Combustion and Emissions Characteristics of Dual Fuel Premixed Charge Compression Ignition with Direct Injection of Synthetic FT Kerosene Produced from Natural Gas and Port Fuel Injection of n-Butanol 2016-01-0787

In this study, Premixed Charge Compression Ignition (PCCI) was investigated with alternative fuels, S8 and n-butanol. The S8 fuel is a Fischer Tropsch (FT) synthetic paraffinic kerosene (SPK) produced from natural gas. PCCI was achieved with a dual-fuel combustion incorporating 65% (by mass) port fuel injection (PFI) of n-butanol and 35% (by mass) direct injection (DI) of S8 with 35% exhaust gas recirculation. The experiments were conducted at 1500 rpm and varied loads of 1-5 bar brake mean effective pressure (BMEP). The PCCI tests were compared to an ultra-low sulfur diesel no. 2 (ULSD#2) baseline in order to determine how the alternative fuels effects combustion, emissions, and efficiencies. At 3 and 5 bar BMEP, the heat release in the PCCI mode exhibited two regions of high temperature heat release, one occurring near top dead center (TDC) and corresponds to the ignition of S8 (CN 62), and a second stage occurring ATDC from n-butanol combustion (CN 28). At 1 bar BMEP, S8 PCCI displayed a single high temperature heat release with an extended diffusion burn phase.

Each PCCI experiment exhibited a drastic decrease in NOx emissions up to 95%. However, at 5 bar BMEP with EGR, the smoke limit was reached and as a result, the soot increased by over 500% and that can be attributed to the near stoichiometric combustion. At the lower loads, a simultaneous reduction in soot and NOx was observed for the PCCI case when compared to ULSD#2. At 3 bar BMEP, the soot decreased by 18% and NOx decreased by 92%. At 1 bar BMEP, soot decreased by 46% and NO_x by 82%. A spike in carbon monoxide and unburned hydrocarbon emissions was observed for all PCCI cases. This increase can be attributed to wall wetting and crevice phenomenon coupled with cold EGR during the port fuel injection of n-butanol.

The alternative dual-fuels used in this study proved to be capable of achieving PCCI combustion at lower engine loads. Future studies include the use of a supercharger to increase the intake pressure and restore the relative air/fuel ratio and mitigate the soot emissions at higher loads with high EGR.