Fuel Accounting Analysis during Cranking and Startup using Simultaneous In-Cylinder and Exhaust Fast FID and NDIR Detectors 2008-01-1309
Optimization of in-cylinder air-fuel mixture preparation in Port Fuel Injected (PFI) engines during all phases of operation is critical for maximizing engine performance while minimizing harmful emissions. In this study, a Cooperative Fuels Research (CFR) gasoline engine is used to evaluate torque and measure in-cylinder and exhaust CO, CO2 and unburned hydrocarbons under various fueling and spark conditions during crank and startup phases. Fast Flame Ionization Detectors (FFID) and Non-Dispersive Infra-Red (NDIR) fast CO and CO2 detectors are used as the principle diagnostics. Additionally, detailed cycle resolved fuel accounting is performed to elucidate the fuel vaporization process from injection to exhaust. The majority of liquid fuel accumulation in the engine puddles occurs within 3 engine cycles after cranking begins. Post combustion UHCs were seen to reach levels of 40-80% of pre-combustion UHC values. Also, 12-25% of these post combustion UHCs failed to oxidize and were detected in the exhaust. Retarded spark timing has a modest effect on reducing exhaust UHC levels. Torque is found to be relatively insensitive to fueling within 5% of baseline-stoichiometric thus providing the engine developer adequate fueling flexibility to control emissions without significantly affecting performance.