# Effects of Propanol on the Performance and Emissions of a Dual-Fuel Industrial Diesel Engine
## 3 Results and Discussion
### Combustion Characteristics  
Combustion in a dual-fuel engine differs from that in a conventional single fuel engine. In a conventional compression-ignition engine, the flame front forms around the jet of injected fuel. The successively formed fuel-air mixture is burned, and the intensity of this combustion is determined by the physical and chemical side of this complex process. In a dual-fuel engine, a stream of fuel is injected directly into a combustion chamber filled with a mixture of another fuel and air. The flame front may also spread towards areas filled with a homogeneous combustible mixture. Figure 3 shows the pressure courses and the corresponding heat release rates for the analyzed energy shares of propanol. As with most PFI powered engines, the vaporization of fuel during the intake stroke and compression reduces the charge pressure before ignition. Lower pressure also means a lower temperature value, which especially affects the initial combustion phase. Along with  
Figure 3: In-cylinder pressure (p) and heat release rate (HRR) characteristics for dual-fuel engine fueled by diesel and propanol with alcohol content from 0 to 65%. Figure 2: Mass of propanol and diesel fuel (**a**) and mass of carbon, hydrogen, and oxygen (**b**) in a dose of fuel supplied for one cycle of engine. the increase in the energy share of propanol, its volume share increases even more, due to the lower LHV value compared to diesel, and this increases the cooling effect of the fresh charge. Along with the increase in the propanol share, up to its 50% share, the maximum pressure value (p\({}_{\rm max}\)) increased in relation to the value obtained for the reference fuel. The greatest difference in p\({}_{\rm max}\) was obtained for 30% propanol content, and it was 0.3 MPa. The propanol fraction shifted the p\({}_{\rm max}\) value to later CA values after TDC. The maximum acceptable 65% propanol content caused a drop in the p\({}_{\rm max}\) value to a value slightly lower than that obtained for the diesel engine. When analyzing the heat release rate, it was found that up to 30% propanol share, there was a significant increase in the kinetic combustion phase; for 15% propanol the HRR increased by over 30 J/deg compared to diesel fuel supply. A different trace of combustion was noticed for the proportion from 50% of propanol, where two characteristic peaks are visible on the HRR curve. It can be stated here that the combustion process takes place in two stages. The second stage of combustion takes place clearly later than the first. Figure 4 shows the courses of the peak pressure rise (PPR) for the analyzed cases. For compression-ignition piston engines, the limit value of PPR is 1 MPa/deg, which is accompanied by the so-called hard work of the engine [32]. The highest recorded increase in PPR was obtained for the 15% proportion of propanol and was higher by 0.25 MPa/deg, in relation to the engine fueled with the reference fuel. From 50% of propanol share, the maximum PPR value did not exceed the value obtained for the engine fueled with diesel. The evaluation of the combustion process was carried out based on the analysis of the heat release. The following combustion stages are assessed: the ignition delay time (ID), the angle of 50% heat release (CA50), and the duration of combustion (CD) (Figure 5). The ignition delay time is defined as the period from the start of the fuel injection to the release of 10% of the heat. The value of the ignition delay depends on the chemical properties of the fuel (the so-called chemical retardation), such as its propensity for self-ignition, molecular structure, or the heat of vaporization, and on the physical side (the so-called physical retardation), i.e., the parameters of the injected fuel stream, charge turbulence, and turbulence in the combustion chamber of the engine. The ignition delay period must be included in the engine control algorithm for optimal operation. The 50% (CA50) heat release angle is important for optimization reasons and its value should be within 7-10 deg after TDC.