Crank Angle and Space Resolved, Speciated Sampling of Engine-out Exhaust Hydrocarbons

In order to understand how unburned hydrocarbons emerge from SI engines and, in particular, how nonfuel hydrocarbons are formed and oxidized, a new gas sampling technique has been developed. A sampling unit, based on a combination of techniques used in the Fast Flame Ionization Detector (FFID) and wall-mounted sampling valves, was designed and built to capture a sample of exhaust gas during a specific period of the exhaust process and from a specific location within the exhaust port. The sampling unit consists of a transfer tube with one end at a specifiable location in the port and the other connected to a three-way valve that leads, on one side, to a FFID and, on the other, to a vacuum chamber with a highspeed solenoid valve. Exhaust gas, drawn by the pressure drop into the vacuum chamber, impinges on the face of the solenoid valve and flows radially outward. Once per cycle during a specified crank angle interval, the valve opens and traps exhaust gas in a storage unit, from which gas chromatography (GC) measurements are made. The solenoid valve's actuation time can be adjusted to allow resolution of a crank angle interval as small as 15CA. Total HC concentrations measured by the FFID by the sampling unit are in good agreement, while the sampling unit goes one step further than the FFID by providing species concentrations. Spatial resolution of the exhaust port reveals that individual plugs of gas are well mixed; that is, there are not significant concentration gradients across the radius of the port. Moreover, spatial resolution reveals that significant oxidation occurs as the flow progresses along the length of the port. Specifically, 36 to 50% of the total HCs are oxidized in transit through the port, while non-fuel HC concentrations drop only 17 to 23% indicating significant amounts of partial oxidation. Crank angle resolution of speciated concentration trends shows that, as the exhaust process progresses, the ratio of non-fuel HC mass to fuel mass in the exhaust increases, which is consistent with increased quenching of oxidation reactions due to rapidly decreasing temperatures. Comparison with previous research suggests that the new sampling unit is fully capable of providing species concentration information as a function of engine speed, load, and air-fuel ratio at specific crank angles or on a mass weighted basis. Thesis Advisor: Professor Simone Hochgreb Associate Professor of Mechanical Engineering