Comparing Unburned Fuel Emission from a Pre-chamber Engine Operating on Alcohol Fuels using FID and FTIR Analyzers

Typical automotive emission testing systems usually employ Flame Ionization Detection (FID) analyzers to measure unburned fuel species in the exhaust, but the technique is not suitable for engines operating on alcohol fuels. The FID method is not sensitive to measuring unburned alcohol fuels due to the presence of oxygen bonds in the fuel molecule. Other techniques, such as Fourier Transform Infrared (FTIR), can provide accurate unburned fuel measurements with alcohol fuel. However, these techniques are expensive and are less accessible compared to FID analyzers. In this study, the unburned fuel emissions from the engine exhaust were measured simultaneously with FID and FTIR analyzers, with the engine operating on pure alcohols, which are methanol, ethanol, and n-butanol. While most previous work focuses on stoichiometric air-fuel mixtures, a wide range of lean operating conditions between global-λ 1.6 to 2.8 will be tested in this study. Such ultra-lean operation was achievable thanks to the narrow-throat pre-chamber combustion concept with the pre-chamber fueled with methane. The unburned fuel measurements from the two analyzers are compared, and correction factors for each fuel are identified to rectify the FID unburned fuel measurements based on the results provided by the FTIR.