Multi-Instrument Comparison of Exhaust Species from a GDI Engine

Jason  Gaudet, University of Michigan

Gasoline engine exhaust is known to contain a large number of hydrocarbon species, primarily unburned and partially-reacted fuel, which together amount to hundreds of individual chemicals. For environmental certification and many other purposes, these species are often grouped together as a total hydrocarbon (THC), non-methane hydrocarbon (NMHC), or non-methane organic gases (NMOG). The development of catalytic aftertreatment systems and many other applications require a more detailed survey of the engine-out hydrocarbon species. Depending on the required degree of speciation, detection limit, and response time various instruments may be selected to identify and quantify hydrocarbons.
This paper compares steady-state hydrocarbon concentration measurements from four commonly used instruments: a Flame Ionization Detector (FID) installed in a traditional emissions bench, a fast response FID, a Fourier Transform Infrared Detector (FTIR), and a gas chromatograph (GC-FID). The source of the hydrocarbons is a 2.0L turbocharged GDI engine that was operated on an engine dynamometer at moderate load while varying λ from 0.9 to 1.1.
Total hydrocarbon measurement of the FID, Fast FID, FTIR, and GC-FID demonstrated a range as large as 1451-2105 ppmC1 at the rich condition and as small as 893-1185 ppmC1 at the lean condition. The trend was FTIR < Fast FID < FID << GC at rich and stoichiometric conditions and Fast FID < FID = FTIR < GC at lean conditions, although in all cases the Fast FID, FID, and FTIR values were within 155 ppmC1 of each other. In this work, the types of species formed at these conditions and their varying sensitivity to different detection methods are used to explain this variability in hydrocarbon measurement.