The preignition of premixed natural-gas mixture induced by the auto-ignition of cylinder oil can trigger the most threatening abnormal combustion, which severely threatens the safety of low-speed two-stroke Otto-cycle dual-fuel (natural-gas/diesel) marine engine. In present study, both the experiment of cylinder oil stripping and numerical simulation of in-cylinder airflow motion were conducted to reveal the motion state of cylinder oil near scavenging port and its spatial distribution after entering combustion chamber. Further, the possible way to suppress the occurrence of abnormal combustion was also researched by numerical study. Experimental results illuminated that cylinder oil both in the form of film and single droplet would strip under the flow velocity of engine’s scavenging port, which demonstrated the oil stripping behavior near scavenging port was one of its pathways into cylinder. Simulation results indicated at high-load condition, the rich-oil-vapor region mainly located near cylinder wall. In contrast, at low-load condition, rich-oil-vapor region distributed at both cylinder wall and the dead-region beyond exhaust valve. Auto-ignition of oil and pre-ignition of natural-gas were more likely to occur in these rich-oil-vapor regions. The decrease of operating load reduced scavenging pressure, which raised the residual mass of cylinder oil. And the reduction of the diameter of stripped cylinder oil promoted oil’s evaporation, which increased the oil concentration in rich-oil-vapor region. These two factors could further intensify the occurrence tendency of auto-ignition of cylinder oil. Moreover, numerical results also showed that the combination of proper adjustment of arrangement angle of natural-gas injector and the advance of injection timing could significantly improve the homogeneity of pre-mixture. The rich-fuel region near cylinder wall and beyond exhaust valve reduced apparently as well, which meant fuel concentration in rich-oil-vapor regions decreased. The reduction of pre-mixture concentration in rich-oil-vapor region could lower the occurrence possibility of auto-ignition of cylinder oil. Thus the occurrence tendency of preignition of natural-gas and subsequent severe abnormal combustion could also be inhibited.


Experimental and Numerical Study on the Motion Characteristics of Cylinder Oil and the Suppressing Methods for Abnormal Combustion in Low-Speed Dual-Fuel Marine Engine

Division / Sponsors: 
Internal Combustion Engine Division (ICED)

Paper Proceedings: https://asmedigitalcollection.asme.org/ICEF/ICEF2020/volume/84034

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