International Scientific Journal

Thermal Science - Online First

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Impact of the pre-chamber nozzle orifice configurations on combustion and performance of a Natural Gas Engine

In this study, a pre-chamber was designed to form near stoichiometric mixture and provide multiple turbulent flame jets to ignite the lean mixture and accelerate the combustion in the main combustion chamber for a natural gas engine. A CFD simulation was employed to investigate the impact of the pre-chamber nozzle configurations on flow and combustion processes inside the engine, as well as on the performance of the engine. Various configurations were investigated, including orifice number of 4 to 8 and orifice diameter ranging from 1.6 m to 2.9mm. A non-dimensional parameter β was used to characterize the relative flow area of these configurations. The numerical results indicate that, for a given nozzle flow area, among the design of different orifice numbers, the 6-orifice design can obtain the optimal combustion and engine performance. Otherwise, a design of more orifices leads to slower flame penetrating speed in the main chamber,and the design of less orifices leads to slower circumferential flames propagations in the main chamber. Moreover, for a 6-orifice pre-chamber, the optimal orifice diameter was found to be 2.0 mm, corresponding to a β value of 0.3. A design of larger diameters leads to slower penetrating for the flame jets and insufficient radial flame propagations in the main chamber, while a design of relatively smaller orifice diameters leads to insufficient circumferential flames propagations in the main chamber. Additionally, for the engine performance, all the pre-chamber designs improve the indicated efficiency and reduce the NOx emission. Especially, the design of 6-orifice with diameter of 2.0 mm achieves a 35.0% increase of indicated thermal efficiency and a 78.0% reduction of NOx emission compared to the prototype engine.
PAPER REVISED: 2017-12-29
PAPER ACCEPTED: 2018-01-06
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