The main goal was to understand the performance of operating engines at variable speeds of 1,200–1,800 RPM compared with fixed speed at 1800 RPM.
The results presented in this article are from two tests:
1. DP (Dynamic Positioning) Operational fuel measurement test – the objective was to verify differences in fuel consumption during a real world vessel operation running at variable and fixed speed.
2. Load step fuel measurement test – the objective was to verify difference in fuel consumption at stable load levels of 10 percent increments.
It was decided to execute a DP mode test with fluctuating loads. The DP operation was deemed the most relevant to execute, as transit, harbor and other operational modes do have a more or less constant load. To show fuel savings in a varying load scenario, a test was done in DP mode on a single engine. Fuel was only measured on a single engine, but two engines were running to keep the position accordingly.
First, the engine was run at variable speed for 45 minutes and then for 45 minutes at constant speed. The PEMS (Power and Energy Management System) data were used to compare time, fuel, power and RPM data. The power was integrated over the time period for the variable speed test and the produced energy in kWh and fuel consumption was calculated.
For the constant speed test, the power was also integrated and the fuel consumption noted at the time when the produced energy was the same as the energy produced during the variable speed test. This makes the results directly and academically comparable.
The purpose of this test was to show the fuel consumption under a stable load, the effectiveness of the SCR system and effect on engine room noise level. This load test was performed with 10 percent load interval from 10 percent to 90 percent.
The engine was run first in variable speed with asymmetric load sharing to a fixed load from 10– 90 percent. The load fluctuated slightly and the burn rate fluctuated accordingly within a few liters/hour. The ship hitting a wave would cause the burn rate to momentarily go up and then settle again. The mean burn rate value was logged during the test procedure, and is later presented in the result section. Only one value was noted for each load level.
Exhaust temperature and sound level were also noted during each load step.