# Medium-Energy Synthesis Gases from Waste as an Energy Source for an Internal Combustion Engine
## 4 Experimental Results
### Internal Parameters of Combustion Engine
The pressure rise rate value for the reference fuel (methane) was 0.225 MPa/1 \({}^{\circ}\)CA. The highest pressure rise rate value (0.249 MPa/1 \({}^{\circ}\)CA) was recorded during the combustion of SG5 gas, which can be attributed to the already mentioned high proportion of hydrogen in the mixture. The lowest value of pressure rise rate (0.144 MPa/1 \({}^{\circ}\)CA) was achieved with SG8 synthesis gas. Figure 6: The course of the mean indicated pressure (IMEP) as a function of the angle of the crankshaft rotation (\(\alpha_{50\%\text{MFB}}\)) when 50% by mass of the fuel is burned when operating on methane and synthesis gases. Conditions: 1500 L/min, full load, stoichiometric mixture. Figure 7: Pressure profile \(\mathbf{p}\) in the cylinder of an internal combustion engine during operation on methane and synthesis gases. Conditions: 1500 L/min, full load, stoichiometric mixture, optimal start of ignition (SOI) angle for each fuel, compression curve is for air. If the dependence of the maximum pressure values on the angle, with 50% by mass of the fuel burned, was plotted, the dependence shown in the following Figures 9 and 10 would be obtained. For each fuel, an analysis of different spark advance regulation characteristics for various angles of spark advance was performed (195 consecutive cycles were analysed for each spark advance), from which a graph was constructed. As can be seen from the graph, the maximum pressure stabilised at about 8.5 MPa and did not significantly change with increasing spark advance values. This is because with increasing SOI angle (e.g., for SG12 at a spark advance angle greater than 35 \({}^{\circ}\)CA BTDC), most of the fuel (90%) burns in time to TDC and at the same time the combustion chamber volume decreases and thus approximately the same maximum pressure in the cylinder is always reached around the TDC. By gradually reducing the spark advance angle, the combustion also shifts behind the TDC, and at the same time as the volume of the combustion chamber volume increases, the maximum pressure in the cylinder begins to change its position behind the TDC and also gradually decreases. At the inflection point of the descending pressure curve (Figures 9 and 10), at the optimum spark advance angle, the best engine performance parameters were always achieved. The dependence of the course of maximum pressure on the angle \(\alpha_{50\%\rm{MFB}}\) had an inverted S-shape. The position of the inflection point for methane had a value of maximum pressure 6.1 MPa at approximately 8.5 \({}^{\circ}\)CA ATDC. The inflection point was located at the point where the combustion engine was operating at optimum spark advance angle (26 \({}^{\circ}\)CA BTDC), thus at the highest IMEP value (0.965 MPa), at which the angle \(\alpha_{50\%\rm{MFB}}\) was just 8.7 \({}^{\circ}\)CA ATDC (Figure 11). The lowest point of the curve of maximum pressure (approximately 7.2 MPa) was when operating on SG5. The inflection point was at the angle of \(\alpha_{50\%\rm{MFB}}\) 5.9 \({}^{\circ}\)CA ATDC, at which the highest IMEP values (0.739 MPa) were achieved. In general, it can be stated that the course of the curve for each synthesis gas had the inflection point at the angle of \(\alpha_{50\%\rm{MFB}}\), at which, at the same time, the highest performance parameters were achieved (Figure 5, Figure 6, Figure 9 and Figure 10). In other words, the inflection point was always located at the point at which the internal combustion engine was running under optimum spark advance angle. Figure 8: Pressure profile p in the cylinder of an internal combustion engine during operation on methane and synthesis gases. Conditions: 1500 L/min, full load, stoichiometric mixture, optimal start of ignition (SOI) angle for each fuel, compression curve is for air. As seen in Figure 10, the burning of SG11 synthesis gas brings about a large variance of the maximum pressure values dependent on the angle \(\alpha_{\rm 500\%,MFB}\).