On the Origin of Pre-Ignition inside a Pre-Chamber Spark Plug – Optical and Thermal Analysis

Pre-chamber spark plugs are currently under development for the usage on passenger car sized combustion engine. Its advantage over a conventional ignition system is its faster combustion due to hot and turbulent flame jets. Unfortunately, sporadic pre-ignition events have been observed during various engine testing. Since the combustion system consists of a pre- and main-chamber it is difficult to identify the root-cause. In the scope of this work we want to provide additional insights to the development of the pre-ignition. Our main assumptions for pre-ignition are: 1) pre-ignition can be triggered by hot pre-chamber surface components or 2) by hot and still reactive residual gasses trapped inside the pre-chamber from previous combustion cycles.
In order to proof our assumptions, we conduct temperature measurements inside the pre-chamber cap, shell, centre- and ground electrodes and monitor via six small sapphire windows the occurrence of the flame. Since the engine will be purposely run in pre-ignition mode and due to packaging reasons for the sapphire windows, the experiment is carried out on a medium-duty natural gas engine with a M14 pre-chamber spark plug. ... mehr
Furthermore, we compare the measurement results to large eddy simulations of the pre-chamber only, which will provide additional information about the conditions inside the pre-chamber.
During pre-ignited cycles no critical component temperatures could be measured, and a first occurrence of the flame in the core nose region before spark timing is detected. Therefore, the origin for pre-ignition must be in the upper portion of the pre-chamber. The numerical results were also reporting higher residual gas concentration during the compression stroke in the core nose region. Finally, a new barrier-free pre-chamber design was built and tested, that did not show pre-ignition under same operating conditions, which proves the importance of internal aerodynamic effects to pre-ignition using passive pre-chamber spark plugs.