All ship engine exhaust pollutants must meet the second stage emission limit. Therefore, the Common rail fuel injection system is adopted on a newly designed marine engine. By taking advantage of the characteristics of flexible control of fuel injection pressure of the common rail system independent of engine speed, injection timing, injection quantity and multiple injection, the engine fuel supply and regulation system can be reasonably and accurately matched under various working conditions, thus greatly improving the engine power and economy, Comprehensive performance in terms of emissions and noise.

The fuel supply system is a key system of the engine, and its main function is to provide timely and high-quality fuel to the cylinder, ensuring the effective formation and combustion of the mixture in the cylinder. At present, marine diesel engines mostly use a pump pipe nozzle fuel system, and the fuel injection pump is driven by the camshaft. The fuel injection pressure and timing cannot be flexibly controlled, and the overall economic and emission indicators are not high. A new marine diesel engine developed by the company adopts the Common rail fuel injection system, which can flexibly control the injection pressure without being affected by speed and load; The fuel injection adopts the control method of solenoid valve opening time, which is easy to adjust the injection time and injection duration, and can achieve ideal injection patterns, greatly improving the comprehensive performance of the engine in terms of power and economy.

The volume of the common rail pipe mainly considers the maximum circulating oil volume and the allowable pressure drop amplitude during fuel injection.

According to general requirements, take Δ P=Pmax * 20%=32MPa, Δ V=Vm * 1.3=520mm3, E=2870MPa, the calculated volume V is about 47ml. The volume V is the minimum required high-pressure chamber volume, including the internal volume of the rail pipe and the volume of the high-pressure oil pipe. The volume of the high-pressure oil pipe (8X3X500) is generally 20-30ml, and it is more suitable to choose a common rail pipe volume of 25-30ml. Considering the stability of the system rail pressure, the rail pipe volume is determined to be 30ml.

The design of a common rail pump needs to comprehensively consider the fuel supply efficiency, fuel margin, and engine peak torque limits of the common rail pump throughout the entire operating range.

The test results show that the fuel supply efficiency of the common rail pump is higher than 80% throughout the entire operating condition, and the fuel margin is greater than 1.3, meeting the requirements for engine use.

Determination of geometric dimensions of fuel injectors

The nozzle is designed according to the combustion chamber and compression ratio, and the basic dimensions of nozzle aperture, angle, aperture, etc. are determined.

Finite element calculation was carried out for preloading condition, working rail pressure of 160MPa, working rail pressure of 180MPa and working rail pressure of 200MPa respectively. The results showed that the minimum part of the Factor of safety of the injector body was in the assembly part of the transverse chamber under each condition, and the Factor of safety was 1.5, which met the use requirements; The contact stress between the fuel injector body and the orifice plate is above 400MPa, and there is a gap between the control piston and needle valve components. The movement is not affected, and the linear deformation of the fuel injector body is within the design allowable range.

Test calibration and emission control

Rail pressure control

Independent control of injection pressure is achieved through the control system, common rail pump, and common rail pipe, overcoming the limitations of traditional mechanical systems such as engine speed and load. The controller controls the opening of the common rail pump solenoid valve to control the amount of fuel entering the plunger. Based on the set data and the current rail pressure feedback from the rail pressure sensor, the opening of the electronic control valve is adjusted to independently control the injection pressure.

Injection timing control

The control system can adjust the fuel injection timing according to specific parameters such as engine explosion pressure, emission indicators, fuel consumption, exhaust temperature, etc. to achieve the optimal state of the engine.