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In order to avoid the abnormal combustion in high-power hydrogen engine, a 3D CFD numerical model of a direct-injection spark-ignition hydrogen engine was built up based on a large-bore medium-speed four-stroke marine diesel engine using CONVERGE software. To obtain the influence of injection parameters on mixture homogeneity, a dimension reduction optimization method was proposed. The results revealed that the turbulence intensity and the penetration distance varied with the injection parameters, determined the level of mixture homogeneity. The performance comparison between the hydrogen engine and prototype diesel engine showed a great potential of hydrogen in internal combustion (IC) engines. • Process of improving homogeneity can be simplified by optimizing turbulence intensity and injection penetration distance. • Turbulence intensity and injection penetration distance varied with injection system parameters. • The higher the turbulence intensity, the faster the mixing rate. • Neither too long nor too short injection penetration distance was conducive to mixing. [ABSTRACT FROM AUTHOR]

Fuel consumption and emissions are growing concerns, driving the need for cleaner alternative fuels in engine research. Ammonia is a competitive alternative fuel. To enhance the effective utilization and provide a new direction for the marine application of ammonia, an ammonia-diesel dual-fuel engine model with the pre-combustion chamber structure was designed. Numerical simulations were carried out in this paper, considering variations in diesel energy fraction, ammonia injection timing, diesel injection pressure, and diesel injection timing. The findings indicate that an appropriate amount of pilot diesel accelerates jet flame formation, improving combustion efficiency. Advancing ammonia injection timing improves mixture homogeneity but increases ammonia slip, while delaying ammonia injection timing leads to mixture stratification. Locally rich areas in the mixture improve combustion efficiency. The timing and pressure of diesel injection significantly impact both combustion efficiency and emissions. Advancing diesel injection timing improves power output but increases NO X emissions. Increasing diesel injection pressure improves combustion efficiency, but excessive pressure leads to deterioration. Overall, this study provides valuable insights into the potential use of ammonia as a sustainable fuel for marine low-speed engines, selecting the optimal energy fraction and injection strategy to achieve efficient and environmentally friendly combustion. • An ammonia-diesel dual-fuel engine model with pre-combustion chamber structure was designed. • The effect of intake and exhaust processes are considered in the study, more closely to the real working conditions. • The ignition effect of 2% diesel energy ratio is the best, when the volume ratio of the pre-combustion chamber is 1%. • Ammonia slip and combustion efficiency can be improved by appropriately delaying ammonia injection. [ABSTRACT FROM AUTHOR]

Ignition characteristics of n -hexadecane/methane mixture under low-pressure high-temperature (P : 2.0 bar, 5.0 bar & T : 1269–1887K) and high-pressure low-temperature (P : 40–140 bar & T : 700–1200 K) conditions were studied by aerosol shock tube and CHEMKIN with LLNL C16 mechanism. The results indicated that at low-pressure high-temperature conditions, increasing initial pressure and decreasing equivalence ratio could reduce ignition delay times (IDT) by 39% and 52% respectively. N-hexadecane's addition and n -hexadecane's replacement also shortened IDT by 88% and 96% separately. Raising n -hexadecane's replacement further reduced IDT. The reduction degree of IDT dramatically decreased when n -hexadecane's content was high. N-hexadecane was fully consumed earlier than methane. Radicals that formed from n -hexadecane's decomposition induced H-abstraction of n -hexadecane, which advanced methane's slow oxidation. H was the crucial radical in n -hexadecane's H-abstraction reactions. At ultra-high-pressure low-temperature condition, adding n -hexadecane and increasing n -hexadecane content dramatically reduced IDT. With n -hexadecane's H-abstraction dominating ignition process, n -hexadecane's decomposition was significantly inhibited at low-temperature condition. OH was the key radical in n -hexadecane's H-abstraction reactions. The obviously suppressed n -hexadecane's decomposition was responsible for the same end time point of complete consumption of two fuels. These results are helpful for providing control methods for natural-gas preignition and abnormal combustion triggered by lubricating oil in dual-fuel marine engine. • Ignition characteristics of n -hexadecane/methane mixture was investigated by aerosol shock tube and kinetic study. •The addition of n -hexadecane obviously shortened ignition delay times of methane mixture. •The replacement of methane with n -hexadecane further shortened ignition delay times. •At low-pressure high-temperature, time point of complete n -hexadecane consumption was earlier than that of methane. •At high-pressure low-temperature, time point of complete n -hexadecane consumption was the same as methane. [ABSTRACT FROM AUTHOR]

To acquire ignition control methods for dual-fuel marine engine and HCCI engine, ignition characteristics of lean n-heptane/methane mixture under pressure of 2.0 bar and temperature range from 1241 to 1825 K were studied by shock tube and CHEMKIN with LLNL3.1 mechanism. And ignition processes under temperature range from 700 to 1200 K and pressure range from 40 to 140 bar were investigated by CHEMKIN with NUI mechanism. The results illuminate that at low-pressure high-temperature condition, n-heptane's replacement and the increase of n-heptane content obviously reduced ignition delay times (IDT). The reduction degree of IDT decreased when n-heptane content was high. N-heptane's addition also reduced IDT. But this reduction magnitude was less than that of n-heptane's replacement. Methane's addition slightly inhibited n-heptane's auto-ignition. The reaction time of n-heptane was obviously earlier than that of methane. N-heptane decomposition induced radical formation firstly, which triggered subsequent n-heptane's H-abstraction and the advance of methane's oxidation. At ultra-high-pressure low-temperature condition, increasing n-heptane's content enhanced negative temperature coefficient (NTC) behavior. The end time point of complete consumption of two fuels was the same. Low-temperature condition inhibited n-heptane decomposition, with n-heptane's H-abstraction dominating ignition process. • Ignition properties of CH4/n-C7H16 mixture was revealed by shock tube and mechanisms. • Active radicals formed from n-heptane's decomposition advanced methane's oxidation. • Methane's addition slightly retarded the ignition of pure n-heptane mixture. • The results provided ignition control method for natural-gas/diesel dual-fuel engine. [ABSTRACT FROM AUTHOR]