Forward projected background oriented Schlieren for study of sparks in internal combustion engines

Abstract The use of renewable fuels, such as hydrogen, in internal combustion engines necessitates the development of innovative combustion strategies, which in turn demand a profound comprehension of the underlying ignition phenomena. Consequently, there arises a necessity for advanced or novel measurement techniques that can offer further insights into these phenomena. As part of a study to better understand the ignition phenomenon, this paper presents a modified Background Oriented Schlieren (BOS) method developed to study the heat transferred from sparks generated by spark plugs utilising a projected background in combination with the fast checkerboard demodulation (FCD) technique. This method provides a flexible and more suitable alternative to other BOS techniques for analysing spark ignition phenomena due to the high-resolution visualisation (spatial and temporal) even at higher pressures. Using this technique, the temperature fields generated by the spark were estimated using a simplified calibration. This work also demonstrates the use of the aforementioned method to obtain a high spatial resolution, high-speed visualisation of the heat transferred from the spark to the surrounding non-combustible medium, and the interaction of the spark with the flow field at 11 bar absolute pressure.