## 2 Materials and Methods  
### Experimental Setup  
The simplified schematic diagram of the experimental setup is shown in Figure 1. A common-rail single-cylinder direct injection diesel engine, four-stroke, water-cooled, with 84 mm \(\times\) 90 mm of the cylinder bore and stroke respectively, connecting rod length of 160 mm, 16:1 of compression ratio, and a displacement of 499 cm\({}^{3}\) was used for this research. The fuel injection pressure could be set in the interval 500-1500 bar and the maximum indicated mean effective pressure (IMEP) could go up to 7 bar. An electric dynamometer was coupled to the engine, enabling the braking and the motoring of the engine. The fuels were tested with the engine kept at a steady-state condition of 2 bar IMEP, representing around 30% of the maximum load, and an engine speed of 1500 rpm. Before the test, the engine was warmed up to minimize the effects of emission variation during the engine cold-start. The IMEP was continuously monitored in order to keep a constant engine IMEP condition as the baseline fuel. All fuels were injected into the combustion chamber at 550 bar and two injection stages, divided into the pilot (15\({}^{\circ}\) before the top dead center, bTDC) and main (5\({}^{\circ}\) bTDC) injection. The pilot injection duration was kept constant (0.150 ms), but the main injection was adjusted during the change of fuels. Therefore, during shifting fuels, an adjustment of the main injection duration was necessary (0.499, 0.529, and 0.546 ms, respectively for Diesel, E15B35D50, and E15B35 FTD50). Shell Global Solutions UK provided the ultra-low sulfur diesel fuel (<10 ppm sulfur) and the Fischer-Tropsch diesel. The ethanol was supplied by Fisher Scientific Company with a purity of 99.8%. The biodiesel was purchased from Eggolas Ltd. (Kidderminster, UK) and the composition consisted of approximately 90% rapeseed methyl ester and 10% (\(v/v\)) palm oil methyl ester. The blends were prepared at the University of Birmingham and the physical and chemical properties of all fuels were calculated or obtained from the respective suppliers or publications [35; 36], as shown in Table 2. Particularly, the diesel fuel that was used as a reference in this work was selected without any biodiesel in the composition (no oxygen content). The blends were prepared by mixing ethanol and biodiesel in the same volumetric proportion (15% of ethanol and 35% of biodiesel) with 50% F-T diesel (E15B35 FTD50) and also with 50% diesel fuel (E15B35 DD50). Moreover, both fuel blends had the same oxygen content, and hence the influence of the oxygen when F-T diesel was blended with ethanol and biodiesel could be investigated. Figure 1: Schematic diagram of the experimental setup. The O\({}_{2}\) emissions were measured using Testo 340 gas analyzer while the gaseous emissions of CO, CO\({}_{2}\), NOx (NO and NO\({}_{2}\)), nitrous oxide (N\({}_{2}\)O), ammonia (NH\({}_{3}\)), formaldehyde (CH\({}_{2}\)O), total HC (sum of heavy and other unburned hydrocarbons), and individual light hydrocarbons species including methane (CH\({}_{4}\)), ethane (C\({}_{2}\)H\({}_{6}\)), acetylene (C\({}_{2}\)H\({}_{2}\)), ethylene (C\({}_{2}\)H\({}_{4}\)), propane (C\({}_{3}\)H\({}_{8}\)), and propylene (C\({}_{3}\)H\({}_{6}\)) were measured using an MKS MultiGas 2030 based on FTIR (Fourier Transform Infrared Spectroscopy) technique. For the calculation of the total hydrocarbons species, the corresponding flame ionization detector (FID) response factors were contained from the FTIR raw file and implemented for each individual HC reading as follows: THC = (1.1 \(\times\) methane) + (2.4 \(\times\) acetylene) + (1.9 \(\times\) ethylene) + (2 \(\times\) ethane) + (2.85 \(\times\) propylene) + (1.35 \(\times\) heavy HC) [39]. The exhaust gas sampling system of the emission analyzer was maintained at a constant temperature of 191 \({}^{\circ}\)C by using a heated sampling line to prevent moisture and condensation during the sampling.