# Medium-Energy Synthesis Gases from Waste as an Energy Source for an Internal Combustion Engine
## 5 Short Discussion  
Synthesis gases are one of the sources of energy from renewable sources and currently they appear to be an energy source for driving internal combustion engines designed for stationary applications (cogeneration units). This type of fuel contributes to reducing environmental burden and gives prevalence to carbon-neutral fuels. The evaluation of output power parameters has shown that the most important parameter is the volumetric heating value of stoichiometric mixture of fuel and air. In the second place, of course, the actual process of burning the mixture has to be taken into consideration, i.e., the rate of heat release and the related pressure profile in the cylinder, as well as the area of heat transfer during combustion. The course of combustion of individual gases is influenced by the SOI value, ignition delay, mixture burning rate, volume change of combustion products, position and value of maximum pressure, differences in expansion of individual gases, etc. All these aspects and parameters that characterise the combustion process, together with the perfection of filling the cylinder with fresh mixture characterized by volumetric efficiency, also affect the final value of the total, i.e., effective engine efficiency. Figure 13 shows relation between the torque at revolutions 1500 L/min and the volumetric heating value for medium-energy gases. The increasing trend of this power parameter is virtually linear. The linear trend line (red straight line in Figures 13 and 14), 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 of \(\pm 5\%\). Figure 14 shows the dependence of engine hourly fuel consumption of SGs at 1500 L/min revolutions at full load on mass heating value of gas (LHV). The highest hourly consumption of mixture SG3 is 8.2 kg/h and, conversely, the lowest hourly consumption of mixture SG11 is 5.7 kg/h. Compared to methane CH4 (1.56 kg/h), the consumptions of SGs are 3.6-5.7 times higher. This is caused by relatively low amount of air and a high amount of SG needed for preparing of stoichiometric mixture (Table 2). A similar low consumption as in SG11 was measured with gases SG12 (6.2 kg/h), and SG10 (6.4 kg/h). The trend in decreasing hourly fuel consumption with increasing mass LHV parameters is virtually linear. The measured pressures in the engine cylinder, plotted for SGs and methane as a function of crankshaft angle, are shown in Figures 7 and 8. From the measured pressures, we can see that all SGs burn faster than methane, and the maximum pressures are slightly closer to TDC. This leads also to faster rising pressures before TDC and to greater spending of compression work. On the other hand, during the expansion stroke, the drop in pressures, compared to methane, is faster, the expansion work is less, which leads to the measured torque values depicted in Figures 3 and 4. The differences in the presence of combustible components in the individual gases also affect the pressures in the engine cylinder, and these are described in more detail in Section 4. The authors of the article also published the influence of individual components of synthesis gases on their combustibility in an internal combustion engine in their works [43; 50; 51]. The burning process during the compression stroke (and hence spent compression work) is different for all SGs; however, more significant differences arise during the expansion stroke in favor of SG10. This part briefly summarizes the achieved results for internal combustion engines (similar to [43] for low-energy SGs) in the field of energy recovery from medium-energy SGs. As already mentioned, SGs help to solve the problem of waste piled up in the environment by both reducing landfills and obtaining clean electrical and thermal energy in the process of cogeneration. Carbon dioxide generated by combustion of SGs is environmentally neutral.