Fuels

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.

CO₂-lean pyrolysis streams from processing industrial or municipal by-products, such as sewage sludge, were tested for catalytic methanation in a bench-scale laboratory plant over a temperature range of 300–450 °C and atmospheric pressure. Two home-made Ni-based catalysts supported on both cordierite and activated vegetable carbon were tested against a commercial Ni catalyst formulation, at a space velocity variable between 250 and 1000 h⁻¹. Quantitative CO conversions were detected at 350 and 400 °C for the Ni catalysts supported on cordierite and activated carbon, despite CO₂ conversion values being averagely low. Methane selectivity approached values up to 90%, accounting for a relative content up to 80 mol% in the outlet methanation mixture. Overall, the cascade integration of a pyrolysis step for processing sewage sludge into a CO₂-lean gaseous stream feeding a catalytic methanation reactor was successfully demonstrated, with the whole chain representing a viable strategy to dispose of by-products and produce bio-synthetic natural gas.

Accurate prediction of particulate matter (PM) emissions from gasoline direct injection (GDI) engines requires investigating soot formation mechanisms under conditions that decouple physical mixing from chemical kinetics. In this study, a quasi-one-dimensional micro-flow reactor was used to provide a uniform, controlled wall-temperature profile reaction field, enabling the measurement of soot particle size distributions (PSDs) during the pyrolysis of isooctane, n-heptane, propane, and a multi-component gasoline surrogate (PM3). Experimental results demonstrated that soot PSDs are dependent on both fuel type and initial fuel concentration. To validate the predictive models, the experimental data were compared with numerical simulations employing a discrete sectional method. To account for the physical complexities of actual soot coagulation and the chemical uncertainties in gas-phase precursor formation, a fuel-specific calibration parameter, $\gamma$, was introduced into the model. With this modification, the simulations reproduced the concentration dependence of the normalized PSDs for all tested fuels. The optimized $\gamma$ values exhibited an empirical trend that correlates with the macroscopic smoke points. Within the limited scope of the tested fuels, this relationship suggests that the smoke point could potentially provide a qualitative indication of the relative magnitude of $\gamma$ within similar fuel classes. This provides a useful starting point for exploratory model calibration, potentially reducing the reliance on extensive baseline experiments.