# Medium-Energy Synthesis Gases from Waste as an Energy Source for an Internal Combustion Engine
## 6 Conclusions
Increasing the proportion of hydrogen in synthesis gases causes an increase in the pressure rise rate values during gas combustion, a decrease in the COV values during the gradual burnout of the fuel, and a shortening of the total combustion period. In other words, synthesis gases with higher hydrogen content lead to a slightly harder engine run, but a more stable combustion process. The effect of hydrogen in the synthesis gases, unless there is abnormal combustion, is positive. The combustion with a higher H\({}_{2}\) content is closer to isochoric burning, which contributes to higher thermal and effective engine efficiency and also to lower fuel consumption. At the same time, an important property of hydrogen in the gas mixture [50] during its combustion should be mentioned, namely, that increasing the proportion of hydrogen in the mixture reduces harmful hydrocarbon emissions. A higher content of hydrogen in SGs reduces environmentally neutral CO\({}_{2}\) in SGs combustion; vice versa, hydrogen increases the content of nitrogen oxides and water vapour in the exhaust of the internal combustion engine. 8. The results presented in this article and summarized in the conclusion give an idea of the integral parameters of the engine (torque and hourly consumption, Figures 1-4), but above all, they give an idea of the internal parameters of the engine that relate to the combustion processes of medium-energy synthesis gases (Figures 5-12), which we have mainly dealt with in this article. The authors can draw the following conclusions that are similar to those reached by the authors for low-energy synthesis gases [43]: * If medium-energy synthesis gases are to be used to drive a cogeneration unit, then we assume that the most important criterion for energy recovery from them must be the criterion of low consumption and high efficiency of their use in the internal combustion engine or for cogeneration. This means, that for the gases that have been measured at 1500 L/min, the lowest fuel consumption is in the range approximately up to 6.7 kg/h (Figure 14.). It relates to the gases SG12, 11, 10, 9, and 8, and the calculated values of effective efficiencies for them are as follows: SG10 (31.2%), SG11 (31.1%), SG8 (31.1%), SG9 (30.8%), and SG12 (28.8%). At the same time, the gases SG10 and SG9 also achieved the highest performance parameters (and had the highest volume lower heating value of the mixture - LHVmixture) out of all gases. The gases that achieve low consumption and at the same time a high value of effective efficiency are the gases SG 8, 9, 10, and 11. As for Table 2, these are gases, which in their composition contain from 30% to 45% volume of methane and hydrogen. Therefore, the general conclusion that we can recommend for the production of medium-energy gases is to set up the gasification technology in such a way that the resulting gases contain as much methane and hydrogen as possible. * In order to prevent abnormal combustion in the form of knocking of the engine or backfire of the mixture in the intake manifold, it is necessary to take into account the fact that in the case of methane-free gases (SG2 and SG5, Table 2), if the hydrogen content exceeds 25% by volume, then the volume of inert gases must not fall below 25% vol. [43]. During experiments with SGs, which contain methane, we did not measure any signs of abnormal combustion. * As for inert gases present in the synthesis gases, if the gasification technology allows, we recommend a higher proportion of nitrogen than carbon dioxide content in the synthesis gases for maximum optimisation of performance parameters [43,51].