# Medium-Energy Synthesis Gases from Waste as an Energy Source for an Internal Combustion Engine
## 6 Conclusions  
The basic knowledge about the influence of medium-energy synthesis gases on the parameters of the internal combustion engine in comparison with the operation on methane at the operating speed of the internal combustion engine of 1500 L/min is briefly summarized here:  
1. The optimum spark advance angle ranged from 12 \({}^{\circ}\)CA BTDC for SG5 gas, as the gas has a high hydrogen content in the mixture (Table 2) that burns the fastest, to 34 \({}^{\circ}\)CA BTDC for SG3 that in turn has the highest inert gas content that prevents the development of chemical reactions. 2. The torque value for the reference fuel (methane) was 43.2 N m; for the other synthesis gases examined (Figures 3, 4 and 13), this value was lower (from 32.3 N m for SG1 to 39.2 N m for SG10), relative to the fact that the volumetric heating value of stoichiometric mixture was lower for all synthesis gases compared to methane. The linear trend line (red straight line in Figure 13), drawn across the measured values, shows that the deviations of the measured data from the trend line in Figure 13 are for most of the points in the range up to \(\pm\)5% (except for SG3, SG5 and SG2). 3. The hourly consumption of synthesis gases (Figures 3, 4 and 14) was 3.7 to 5.2 times higher than in operation on methane (1.56 kg/h), because in operation on synthesis gases, a small amount of air is consumed to form a stoichiometric mixture (from 2.23 kg/kg for SG2 up to 3.55 kg/kg for SG11, A/F ratio in Table 2) compared to methane (17.12 kg/kg). The trend in decreasing hourly fuel consumption with increasing values of the mass LHV parameter is virtually linear (red straight line in Figure 14). 4. Out of the synthesis gases, the highest value of maximum pressure (5.98 MPa) was reached by synthesis gas SG5 (Figure 7) and, conversely, the lowest value of maximum pressure (4.77 MPa) at optimum spark advance angle was achieved by burning SG8 synthesis gas (Figure 8). The coefficient of maximum pressure variation had the lowest value (3.2%) when operating on SG2 synthesis gas and, conversely, the highest value (8.9%) was when SG11 gas was burned. 5. The lowest value of the maximum of pressure rise rate was achieved when operating on SG11 synthesis gas (0.155 MPa/1 \({}^{\circ}\)CA), which contained 45% vol. of internal gases and at the same time approximately the same share of methane (20% vol.) and hydrogen (25% vol.). The synthesis gases, which contained mainly large amounts of hydrogen (35% vol. in SG4 and 50% vol. in SG5), also reached the highest values of the pressure rise rate (0.2518 MPa/1 \({}^{\circ}\)CA or 0.2493 MPa/1 \({}^{\circ}\)CA) of the engine. 6. The course of fuel combustion (Figures 11 and 12) shows that the SG8 synthesis gas has the longest main combustion time (10-90% MFB) and represents a value of 28.9 \({}^{\circ}\)CA. The shortest combustion time (15.3 \({}^{\circ}\)CA) is for the SG5 synthesis gas combustion, which relates to the highest proportion of hydrogen in the mixture (50% vol.). The angle at which half of the fuel was burned ranged from 5.9 \({}^{\circ}\)CA ATDC for SG5 to 11.3 \({}^{\circ}\)CA ATDC for SG8. The combustion onset time (SOI-5% MFB) was the shortest (7.4 \({}^{\circ}\)CA) for SG5 synthesis gas with a high hydrogen content and, conversely, the longest (24.8 \({}^{\circ}\)CA) for SG3 synthesis gas with the highest inert gas content. The coefficients of variation of the positions during the gradual burning out of the fuel were the lowest for the synthesis gas SG5 and the highest for the synthesis gas SG11. If we briefly summarize the performed analyses of the influence of hydrogen in synthesis gases on the combustion process in the internal combustion engine, then we can state the following findings. The hydrogen content in SGs is one of the main causes of their different behaviour during their combustion in the engine.