OBS-TRPM On Board System Transient PM Mass Measurement PEMS-PM Evaluation Program Meeting 13-3-08
PM is a complex, variable mixture of several components Tail Pipe Formation continues in ambient upon dilution with air SO 4 Ash Carbon Nitrate SO 4 Soot SOF HC H 2 O Soot: Carbonaceous Solid (Combustion Generated) SOF: Heavy HC condensed/absorbed on soot (Unburned fuel, Oil, Compounds formed during combustion) SO 4 : (Sulfur from the Fuel and Oil) combined with H2O Nitrate : Formed as by-product from some exhaust aftertreatments Ash : solid particles formed from combustion of oil or additives in fuel
OB Real Time Mass Measurement Technical Difficulties Accuracy Specifically, correlation to the filter based gravimetric measurement principle that is used currently for all engine / vehicle certification Sensitivity Requires higher sensitivity than filter gravimetric principle Laboratory has whole test cycle for PM loading, real time can have as little as 30 seconds of PM mass loading Traceability Calibration method Traceability to a mass standard Repeatability / Reproducibility Short term and long term drift PM Sensitivity to Fuel Composition, After-Treatment, Test Cycle, Ambient Conditions etc PM composition can change with the above, not consistent Rugged and Practical for On Board Use Insensitive to vibration, ambient temperature change, altitude, ambient humidity Size, power consumption, control signals etc
Combination of PFDS and Real Time Detector Filter Gravimetric Method Real time instruments Advantage Conventional Method Gravimetric result Disadvantage Low Sensitivity Batch result Disadvantage Correlation? Traceability? Advantage High sensitivity Real time result
Basic Components for the Combined System A filter based partial flow diluter (proportional control) A cyclone has the cut point at 6.0 µm Dilution and PM sampling at 47 deg C, same as 1065 An diffusion charge sensor (DCS) used as a real-time PM detector TSI OEM of their EAD (Electrical Aerosol Detector) Measure particle length in real-time Integrated cyclone has the cut point at 1.0 µm Pitot tube flow meter and OBS-2200 providing exhaust flow signal for proportional control Assumption that the PM mass being collected on the filter is proportional to the PM length parameter
Schematic For OB-PFDS Module Short transfer tube Mixer 47degC Cyclone Makeup Air MFC Venturi Filter holder Venturi P FO Dilution Air Piezo Valve Potential for multiple filters Accurate Flow Measurement Venturi flow meter has low effect of exhaust composition Fast Flow Control Piezo Valve & FO is applied for dilution air flow control
Layout for the prototype PFDS 47mm Filter holder (47±5 degree C) Heated Enclosure Control Unit Open Exhaust Flow Signal (for proportional dilution control)
Dilution Ratio Verification 0 Difference to reference [%] -1-2 -3-4 0 10 20 30 40 50 Dilution ratio Dilution factor verified using high accuracy flow measurement of net sample flow rate under steady state conditions
Proportional control for FTP cycle Using air flow + fuel flow data 8 7 Sample ratio: 4000:1 Sample Ideal sample y = 0.0003x - 0.0013 8 7 R 2 = 0.9988 Sample flow [slpm] 6 5 4 3 2 Sample flow [slpm] 6 5 4 3 2 Standard error: 0.948% 1 1 0 0 200 400 600 800 1000 1200 Time [s] 0 0 5000 10000 15000 20000 25000 30000 35000 Exhaust flow [slpm] Standard Error = 0.9988 (>0.95 ; ISO-16183) Correlation Coefficient(R 2 ) = 2.93% (<5.0% ; ISO-16183)
Proportional control for FTP cycle Using exhaust flow meter Flow [slpm] 8 7 6 5 4 3 2 Sample flow [slpm] 9 8 7 6 5 4 3 2 y = 0.0003x + 0.0018 R 2 = 0.9964 Standard error: 5.499% Max. delay time: 0.1 s 1 1 0 0 200 400 600 800 1000 1200-1 Time [s] Sample Ideal sample 0-2000 3000 8000 13000 18000 23000 28000 33000-1 Negative exhaust flow obtained from exhaust flow meter Exhaust flow [slpm] Sample flow Linear (Sample flow) Exhaust flow metering system accuracy / characteristics are important factor in the performance of PM Mass measurement
Test Engine Configuration @ SWRI Test Engine Specification Description Specification Model Year Designation Engine Family Power Rating Torque Rating 1998 DDC Series 60 with CRT-DPF 400hp at 1810rpm 1550 lb-ft at 1200rpm CRT-DPF Bypass
Test Configuration @SWRI Sample Probe Test Engine On Board PM Pitot tube & Sample Probe OBS (Gaseous) Primary Dilution Tunnel Analyzers Dilute Exhaust Measurement Secondary Dilution Tunnel CVS F P B EPA 2007 sampling protocol Partial Flow Sampling for PM Measurement Raw Exhaust Gas & Flow Measurement
PM Emission Results
Combination of PFSS and EAD Exhaust Pipe Note : Second stage diluter has proved not to be necessary due to the wide dynamic range of the EAD module Mixer Dilution Air Dilution Air Cyclone FO Mixer EAD Filter P 47degC P 2 nd Stage Diluter Partial Flow Sampling System
Concept for NTE or real time PM mass measurement procedures EAD signal (mm/m3) 50 40 30 20 10 0 NTE-1 NTE-2 NTE-3 NTE-4 NTE-5 Invalid event 0 200 400 600 800 1000 1200 Bypass Bypass Bypass Bypass Bypass Filter Filter Filter Filter Filter PM mass in VALID NTE events = Total PM X Ratio EAD Ratio of PM ( EAD t ) i ( t) n EAD i i = 1 PFDS Total PM
Advantage of the combination method Advantage Total PM measurement over NTE events same as conventional method. Filtering PM in NTE region (with 0 secs averaging) for more than 2 hours should typically load sufficient PM on the filter (depending on the road cycle) EAD has sensitivity for real time measurement of post 2007 PM standard. EAD measures all particles soot, sulfate, volatile particle, etc.
Minimizing the Assumptions Assumptions; Same size distribution, Same density Minimizing factors By using filter gravimetric mass result as reference on each specific engine, this will eliminate assumption errors for engine family, after treatment strategy, etc. By using EAD to gravimetric mass ratio, we will reduce the impact of different PM species on measurement. Method can be adapted for a variety of measurement models (NTE, Moving Work Window etc) Assumed Composition, Density or Size Distribution parameters are not used to calculate mass
Real Time Data : EU Stage 3 vehicle on chassis dynamometer 1800 140 1600 120 1400 100 1200 Length [mm/cm3] 1000 800 80 60 Speed [km/h] 600 40 400 200 20 0 0 0 200 400 600 800 1000 1200 1400 Time [s] Hot 1, L Hot 2, L Hot 3, L Hot 1, S Hot 2, S Hot 3, S
Accumulative particle diameter length v time 3500 140 Particle length [mm/cm3], Exhaust flow [slpm] 3000 2500 2000 1500 1000 NEDC, Hot 1 120 100 80 60 40 Speed [km/h], Fraction of the length [%] 500 20 0 0 200 400 600 800 1000 1200 0 Time [s] Length Speed Fraction of Length
Accumulative particle diameter length v Gravimetric PM Mass 250000 25 Total Length [mm] 200000 150000 20 15 PM mass [mg/km] 100000 Hot 1 Hot 2 Hot 3 Test 10 Length Mass
CE-CERT Trial Installation
Current Status : EPA PM Mass Measurement Allowance Program Three systems supplied to SWRI Systems are undergoing preliminary evaluation Auditing, calibration, simulation Additional systems Under quotation to interested regulatory and technical authorities Participation in the EU PEMS-PM program