Study On The Emission Of High-speed Marine Diesel Engine Burning Heavy Fuel Oil

With the development of world economy, shipping industry has been rapidly developed and the possessing capacity of ship is increasing continually. All this has made the emission problem of diesel engines, as the main power source of ship, becoming more and more serious. In order to control the damage to environment from the emission of marine diesel engine, governments and relevant organizations have established corresponding laws to limit the pollutant emission of marine diesel engine. Especially the Annex VI of MARPOL, made by the international maritime organization (IMO), plays a crucial role in controlling the pollutant emission of marine diesel engine and provides guidance to other governments and organizations for establishing emission regulations of own country and area.Taking into account the cost factor, marine diesel engine uses cheap heavy fuel oil as main fuel. Heavy fuel oil is formulated by atmospheric oil, vacuum residual oil, cracked residual oil, cracked diesel oil and catalyzed diesel oil, which are produced in the processing of the crude oil. And it has high viscosity, density, complex ingredient, and poor firing character, which can directly influence the atomization and combustion of fuel in cylinder and the emission character of fuel. In order to protect environment, it is urgent to research how to reduce the emission pollutant of marine diesel engine using heavy fuel oil.At present, the studies of the control of diesel engine emissions are mainly focused on SOx and NOx. Using low sulphur fuel and stack desulfurization are the main measures to reducing SOx emission of ship now. On the one hand, using low sulphur fuel can increase operating cost of ship. On the other hand, the refining and desulphurisation of fuel can expend a vast amount of energy and increase the emission of greenhouse gas CO2. Because seawater is alkalescent, therefore marine diesel engine can directly use seawater to desulfurize. Practice has proved desulphurization results can reach more than 90% by using seawater. But this technology has some disadvantage such as influencing the quality of seawater and increasing exhaust back pressure of diesel engine. Now the NOx emission control methods are mainly divided into two aspects:inside combustion control and outside exhaust treatment. The purpose of the former is to reduce NOx formation, from the source control NOx emission. And the purpose of the latter is to remove NOx in exhaust. The source control is mainly realized by optimizing combustion and controlling in-cylinder combustion temperature, such as emulsifying fuel, wet control and exhaust gas recirculation. Emissions post-processing is mainly through a series of physical and chemical reaction to realize the purification processing of exhaust emissions, such as selective catalytic reduction and low-temperature plasma technology.The emissions of a marine high-speed diesel engine were measured under different advance angle of fuel supply, fuel spray nozzle and fuel supply pressure of oil-feed unit when burning light oil and heavy fuel oil. The experiment results show that under the same advance angle of fuel supply, fuel spray nozzle and fuel supply pressure, the engine has a similar NOx emission level and a quite different variation trend of HC emission, and the CO and smoke emission when burning heavy fuel oil apparently higher than burning light oil. By changing advance angle of fuel supply from 20℃A BTDC to 25℃A BTDC, the NOX and smoke emission increased, and the CO an HC emission varied inconspicuously. By changing advance angle of fuel supply from 25℃A BTDC to 28℃A BTDC, the NOX and smoke emission increased sharply, and the CO an HC emission increased to a certain extent. Only changing fuel spray nozzle and remaining other conditions unchanged, the NOx emission of fuel spray nozzle with smaller hole diameter was higher then the one with bigger hole diameter, and the smoke emission was opposite. It means the diameter of the fuel spray nozzle plays a decisive role in the atomization of fuel and further influence the combustion and the emission of fuel. When changing fuel supply pressure of oil-feed unit, the NOx and smoke emission had hardly changed. It means that fuel supply pressure has a little influence on the emission of engine.