Speciated Engine-Out Organic Gas Emissions from a PFI-SI Engine Operating on Ethanol/Gasoline Mixtures

Engine-out HC emissions from a PFI spark ignition engine were measured using a gas chromatograph and a flame ionization detector (FID). Two port fuel injectors were used respectively for ethanol and gasoline so that the delivered fuel was comprised of 0, 25, 50, 75 and 100% (by volume) of ethanol. Tests were run at 1.5, 3.8 and 7.5 bar NIMEP and two speeds (1500 and 2500 rpm). The main species identified with pure gasoline were partial reaction products (e.g. methane and ethyne) and aromatics, whereas with ethanol/gasoline mixtures, substantial amounts of ethanol and acetaldehyde were detected. Indeed, using pure ethanol, 74% of total HC moles were oxygenates. In addition, the molar ratio of ethanol to acetaldehyde was determined to be 5.5 to 1. The amount (as mole fraction of total HC moles) of exhaust aromatics decreased linearly with increasing ethanol in the fuel, while oxygenate species correspondingly increased. These results suggest that the change in ethanol and aromatics exhaust emissions were due to fuel replacement. It was also found that the oxygenate fraction of total hydrocarbons (as ppmC1) depended mostly on the ethanol fuel content, not on engine speed and load. Therefore, a simple FID response correction equation was developed and validated. A FID reading can now be corrected to 90% accuracy when a PFI-SI engine is fuelled with gasohols.