## 3 Results and Discussion
### Experimental Biogas Diesel Engine--Tests
2—Biodiesel fuel tank with heating system. 3—Biogas fuel tank. 4—CNG fuel tank. 5—LPG fuel tank. 6—Diesel mass flow meter. 7—Fuel temperature measurement. 8—Gas pressure regulator. 9—Gas flow control value. 10—Gas injector system control. 11—Air filter. 12—Temperature, humidity and pressure system measurement. 13—Energetic control and measurement system. 14—Electrical network. 15—Exhaust gas temperature. 16—Emission analyzer. 17—Exhaust volume flow measurement. 18—Thermal energy measurement. 19—Cooling system. 20—Oil temperature measurement. 21—The main measurement and control system. \begin{table}
\begin{tabular}{l c c} \hline \hline
**Fuel Property** & **Unit** & **BG** \\ \hline Viscosity at 40 \({}^{\circ}\)C & m\({}^{2}\)-s\({}^{-1}\) & - \\ Density at 15 \({}^{\circ}\)C & kg\(\cdot\)m\({}^{-3}\) & 1.25 \\ Calorific value & MJ\(\cdot\)kg\({}^{-1}\) & 17.15 \\ Octane number & & 110 [37] \\ Flash point & \({}^{\circ}\)C & 630 [37] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Physical properties of liquid fuels [31]. an ambient temperature of 20 \(\pm\) 2 \({}^{\circ}\)C while maintaining air parameters, i.e., humidity of 46 \(\pm\) 10% and a pressure of 995 hPa \(\pm\) 2 hPa. The share of gases, i.e., NO, NO\({}_{2}\), PM and CO, was measured quantitatively in relation to the mass of exhaust gases. Some simplification has been introduced to express mass exhaust emissions. The exhaust gas was a model of an ideal gas and consisted of a mixture of oxygen, nitrogen and dioxide, excluding traces of other gases. The Clapeyron Equation (1) was used to determine the mass amount of gases:  
\[A^{*}=\frac{V^{*}p}{TR}\left[\frac{\mathrm{kmol}}{\mathrm{h}}\right] \tag{1}\]  
where \(V^{*}\) denotes the exhaust gases flow m\({}^{3}\) in normal conditions per hour [m\({}^{3}\cdot\)h \({}^{-1}\)], \(p\) denotes the pressure in the exhaust manifold [Pa], \(T\) denotes exhaust gases temperature [K], and \(R\) denotes the universal gas constant [J\(\cdot\)kg\({}^{-1}\cdot\)K\({}^{-1}\)]. The quantitative exhaust gas stream was converted into a mass based on the molar mass of the O\({}_{2}\), N\({}_{2}\) and CO\({}_{2}\) gas mixture. The proportion of gases was measured using an exhaust gas analyzer, except for nitrogen. Relative to the exhaust gas mass, the mass flow \(x\) for NO, NO\({}_{2}\), PM and CO was calculated according to Formula (2):  
\[X=\sum_{i=\mathrm{O}_{2}\mathrm{N}_{2}\mathrm{CO}_{2}}^{3}\left(y\cdot M \right)_{i}\cdot A^{*}B_{x}\left[\frac{\mathrm{mg}}{\mathrm{h}}\right] \tag{2}\]  
where \(M\) denotes the molar mass of the \(i\)-th gas [kg\(\cdot\)kmol\({}^{-1}\)]; \(y\) denotes the quantitative share of the \(i\)-th gas [-]; \(B\) denotes the share of \(x\)-th gas (CO, NO, NO\({}_{2}\)) in the exhaust [mg\(\cdot\)kg\({}^{-1}\)]; and \(i\) denotes O\({}_{2}\), CO\({}_{2}\) and N\({}_{2}\). As the share of BG in the engine fuel increases, the amount of carbon oxides increases significantly. This is caused by a change in the engine power supply parameters while operating parameters remain unchanged. Changing the injection angle can reduce CO emissions, but only slightly compared to engine emissions. The place and method of BG injection, i.e., injection into the intake manifold, are also important. The use of multi-point or even direct injection could significantly reduce CO emissions. The presence of BG supplying the engine significantly reduces NOx. However, if we analyze NO and NO\({}_{2}\) emissions separately, we can see a clear increase in the emissions of toxic NO\({}_{2}\) particles. It follows that the presence of BG has a negative impact on the qualitative and quantitative composition of nitrogen oxides emitted in exhaust gases [31].