## 4 Discussion  
The main assessed parameter was the energy consumption of work of chipping machines expressed by fuel consumption. The first stage research results enabled a comparison of fuel consumption in constant exploitation conditions. Selected test results are shown in Figure 3. The analysis of the fuel consumption in these three conditions allowed us to determine the range of fuel consumption that one can expect in periodically-variable exploitation conditions. Idle work at low rotational speed is more effective in the case of a system with electronic fuel injection (B). The operation at high rotational speed under the same load conditions is more advantageous in the case of a system with a carburetor fuel feed (A). The reason for this is the lower rotational speed during active work (while chipping, i.e., about 3800 rpm). The drive with the injection system (B) operates at 4200 rpm, where more combustion cycles occur. The differences in the rotational speed values were related to the different control concept, that resulted from the reference characteristics \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Operating Conditions**} \\ \hline \multirow{3}{*}{**Test No.**} & \multicolumn{2}{c}{**Percentage of Time for the Different Operating States: Chipping/Idle Work**} \\ \cline{2-4}  & **78\%/22\%** & **71\%/29\%** & **65\%/35\%** \\ \cline{2-4}  & \multicolumn{3}{c}{**Average Fuel Consumption [1 h\({}^{-1}\)]**} \\ \hline AVG & 0.951 & 0.633 & 0.515 \\ SD & 0.0509 & 0.0484 & 0.0432 \\ I & 0.1135 & 0.1080 & 0.0962 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The results of fuel consumption of the cylindrical wood chipper with an injector fuel supply system equipped with an adaptative drive control system in periodically-variable exploitation conditions. AVG–arithmetic average, SD–standard deviation of the mean, I–incertitude limits using the Student’s t distribution for a 95% confidence level. Figure 3: Fuel consumption in selected operating conditions: Idle work with high (1) and low (2) rotational speed, with a continuous chipping process (3). \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Operating Conditions**} \\ \hline \multirow{3}{*}{**Test No.**} & \multicolumn{2}{c}{**Percentage of Time for Different Operating States: Chipping/Idle Work**} \\ \cline{2-4}  & **78\%/22\%** & **71\%/29\%** & **65\%/35\%** \\ \cline{2-4}  & \multicolumn{3}{c}{**Average Fuel Consumption [1 h\({}^{-1}\)]**} \\ \hline AVG & 1.252 & 1.260 & 1.279 \\ SD & 0.0117 & 0.0136 & 0.0115 \\ I & 0.0261 & 0.0303 & 0.0255 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The results of fuel consumption of the cylindrical wood chipper with injector fuel supply system (B) in periodically-variable exploitation conditions (3); AVG–arithmetic average, SD–standard deviation of the mean, I–incertitude limits using the Student’s t distribution for a 95% confidence level. of the engine. In the carburetor system (A), a significant load on the working mechanism caused the rotational speed to decrease. This was limited by a change in throttle position that caused an increase in the fuel-air mixture inflow to the combustion chamber. The process provided a greater fuel-air mixture volume making it possible to increase rotational speed, thereby allowing maximum torque to be reached again. This action was carried out by a centrifugal regulator integrated with the carburetor. In the constant branches chipping process (3) this caused a significant load on the working mechanism. Because of this, fuel consumption differed significantly depending on the fuel supply system used. In the injection system (B), the load value was recognized based on the signal from the throttle position sensor. Hence, the load caused by the object to be fragmented was not detected by the system. In the injection system, the current load value was known due to the signal from the throttle angle sensor.