In this study, the influence of direct steam injection (DSI) on the performance and emissions of marine engines is investigated. Simulation models are developed and tested based on experimental data. Steam is obtained by waste heat recovery in a marine engine. The limitations of DSI parameters are investigated based on the exhaust gas temperature. The steam quantity and temperature decrease with a decrease in load. The results show that steam mass plays an important role in NOx reduction and improving power. For a steam/fuel ratio of 1.27 at 100% load, the brake power improved by 3.09% and NOx emissions decreased by 4.67%. A higher degree of improvement is obtained with an increase in steam mass. The steam temperature and injection timing only slightly influenced the brake power and NOx emissions. When steam-injection timing improved to 12°CA at 100% load with injection duration decreasing from 85°CA to 25°CA, brake power improved from 3,485.7 to 3,529.7 kW. All of this demonstrates that the DSI approach has excellent energy-saving and emission reduction potential for marine engines. The steam-injection strategy should be optimized in the future.
Ammonia/hydrogen blend fuels have been extensively used as alternative fuel for engines. The combustion and emissions characteristics of ammonia/hydrogen engines have been investigated utilizing a CFD model. Developing a robust and accurate chemical reaction mechanism for ammonia/hydrogen blend fuels is of utmost importance. In this paper, a chemical mechanism has been developed and validated for the combustion characteristics of ammonia/hydrogen, which includes 31 species and 223 reactions. Extensive validation has been conducted using experimental data as the basis. The obtained data indicate that the simulated values for the ignition delay times of the shock tube and the concentration of the main components in the stirred jet reactor align well with the measured values. The simulated laminar flame speed under turbulent flow conditions shows a remarkable agreement with the corresponding experimental data The study compared simulated flame evolution values with experimental data from a constant volume combustion bomb. The results indicate that the proposed mechanism is able to produce favorable flame evolution and combustion characteristics. The presented detailed mechanism demonstrates credible overall performance in terms of combustion behaviors, indicating its suitability for effectively modeling ammonia/hydrogen combustion in real engines.
Herein, as an alternative to heavy fuel oil (HFO), a multi-component surrogate fuel was developed, which comprised n-tetradecane, n-hexadecane, i-hexadecane, n-eicosane, decalin, toluene, A2, and A3. The proportions of the components of the surrogate fuel were determined by studying the chemical and physical characteristics of HFO. The surrogate fuel was optimized by matching the cetane number (CN), density at 20°C, lower heating value (LHV), and hydrogen-carbon (H/C) ratio. The developed skeletal surrogate mechanism constituted 128 species and 375 reactions. It was extensively validated using various fundamental experiments based on its single components and HFO performance under relevant engine conditions. The predicted ignition delay time in shock tubes and the concentrations of primary species in jet stirred reactors and flow reactors were in good agreement with the measured values. The predicted laminar flame speed in counterflow configuration was close to the experimental data. The flame spray and combustion characteristics were found to be well produced by the proposed mechanism in a fuel ignition analyzer and a two-stroke marine diesel engine. The proposed skeletal mechanism exhibited reliable overall performance for combustion behavior, indicating that it can be used for modeling HFO in realistic engine applications.
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