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Ammonia has attracted the attention of a growing number of researchers in recent years. However, some properties of ammonia (e.g., low laminar burning velocity, high ignition energy, etc.) inhibit its direct application in engines. Several routes have been proposed to overcome these problems, such as oxygen enrichment, partial fuel cracking strategy and co-combustion with more reactive fuels. Improving the reactivity of ammonia from the oxidizer side is also practical. Ozone is a highly reactive oxidizer which can be easily and rapidly generated through electrical plasma and is an effective promoter applicable for a variety of fuels. The dissociation reaction of ozone increases the concentration of reactive radicals and promotes chain-propagating reactions. Thus, obtaining accurate rate constants of reactions related to ozone is necessary, especially at elevated to high pressure range which is closer to engine-relevant conditions.

To achieve higher efficiencies and lower emissions, dual-fuel strategies have arisen as advanced engine technologies. In order to fully utilize engine fuels, understanding the combustion chemistry is urgently required. However, due to computation limitations, detailed kinetic models cannot be used in numerical engine simulations. As an alternative, approaches for developing reduced reaction mechanisms have been proposed. Nevertheless, existing simplified methods neglecting the real engine combustion processes, which is the ultimate goal of reduced mechanism. In this study, we propose a novel simplified approach based on fuel reactivity. The high-reactivity fuel undergoes pyrolysis first, followed by the pyrolysis and oxidation of the low-reactivity fuel. Therefore, the simplified mechanism consists of highly lumped reactions of high-reactivity fuel, radical reactions of low-reactivity fuel and C0-C2 core mechanisms.

A computational fluid dynamics (CFD) simulation model for a two-stroke low-speed marine engine has been established in CONVERGE software, to study the impact of different injection directions on fuel consumption and emissions of the engine. The goal of this research was to investigate injection angles in horizontal and vertical directions respectively. According to the simulation results, “trade-off” relationship was found in both directions between fuel consumption and NOx emission. Based on these results, 8° and -16° were considered as optimal injection angles in horizontal and vertical directions. With the optimized injection angles, lower NOx emission can be achieved with a little penalty on fuel consumption.

Combustion instability often occurs inside the combustion chamber of aero engine. Fuel atomization and evaporation, one of the controlling processes of combustion rate, is an important mechanism of the combustion instability. To tackle combustion instability, it challenges a deep understanding of the underlying mechanism of fuel atomization and evaporation. In this paper, acoustic field was established to simulate the pressure oscillation. Transient spray images of ethanol and kerosene were recorded using high-speed camera. The obtained images were processed by MATLAB to extract and analyze the related data. Spatial fuel atomization characteristics was analytically examined by multi-threshold image method to analyze the effect of the high frequency acoustic field on the fuel break-up and disintegration. The results show that the half spray cone angle on the side with speaker is suppressed by the presence of the imposed acoustic field compared with the case without speaker.

Ignition quality tester (IQT) is a standard experimental device to determine ignition delay time of liquid fuels in a controlled environment in the absence of gas exchange. The process involves fuel injection, spray breakup, evaporation and mixing, which is followed by auto-ignition. In this study, three-dimensional computational fluid dynamics (CFD) is used for prediction of auto-ignition characteristics of diethyl ether (DEE) and ethanol. In particular, the sensitivity of the ignition behavior to different injection rate profiles is investigated. Fluctuant rate profile derived from needle lift data from experiments performs better than square rate profile in ignition delay predictions. DEE, when used with fluctuant injection rate profile resulted in faster ignition, while for ethanol the situation was reversed. The contrasting results are attributed to the difference in local mixing.

Engine lubricating oil perform functions including wear reduction, friction reduction, piston cooling, corrosion prevention, cleaning pistons, preventing leakage and serving as a hydraulic media. Oil aeration is the entrapment of air into engine oil during operation. Aeration would affect oil density, viscosity and its sound velocity, with a detriment to such properties as lubricity, cooling and lubricating temperature, possibly resulting in worse engine working environment. In this paper, a new volume method with temperature compensation is introduced and proved to be indispensable. The measurement of oil aeration rate is performed with the main oil gallery of a four cylinder, turbocharged, high-speed diesel engine under different operating conditions. The temperature compensation is carried out for the measured oil aeration rate and the compensation effect evaluated. The variation of oil aeration rate with time after oil leaving the main oil gallery is also presented.

In order to quantitatively investigate the macroscopic characteristics of flash-boiling atomization, the spray injected through a plain-orifice nozzle under atmospheric conditions was directly imaged and analyzed by the multi-threshold algorithm. The spray images were acquired at various times after the start of actuation using a high-speed visualization system. The light intensity level of images implies the local relative mass concentration of droplets in the spray. Transient contour plots of spray images at various thresholds were analyzed and compared with turbulent round jets of diesel. A new term, transient continuous cone angle, was defined to characterize the flash-boiling spray. The relative mass concentration distributions and continuous cone angles of the sprays during the start, development and end periods of the atomization were discussed for two different sprays.

In-cylinder thermochemical fuel reforming (TFR), which involves running one cylinder rich of stoichiometric and routing its entire exhaust back into the intake manifold, is an attractive method for improving engine performances. Compared with other hydrocarbon fuels, the chemical structure of methane is more stable owing to much shorter carbon chain. As ethanol contains hydroxyl in chemical structure, it potentially generates OH radical during the combustion. Therefore, adding ethanol into natural gas (NG) might help the thermochemical reforming process in engine cylinder. This paper focused on researching the effects of ethanol-NG combined in-cylinder TFR on engine performances, before which the effect of NG in-cylinder TFR was examined in detail. Cylinder #4 (TFR cylinder) was running rich and its cooled exhaust was coupled to the intake manifold of a four-cylinder engine during the experiments.