONS & PEAK FREE ACCELERATION SMOKE DENSITY AND STATE OF VEHICLE REPAIR. ...........................................................................19

A4.4 Conclusions.............................................25 A4.4.1 TYPES OF TEST PROCEDURES TO BE CONSIDERED .................25 A4.4.2 SENSITIVITY OF FAS RESULTS TO 4 PARAMETERS..................25 A4.4.3 CORRELATION BETWEEN PM EMISSIONS OVER DRIVE CYCLES

AND FAS RESULTS .............................................................27 A4.4.4 CORRELATION BETWEEN PM EMISSIONS AND FAS RESULTS AND

STATE OF VEHICLE MAINTENANCE .......................................27 A4.4.5 TECHNICAL OPTIONS FOR COST EFFECTIVENESS ANALYSIS ....28

netcen

UNCLASSIFIED Low Emission Diesel Research – Phase 3 Report AEAT/ENV/R/1873 Issue 1 Annex 4 – Measurement techniques for PM for LDVs

A4.1 Introduction and objectives of Task 4

This annex reports the results obtained for Task 4, “The evaluation of test measurement procedures for PM for light-duty vehicles” of Phase 3 of the research into the in-service testing of low emission diesel vehicles project. Section 4.1 of the main report gives an overview of this portion of the project, together with an overview for the analogous study on heavy-duty vehicles, Task 3.

The objective of this task was to assess the potential effectiveness of candidate loaded and unloaded tests procedures for light-duty vehicles.

The conclusions and recommendations from the Phase 2 report1, which provide the reasons for this task, were:

Conclusion 1 PM is an issue in terms of air quality. Conclusion 2 Smoke is a reasonable proxy for PM provided it is recognised that smoke

is a concentration measurement whereas PM is accumulated mass flux. Conclusion 3 Anticipated smoke levels for Euro IV light-duty vehicles are around 0.1

-1m . Conclusion 4 There is concern that for vehicles with electronic control systems

(virtually all Euro III and IV specification vehicles) the unloaded test is further decoupled from being representative of on-the-road driving.

Conclusion 5 Cost effectiveness of in-service testing of PM emissions for HDVs is much greater than for LDVs.

Recommendation 6 Improvement on the 2.5/3.0 m-1 pass/fail limit be sought (these were the current limits at the time of writing the Phase 2 report).

Recommendation 8 The relationship between emissions over drive cycles on a dynamometer and FAS tests needs to be investigated to establish the relevance/potential of FAS testing to modern electronically controlled diesel vehicles.

Recommendation 9 Input is required from the corresponding project on spark ignition vehicles regarding the potential requirement of dynamometers for their in-service testing.

Recommendation 10 A steering group should practically assess the viability of the test options.

1 Reference to Phase 2 final report

UNCLASSIFIED


A4.2 Feedback from SI project and steering group

A4.2.1 CONCLUSIONS AND RECOMMENDATIONS FROM SI PHASE 2 STUDY

The conclusions and recommendations from the Phase 2 study into the in-service testing of SI engined vehicles highlighted areas where the test could be improved, and suggested a number of unloaded tests to better identify excess emitters. An implicit corollary to these conclusions and recommendations is that there does not appear to be a cost effectiveness, air quality improvement argument to support the introduction of a dynamometer (loaded) in-service test for the decentralised testing regime of SI vehicles.

This being so, if dynamometer testing were to be introduced for the in-service testing of CI engined light-duty vehicles the whole of the capital and installation costs would need to be borne by the in-service diesel test (rather than a major proportion being off-set against the in-service petrol vehicle test).

A4.2.2 STEERING GROUP PRIORITISATION OF POSSIBLE TEST PROCEDURES

Recommendation 10 of the Phase 2 report for this project suggests a steering group should be convened to assess the practicality of the in-service test procedure options. The steering group comprised people from: • DfT’s Vehicle Standards and Engineering Division, • DfT’s Licensing, Roadworthiness and Insurance division, • VOSA’s Testing Standards Policy and sStrategy group and • AEA Technology’s Engines and emissions team.

The three options considered were: • on-the-road driving, • loaded testing using a chassis dynamometer and • unloaded testing.

The final report from Phase 2 gave a matrix of four possibilities2, detailing positive and negative aspects of the options. It included using the vehicles’ brakes to provide a load – an option that was discounted by the LED Project’s Board as not being practical.

The steering group used its knowledge and experience to narrow down the viable possibilities. The framework/structure used for making the prioritisation is shown in Figure A4.1.

2 Phase 2 final report, Table on pages 20 and 30

UNCLASSIFIED


Is this type of test really practical

after considering: * safety, * insurance aspects No* space requirements and Reject test type * environmental factors (e.g. noise)

in the context of there being around 10,000 decentralised light-duty

diesel test stations?

Yes

NoFrom a preliminary cost effectiveness Reject test type analysis does this option appear plausible?

Yes

Undertake detailed assessment of options to prioritise those left, to reach a politically acceptable conclusion.

Figure A4.1 Framework for deciding on viability of various testing options

UNCLASSIFIED


A4.2.2.1 On-the-road driving On-the-road driving is, superficially at least, the technically most attractive option in terms of potentially being representative of PM emissions from real vehicles on the roads.

However, after discussion the steering group felt it was impractical to implement. It was rejected because of: • safety issues, • insurance issues, • space requirements and • environmental issues (including noise).

In reality a test could not be driven on public roads, and therefore it would require space within the test areas. There are around 10,000 decentralised MoT test stations for light-duty diesel vehicles. Their localities vary from city centres to rural areas. An on-theroad test is incompatible with the current testing programme and the requirement that the in-service test is equally applied to all vehicles.

A4.2.2.2 Dynamometer testing Dynamometer testing overcomes many of the practical issues that prevents an on-theroad driving test from being a practical option (e.g. insurance and environmental issues and the space requirements). There remain significant safety challenges, but it is believed that these could be managed such that the risk of injury to people, or damage to a vehicle or test facility, from a dynamometer test could be made acceptably low.

However, as was noted in the cost effectiveness analysis presented in the Phase 2 report, this is an expensive option. Table A5.13 (in Appendix 5 of the Phase 2 report) predicts an increased cost per test of £25.80 and £22.50 for 2005 and 2015, respectively. The Appendix also calculates that the “emissions saving potential”, i.e. the maximum emissions savings that would occur if all excess emitters were detected and rectified, is diminishing as measured in ktonnes/year with more modern technology. This is principally a consequence of the improved design leading to both lower emissions from new vehicles, and lower “excess” emissions when faults occur.

The primary technical reason for choosing loaded testing on a dynamometer, relative to unloaded testing, is the premise that the former will better correlate with on the road emissions. A reason cited for the continued, or even diverging, poor correlation between the PM emissions from unloaded tests and on-the-road driving is the introduction of electronic control units, breaking what a mechanical link between the accelerator and the fuelling rack. However, alongside the engine control computer there has been a proliferation of other electronic systems, e.g. antilock-brake systems. Many modern vehicles on a single roll dynamometer immediately flag up the “unusual” axle rotation pattern that is occurring and often revert to a “limp-home” or another “safer” set of engine maps. Consequently, the author has serious concerns as to how much of an improved correlation would be afforded by a simple dynamometer, particularly for future technologies. As a result, it appears likely that the fraction of the “emissions savings potential” that would be delivered by dynamometer testing is likely to be less than that initially anticipated, unless more sophisticated, and hence expensive, dynamometers were to be used.

The conclusion is the same: a preliminary cost effectiveness analysis of using dynamometers for an in-service IM test for light-duty vehicles indicates there would be insufficient emissions savings to outweigh the increase in test cost, and consequently this testing option is rejected.

UNCLASSIFIED


A4.2.2.3 Unloaded testing As a consequence of the conclusions summarised in the preceding two sub-sections, the steering group’s decision was: for light-duty vehicles on road testing and dynamometer testing were discounted on practical and cost effectiveness grounds, meaning AEAT would now focus on developing an unloaded test.

The experimental investigations were designed to critically assess two theories. 1. That the correlation between PM emissions over a loaded drive cycle and the peak

smoke emissions during a FAS test is still poor for the latest technology light-duty vehicles when considering all different vehicle types.

2. That there is some correlation between PM emissions over a loaded drive cycle and the peak smoke emissions during a FAS test for light-duty vehicles for a single vehicle type as a function of the vehicle’s state of repair/maintenance.

The majority of the available data that demonstrates the poor correlation between PM emissions over a loaded drive cycle and the peak smoke emissions during a FAS test was collected from older vehicles (i.e. pre-Euro II specification). It is conceivable, although in the author’s opinion unlikely, that recent advances in diesel engine technology have improved this correlation. Should there have been an improvement in correlation, then the argument for the in-service test continuing to be the FAS test is strengthened and the focus for improving the test would be to characterise the correlation and thereby to derive appropriate pass/fail limits for the different type approval standards.

Hypothesis 2, above, presupposes that hypothesis 1 is correct, i.e. that correlation remains poor even for modern vehicles, when comparing data from different vehicle types. It is founded on the observation that peak PM emissions occur during the rapid acceleration phases during transient road cycles. This is mimicked, albeit in a vehicle type dependent manner, by an unloaded acceleration of the engine. It is also hypothesised that many of the faults/degradation mechanisms that would lead to an increase in PM emissions over a loaded cycle would also cause an increase in the peak smoke density observed during a FAS test from whatever the baseline value was.

Despite searching, no data to either support or refute this hypothesis has been found in the open literature.

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A4.3 Experimental investigations

These comprise the testing of the two theories described in section 2.3.

In addition to these two investigations (described in sections A4.3.2 and A4.3.3 of this annex) the sensitivity of FAS test results to four parameters (the rate at which, and the extent to which, the accelerator pedal is depressed, effects of ambient temperature and effects of vehicle preconditioning were studied.

A4.3.1 SENSITIVITY OF FAS RESULTS TO PARAMETERS FOR LIGHT-DUTY VEHICLES

A study similar to that described in sections A3.4 and A3.5 of Annex 3 was undertaken for light-duty vehicles. Whilst the principal focus of the investigation into the sensitivity of FAS results to various parameters within the project has been on heavy-duty vehicles (reported in Annex 3), a smaller study of two light duty vehicles was also undertaken. This investigation occurred in the context of a sizeable research programme having been completed and reported by German researchers3, albeit around 4 years ago; hence its reduced scale.

Its objectives were the same as for the heavy-duty vehicles, namely to study the influence of four parameters listed in Section A3.3.1.2 on the FAS result. (The lag of engine oil temperature relative to the engine’s indicated water temperature was not studied for light-duty vehicles because experience has indicated this is much smaller than for heavy-duty vehicles.)

The answers sought, approaches adopted, equipment used and data analysis techniques used are identical to those described in Section A3.4.1 of Annex 3, and are not repeated here.

Table A4.1 lists the vehicles used during this task.

3 Research project FE 85.007/1999, Exhaust test- performance check / part 2 Diesel, DEKRA, TÜV Rheinland, RWTÜV,

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Table A4.1 Vehicles whose PM and FAS were measured

Vehicle Year of manufacture

Mileage Engine Comments Peak smoke density during FAS test

PM emissions over the NEDC

Vehicle 1 1998 10,750 1.8 litre Di with turbo, oxycat and EGR

Euro II spec 0.53 m-1 0.0830 g/km

Vehicle 2 2003 18,700 2.0 litre Di, common rail with turbo, oxycat and EGR

Euro III spec 1.04 m-1 0.0420 g/km





Vehicle 6 2003 6,000 2.7 litre Di common rail with turbo, oxycat and EGR






Vehicle 29 2002 23,000 1.7 litre Di, with turbo, oxycat and EGR


Vehicle 30 (same model as Vehicle 2)

2002 23,000 2.0 litre Di, common rail with turbo, oxycat and EGR


UNCLASSIFIED AEA Technology A4.8


A4.3.1.1 Rate of accelerator pedal depression Figure A4.2 shows the relationship between the FAS test result and the time taken to depress the accelerator

LD Vehicle 1 Accelerator depression time vs smoke

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LD Vehicle 2 Accelerator depression time vs smoke

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Time to depress accelerator pedal (s)

Figure A4.2 Effect of accelerator depression time on free acceleration smoke result



Figure A4.3 shows the equivalent relationship between the time taken for the engine to reach its governor limited speed and the pedal depression time. As for the heavy-duty vehicles, if the time taken to depress the accelerator is 1.5 seconds or less, the resulting smoke peak, and the acceleration time are unaffected. For both vehicles studied for times of 2.5 s or longer there is a clear increase in the engine’s acceleration time and a change in smoke level. The latter decreases for on vehicle, as expected, but increases for the second vehicle.

LD Vehicle 1 Accelerator depression time vs time for engine to reach top speed

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LD Vehicle 2 Accelerator depression time vs time for engine to reach top speed

3

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1.5

1

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0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Time to depress accelerator (s)

Figure A4.3 Effect of accelerator depression time on time taken by engine to reach top speed



A4.3.1.2 Extent of accelerator pedal depression Figures A4.4, A4.5 and A4.6 show the effects on the FAS test smoke, the time taken by the engine to reach its top speed, and the value of the top speed, respectively, against variable extents of accelerator pedal depression.

LD Vehicle 1 Extent of accelerator depression vs smoke

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LD Vehicle 2 Extent of accelerator depression vs smoke

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Figure A4.4 Effect of accelerator depression extent on free acceleration smoke result



LD Vehicle 1 Extent of accelerator depression vs time for engine to reach top speed

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LD Vehicle 2 Extent of accelerator depression vs time for engine to reach top speed

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Figure A4.5 Effect of accelerator depression extent on time taken by engine to reach top speed



LD Vehicle 1 Extent of accelerator depression vs top speed reached by engine To

p sp

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Top

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LD Vehicle 2 Extent of accelerator depression vs top speed reached by engine

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Figure A4.6 Effect of accelerator depression extent on top speed reached by engine

For Vehicle 1 depressions less than 45% were required before the smoke emissions were reduced, or the engine acceleration time increased from a plateau level, whilst for Vehicle 2 the analogous threshold occurred at 70% depression. The top speed reached by the engine fell below its governor limited value when the accelerator pedal was depressed by less than these thresholds. i.e. 30% and 60%, respectively.



A4.3.1.3 Effects of ambient temperature Figure A4.7 shows the smoke values from successive FAS tests from two light-duty vehicles as they were tested indoors, outside and then indoors again. The key data is summarised in Table A4.2

LD Vehicle 1 Successive FAS results for warm/cool ambient temperatures

1

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0

Ambient temperature Ambient temperature 3.3°C Ambient temperature 17.3°C

FAS

LD Vehicle 2 Successive FAS results for warm/cool/warm ambient temperatures

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Ambient temperature 26.7°C Ambient temperature 13.4°C Ambient temperature 30.5°C 0.8

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Figure A4.7 Smoke values from successive FAS tests for vehicles in warm/cold/warm ambient environments



Table A4.2 Summary of smoke test results and ambient temperatures Vehicle 1 Vehicle 2 Smoke Temperature Smoke Temperature

Indoors 0.420 ± 0.023¶ 19.8°C 0.76 ± 0.019 26.7°C Out side 0.326 ± 0.034 3.3°C 0.73 ± 0.019 13.4°C Indoors repeat 0.281 ± 0.021 17.3°C 0.70 ± 0.030 30.5°C ¶ Only the last 5 peaks of this group of 8 are included in this average (i.e. first 3 peaks excluded)

For both vehicles the average from the FAS result decreases for successive groups of tests. The primary cause of this is believed to be preconditioning effects, see the next section. There is no consistent change for the group measured at the lower temperature, despite there being a 15 ± 2°C temperature change between the cool/warm data sets. From the data any effect is taken as being less than 0.03 m-1 for a 15°C change in ambient temperature.

A4.3.1.4 The influence of vehicle preconditioning Evidence from previous studies have indicated that the effect of preconditioning is more important in determining the FAS test result for light-duty vehicles than for heavy-duty vehicles. The questions investigated in this portion of the task were: • Is the current preconditioning cycle specified in the UK testers’ manual satisfactory? • How does the effectiveness of the preconditioning specified by the UK testers’ manual

compare with that recommended by the German research?

The top portion of Figure A4.7 shows the smoke values for the first 28 successive FAS tests following the standard preconditioning for Vehicle 1. (The ambient temperature changed during this sequence but any effect this causes is secondary to the preconditioning.) The smoke density from the first free acceleration, off the top of the scale in the figure, was 2.17 m-1. Unfortunately equivalent data were not available for the first series of tests from the second light-duty vehicle. After 10 FAS tests all subsequent values lie within 0.06 m-1 (21%) of the mean value for the last group. It is noted that this vehicle is probably well towards the “unpreconditioned” end of the range likely to be encountered by testers because of its driving history prior to these tests, i.e. it represents a worst case.

A second approach used to investigate preconditioning made use of a phenomenon described earlier, namely that deliberately fixing the EGR valve in the fully open position led to very high FAS test values. The sequence used was: 1. to start with a fully warmed up vehicle following some FAS tests, 2. then fix the EGR valve fully open, 3. to do 5 free accelerations to dirty the vehicle’s exhaust system, 4. to restore the EGR valve to its normal automated mode of operation and 5. to measure around 10 successive FAS for this dirtied vehicle.

At the end of this sequence the vehicle is in the same condition as for step 1. The sequence was repeated but with a standard UK preconditioning cycle introduced between steps 4 and 5. The smoke emissions at step 3, i.e. when the EGR valve was fully open, were monitored using a Hartridge SP MOT smoke meter. This gave values of > 9.0 m-1 for each acceleration! (The Crypton Dieseltune DX250 was not used here because it was important that it was not contaminated during this activity.)

Figure A4.8 shows the data for successive FAS tests after the vehicles had been “contaminated” using the above procedure with and without the standard UK



preconditioning. Overall it is hard to see what difference preconditioning does make. For both vehicles around 3 further FAS tests were required before the FAS measurements were close to the average of the last 4 in the test sequence. This, in conjunction with the data in Figure A4.7 strongly indicates the current preconditioning procedure is insufficient for the results from subsequent FAS tests to be independent of the vehicles initial condition.

LD V eh ic le 1 S uccessive FAS s w ith and w ithout precondition ing

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LD V eh ic le 2 FAS s w ith and w ithout precondition ing

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N o precond ition ing s tandard precondition ing

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Figure A4.8 Successive FAS tests on "dirty" light-duty vehicles with and without preconditioning



A4.3.2 CORRELATION BETWEEN PM EMISSIONS OVER DRIVE CYCLES AND PEAK SMOKE DENSITY FROM FAS TEST FOR MODERN DIESELS.

The hypothesis evaluated was that the correlation between PM emissions over a loaded drive cycle and the peak smoke emissions during a FAS test is still poor for the latest technology light-duty vehicles when considering all different vehicle types. The information about the vehicles tested, their PM emissions and their peak smoke density during a FAS test are listed in Table A4.1.

Figure A4.9 shows the correlation found. Despite the relatively small number of vehicles tested overall it remains poor. Figure A4.10 shows the same data but with two lines added. The black line is that resulting from a least squares regression analysis. The value of R2 = 0.227, which when combined with the line’s unrealistic gradient, illustrates a poor overall correlation.

0.0000

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PM o

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Vehicle 30

Vehicle 4

Vehicle 5

Vehicle 1

Vehicle 28

Vehicle 7

Vehicle 6 Vehicle 29

0 0.2 0.4 0.6 0.8 1 1.2 1.4

FAS peak (m-1)

Figure A4.9 Correlation between PM emissions over a drive cycle and the peak smoke emissions during a FAS test



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y = -0.0266x + 0.073 R2 = 0.2274

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FAS peak (m-1)

Vehicle 2

Vehicle 30

Vehicle 4

Vehicle 5

Vehicle 1

Vehicle 28

Vehicle 7

Vehicle 6 Vehicle 29

Figure A4.10 Correlation between PM emissions and FAS peak smoke with 2 analyses

A (blue) line was drawn through the origin and illustrates some of the challenges of the current test. Firstly, it is notable that 5 of the 9 data points lie close to this line. Vehicles 1 and 5 lie above the line because they gave below average peak smoke densities during a FAS test, when compared with their PM emissions over the drive cycle. (Vehicle 5 is a Class III vehicle, it being a light-duty truck. Its PM emissions are within the Euro 3 type approval emissions standard of 0.10 g/km.)

The most significant deviations from the blue line are the two data points from vehicles whose peak smoke levels were greater than 1.0 m-1 during the FAS test despite their PM emissions over the regulatory cycle being around 0.04 g/km (below the 0.05 g/km Euro 3 standard). These two data are from two different vehicles of the same type, see Table A4.1. This, together with other unreported data, confirms that the high smoke density is a characteristic of the vehicle type rather than a single rogue vehicle.

It is known from discussions with vehicle manufacturers, and from feedback from test stations, that this deviation is not unique to this single vehicle type, nor to this vehicle manufacturer.

The data in Table A4.1 and Figure A4.10 lead to the following conclusions: 1. The correlation between PM emissions over the regulatory loaded drive cycle and the

peak smoke values obtained during a FAS test remains poor, i.e. hypothesis 1 is correct.

2. A universal pass/fail limit designed so as not to unfairly fail vehicles which meet the type approval PM emissions standard would have to be set at a smoke density above that of the highest vehicle type.

The consequence of the second conclusion would be a test that unfairly disadvantaged some vehicle types and is poor at detecting gross emitters from the majority of vehicle types. The data in Table A4.1 and Figure A4.10 can be used to illustrate these points. If



the pass/fail limit were set to 1.5 m-1 and the ratio of PM emissions over the NEDC to the peak smoke value seen during a FAS test remained constant as a function of a vehicle’s state of repair and maintenance then • Vehicles 2 and 30 would fail the FAS test (i.e. have a peak smoke just above 1.5 m-1)

when their PM emissions were around 0.05 g/km (i.e. there would be no degradation factor allowance for this vehicle type).

• The cluster of vehicle close to the blue line of Figure A4.10 would not fail the FAS test (i.e. have a peak smoke just above 1.5 m-1) until their road PM emissions had risen to around 0.18 g/km, (i.e. the test would fail to identify these vehicles when they are significant excess emitters).

A4.3.3 CORRELATION BETWEEN PM EMISSIONS & PEAK FREE ACCELERATION SMOKE DENSITY AND STATE OF VEHICLE REPAIR.

Given the findings of the preceding section, the second theory assessed in this part of the work was that there is some correlation between PM emissions over a loaded drive cycle and the peak smoke emissions during a FAS test for light-duty vehicles for a single vehicle type as a function of the vehicle’s state of repair/maintenance. This was assessed by taking vehicles in what was generally a good state of repair and maintenance and: • characterising the PM emissions over the NEDC and peak smoke density during a FAS

test, • deliberately inducing a fault, • remeasuring the PM emissions (NEDC) and peak smoke density (FAS), • restoring the vehicle back to its original state, • remeasuring the peak smoke density.

The exception to this approach was one vehicle whose owner offered it for testing saying it seemed to be operating poorly.

A number of franchised garages, for different OEMs, were surveyed to find the most common faults encountered by modern diesel passenger vehicles. The consensus list was: • faulty air mass meter (noticed by customers as a reduction in power and sometimes

increased smoke) • faulty pressure or temperature sensors • EGR faults (usually a stuck valve) • faulty throttle position sensors (usually badly fitted rather than broken) • injector faults (usually caused by contaminated fuel rather than faulty units) and • all the garages surveyed said that ECU faults are very rare.



Table A4.3 Vehicles whose PM and FAS were measured in normal and defective states Vehicle Year of

manufacture Mileage Engine Comments Fault induced

Vehicle 3 – Fault A

1996 136,400 2.0 litre DI Rover engine, type 20T2R

Euro 2 spec Need of general servicing plus sticking EGR

Vehicle 7 – Fault B


Euro 3 spec Turbo waste-gate disabled

Vehicle 28 – Fault C


Euro 3 spec Leak from hose on high pressure side of turbo-compressor

Vehicle 30 – Fault D

2002 23,000 2.0 litre HDi, common rail with turbo, oxycat and EGR

Euro 3 spec EGR valve fixed in a semi-open position

Vehicle 30 – Fault E

2002 23,000 2.0 litre HDi, common rail with turbo, oxycat and EGR

Euro 3 spec Faulty air mass flow sensor fitted

Table A4.4 Emissions from vehicles in normal and defective states Vehicle State of

maintenance PM emissions (g/km) FAS NOX emissions (g/km)

ECE EUDC Combined ECE EUDC Combined Vehicle 3 – Normal 0.0860 0.0977 0.0934 2.15 ± 0.36 0.672 0.757 0.726 Fault A Faulty 0.1152 0.1274 0.1230 3.46 ± 0.16 0.722 0.861 0.810 Vehicle 7 – Normal 0.0513 0.0608 0.0573 0.50 ± 0.04 0.439 0.429 0.433 Fault B Faulty 0.0353 0.2829 0.1915 0.94 ± 0.08 0.601 0.490 0.531 Vehicle 28 – Normal 0.0683 0.0743 0.0721 0.62 ± 0.03 0.447 0.395 0.414 Fault C Faulty 0.0899 0.1848 0.1498 0.82 ± 0.04 0.340 0.360 0.353 Vehicle 30 – Normal 0.0232 0.0376 0.0323 1.30 ± 0.14 0.390 0.397 0.394 Fault D EGR fault 0.0169 0.0338 0.0276 2.14 ± 0.17 0.565 0.574 0.571 Vehicle 30 – Normal 0.0232 0.0376 0.0323 1.30 ± 0.14 0.390 0.397 0.394 Fault E MAF fault 0.0233 0.0390 0.0332 0.98 ± 0.05 0.353 0.401 0.383


UNCLASSIFIED Low Emission Diesel Research – Phase 3 Report AEAT/ENV/R/1873 Issue 1 Annex 4 – Measurement techniques PM for LDVs

The results of this survey guided the faults that we introduced into vehicles for this investigation. The vehicles studied and the faults introduced are listed in Table A4.3.

The leaking air hose on the high pressure side of the turbo-compressor reduces the quantity of charge air entering the engine, particularly at high engine speeds and loads. This is also equivalent to the following faults: • partially blocked air filter • reduced efficiency or faulty turbo-compressor • reduced inter-cooler efficiency and • partially blocked inter-cooler.

The effect of disabling the EGR valve in the fully off state (no EGR) is to reduce smoke but to increase NOX (see Annex 1). It was found that disabling the EGR in the fully on state (maximum EGR) led to very significant increases in peak smoke density during a FAS test (> 9 m-1 for the two different vehicle type assessed). This also led to a significant change in driveability, and was believed to be an unrepresentatively large degree of degradation. Consequently, the data reported here is from a vehicle whose EGR valve was fixed in a semi-open state. This would lead to a reduction in EGR over the design level for some points on the engine map (e.g. at lower engine speeds and loads) but an increase in EGR at other points (e.g. at higher engine speeds and loads).

The faulty air mass flow sensor was a unit that had been replaced by a franchised dealer because the OEM diagnostic reader identified it as being out of its specified range. Further information on the extent of its fault was not available.

Table A4.4 lists PM and NOX emissions data for these vehicles over the two components of the NEDC, together with the peak smoke density measured (using a standard older MOT-type smoke meter).

Table A4.5 lists the change in PM emissions and FAS data expressed as the percentage change from the vehicle in its normal state of maintenance/repair to its faulty state. These data are shown pictorially in Figure A4.11. Table A4.6 lists the change in NOX emissions (again as a percentage change) caused by the introduction of the faults.

Table A4.5 Percentage increase in PM and FAS emissions caused by introduction of fault Vehicle Fault ECE EUDC Combined FAS Vehicle 3 – Fault A

service/EGR problems

33.95% 30.40% 31.69% 60.93%


turbo waste gate -31.19% 365.30% 234.21% 88.00%


leak from turbo 31.63% 148.72% 107.77% 32.26%


EGR stuck semi-open

-27.16% -10.11% -14.55% 64.62%


faulty MAF sensor 0.43% 3.72% 2.79% -24.62%



-100.00%

-50.00%

0.00%

50.00%

100.00%

150.00%

200.00%

250.00%

300.00%

350.00%

400.00%

Fault A Fault B Fault C Fault D Fault E

% c

hang

e in

em

issi

ons

ECE PM EUDC PM Combined PM FAS

Figure A4.11 Changes in emissions caused by introducing faults

Table A4.6 Percentage increase in NOX emissions caused by introduction of fault Vehicle Fault ECE EUDC Combined Vehicle 3 – Fault A

service/EGR problems

7.44% 13.74% 11.57%


turbo waste gate 36.90% 14.22% 22.63%


leak from turbo -23.94% -8.86% -14.73%


EGR stuck semi-open

44.87% 44.58% 44.92%


faulty MAF sensor -9.49% 1.01% -2.79%

An important message to be drawn from Figure A4.11 is that the effect on the PM emissions over the two components of the NEDC varies from fault to fault (compare the heights of the first two columns in the figure). For example, detaching the turbo waste-gate control line Fault B caused a 30% decrease in PM emissions over the ECE cycle component of the NEDC cycle, but a 365% increase over the EUDC. This leads to the important conclusion that it is naïve to believe that Fault X leads to a change Y in PM emissions over all loaded cycles: The change in PM emissions depends both on the fault and the speed/time characteristics of the drive cycle.

Since a given fault leads to a range of changes in PM emissions over different loaded drive cycles but only a single value for the change in peak smoke during a FAS test, the latter can not correlate well with all loaded drive cycles.



Another observations from Figure A4.11 is that there is a better correlation between the change in PM emissions over the EUDC and the combined cycle (the NEDC) than between the ECE and the combined cycle. This is an inevitable consequence of the units used combined with the distances driven during the component cycles. The emissions of a pollutant, E(p), over the combined cycle is given by:

4 7E(p) ≈ E(p) + E(p)NEDC ECE EUDC11 11

Overall the relationship between the change in peak smoke density observed during the FAS test and the change in PM emissions over the NEDC (or either component of this) is at best “moderate”. It can not be described as “good”.

However, the deviations from a “good” correlation are systematic, and are a consequence of the limited area of the engine’s performance map probed by the FAS test and the weighted average of the wider range of areas of the map probed by the NEDC.

For Faults B and C the faults introduced led to a reduction in the quantity of charge air entering the engine particularly at high engine speeds and loads. This leads to the much larger increase in PM emissions seen over the EUDC relative to the ECE component cycles. The FAS test is not a high load test, the turbo boost pressure does not rise to its higher levels during the test, and consequently it shows a reduced sensitivity to such faults relative to the PM increase over the NEDC.

This is in marked contrast to Fault D, where the EGR valve was fixed partially open. Generally higher rates of EGR lead to more PM emissions and smoke. For the ECE cycle, the EGR valve being fixed only partially open, as opposed to being wider open when the EGR valve is functioning correctly, leads to a reduction in EGR for the faulty vehicle and, consequently, a reduction in PM emissions. During the EUDC the EGR valve would, when functioning correctly, allow a higher rate of EGR for some of the cycle and a lower rate for the high speed (100 and 120 kph) portions of the cycle. Overall, this led to the observed small reduction in PM emissions. During the FAS test the rapid depression of the accelerator indicates the driver’s wish to accelerate rapidly. The ECU turns off the EGR under these circumstances and supplies additional fuel (to produce the required additional power to effect the acceleration). For the faulty vehicle, therefore, during the FAS test there was more EGR than would be the case for a correctly operating vehicle, leading to an overall increase in smoke emissions.

The test driver reported that Vehicle 30 with Fault E was “less responsive” when fitted with the “faulty” air mass flow meter that it was initially. This agrees with the findings from our survey of franchised garages (see Section A4.3.3). It is believed, although not confirmed by a detailed analysis of the faulty component, that the faulty sensor was under reporting the air flow. This led to a lower fuel charge relative to when the vehicle had a correctly operating sensor.

In the FAS test the time profile of the accelerator’s position is specified as part of the test and “performance” is neglected. For a vehicle that is somewhat under-fuelling this would lead to a reduction in peak smoke during a FAS test. In contrast, when driving the NEDC the time profile of the accelerator’s position is less important than the “performance”, i.e. achieving the correct speed. For a vehicle that is somewhat under-fuelling this would lead to the driver depressing the accelerator a little more, and PM emissions being little changed over the drive cycle relative to a vehicle with a correctly functioning sensor. This explanation would account for the changes in emissions for Fault E as reported in Table A4.5 and Figure A4.11.

The preceding explanations illustrate the tenet that the changes in peak smoke during a FAS test deviate from the changes in PM emissions over the NEDC because the former only



probes particulate emissions over a limited area of the engine’s performance map whilst the latter is a weighted average over a wider range of speeds and loads. The FAS test is, therefore, only indicative of faults.

Overall, it is evident that the result of a FAS test is not a proxy for PM emissions over the loaded regulatory cycle (the NEDC) but is best viewed as a diagnostic test that has a range of sensitivities to different faults. It sometimes under reports the change in PM emissions over the NEDC (e.g. as for Faults B and C) and sometimes over reports them (e.g. Fault D).



A4.4 Conclusions

A4.4.1 TYPES OF TEST PROCEDURES TO BE CONSIDERED

The feedback from the project’s steering group regarding which test procedures were cost effective and practical options produced a clear recommendation.

Recommendation A4.1 Only unloaded test procedures should be considered for the in-service testing of light-duty vehicles.

Unloaded testing can range from steady state running, e.g. at an engine speed above low idle as for the current in-service test for petrol cars fitted with three way catalysts, to transient tests. Unloaded transient testing is the basis of the current FAS test. This leads to the recommendation below.

Recommendation A4.2 The focus of research should be on improving FAS testing for modern light-duty vehicles.

The next three sections consider weaknesses of the FAS test, and assumptions on which the FAS test approach is based.

A4.4.2 SENSITIVITY OF FAS RESULTS TO 4 PARAMETERS

As for heavy-duty vehicles, the change from mechanically controlled to electronically controlled fuelling systems has led to a large reduction in the sensitivity of FAS results to the rate and extent of accelerator depression. As was reported in the German study on light-duty vehicles(ref 3) and reported in Annex 3 of this report for heavy-duty vehicles, the studies of light-duty vehicles showed there is a plateau in the relationship between the rate and extent of accelerator pedal depression and the FAS smoke value (and the rate at which the inloaded engine accelerates). Again the experimental data indicates that for depression rates faster than a threshold time, or beyond a threshold depression extent, the engines ECU limits the rate of increase in fuelling irrespective of the drivers action. For the two vehicles tested the threshold was around 1.5 seconds. This value is totally consistent with that found in the German study(ref 3). These observations lead to the same recommendation that was made regarding heavy-duty vehicles, see Recommendation A4.3.

Recommendation A4.3 There is no case for introducing further functionality into the test meter to control the range and extent of accelerator depressions because the range of accelerator depression times and extents within which the variations made by the tester cause no change in the vehicle’s acceleration, are sufficiently wide for it to be assumed that all honest attempts to perform a FAS test are within this envelope.

The dependence of the FAS test result on ambient temperature was observed to be < 0.03 m-1 for a 15°C change. For the two vehicles tested this amounts to < 7% and < 3% change in FAS per 10°C in ambient temperatures, for vehicles 1 and 2, respectively.



Recommendation A4.4 There is not a case introducing a correction for ambient temperature into the measurement meter/procedure because temperature variations likely to be encountered at test stations in the UK cause insufficient changes in FAS test results to warrant this.

The dependence of FAS test result on vehicle preconditioning is more marked. It appears that the current preconditioning cycle specified in the UK testers manual is unsatisfactory since it is not effective at preparing vehicles such that successive FAS results show little variability.

On the basis of the above conclusion it is tempting to form a recommendation that “for light-duty vehicles the current preconditioning cycle specified in the UK testers manual does need to be changed”. However, it is informative to look at the details of the meter specification4. This was done by applying the calculation methodology specified in Paragraph 5.1.6 of the specification to the 4 sets of FAS data plotted in Figure A4.7.

For Vehicle 1 the third FAS result is less than 75% of the arithmetic mean of the first three for both data sets. As a consequence the meter would have required a fourth test for both data sets, and the first, anomalously high, reading would have been rejected. For Vehicle 2 all three data points are greater than 75% of the arithmetic mean of the first three, for both data sets. Hence the result the meter would display is the arithmetic mean of the first three results. For the data set where no preconditioning occurred this would include the first, anomalously high, peak.

Consequently, it is seen that filtering data by rejecting some peaks according to Section 5.1.6 of VOSA’s meter specification provides some further safeguard for vehicles that require further preconditioning.

This safeguard would be improved if Section 5.1.6 of VOSA’s meter specification were amended so that any reading further than 25% from the mean smoke level was rejected. Mathematically:

current specification reject if Reading < 75% of mean of last 3 suggested specification reject if Reading < 75% or > 125% of mean of last 3.

This modification would lead to the rejection of the first peak of the no-preconditioning data set for Vehicle 2.

Further “fine tuning” of the algorithm, for example rejecting tests which lay outside 15% (rather than 25%) of the mean value would further overcome variability due to preconditioning.

A primary objective of testing is to identify vehicles above the threshold (those that require maintenance or rectification) but to do so using the minimum number of FAS tests, thereby minimising the likelihood of damaging the vehicle’s engine. Consequently, it should be remembered that anomalously high FAS results are only a problem if one is considering failing a vehicle – if all the FAS results are below the pass/fail limit then their variation is not an issue.

Overall, these observations and discussion lead to the recommendations below.

Recommendation A4.5 The wording of Paragraph 5.1.6 of the VOSA MoT Smoke Manual specification should be amended to read: Calculate continuously and automatically the arithmentic mean of the

4 Specification for diesel smoke meters, VI, document MOT/05/01/01



latest 3 readings. If the mean reading is above the pass/fail limit for the vehicle and any of the 3 readings………………

Recommendation A4.6 The wording of the second half of the second sentence should amended to read: ………. any of the 3 readings is more than 15%5* or 0.1 m-1 (whichever is the greater) from the mean smoke level then that individual reading should be rejected (for the purpose of this average only) and no mean value shall be displayed.

A4.4.3 CORRELATION BETWEEN PM EMISSIONS OVER DRIVE CYCLES AND FAS RESULTS

Although the change from mechanically controlled to electronically controlled fuelling systems has led to a large reduction in the sensitivity of FAS results to the rate and extent of accelerator depression, it has been found that the correlation between the peak smoke emissions during a FAS test and PM emissions over the NEDC for different vehicle type remains poor. In other words, the known poor correlation has not improved as a result of technical developments.

A consequence of this is the use of universal limits that apply to all vehicle type is problematic. A universal pass/fail limit designed so as not to unfairly fail vehicles which meet the type approval PM emissions standard would have to be set at a smoke density above that of the highest vehicle type. This leads to a test that unfairly disadvantages some vehicle types and is poor at detecting gross emitters from the majority of vehicle types.

Recommendation A4.7 Consideration is given to devising a pass/fail limit that is more equable for all vehicle types, at the same time being a more demanding assessment of the state of maintenance for the majority of vehicles.

A4.4.4 CORRELATION BETWEEN PM EMISSIONS AND FAS RESULTS AND STATE OF VEHICLE MAINTENANCE

For loaded drive cycles the first important conclusion demonstrated by this study is that the effect of each fault does not cause a constant percentage increase in PM emissions over all drive cycles. Rather it is dependent on the details of the drive cycle, specifically depending on the vehicle speed/time characteristics of the cycle. This is a consequence of the change in loaded PM emissions varying at different positions within the engine speed/load map.

The FAS test only probes emissions from a very limited part of the engine’s performance map. Consequently, the correlation between the change in peak smoke emissions during a FAS test and PM emissions over the NEDC caused by a fault is at best “moderate”. A corollary to this is that the FAS test cannot be a proxy for the PM emissions over the NEDC,

5 It is recommended that further studies be undertaken to check/confirm that this is an appropriate margin for error.



but it is a diagnostic test that has a range of sensitivities to different faults. It sometimes under reports the change in PM emissions over the NEDC and sometimes over reports them.

That there is only a moderate correlation between changes in the peak smoke emissions during a FAS test and the PM emissions over the NEDC, for faulty relative to rectified vehicles, has an important consequence in that the setting of an appropriate pass/fail limit for the FAS test is a matter of subjective judgement: it can not be calculated objectively as would be the case if the correlation was good.

Overall, these findings lead to the following recommendation

Recommendation A4.8 The FAS test continues to be used as an in-service check of PM emissions appreciating it is a diagnostic test that has variable sensitivity to different faults.

A4.4.5 TECHNICAL OPTIONS FOR COST EFFECTIVENESS ANALYSIS

The crux of the improvement required distils down to the options for changing the pass fail limits for the FAS test. The plausible technical options range from do nothing, through continuing use a universally applied limit, to tailoring the pass/fail limit to each vehicle type. In addition, the option of “improving” the smoke meters’ sensitivity is also included.

The five options are summarised as:

Option PL1: Change nothing – i.e. continue to test for smoke using the current free acceleration test, equipment and pass/fail limits, including the new lower limits to be introduced as described in EU Directive 2003/27/EC.

Option PL2: Further stepwise decrease in pass/fail limit that applies to all vehicles. Option PL3: Introduce vehicle specific pass/fail limits for each type of vehicle. Option PL4: Further stepwise decrease in generic pass/fail limit plus option that

manufacturers can declare a higher value for vehicles that meet the type approval emissions specification in all other respects.

Option PL5: Change from smoke meter to a more sensitive meter.

The cost effectiveness of these five options is assessed in Annex 5.


Documents

Annex 4 Evaluation of test measurement procedures for PM ... · UNCLASSIFIED Low Emission Diesel Research – Phase 3 Report AEAT/ENV/R/1873 Issue 1 Annex 4 – Measurement techniques