## 3 Results
### Measurements of the In-Cylinder Pressure of the Tested Engine
The indicated power in the working cylinders (P\({}_{\text{i\_{frd}}}\)) was then calculated using Formula (1):  
\[\text{P}_{\text{i\_{frd}}}=\frac{2\cdot\text{IMEP}_{\text{frd}}\cdot\text{V}_ {\text{frd}}\cdot\text{n}}{120000},\text{ kW} \tag{1}\]  
The formula presented above takes into account the used units, including the speed and four-stroke nature of the work of the two working cylinders. Similarly, the formula for calculating the indicated power of the cylinder of additional expansion (P\({}_{\text{i\_{add}}}\)) is presented as Formula (2):  
\[\text{P}_{\text{i\_{add}}}=\frac{\text{IMEP}_{\text{add}}\cdot\text{V}_{ \text{add}}\cdot\text{n}}{60000},\text{ kW} \tag{2}\]  
Figure 10: p-V diagrams for the fired cylinder and additional expansion cylinder recorded at 3000 rpm and a torque equal to 123 Nm. This formula takes into account that both cylinders of additional expansion work in a two-stroke mode as a single working volume. The calculated value of the indicated power of the fired cylinders at this operating point is 42.77 kW, and the value of the indicated power in the cylinders of additional expansion is approximately 3.98 kW, which is more than 9% of the P1_frd value. A similar analysis of the waveforms of in-cylinder pressure for the fired and additional expansion cylinders was carried out for the results obtained in the other measuring points. This made it possible to determine the relationship between IMEP\({}_{\text{frd}}\) and IMEP\({}_{\text{add}}\). This is shown graphically in the form of a plot in Figure 11.  
The course has been approximated by a straight line, and the equation is presented in the chart. The achieved value for the IMEP\({}_{\text{add}}\)/IMEP\({}_{\text{frd}}\) ratio is greater when the IMEP\({}_{\text{frd}}\) is higher. The highest value (the last point on the top of the graph) is 0.063. With regards to the relations of the indicated power, the mentioned ratio will be about 12.6%, as the additional expansion cylinders operate in a two-stroke mode. This is an important energy recovery ratio in the additional expansion process of the working medium. In order to determine the load of the five-stroke engine from which the cylinders of additional expansion start to give power to the output, the dependence of the Brake Mean Effective Pressure (BMEP) as a function of the Indicated Mean Effective Pressure of the additional expansion cylinders (IMEP\({}_{\text{add}}\)) was defined. Figure 12 shows a graph of this function. Similarly, as in the previous case, the obtained waveform is approximated by a straight line whose equation is given in the chart. Figure 11: The Indicated Mean Effective Pressure in the cylinders of additional expansion as a function of the Indicated Mean Effective Pressure in the fired cylinders. Figure 12: The Brake Mean Effective Pressure of the five-stroke engine as a function of the Indicated Mean Effective Pressure of the additional expansion cylinders. BMEP values were determined from the value of the torque, taking into account the displacement volume of the fired cylinders (2 \(\times\) V\({}_{\text{fnd}}\) = 992 cm\({}^{3}\)). The volume of the cylinders of additional expansion cannot be taken into account while calculating BMEP, because there is no combustion process in these cylinders. The determination of this function was aimed at finding a load limit before which the additional expansion cylinders take power from the engine instead of delivering power to the engine. The value of the intercept of the function from Figure 12 is equal to about 0.6. This means that if the BMEP is lower than 0.6 MPa, then additional expansion cylinders require power from the engine. Above this value, the additional expansion process becomes positive for the engine work. Taking into account the volume of the cylinder, the engine, and the mechanical efficiency, this means that the assembly of the cylinders of additional expansion transmit additional power to the engine output from the time when the measured torque exceeds 60 Nm.