Hydrotreated Vegetable Oil and Miller Timing in a Medium-Speed CI Engine

The objective of this paper is to analyse the performance and the combustion of a large-bore single-cylinder medium speed engine running with hydrotreated vegetable oil. This fuel has a paraffinic chemical structure and high Cetane number. These features enable achievement of complete and clean combustion with different engine setups. The main benefits are thus lower soot and nitrogen oxides emissions compared to diesel fuel. The facility used in this study is a research engine, where the conditions upstream the machine, the valve timing and the injection parameters are fully adjustable. In fact, the boundary conditions upstream and downstream the engine are freely controlled by a separated supply air plant and by a throttle valve, located at the end of the exhaust pipe. The injection system is common-rail: rail pressure, injection timing and duration are completely adjustable. The gas exchange system consists of electro-hydraulic actuators, used for controlling the intake and exhaust valve timing. Using the flexibility of the engine parameters, several configurations have been tested to realize different in-cylinder conditions before the combustion: the compression temperature and the exhaust fraction have been changed by modifying valve timing and boundary conditions. The in-cylinder compression pressure and the injection parameters have been kept unchanged. The results are promising and show the benefits of hydrotreated vegetable oil compared to diesel fuel. NOx emissions have been reduced almost by 50% running with hydrotreated vegetable oil and opportunely tuned valve timing. Among all the other values, fuel consumption and soot values do not increase appreciably.