Partially premixed compression ignition of fischer tropsch synthetic paraffinic kerosene (S8) with PFI of N-butanol

The combustion in an experimental medium duty direct injected engine was investigated in a dual mode process known as partially premixed compression ignition (PPCI). Both a common rail fuel injection system and port fuel injection (PFI) system have been custom designed and developed for the experimental single cylinder engine in order to research the combustion and emissions characteristics of Fischer Tropsch synthetic paraffinic kerosene (S8) with PFI of n-butanol in a low temperature combustion mode (LTC). Baseline results in single fuel (ULSD) combustion were compared to dual fuel strategies coupling both the low and high reactivity fuels. The low reactivity fuel, n-butanol, was port fuel injected in the intake manifold at a constant 30% fuel mass and direct injection of a high reactivity fuel initiated the combustion. The high reactivity fuels are ULSD and a gas to liquid fuel (GTL/S8). Research has been conducted at a constant speed of 1500 RPM at swept experimental engine loads from 3.8 bar to 5.8 bar indicated mean effective pressure (IMEP). Boost pressure and exhaust gas recirculation (EGR) were added at constant levels of 3 psi and 30% respectively. Dual fuel combustion with GTL advanced ignition timing due to the high auto ignition quality and volatility of the fuel. Low temperature heat release (LTHR) was also experienced for each dual-fuel injection strategy prior to the injection of the high reactivity fuel. Peak in-cylinder gas temperatures were similar for each fueling strategy, maintaining peak temperatures below 1400°C. Combustion duration increased slightly in ULSD-PPCI compared to single fuel combustion due to the low reactivity of n-butanol and was further extended with GTL-PPCI from early ignition timing and less premixing. The effect of the combustion duration and ignition delay increased soot levels for dual fuel GTL compared to dual fuel ULSD at 5.8 bar IMEP where the combustion duration is the longest. NOx levels were lowest for GTL-PPCI at each load, with up to a 70% reduction compared to ULSD-PPCI. Combustion efficiencies were also reduced for dual fuel combustion, however the atomization quality of GTL compared to ULSD increased combustion efficiency to reach that of single fuel combustion at 5.8 bar IMEP.