Calculation studies of fuel equipment for marine diesels

Abstract

The paper presents a method and calculation of the cyclic fuel delivery, plunger pairs of high-pressure pumps and nozzle holes of fuel oil atomizers for low-speed marine two-stroke diesel MAN B&W engines with a cylinder capacity from 1310 to 4880 kW. It is shown that for the given power range of marine diesel engines, cyclic delivery at the nominal mode varies from 31 to 188 cm³ , a plunger diameter – from 44 to 80 mm, and holes diameter- from 0.58 to 1.1 mm. It has been found that for MAN B&W 6S50MC diesel engine, with a constant cyclic fuel supply by one nozzle (18500 mm³) at injection duration (0.039 s), an increase in the average pressure in front of the nozzle holes from 30 to 100 MPa makes it possible to reduce the nozzle holes diameter from 0.75 to 0.55 mm, while reducing the average diameter of the sprayed fuel from 49 to 36 microns. Calculations have been performed of the fuel flame, the length of which depends on the nozzle hole diameter; of the speed and time of the fuel expiration, of the density and Weber criteria. Its self-ignition delay period has been found. It depends on the pressure and temperature of the air in the combustion chamber, the average speed of the piston and the excess air coefficient. It is proposed that the time the fuel flame travels from the nozzle opening to the wall of the combustion chamber should be coordinated and approximately equal to the delay time of the fuel selfignition. The proposed method of calculating fuel delivery, a plunger pair of the highpressure pump, nozzle holes diameter of the nozzle sprayer, fuel atomization fineness, a fuel flame length, and a delay period of self-ignition can be useful in improving and developing new designs of the fuel equipment of marine diesel engines