Partially Premixed Combustion Study between n-Butanol and Ethanol for the Reduction of NOx and Nonrenewable Carbon Emissions

A comprehensive study was conducted in an experimental engine, on the combustion/emissions characteristics of Partially Premixed Combustion (PPC) with either n-butanol or ethanol at either 30% or 40% Port Fuel Injection (PFI) by mass, and Conventional Diesel Combustion (CDC) was used to compare the performance of each PPC test conducted.

It was found in the combustion analysis that PPC with either n-butanol or ethanol had several advantageous combustion characteristics compared to CDC, such as Peak Pressure Rise Rate (PPRR, bar/CAD), Ringing Intensity (RI, MW/m²), and Apparent Heat Release Rate (AHRR). As the load was increased, Low Temperature Heat Release (LTHR) and Negative Temperature Coefficient (NTC) regions were extended for PPC with n-butanol when comparing PPC with ethanol. Although PPC consisted of 30% and 40% low-reactivity PFI fuel by mass, combustion pressure was observed to have similar peak values with CDC experiments. It was found that as the PFI percentage (%) increased, peak pressure increased for PPC with either n-butanol or ethanol and only PPC 40BU reached a peak pressure greater than CDC at 67.8 bar.

It was found that the PPRR and RI for PPC with ethanol were higher than PPC with n-butanol at both 30% and 40% PFI by mass. The PPRR values at a load of 4 bar and 5 bar Indicated Mean Effective Pressure (IMEP) for n-butanol at a 30% PFI are 2.3 bar/CAD and 3.4 bar/CAD, respectively, and the values with 40% PFI are 2.9 bar/CAD and 2.8 bar/CAD, respectively. The PPRR values at a load of 4 bar and 5 bar IMEP for ethanol at a 30% PFI are 2.6 bar/CAD and 5.0 bar/CAD, respectively, and the values with 40% PFI are 4.7 bar/CAD and 5.5 bar/CAD, respectively.

The RI values at a load of 4 bar and 5 bar IMEP for n-butanol at a 30% PFI are 0.15 MW/m² and 0.39 MW/m², respectively, where the RI values at 40% PFI of n-butanol are 0.39 MW/m² and 0.15 MW/m², respectively. The RI values at a load of 4 bar and 5 bar IMEP for ethanol at a 30% PFI are 0.35 MW/m² and 0.69 MW/m², respectively, whereas the RI values at 40% PFI of n-butanol are 0.75 MW/m² and 0.64 MW/m², respectively.

In PPC mode, PPRR and RI remained lower than in CDC mode. At 4 bar and 5 bar IMEP, CDC has values of 1.48 MW/m² and 1.32 MW/m² for RI, respectively. The CDC values for PPRR for CDC in 4 bar and 5 bar are 5.79 bar/CAD and 6.76 bar/CAD, respectively. PPC reduced Nitrogen Oxides (NOx) and soot emissions significantly compared to CDC. The 40BU resulted in the greatest NOx emissions reduction of 62.06% (−9.31 g/kWh) at 5 bar IMEP compared to CDC, respectively. The 40ET achieved the lowest soot emissions with reductions of 84.71% (−1.48 g/kWh) at 5 bar IMEP compared to CDC. Additionally, the nonrenewable carbon was reduced at a load of 5 bar IMEP by 15.3% for PPC 30ET and 38.8% for PPC 40BU. As is typical with Low Temperature Combustion (LTC) methods such as PPC, the reduction of NOx and soot emissions come at the cost of Unburnt Hydrocarbon (UHC) emissions and Carbon Monoxide (CO) emissions. In this study, it was observed that PPC had higher emission outputs of UHC and CO than CDC.