In recent years, diesel generators have been used more and more on ships.In addition to being used as a conventional unit to power boats, it is increasingly being used for electric propulsion.Due to its unique advantages, full or semi-electric propulsion has become the development trend of thousands of tons of ships, especially military ship propulsion systems.Mainly used as the prime mover of the ship generator set, diesel engine oil cooler for the diesel engine of diesel engine oil cooling to view important, diesel fuel through seawater cooling, in order to achieve the performance of the diesel engine is needed.

The main measures

Modern Marine large - scale low - speed diesel engines have been more effective in improving the economy in the last decade than in the past few decades.All kinds of energy-saving measures appear one after another and are improving day by day.These measures mainly include:

1.Fixed pressure turbocharging system and high efficiency exhaust turbocharger are adopted

It is a remarkable feature of modern diesel engine to replace impulse turbocharging system with fixed pressure turbocharging system in high pressure diesel engine, and it is also beneficial to improve the efficiency of supercharger.The development and application of the new turbocharger increased the efficiency of the turbocharger from 50-60% in the 1960s to 60-76%, which significantly reduced the fuel consumption rate of diesel engines.

2.Increase stroke cylinder diameter ratio S/D

Increasing the cylinder diameter than the main purpose of the S/D is under the condition of invariable in keeping the average speed of piston Vm greatly reduce diesel engine rotating speed, to improve the efficiency of the propeller, so as to improve the overall efficiency of power plant.This is an important measure to improve the economy of diesel engine power plant since oil crisis.Therefore, since the late 1970s, S/D has increased rapidly, and a series of low-speed diesel engines with long stroke and ultra-long stroke have been developed gradually.The increase of S/D also improved the economy of diesel engine.However, the increase of S/D will complicate the structure of diesel engine and increase the cost, so the increase of S/D is limited.

3.Increase the ratio of maximum burst pressure pz to average effective pressure PE

It is proved by the theoretical circulation research and practice of diesel engine that improving pz/ PE can significantly reduce fuel consumption rate.The study showed that when pz/ PE increased from 7.8 to 12, fuel consumption could decrease by about 12g/kW·h.Therefore, modern Marine diesel engines adopt this measure to reduce fuel consumption.However, it is very difficult to greatly improve the pz, which is limited by the diesel load, and corresponding measures must be taken to ensure the reliability of the diesel engine.Thus, from the 1960s to the mid-1970s, pz of Marine diesel engines increased gradually, but not by much (pz increased by only about 2.5mpa in the last 20 years).From the mid-1970s to the mid-1980s, the pz value of diesel engines increased significantly, increasing by about 5MPa.Some diesel engines now have a pz of 15 MPa(such as Sulzer RTA) or even 18MPa.Reducing PE value while keeping pz constant can also reduce fuel consumption rate, which is also a widely adopted energy-saving measure.Reducing PE is the use of diesel engine with reduced power.

4.Increasing compression ratio

In supercharged diesel engine especially high supercharged diesel engine, in order to limit the pz, ensure the diesel engine has enough mechanical strength, used to measure is to reduce diesel engine compression ratio, but it also reduces the efficiency.Obviously, this measure is no longer in line with the development needs of modern diesel engines.In order to improve the economic efficiency of modern Marine low-speed diesel engines, measures to increase the compression ratio are still adopted according to the conclusion of theoretical cycle, and the compression ratio is increased from about 10 to between 16 and 19.

5.Adopt variable injection timing (VIT) mechanism

When improving pz as an energy saving measure, more attention should be paid to increasing pz value of diesel engine under partial load.For one thing, the actual power of modern Marine diesel engines is usually less than the calibrated power.Secondly, the pz of diesel engine decreases with the decrease of the load.If the pz value can be kept as its calibration value at partial load, the result is that the ratio of pz to PE becomes larger, the fuel consumption rate decreases.VIT institutions in the diesel engine load changes automatically adjust the fuel injection advance Angle, ensure that the partial load (usually a load of 80% ~ 100%) of diesel engine when pz basically remain unchanged, and within the scope of 50% ~ 80% load also have higher p z value (compared with no VIT institutions).

6.The friction loss work is decreased and the mechanical efficiency is increased by m

The friction loss of diesel engine accounts for about 40% of the mechanical loss, so reducing friction loss is the main way to improve m.Modern Marine low speed diesel engines adopt short skirts and short skirts piston, reduce the number of piston rings and improve working conditions of piston rings to reduce friction loss and improve mechanical efficiency.

7.Shaft band generator (PTO)

During the normal operation of the main diesel engine (> is usually required to calibrate the main engine speed by 70%), the generator can be driven by the special constant speed drive device to generate the power needed for the navigation of the ship.When the speed of the main engine changes or fluctuates, the constant speed drive device can guarantee the constant speed of the generator, or the voltage and frequency of the generator can be kept constant through the frequency conversion device.The operation of diesel generator can be stopped during navigation by using axial generator.This device does not directly reduce the fuel consumption rate of diesel engine, but improves the economy of Marine power plant.The advantages of the device is mainly include: can use lower fuel consumption rate of power supply of main diesel engine can save oil consumption in the operation of diesel generators, reduce the number of the diesel generator and maintenance costs.

8.Reuse of diesel engine waste heat

Diesel exhaust and cooling media take about 50% of the fuel's total heat.It is important to make full use of the energy of this part of waste heat to improve the economy of the whole power plant.Such as the use of waste gas turbine generators, exhaust gas boiler generators.At present, these problems are still being studied and explored.

9.Improved injection and combustion technology

It is one of the important research subjects of high pressure diesel engine to shorten the duration of injection and improve atomization quality and combustion efficiency.For this reason, the development of high injection pressure (100 Mpa to 140 Mpa), high injection rate so as to shorten the injection system of injection duration, and adopt measures to optimize the injection system structure to improve the quality of atomization, improve combustion efficiency.At present, intelligent electronic control injection diesel engine has begun to ship applications.