Heavy-Duty Diesel (HDD) engines' particulate matter (PM) emissions are most often measured quantitatively by weighing filters that collect diluted exhaust samples pre- and post-test. PM sampling systems that dilute exhaust gas and collect PM samples have different effects on measured PM data. Those effects usually contribute to inter-laboratory variance. The U.S. Environmental Protection Agency (EPA)'s 2007 PM emission measurement regulations for the test of HDD engines should reduce variability, but must also cope with PM mass that is an order of magnitude lower than legacy engine testing.
To support the design of a 2007 US standard HDD PM emission sampling system, a parametric study based on a systematic Simulink® model was performed. This model acted as an auxiliary design tool when setting up a new 2007 HDD PM emission sampling system in a heavy-duty test cell at West Virginia University (WVU). It was also designed to provide assistance in post-test data processing.
Modeling of gas chemical composition, mass, and heat transfer, as well as modeling of the primary and the secondary tunnel, were addressed. The chemical composition of exhaust from an HDD engine burning diesel fuel (C12.5H22.2) was compared against that of dry air. Gas chemical composition was modeled to change as a result of engine running condition and exhaust dilution. Temperature responses of the exhaust gas through systems with different geometries and test conditions were analyzed with actual transient Federal Test Procedure (FTP) data for a Cummins ISM370 HDD engine. Geometry parameters that were varied included diameters, lengths and wall thicknesses of the primary and the secondary tunnels. Variable test conditions included engine running condition, primary flow rate, secondary flow rate, and the preset wall temperature of the secondary tunnel. The model monitored the tunnel flow and wall temperature, the PM filter face temperature, and the system's estimated theoretical PM diffusion losses. The study's results showed how geometries and test conditions affect the filter face temperature. Under different test conditions, PM sampling systems with certain geometries may or may not meet 2007 HDD PM emission measurement regulations. A major objective of this parametric study was to determine what geometries and test conditions would keep the filter face temperature between 42 %C and 52 %C for a typical on-road engine test.