Visualization of the PCCI combustion of Light Cycle Oil (LCO) in diesel engines

The present research focuses on the application of Light Cycle Oil (LCO) in a middle speed diesel engine under PCCI (Premixed Charge Compression Ignition) combustion conditions. LCO is a middle distillate from the fluid catalytic cracking (FCC) process during petroleum refining. The industries gaining interest in the use of LCO in diesel engines comes mainly due to its low sulphur content (<0.2%) in order to conform to the tight future emission restrictions for marine vessels. The use of LCO in marine diesel engines, however, is known to be problematic due to the bad combustion properties of LCO. This study shows the application and suitability of LCO by means of PCCI combustion in comparison with Marine Diesel Oil (MDO), usually used in ship engines. Experiments were carried out on a medium size, single cylinder, two stroke diesel engine (NDT) with 190mm in bore and 350mm in stroke. The visualization of the PCCI combustion was realized using an optical laser setup for shadowgraph imaging. The investigation of the shadowgraph pictures indicate that no soot was formed during PCCI combustion. Further the NO_x emissions of the two-stage combustion, composed of PCCI- and diffusive combustion were reduced of nearly 10% compared to ordinary diesel combustion. The thermal efficiency was increased of nearly 1.5% to 34.6% by using LCO compared to MDO due to shifting of the ignition to TDC. Furthermore intake air cooling from 65°C to 34°C results in an additional increase of thermal efficiency to 34.9% at constant level of NO_x emission.