Investigation of impacts of spark plug orientation on early flame development and combustion in a DI optical engine

The influence of spark plug orientation on early flame kernel development is investigated in an optically accessible gasoline direct injection homogeneous charged spark ignition engine. This investigation provides visual understanding and statistical characterization of how spark plug orientation impacts the early flame kernel and thus combustion phasing and engine performance. The projected images of flame kernel were captured through natural flame chemiluminescence with a high-speed camera at 10,000 frames per second, and the ignition secondary discharge voltage and current were measured with a 10 MHz DAQ system. The combustion metrics were determined using measurement from a piezo-electric in-cylinder pressure transducer and real-time engine combustion analyzer. Three spark plug orientations with two different electrode designs were studied. The captured images of the flame were processed to yield 2D and 1D probability distributions. Charge motion interaction with kernel development was characterized. The data was segregated according to the initial flame kernel convection directions and investigation was conducted to understand how the different spark plug orientations influence the flame kernel propagation cycle-to-cycle. The results revealed that the two electrode designs produce the same trend for the cycles whose initial flame kernels are convected to the exhaust side of the cylinder: the 90° index orientation (crossflow) produces the largest and fastest growing flame kernels while the 0° index orientation where flame kernel is convected onto the ground strap produces the smallest and slowest growing flame kernels. For the cycles whose initial flame kernels are convected to the intake side, 0° index orientation, however, exhibits slight advantage over the other two index orientations