The following experiments and analyses were carried out to develop technology that complies with the IMO Tier III NOx regulations without deterioration of the specific fuel consumption (SFC). First, changes in engine performance and exhaust gas characteristics were investigated using an oxygen reduction membrane (ORM) while varying the oxygen concentration in the suction air from 21 to 17%. Next, the utility and limits of the NOx reduction technology based on the ORM were determined by analyzing the results. Additionally, the oxygen concentration in the suction air was lowered using the ORM, after which experiments in combination with water mixed fuel (WMF) technologies were carried out and the results were analyzed. Based on the results, the following conclusions were made: (1) The IMO Tier III NOx regulations can be met by reducing the oxygen concentration in the suction air to 17% at 75, 50, and 25% load. (2) The SFC deteriorates with decreasing oxygen concentration. This behavior intensifies particularly at oxygen concentrations of 19% or less, e.g., the SFC deteriorates by about 3% at 17% oxygen concentration. (3) By mixing water in the fuel with the oxygen concentration adjusted to 19%, the IMO regulations can be met without increasing the SFC. Finally, a discussion regarding compliance of the proposed technology with IMO regulations is made from the point of view of the operator.
