The influence of in-cylinder flows on the flame kernel growth in natural gas fuelled spark ignition engines.

摘要

The objective of this work was to determine the influence of in-cylinder flows on the natural gas combustion process in configurations representative of light duty vehicle spark ignition engines. Specifically, the influence of the flow field on the flame kernel development period was of interest. The interactions between the flow field and the combustion process were quantified by correlating characteristic in-cylinder fluid flow and mass burn rate parameters. The fluid motion, flame kernel development and the overall combustion duration were characterised using: (i) a two-component laser Doppler velocimeter for the in-cylinder fluid flow, (ii) a fibre-optic instrumented spark plug for the flame kernel growth rate, and (iii) a piezo-electric pressure transducer for the in-cylinder pressure from which the overall mass burn rate data is obtained. The measurements were made on an individual cycle basis. Results from a single cylinder V6 optical engine are reported. Physical interpretations of: (i) the flow field evolution and (ii) the interactions between the flow field and the natural gas combustion process are presented.; The main contributions of this work are through: (i) the application of novel data processing techniques, and (ii) the exploration of the fibre-optic instrumented spark plug as a measurement technique in high swirl engines. For example, the discrete wavelet transform is used to show: (i) the energy cascade process in the non-stationary engine flow field over crank angle phase and frequency; and (ii) how the flow field evolution influences the early stages of the natural gas combustion process. The fibre-optic instrumented spark plug is shown to measure a mass-weighted velocity. Data from the fibre-optic instrumented spark plug data are shown to be biased by the large convection velocities in high swirl engines. This work provides the foundation upon which further investigations into the influence of different in-cylinder flows on the natural gas combustion process in spark ignition engines can be based.