# Nozzle Design of Plug-and-Play Passive Pre-Chamber Ignition Systems for Natural Gas Engines
## 3 Results and Discussion
### Influence of Nozzle Design on Savenging
Figure 5c, Figure 5d, and Figure 5e have a large amount of  
Figure 4: Velocity contours in the pre-camber of 7 cases at \(-9^{\circ}\)CA during scavenging. residual gas remaining in the top area of the PC, but for different reasons. Figure 5c has a lateral angle of 20\({}^{\circ}\) and a vertical angle of 130\({}^{\circ}\). Its steady swirl spontaneously concentrates the residual gases towards the center. The lateral angle in Figure 5d is 10\({}^{\circ}\) and the vertical angle is 120\({}^{\circ}\). The linear velocity and radius of the swirling flow decrease synchronously, and the stable swirl still gathers the residual gas towards the center. Figure 5e has lateral and vertical angles of 10\({}^{\circ}\) and 140\({}^{\circ}\), respectivley. The height and stability of the swirl flow are reduced, therefore, the residual gas is squeezed toward the top and one side area of the PC. High turbulent kinetic energy can support faster flame propagation and improve efficiency. Figure 6 shows the distribution of turbulent kinetic energy for each PC at \(-9\)\({}^{\circ}\)C. As the lateral angle increases, the turbulent kinetic energy level decreases rapidly. In Figure 6c, with a maximum lateral angle of 20\({}^{\circ}\), the turbulent kinetic energy near the spark plug tends to be zero, which is not conducive to the propagation of initial fire nuclei. In Figure 6b, the turbulent kinetic energy level reaches the highest value, with a lateral angle of 0\({}^{\circ}\); however, the high CO\({}_{2}\) concentration near the spark plug offsets this advantage. The trade-off between the turbulent kinetic energy and the CO\({}_{2}\) concentration is also reflected in the influence of the orifice diameter. In Figure 6f, the average turbulent kinetic energy near the orifice region reaches the highest value, compared to the other schemes. However, the CO\({}_{2}\) near the spark plug also reaches its maximum, leading to a decreased ignition performance. The influence of the vertical angle is complex. In Figure 6d, with a vertical angle of 120\({}^{\circ}\), the swirl intensity increases, and a turbulent kinetic energy distribution similar to that in Figure 6c appears. The difference between the two swirl flows is worth noting. The swirl flow in Figure 6c is formed near the orifice with more stability. In contrast, the swirl flow in Figure 6d is formed at a higher height with less stability, homogenizing the turbulent kinetic energy distribution. Figure 5: Residual CO\({}_{2}\) mass fraction in the PC of 7 cases at \(-9\)\({}^{\circ}\)CA during scavenging. In conclusion, the nozzle design should consider the trade-offs of the main parameters. The lateral angle determines the swirl intensity of scavenging. If a stable swirl is formed in the PC, the lateral angle should be appropriately reduced. If the swirl intensity is so slight that the airflows impact each other, the lateral angle should be appropriately increased. The vertical angle is another crucial factor affecting the swirl. If the swirl height cannot reach near the spark plug, the vertical angle should be appropriately reduced. If there is too much dissipation due to the swirl radius reduction, the vertical angle should be increased appropriately. The orifice diameter affects the residual gas and jet penetration distance. If the jet penetration distance is insufficient, the orifice diameter should be reduced. If too much gas remains, the orifice diameter should be increased.