# Medium-Energy Synthesis Gases from Waste as an Energy Source for an Internal Combustion Engine
## 4 Experimental Results
### Internal Parameters of Combustion Engine  
Figures 5 and 6 show the mean indicated pressure (IMEP) profiles as the function of the crankshaft rotation angle at which 50% of the fuel is burned. The IMEP profile for each fuel was created from a set of measurements at different spark advance angles, ranging from the smallest spark advance, ensuring continuous engine operation up to 40 \({}^{\circ}\)CA BTDC. For each operating mode, 195 consecutive cycles were evaluated. The highest average  
Figure 4: Course of brake torque M\({}_{\text{t}}\) and hourly fuel consumption M\({}_{\text{fuel}}\) in the engine speed characteristics for methane and synthesis gases at full load, stoichiometric mixture, and optimal angle of advance. Figure 3: Course of brake torque M\({}_{\text{t}}\) and hourly fuel consumption M\({}_{\text{fuel}}\) in the engine speed characteristics for methane and synthesis gases at full load, stoichiometric mixture, and optimal angle of advance. IMEP value (0.965 MPa) was reached when operating on methane. At this IMEP value, the angle, at which 50% fuel is burned, was 8.6 \({}^{\circ}\)CA ATDC. The optimum spark advance angle for methane combustion was 26 \({}^{\circ}\)CA BTDC. Out of the synthesis gases, the highest IMEP value (0.863 MPa) was reached by the gas marked SG10 (angle \(\alpha_{\rm 50 MFB}\) has a value of approx. 7.5 \({}^{\circ}\)CA ATDC). The lowest value of IMEP (0.702 MPa) occurred when burning the gas with the designation SG1 and at reaching the angle when 50% of the fuel is burned approx. at 9.1 \({}^{\circ}\)CA ATDC. The variance of the individual IMEP values, as can be seen in Figures 5 and 6, is characterized by the coefficient of variation (COV) of the mean indicated pressure. For the optimum spark advance angle, this value for methane combustion was 0.58%. During the operation of the combustion engine on synthesis gases, the coefficient of variation ranged from 1.01% for synthesis gas SG10 to 2.04% for synthesis gas SG12. This phenomenon is caused by the high proportion of hydrogen (40% vol.) in the mixture and, at the same time, a low proportion of methane (10% vol.) in SG12 gas. The following developed p-\(\alpha\) diagrams (Figures 7 and 8) show the average pressure profiles p in the cylinder during compression and expansion as a function of the crankshaft angle \(\alpha\), for synthesis gases and methane. The pressure curves are plotted at the optimum spark advance angles (maximum IMEP achieved) for each fuel. When operating on methane, the highest pressure value (6.04 MPa) was reached at the angle 12.8 \({}^{\circ}\)CA ATDC. Out of the synthesis gases, during operation with the optimum spark advance angle, the highest pressure (5.98 MPa) was reached for SG5 synthesis gas. The lowest value for maximum pressure (4.77 MPa) was measured in operation on SG8. From the comparison of the coefficient of variation of the maximum pressure, the highest value (8.9%) was for the synthesis gas SG11. On the contrary, the lowest value (2.7%) was for SG5 fuel, which contained the highest proportion of hydrogen (50% vol.) out of the studied gases. Further, SG2 gas, which in its base has 40% vol. of hydrogen, had a relatively low value of the coefficient of maximum pressure variation (3.2%). The reference fuel methane had the maximum coefficient of variation for pressure (6.8%). In general, it can be stated that by increasing the percentage of hydrogen in the synthesis gases, the value of the coefficient of variation decreases. Figure 5: The course of the mean indicated pressure (IMEP) as a function of the angle (\(\alpha_{\rm 50\%\times\rm{MFB}}\)) of the crankshaft rotation when 50% by mass of the fuel is burned when operating on methane and synthesis gases. Conditions: 1500 L/min, full load, stoichiometric mixture. The value of the optimum spark advance angle ranged from 12 \({}^{\circ}\)CA BTDC for SG5 (high hydrogen content 50% vol., which has a high burning rate) to 34 \({}^{\circ}\)CA BTDC for SG3, because of a high inert gas content (60% vol. ), which slows down the burning rate.