A Key to Fuel Saving in Combustion Engines—Part 1: General Approaches and Concept of Cooling Cyclic Air in Marine Cogeneration Plants

Low-speed diesel engines are the most widespread in marine power plants. Their fuel efficiency falls with growing intake and charge air temperatures. Therefore, cyclic air cooling ensures sustainable performance of ship engines along the voyage with high fuel efficiency. Absorption lithium bromide chillers (LBCh) are the most widely used due to their high efficiency, with a COP of about 0.7. However, they are complicated and need a special room. The ejector chillers (ECh) consist mostly of heat exchangers, which might be placed on the board side and transverse bulkheads in the engine room, but their efficiency is considerably less than that of LBCh. The cogeneration engines produce hot water of about 90 °C, which leads to a lowered COP of ECh: nearly 0.2, which causes reduced refrigeration capacity and undercooling of the engine cyclic air. The aim is to balance conflicting constraints in chiller downsizing and fuel saving due to engine cyclic air cooling through rational redistribution of thermal loads between LBCh and ECh. This requires the realization of a new hypothesis based on paradoxical alternative approaches to unload a highly efficient LBCh and overload a less effective ECh. Herewith, the lack of ECh capacity is boosted by the heat left from the unloaded, downsized LBCh as an alternative to its boosting by LBCh cooling capacity gained at a high COP and accepted in typical design and operation practice. An advanced method to determine the loads on the chillers has been developed, and an innovative heat recovery cooling system is synthesized to satisfy conflicting constraints: reduced sizes of ACh by about 25% and practically maximum fuel saving. Herewith, the ECh cooling deficit is covered down to its average weighted value along the route of about 7.5% due to utilization of the heat excess left from LBCh. A concept of engine cyclic air cooling by combining downsized LBCh and ECh in the core of a new trend in ship cogeneration plants has been substantiated and approved by the results of simulation of thermal load distribution between the chillers along the voyage.