Test Rig for Fundamental Investigations of Ignition System Characteristics under Severe Flow Conditions

supply concepts. To achieve further improvements in efficiency and to decrease emissions, engine operating strategies with very lean air-fuel mixtures and high turbulence levels are required. However, these severe conditions have a significant impact on the inflammability of the mixture and compromise combustion stability. Reliably igniting the mixture and keeping cycle-to-cycle variation of the combustion process at a low level is challenging and requires deeper understanding of the fundamentals of the ignition process. The electric arc, which transfers the electric energy to the air-fuel mixture and initiates the inflammation, plays a central role in the ignition process. Thus, the paper at hand presents a test rig that was developed for detailed investigations of electric arc behavior under flow conditions similar to those in spark ignited large gas engines. The test rig consists of a closed loop flow circuit. Flow velocities at the spark plug up to 30 m/s, pressures up to 60 bar and temperatures up to 80 °C can be achieved under non-combustible conditions. The centerpiece of the test rig is the test cell, which provides excellent optical access from three sides for high-speed imaging of the arc without disturbing the flow field at the spark plug. A sufficiently long stabilizing path upstream of the test cell guarantees defined and fully developed turbulent pipe flow conditions at the spark plug. Sophisticated post-processing algorithms were developed that automatically extract relevant data from the high-speed images (e.g., arc length) and compare the information with electrical signals such as current and voltage on both the primary and secondary sides of the electronic ignition system. The results provide a deeper understanding of the ignition process and serve as basis for model validation. Finally, measurement results of a pressure variation are presented and discussed. The results show greater arc stretching and increased cycle-to-cycle variation in arc length at higher pressures