## 3 Results
### Measurements of the In-Cylinder Pressure of the Tested Engine  
After testing the engine the results saved to the files were calculated in a popular spreadsheet software, but using a specialized template in order to shorten the calculation time. This allowed us to obtain the average waveforms of pressure in the fired cylinder and in the cylinders of additional expansion as a function of the crank angle (CA). Furthermore, after introducing the geometrical data of the engine into the calculation program, p-V diagrams were developed for the fired cylinders, as well as for the cylinders of the additional expansion. Development of the p-V indicator diagrams allowed the calculation of the indicated mean effective pressure and the indicated power for fired cylinders and additional expansion cylinders for each of the measurement points. The following are examples of the work carried out on the recorded waveforms of in-cylinder pressure for the fired and additional expansion cylinders. In Figure 9 the p-CA diagram of the engine with the additional-expansion registered for a full load 123 Nm at 3000 rpm rotational speed is presented. A turbocharger wastageate valve remained closed, and the boost pressure was 0.5 bar. The exhaust gas temperature measured at the outlet of the turbine had a value of 437 \({}^{\circ}\)C.  
The peak pressure in the fired cylinder reached 7 MPa for the case above, for the position of the crankshaft at 380 CAD ATDC (Crank Angle Degrees) (After Top Dead Center). The difference in pressure peaks recorded in the cylinders of additional expansion in the case of filling by exhaust cylinder No. 3 from fired cylinder No. 4 and No. 1 (through cylinder No. 2 and the passage) was approximately 0.06 MPa. The aforementioned difference in the value of the maximum pressure in the additional expansion cylinder for the crank angle of approximately 180 CAD and approximately 540 CAD are caused by throttling the flow in the connecting passage between the expansion cylinders 2 and 3. The pressure  
Figure 9: Chart in a p-CA for the fired cylinder and additional expansion cylinder recorded at 3000 rpm and a torque equal to 123 Nm. value obtained for 540 CAD occurs when the exhaust goes to the additional expansion cylinder No. 3 from the adjacent fired cylinder No. 4, in which the in-cylinder pressure is also measured. The pressure registered at 180 CAD resulted from filling the assembly of the cylinders of additional expansion by exhaust gases from cylinder No. 1. In this case, the exhaust gases were first delivered into cylinder 2, then through the connecting channel in the cylinder head to cylinder No. 3, where the measurement was carried out. During the calculation of the indicated work of the additional expansion cylinders, its value was determined in consideration of the fact that in the cylinders of additional expansion, the pressure is variable in a cyclic manner as described above. In Figure 10, the in-cylinder pressure curves are shown as a function of cylinder volume (V\({}_{c}\)) for the fired and additional expansion cylinders registered for a full load of 123 Nm at 3000 rpm rotational speed. The assembly of additional expansion cylinders of the engine works in a two-stroke mode, therefore the in-cylinder pressure waveform shown in the above chart includes two complete processes of additional expansion and the exhaust process, as shown in the p-CA diagram. The values of the indicated mean effective pressure in the fired cylinder (IMEP\({}_{\text{frd}}\)) and in the additional expansion cylinders (IMEP\({}_{\text{add}}\)) were calculated by numerical integration of relevant areas of the p-V chart. These values were: IMEP\({}_{\text{frd}}\) was equal to 1.72 MPa, and IMEP\({}_{\text{add}}\) was equal to 0.08 MPa.