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2 Polish Maritime Research

2 2024

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Effects of pilot oil injection timing on combustion, covariance and knocking of a natural gas–diesel duel-fuel low-speed engine

100%

Wei C. , Chen X.-X. , Chen L. , Li P. , Liu M.

Polish Maritime Research

2024

tom nr 4

69--75

Dual-fuel engines, which are powered by natural gas while using a small amount of diesel for ignition, have become an attractive option in the marine sector due to their fuel flexibility and relatively good emission characteristics. Altering the fuel injection timing can change the combustion state of natural gas in the cylinder, which in turn affects engine stability and leads to engine knocking. In this study, the effects of different pilot oil injection timings on the combustion stability of a marine low-speed natural gas dual-fuel engine with a pre-combustion chamber are evaluated in terms of the pressure rise, covariance of Pmax and IMEP, combustion phase, and knocking. It is found that the maximum cylinder pressure and pressure rise rate increase with an advance in the pilot oil injection time. After the natural gas enters the combustion chamber, it undergoes a process of mixing with air in the combustion chamber, and earlier pilot oil injection leads to an increase in the ignition delay period and shortens the combustion duration of the engine. Moreover, it is found that earlier pilot oil injection times result in an increase in engine IMEP and Pmax cycle fluctuations, and engine knocking also undergoes an increase when the pilot oil injection time is advanced. Hence, an appropriate pilot oil injection time should be considered in the process of optimising engine performance.

Effects on of blended biodiesel and heavy oil on engine combustion and black carbon emissions of a low-speed two-stroke engine

100%

Wei C. , Jiang G. , Wu G. , Zhou Y. , Liu Y.

Polish Maritime Research

2024

tom nr 1

94--101

The effects of heavy fuel oil and biodiesel blends on engine combustion and emissions were studied in a marine twostroke diesel engine. The engine was operated under propeller conditions using five different fuels with biodiesel blends of 10% (B10), 30% (B30), 50% (B50), and sulphur contents of 0.467% low sulphur fuel oil (LSFO) and 2.9% high sulphur fuel oil (HSFO). Tests have shown that using a biodiesel blend increases the engine fuel consumption due to its lower calorific value. Heavy fuel oil has a high Polycyclic aromatic hydrocarbons (PAH) content, which leads to higher exhaust temperatures due to severe afterburning in the engine. A comparison of engine soot emissions under different fuel conditions was carried out, and it was found that the oxygen content in biodiesel promoted the oxidation of soot particles during the combustion process, which reduced the soot emissions of biodiesel. Compared to HSFO, B10, B30, B50 and LSFO, the soot emission concentrations were reduced by 50.2%, 56.4%, 61% and 37.4%, respectively. In our experiments, the soot particles in the engine exhaust were sampled with a thermal float probe. Using Raman spectroscopy analysis, it was found that as the biodiesel ratio increased, the degree of carbonisation of the soot particles in the exhaust became less than that in the oxygenation process, resulting in a decrease in the degree of graphitisation.