Pressure drop characteristics of soot generated by a DPG and a Euro IV, 2 litre

diesel engine

Greg Inman, Andrew Todd, Kingsley Reavell, Tim Hands

2

Introduction

� The DPG is part of the Cambustion DPF Testing System which tests Diesel Particulate Filters for

– Backpressure vs soot load

– Regeneration characteristics

– Filtration efficiency (with a soot monitoring system)

� This is done by loading filters with soot generated in a Diesel burner, at flows and temperatures similar to engine conditions.

� This work compares the backpressure produced by the soot from the DPG burner with that from and engine.

� Effects causing variability in the backpressure associated with

– Engine cold starts

– High flow conditions

were measured in these tests and are discussed.

3

The Cambustion DPG

� More repeatable and rapid testing of DPGs than engine tests� Burner conditions unaffected by DPF backpressure� Automated, unattended testing except for loading & weighing the filter.

4

DPG Schematic

5

DPG Flow – Temperature CapabilityStandard LD version

DPG - LD Operating Temperature : Flow Rate Capabi li ty

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800 900

DPF flow kg / hr

DPF

in

let

tem

pe

ratu

re º

C

regenerat ion mode

max imum system loading capabil it y

standard loadingcondi t ions

burner o ff condit ions

6

DPG Flow – Temperature CapabilityNew MD Version

DPG - Medium Duty Operating Temperature : Flow Rate Capability

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800 900

DPF flow kg/ hr

DP

F in

let

tem

per

atu

re º

C

typical loading setpoint

burner off condit ions

regen / warm up

max possible loading limits

Increased fuel flow: approximately doubled loading & regeneration flows

7

DPG Application for Dp vs Soot Mass Testing

Instrument : instrument repeatability

0

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90

0 2 4 6 8 10 12 14 16

Corrected soot mass (g)

Bac

kpre

ssur

e m

bar

part 1

part 2

2 parts, nominally identical are clearly distinguished on all instruments.

Uncoated 2.8 l SiC filters

pore filling and cake formation behaviour clearly quantified

8

DPG Flow Sweep Testing

� DPG measures backpressure vs flow up to ~ 600 m3/h� For comparison with engine results, Reynolds number should be the same

– Cold flow test at a lower flow rate than the engine!

– This keeps the balance of viscous & inertial pressure drops the same.

0

5

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45

50

0 100 200 300 400 500 600 700

Flow rate m3n/hr

Bac

kpre

ssur

e m

bar

Blown Bench Measurements

DPG measurements at 50 C

DPG measurements ambient temp

9

Previous Engine Correlation WorkT Hands et al, DEER 2007:Pressure drop vs soot load for Engine soots compare d with DPG soot

0

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80

100

0 5 10 15 20 25 30 35

Total Soot (g)

Nor

mal

ised

Pre

ssur

e dr

op

Transient Cycle

High Load Steady State

DPG

� Difference between cycle & steady state engine soot� Engine soot backpressure measured on engine: less accurate� Other private data also shows significant variation between engines

10

New Test Programme� DPF canned for easy connection to engine� Load on engine or DPG.� Cold flow test at 0g, 5g, 15g, 20g & 30g on DPG

– Improved accuracy compared with engine backpressure measurement due to accurate & stable temperature and flow

� Original plan:

load

load

load

load

regen

weigh

weigh

weigh

weigh

weigh

flow test

flow test

flow test

flow test

flow test

warmup0g

5g

15g

20g

30g

Engine / DPG DPG

11

Engine Details

� 2l Common rail Diesel engine� Stage 4 emissions compliant� Mounted on dynamic dyno

– Comparisons made with cycle soot

� Fitted with Diesel Oxidation Catalyst upstream of DPF

– In this test programme, the DPG testing was not fitted with the DOC. This is to simulate best the application of the DPG for testing filters which are then used with an upstream DOC, currently the majority application.

– For single brick systems, the engine soot would differ mainly via higher levels of volatile components.

� All tests performed on the same DPF:

– 5.66” dia x 10” 4.1 l

– Uncatalysed SiC.

12

Soot Loading Conditions

� Engine – 3 conditions used

– NEDC – approx 3g/h for this engine

– ‘Rural’ drive cycle – 6g/h

– Steady state accelerated soot loading (modified engine operating points) – 10g/h

� DPG

– All tests at approx 10 g/h setpoint

13

Effect 1: Backpressure ‘Relaxation’ in flow test27g load

0

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0 50 100 150 200 250 300 350 400

Equivalent flow (m3/hr)

first flow test

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0 50 100 150 200 250 300 350 400

Equivalent flow (m3/hr)

first flow test

repeat test

Flow test sweeps flow up and then down.First flow test shows reduced pressure on downsweep

Further repeats then stable up and down same trajectoryShape closer to expected quadratic

14

High Flow Relaxation Conclusions

� Deposited soot is disturbed by high flow conditions� Once relaxation has occurred, soot is then stable.� Flow tests all repeated twice in this work, and data quoted from repeat.

15

Backpressure reduction in multistage loading (1)

0

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120

0 5 10 15 20 25

Soot load (g)

Equ

ival

ent d

elta

p @

300

m3/

hour

(m

bar)

Accelerated soot load

Loaded to 14.3g and then on to 19.7g

Backpressure lower at 19.7g than 14.3!

16

Backpressure Reduction In multistage loading (2)

0

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50

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0 5 10 15 20 25 30 35

Sootload (g)

Pre

ssur

e dr

op a

t 300

m³/

hr (

mba

r)

Loaded and flow tested same day

Part loaded and topped up from cold, then flow tested

SS Engine sootloads

17

DPG soot subjected to cold start on engine

Load on DPG

Flow test

Engine cold start

Flow test

Load on DPG

Flow test

Engine cold start

Flow test

Flow test

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0 5 10 15 20 25 30 35

Sootload (g)

Pre

ssur

e dr

op a

t 300

m³/

hr (

mba

r) DPG sootloads

18

Cold Restart Backpressure Reduction

0

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30 35 40 45 50 55 60 65 70

Time (s)

MA

F (

kg/h

r), T

empe

ratu

re (°

C)

0

2

4

6

8

10

12

14

16

dP (

mba

r)

maf_kgh_mes

DPF In

delta p

Engine Started

Speed increasedto 2000rpm

Dry gas enetering DPF

Pressure drop decreasing

MAF constant

'Wet' gas entering DPF (Condensate heating)

19

Recovery of Reduced Backpressure

0

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140

160

0 5 10 15 20 25 30

DPF dP corr DPF dP corr DPF dP corr

Part loaded to 17g on DPG

Cold start on EngineLoading continued to 29.5g

Compared with continuous load to 29g

20

Effect of Cold Start - summary

� Regardless of soot type, engine cold start appears to cause reduction in backpressure

� Does not occur with restart in loading on DPG� Reduction in backpressure is visible in real time during engine start� Possibly connected with condensation & re-evaporation of water from soot

cake, damaging the structure.� Reduction in backpressure not fully recovered with further loading.� All engine loaded data in the comparison is therefore loaded directly from

zero to the final weight.

– Significant increase in the amount of testing required.

21

Backpressure vs Soot Load Engine & DPG

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35

Sootload (g)

Pre

ssur

e dr

op a

t 300

m³/

hr (

mba

r)

NEDC Soot (3g/hr)

Accelerated Steady State Soot (10g/hr)

Rural Drivecycle Soot (6g/hr)

DPG Soot (10g/hr)

Empty

Coated DPF DPG Soot (10g/hr)

All cycles produce effectively identical backpressureDPG also the same, except for possible slight increase at very high loads

22

Conclusions

� Significant effects on backpressure measurement noted in this work:

– Relaxation of soot at high flow rates

– Permanent reduction in backpressure by engine cold start

� With these effects avoided, all engine cycles produced very similar backpressure vs soot load.

� DPG soot also behaves the same as engine soot.� Inconsistent with earlier experience

– Previous tests did not carefully avoid effects above

– Increased variability in engine rather than DPG tests

– Different behaviour of different engines.

23

Further Work

� There is scope for further work:

– Variation in soot behaviour between different engines.

– Effect of different filter types (catalysed, materials)

– Investigation of effects at very high loads

– Comparison of regeneration behaviour of engine & DPG soot – ongoing.

24

Acknowledgements

Thanks to all the coauthors who did more of this work than me, and also Ray Brand and Jason Sumner who did most of the testing.