A combination of optical and laser based methods have been employed for simultaneously studying fuel jet penetration and ignition behaviour of fuel jets inside the cylinder of a large marine two-stroke diesel engine during operation. Tests were performed on a four-cylinder Diesel engine with a bore diameter of 0.5 meter. Optical access was obtained through a custom designed engine cover. A double pulsed laser was employed for global illumination of the liquid fuel jet. For detection a dual camera set-up was employed, which allowed both simultaneous fuel jet and flame emission imaging, or dual frame fuel jet imaging for velocity measurements. From the data recorded the liquid penetration, jet cone angle, jet penetration velocity, ignition location, ignition time and flame lift-off could be extracted.Data was recorded for two different charge densities and temperatures, for two different atomizer designs, and for two different fuels. The fuel jet was observed to ignite at a position around 1/4 of the length downstream. The penetration length, ignition time and lift-off length were found to decrease with increased cylinder pressure and temperature. A conventional atomizer was observed to produce a slightly narrower and longer fuel jet with increased lift-off, compared to a sliding valve atomizer. For heavy fuel oil an increase of width towards the end of the jet and a more wrinkled appearance was observed, compared to marine gas oil. Fuel jet front velocities were found to peak just above 100 m/s after about 0.3 CAD after start of injection.