Investigation Effects of Pre-chamber Volume Variations on the Performance of a Natural Gas Lean-Burn Engine

The pre-chamber ignition system accelerates combustion efficiently by supplying multiple ignition points, high ignition energy, and strong turbulent disturbance. This system expands the lean combustion limit and improves combustion stability on natural gas engines. This work studied the effects of pre-chamber volume variations on combustion, performance, and emission behaviors of a natural gas lean-burn engine under experimental and numerical methods. Results show an increase in the pre-chamber volume from 0.3% to 4.4% of compression volume can increase the in-cylinder pressure in single-stage combustion. The energy and exergy efficiency of the engine Model-1.3% increased up to 43.7% and 41.9%, respectively, which are the highest values among the prepared models. Simultaneously, the model heat loss with the maximum pre-chamber volume was two times higher than the minimum pre-chamber volume. The exhaust gas exergy of Model-1.3% and Model-2.1% are the lowest values, approximately 29% of the fuel exergy. Increasing the volume of the pre-chamber from 1.3% of compression volume led to a reduction in emissions. An increase in the pre-chamber volume increases the exit velocity of gases from the pre-chamber bores, and turbulence in the entrance, exit, and inside the bores, which generates uniform and isothermal heat across the cylinder. Therefore, a pre-chamber with a compression volume below 5% stabilizes the combustion. Under stable working conditions, a pre-chamber volume can be defined such that the spark ignition (SI) engine would have the highest energy and exergy efficiencies with the lowest emission.