# Medium-Energy Synthesis Gases from Waste as an Energy Source for an Internal Combustion Engine
## 4 Experimental Results
### Internal Parameters of Combustion Engine
The following two graphs (Figures 11 and 12) show the fuel burn-up profiles (MFB) as a function of the crankshaft rotation angle for different synthesis gas compositions compared to methane. The ignition delay (the period between the start of ignition (SOI) and the visible combustion moment (start of combustion SOC)) for methane is around 12.5 \({}^{\circ}\)CA for the optimum spark advance angle. The time between the SOI and the 5% by mass of methane combustion, is approximately 20.4 \({}^{\circ}\)CA. The main combustion period (10-90% MFB) lasts 24.4 \({}^{\circ}\)CA. The total burning period for methane (the period between SOC and end of combustion SOC) is 56 \({}^{\circ}\)CA. Figure 10: The course of the maximum pressure depending on the angle at which 50% mass of methane or synthesis gases is burned. Conditions: 1500 L/min, full load, stoichiometric mixture. Figure 9: The course of the maximum pressure depending on the angle at which 50% of the fuel for methane and synthesis gases is burned. Conditions: 1500 L/min, full load, stoichiometric mixture. Of the synthesis gases, the SG8 synthesis gas has the longest main combustion period (28.9 \({}^{\circ}\)CA). The SG5 synthesis gas has the shortest main combustion period (15.3 \({}^{\circ}\)CA). The reason for this is the already mentioned high proportion of hydrogen in the mixture. The shortest period between the moment of spark ignition and the angle at which 5% of the fuel is burned is the one (7.4 \({}^{\circ}\)CA) pertaining to SG5 synthesis gas and, conversely, the longest period (24.8 \({}^{\circ}\)CA) is the one related to operating on SG3 fuel that  
Figure 11: Course of burning of fuel as dependent on the crankshaft angle for methane and synthesis gases (MFB—Mass Fraction Burned, \(\alpha\)—Crankshaft Rotation Angle, TDC—Top Dead Centre, SOI—Start of Ignition, SOC—Start of Combustion, EOC—End of Combustion) Conditions:1500 L/min, full load, stoichiometric mixture, optimal SOI angle for each fuel. Figure 12: Course of burning of fuel as dependent on the crankshaft angle for methane and synthesis gases (MFB—Mass Fraction Burned, \(\alpha\)—Crankshaft Rotation Angle, TDC—Top Dead Centre, SOI—Start of Ignition, SOC—Start of Combustion, EOC—End of Combustion) Conditions:1500 L/min, full load, stoichiometric mixture, optimum SOI angle for each fuel. is composed of the largest proportion of inert gases (60% vol.) out of the gases analysed. The coefficient of variation of the position angle (COV\({}_{\alpha}\)), at which a given mass fraction of fuel is burned, generally increases with increasing mass proportion of the fuel burned. For methane combustion, the values are as follows: COV\(\alpha_{\rm 10\%\rm{MFB}}=0.36\%\), COV\(\alpha_{\rm 50\%\rm{MFB}}=0.53\%\), COV\(\alpha_{\rm 50\%\rm{MFB}}=0.71\%\). The SG11 synthesis gas has the largest variance of the coefficients of variation during each combustion period, which has the following COV: COV\(\alpha_{\rm 10\%\rm{MFB}}=0.50\%\), COV\(\alpha_{\rm 50\%\rm{MFB}}=0.81\%\), COV\(\alpha_{\rm 90\%\rm{MFB}}=1.24\%\). On the contrary, the highest repeatability of the combustion process has the synthesis gas with the designation SG5, which has the individual coefficients of variation with the following values: COV\(\alpha_{\rm 10\%\rm{MFB}}=0.10\%\), COV\(\alpha_{\rm 50\%\rm{MFB}}=0.19\%\), COV\(\alpha_{\rm 90\%\rm{MFB}}=0.28\%\). These low values for SG5 are caused by high hydrogen content in the fuel mixture. A brief analysis of the pressure rise rate values and the COV values during the gradual burning out of the fuel suggests that synthesis gases with a higher hydrogen content have a more harder engine run, but also a more stable course of their combustion process.