Single vs Double Stage Partial Flow Dilution System: Automobile PM Emission Measurement 2020-01-0366
The US Code of Federal Regulations (CFR) Title 40 Part 1065 and 1066 require gravimetric determination of automobile Particulate Matter (PM) collected onto filter media from the diluted exhaust. PM is traditionally collected under simulated driving conditions in a laboratory from a full flow Constant Volume Sampler (CVS) system, where the total engine exhaust is diluted by HEPA filtered air. This conventional sampling and measurement practice is facing challenges in accurately quantifying PM at the upcoming 2025-2028 CARB LEVIII 1 mg/mi PM emissions standards. On the other hand, sampling a large amount of PM emitted from large size high power engines introduces additional challenges. Applying flow weighting, adjusting the Dilution Ratio (DR) and Filter Face Velocity (FFV) are proposed options to overcome these challenges. The Partial Flow Dilution System (PFDS) technique has been recognized as a viable alternative to the CVS method, to meet the wide range DR and FFV requirements for PM determination from both Light-Duty Vehicles (LDV) and Heavy-Duty Engines (HDE) [4, 5, 6, 7, 8].
In this study, performance of a PFDS for PM measurement with Single Dilution (SD) and Double Dilution (DD) configurations against conventional CVS sampling was investigated. Tests were run on a Cummins heavy-duty 8.9L engine with maximum rated power of 380 HP in an engine test cell. The engine aftertreatment system is comprised of a combined Diesel Oxidation Catalyst (DOC) and Selective Catalyst Reduction (SCR). The reference data, also referred to as historical data, was generated in a test cell using the CVS method. PM measurements were made over the US Non-road Transient Cycle (NRTC) and Ramped Modal Cycle (RMC). The brake-specific particulate matter (BSPM) was calculated using the raw chemical balance utilizing intake airflow measurements and the measurement of gases in the exhaust.
The PFDS with single and double tunnel configuration showed good repeatability with a COV of <6% when compared against the historical data which has a COV of <8%. The PFDS with single and double dilution met all the global regulatory requirements with the correlation coefficient of 1.005 and the coefficient of determination (R2) greater than 0.98.