Patterns of lean methane-air mixtures combustion in piston engine

The article is devoted to the study of the patterns of combustion of lean methaneair mixtures in marine internal combustion engine. Literature review shows that the implementation of combustion technology for a homogeneous lean methaneair mixture will increase the compression ratio, reduce fuel consumption and improve the environmental engine performance. However due to an increase in misfires and a decrease in the speed of flame propagation, the combustion of lean methaneair mixtures remains an unresolved problem. The article studies the influence of the excess air coefficient (from 1 to 1.4) on the turbulent combustion regime (assessed by the Karlowitz and Damkoehler criteria), the completeness and rate of fuel combustion. It was revealed that depletion of the air fuel mixture under conditions of intense turbulence leads to an increase in the Karlowitz criterion and a decrease in the Damköhler criterion. This indicates that the rate of chemical reactions in the flame front decreases, as a result of which the combustion process is characterized by stretching and rupture of the flame front. Therefore, to intensify the combustion of lean methaneair mixtures, it is advisable to increase the average speed of the vortex flow, and not the intensity of turbulence. A study of the influence of the excess air coefficient on the completeness and rate of fuel combustion showed that depletion of the mixture leads to a decrease in the completeness of fuel combustion from 93.5 % (at α=1) to 83 % (at α=1.4). The combustion rates also decrease and their maximum values shift from 13° (at α=1) to 24° (at α=1.4) degrees after top dead center. Therefore for efficient engine operation on lean mixtures, it is necessary to increase the fuel combustion rate through additional swirling of the gasair mixture or the use of combustion promoters.

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