Influences of the control parameters and spark plug configurations on the performance of a natural gas spark-ignition engine

Lean-burn and exhaust gas recirculation (EGR) strategies have been used in natural gas spark ignition (SI) engines for meeting the increasingly stringent emission standards. However, the combustion rate of the natural gas (NG) decreases under the lean or ultra-lean and EGR operating conditions. In this paper, a simulation model based on the two-zone combustion modelling approach is established and validated with the experimental data. Then, configuration with different lambdas and EGR ratios, and twin-spark plugs are simulated by using this calibrated model to predict the performance of the NG SI engine. The results indicate that the EGR strategy is more effective in decreasing NOx emissions than that of the lean-burn strategy due to its thermal, dilution, and chemical effects of the EGR components. In addition, the formations of the HC emissions are amplified due to the dilution and chemical effects of the EGR components. Furthermore, under the lambda value of 1.5, the 50% mass fraction burned of the NG SI engine is located at 21.77 degrees CA after the top dead center (TDC) when the single-spark plug configuration is used, while it is located at 16.58 degrees CA after the TDC when the twin-spark plugs configuration is used. Besides, compared to the single-spark configuration, using the twin-spark plugs configuration in the NG SI engine is more conducive to decreasing the ignition delay period and combustion duration. Overall, it is verified that the use of twin-spark plugs configuration can effectively extend the lean-burn limit and enhance the combustion rate for the NG SI engine, particularly under the ultra-lean mixture.