An Experimental Study on the Interaction between Flow and Spark Plug Orientation on Ignition Energy and Duration for Different Electrode Designs

The effect of flow direction towards the spark plug electrodes on ignition parameters is analyzed using an innovative spark aerodynamics fixture that enables adjustment of the spark plug gap orientation and plug axis tilt angle with respect to the incoming flow. The ignition was supplied by a long discharge high energy 110 mJ coil. The flow was supplied by compressed air and the spark was discharged into the flow at varying positions relative to the flow.

The secondary ignition voltage and current were measured using a high speed (10MHz) data acquisition system, and the ignition-related metrics were calculated accordingly. Six different electrode designs were tested. These designs feature different positions of the electrode gap with respect to the flow and different shapes of the ground electrodes. The resulting ignition metrics were compared with respect to the spark plug ground strap orientation and plug axis tilt angle about the flow direction.

Analysis of the experimental data indicates that the position of the ground strap with respect to the flow is a primary factor that causes variations in ignition discharge energy and discharge duration. The different types of electrodes are influenced differently as the incoming air flow direction changes with respect to the electrode gap. Double fine wire electrodes produce a wide constant ignition energy and duration window; while side electrode gap has a great variation in gap energy output. The experimental results show that the normalized gap energy increased by 67.7% as the incoming flow changes from 0° index angle to 90° angle.