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Dual-fuel engines for marine propulsion are gaining in importance due to operational and environmental benefits. Here the combustion in a dual-fuel marine engine operating on diesel and natural gas, is studied using a multiple high-speed camera arrangement. By recording the natural flame emission from three different directions the flame position inside the engine cylinder can be spatially mapped and tracked in time. Through space carving a rough estimate of the three-dimensional (3D) flame contour can be obtained. From this contour, properties like flame length and height, as well as ignition locations can be extracted. The multi-camera imaging is applied to a dual-fuel marine two-stroke engine, with a bore diameter of 0.5 m and a stroke of 2.2 m. Both liquid and gaseous fuels are directly injected at high pressure, using separate injection systems. Optical access is obtained using borescope inserts, resulting in a minimum disturbance to the cylinder geometry.

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.

In-cylinder flow velocity measurements using particle image velocimetry (PIV) have been performed for the first time in a full-size marine Diesel engine. The engine was a four cylinder two-stroke engine with a bore diameter of 0.5 meter and a stroke of 2.2 meter. For such engines uniflow scavenging is used, with fresh air entering through angled ports at the bottom of the cylinder to generate a swirling flow and burnt gases exiting through a centrally located exhaust valve at the top. For efficient design of this process and for validation of CFD models it is essential to obtain an experimental characterization of the flow inside a fully operational engine. Optical access was obtained through a custom designed engine cover, fitted with a number of optical ports into which sapphire windows were mounted. Both the laser and camera used for PIV were mounted directly onto the engine in order to minimize effects of vibrations on optical alignment.

The scavenging process is an integral part of any two-stroke internal combustion engine cycle whether it is spark ignited or compression ignited. The scavenging process is responsible for transporting the burned gases from the previous working stroke out of the combustion chamber to allow for the fresh charge or fresh air to enter for the next combustion/working stroke. This implies that the scavenging process is responsible for setting the initial condition for the combustion process, consequently affecting fuel economy, power output and emission of hazardous gases. Two-stroke diesel engines for marine propulsion are usually uniflow scavenged cross-head engines. In uniflow scavenged engines the scavenge air enters the cylinder via ports located near the bottom dead center and exits through an exhaust valve located in the cylinder head. The in cylinder flow is therefore concentrated in one direction which gives the method its name.