## 4 Discussion  
The results of the experimental test of the engine with an additional expansion of exhaust gases are presented in this study. After the analysis, the author attempted to compare the obtained results mainly to that from [14], which shows the results obtained for a similar engine, but which was designed and built from scratch. Summary of the results of the comparison is as follows:  
* During the tests, significant differences in the maximum pressure in the two cylinders of additional expansion were observed. These differences arise from the small area of the cross-section of the passage between the cylinders. This is a limitation of the base engine. In the developed engine, there are two smaller cylinders of additional expansion instead of one larger cylinder. Improvement of the existing motor can consist only of a larger cross-section of the channel, which connects the cylinders of additional expansion. * The energy recovery ratio--the indicated power of the additional expansion cylinders--is up to 12.6% of the indicated power of the fired cylinders. Obstacles to achieving better results were: high volume of the transfer ports between the fired cylinders and additional expansion cylinder, as well as the unchanged volume of the former combustion chambers in the cylinders of additional expansion, and also the division of the additional expansion volume into two cylinders. [PERSON] et al. showed a significantly higher ratio of the indicated work of the additional expansion cylinder to the indicated work of the fired cylinder. They obtained a value of about 18%--[14] (p. 265). Figure 15: Mechanical efficiency and boost pressure as a function of the rotational speed at WOT. * During the engine testing, a high value of load was obtained, from which the cylinders of additional expansion of the engine gave power to the output. This was about 60 Nm and was caused by the limitations of the above-mentioned structure of the base engine, mainly from the loss of energy in the parasitic volumes. Below 60 Nm of torque, the engine still operates at a relatively low BSFC, but is related to the effect of downsizing, instead of the additional effects of the second expansion of exhaust gas. This aspect of the five-stroke engine was not strongly emphasized in [14]. The problem of the selection of an appropriate displacement volume of the second expansion cylinder linked to this issue was analyzed by [PERSON] et al. in [18]. * This research revealed an additional problem, which was not described in the work content; the increased consumption of oil lubricating the engine when working with low load. The increased consumption of lubricating oil is caused by the occurrence of negative pressure in the inlet channel of the turbine at the opening of the exhaust valves of the engine. This significantly changes the operation of an oil seal of the turbocharger rotor shaft and the sucking of oil into the exhaust system occurs. * The maximum values of the mechanical efficiency of the engine achieved by the author correspond to the results presented in [14]. This indicates a good level of technical modification made to the engine. * The minimum brake specific fuel consumption amounted to 240 g/kWh. One should remember that the tested engine worked with all the equipment necessary for autonomous operation, i.e., with the alternator, oil pump, coolant pump, and the high pressure fuel pump. A low-pressure fuel pump was also supplied from the engine power grid. [PERSON] et al. obtained a BSFC of 226.4 g/kWh, but the engine was working without propelling an oil pump and a water pump, and probably also without the alternator. A drive of these devices by the engine undoubtedly caused an increase in the brake specific fuel consumption. As a summary of this part of the work, Figure 16 shows the results of the above-described comparisons of these two engines, presented in graphical form.