Passive Pre-Chamber Spark Plug for Future Gasoline Combustion Systems with Direct Injection

The challenge of using a pre-chamber spark plug for future gasoline combustion processes with direct injection is, on the one hand, to realize an ignitable mixture in the pre-chamber at low load and speed. On the other hand, at high speed and high load, keeping component temperatures have to be kept low in order to prevent irregular combustions (pre-ignition, glow ignition). With increasing requirements regarding fuel consumption and emissions, the challenges to modern combustion strategies are growing steadily. Measures to further increase the efficiency of the combustion engine are required for this purpose. There are different approaches to increase efficiency. These include increasing the compression ratio and diluting the air-fuel mixture. The latter can be generally classified into two broad categories: Dilution with air and dilution with residual gas. In both cases, it turns out that the highest possible dilution is to be preferred with respect to combustion efficiency. Increasing dilution, however, leads in both cases to a deterioration in flammability and a decrease in the flame velocity of combustion. In the resulting requirements for the ignition system, the passive pre-chamber spark plug is an interesting alternative to the conventional spark plug. ... mehrDue to its functional principle, it can simultaneously improve the ignition and shorten the burn duration. In the present work, the focus is on the behavior of the pre-chamber spark plug while diluting the cylinder charge with air. A particular challenge for the passive pre-chamber spark plug is to safely ignite the mixture at idling and in the low to medium part load with a correspondingly high internal residual gas content. Dilution of the cylinder charge with air also complicates the possibility to have a good air-fuel mixture within the pre-chamber. In order to ensure a reliably ignitable mixture in the pre-chamber even under these boundary conditions, it is necessary to design a suitable pre-chamber geometry in conjunction with the direct injection. This work describes the behavior of different passive pre-chamber spark plugs when using lean mixtures at low and medium part load with CFD simulation. Criteria such as residual gas content and air-fuel ratio at start of ignition at the ignition point as well as other flow parameters such as temperature, velocity and turbulent kinetic energy are examined in detail. The effect of the torch coming out of the pre-chamber is finally assessed by combustion simulation.