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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.

Seven biofuel-diesel fuel configurations were tested in a single-cylinder research diesel CFR engine that allowed variable injection timing. These seven configurations included three biodiesel-diesel blends (20% and 100%); two ethanol-diesel blends (15% and 20%), and two cases in which ethanol was injected into the intake air flow (20% and 33%). Combustion characteristics, NOx emissions, and soot emissions were compared with diesel operation across a range of injection timings. The effect of fuel compressibility affected the timing of injection, with biodiesel-diesel blends having advanced injection and ethanol-diesel blends having delayed injection. Biodiesel-diesel blends showed reduced ignition delay with only modest changes in combustion duration, while ethanol-diesel mixtures showed longer ignition delay but much shorter combustion duration and earlier phasing.

Fast emissions analysis, soot analysis, and pressure sensing is utilized to examine the first few seconds before, and after startup in a single-cylinder CFR diesel engine. The equivalence ratio, compression ratio, and injection timing are varied. The data show that UHC and CO emissions are highest at the highest and lowest fueling conditions, while NOx emissions peaked at intermediate fueling conditions. Leaner operating conditions show delayed starting but reduced ignition delay. Oil vapor causes soot emissions prior to first combustion, and soot particle size shifts higher during the first few seconds after combustion begins. Injection timing has little effect except at the leanest equivalence ratios, where a retarded injection timing increases the delay until a successful combustion event. At lower compression ratios, large IMEP oscillations occurred during startup. The data suggest possible strategies to optimize diesel startup.

Fischer-Tropsch (FT) synthetic fuels have been shown to produce lower soot and oxides of nitrogen emissions than petroleum-based diesel #2 (D2) in previous studies. This performance is frequently attributed to the very low aromatic content as well as essentially zero sulfur content. The objective of this empirical study was to investigate the high engine load regime using a military FT and D2 fuel in a CFR diesel engine at fueling levels approaching stoichiometric. A testing matrix comprised of various injection advance set points, fueling amounts (e.g. load) above 6 bar gross indicated mean effective pressure (IMEPg), and three different compression ratios (CR) was pursued. The results show that oxides of nitrogen emissions are always equal to or lower running FT compared to diesel. This result is attributed to the higher cetane number of FT leading to lower peak in-cylinder pressures as compared to D2.