I. overview of diesel engines.

1.Heat engine

A heat engine is a power machine that converts heat energy into mechanical energy.
Steam engine, steam turbine and diesel engine, gasoline engine are the more typical models in the engine.
     

The steam engine is the same as the steam turbine.
In this type of machine, combustion (the chemical energy of the fuel is converted to heat) occurs outside the cylinder (boiler), and the heat energy is converted into mechanical energy that occurs inside the cylinder.
Because heat energy needs to be transported by some intermediate working medium (water vapor), the heat loss is inevitable, so its thermal efficiency is not high, and the whole power plant is very heavy.
The energy problem is so prominent that it cannot compete with the internal combustion engine and has been lost in the ship's power plant.
 

2.The internal combustion engine

Gasoline engines, diesel engines and gas turbines are the same internal combustion engines.
Although they form of mechanical motion (reciprocating and rotating) is different, but with the same characteristics ─ ─ are fuel inside the engine cylinder combustion and direct use of high temperature and high pressure gas from the burning of fuel in the cylinder expansion work.
From the viewpoint of energy conversion, such mechanical energy loss is small and has high thermal efficiency.
In addition, it has obvious advantages in terms of size and weight, so it has achieved a clear leading position in the competition with external gas turbine.
    

Depending on the fuel used in the internal combustion engine, it can be roughly divided into gasoline engine, gas engine, diesel engine and gas turbine.
They all have the common characteristic of internal combustion engine, but have their respective working characteristic.
Due to these different characteristics, they are different in terms of working principle, working economy and use range.
If the gasoline engine USES volatile gasoline to make fuel, it USES the external mixing method (gasoline and air are mixed with the carburetor in the external air intake of the cylinder) to form a combustible mixture.
The internal combustion is electric ignition (spark plug ignition).
This kind of job characteristics make gasoline engine can't use high compression ratio, thus limits the efficiency of gasoline engine cannot be improved, but also not allowed to use as Marine engine (gasoline fire danger).
But it is widely used in transport vehicles.
 

3.The diesel engine

Diesel engine is a reciprocating internal combustion engine with compression ignition.
It USES less volatile diesel or poor fuel oil for fuel.
The internal mixing method (the mixture of fuel and air occurs inside the cylinder) to form a combustible mixture;
The combustion in the cylinder adopts compression type (the high-temperature self-ignition caused by compressed air in the cylinder).
This kind of work features the highest thermal efficiency of diesel engine in the field of engine (55% or so), and is allowed to be used as Marine engine.
Therefore, diesel engine is widely used in engineering.
Especially in Marine engine, the diesel engine has achieved the absolute leading position.
According to the Lloyd's register of shipping, in 1985, 99.89% of the ships manufactured in the world (2000t) were powered by diesel engines, and by 1987 100% were diesel engines.
Marine engine fuel economy, reliability, is the first life, size, weight, is the second, machine applicable for Marine engine at low speed, high power 4-stroke medium-speed machine applicable for ro-ro and container ships, medium and high speed machine suitable for generator set.

Diesel engines usually have the following advantages:

(1) good economy.
The effective thermal efficiency can reach over 50%, can use the cheap heavy oil, the fuel cost is low.
    

(2) the power range is wide, and the power of single machine ranges from 0.6kW to 45600kW.

(3) small size and light weight, which is conducive to the arrangement of ship engine room.
     

(4) good maneuverability.
It is easy to start up, has good acceleration, has wide speed and load regulation range, can be reversed directly, and can adapt to various operating conditions of the ship.
    

At the same time, diesel engine has the following disadvantages:

(1) vibration of fuselage and torsional vibration and noise of shafting.
 

(2) the working conditions of certain parts are poor, withstanding high temperature, high pressure and impact load.
 

The development trend of modern Marine diesel engines.

After decades of development, especially in the last decade, modern Marine diesel engines have developed to a higher level of technology.
In the future, with the development of productivity, the Marine diesel engine will be more demanding, and the ship diesel engine will continue to develop and improve.
The current development of diesel engine can be summarized as: energy saving as the center, fully taking into account the requirements of emission and reliability, comprehensively improving the performance of diesel engines.

According to this development goal, the future research trends are as follows:

1) research on improving economy, including research on combustion, supercharging, low wear and so on;
 

2) reduce the emissions of diesel engine research, modern diesel engine emissions are facing serious challenges, with restrictions on ship diesel engine emission control, making it harder for the improvement of economy, this is also a new topic in the development of Marine diesel engine;
 

3) improve reliability and durability;
 

4) research on electronic control technology;
 

5) research on alternative fuels.
 

Modern Marine diesel engines have achieved more economical efficiency than the past few decades.

All kinds of energy-saving measures have appeared and improved gradually. These measures mainly include:

1) adopt the constant pressure turbocharging system and the high efficiency exhaust turbocharger.
    

2) increase the stroke diameter ratio S/D.
     

3) increase the maximum outburst pressure pz and the average effective pressure PE ratio pz/PE.
 

4) increase the compression ratio.
         

5) variable injection timing (VIT) mechanism is adopted.
    

6) reduce friction loss work and improve mechanical efficiency.
    

7) power turbine system (TCS) is adopted.
    

8) shaft generator (PTO).
    

9) waste heat reuse of diesel engines.
    

10) improved injection and combustion technology.
 

The structural features of modern Marine low-speed diesel engines.

1) borehole cooling structure is widely used in combustor parts.
    

2) rotary exhaust valve and hydraulic valve actuator are adopted.
    

3) spray pump adopts variable injection timing (VIT) mechanism.
    

4) thin wall bearings are used.
     

5) adopt independent cylinder lubrication system.
 

6) axial shock absorber is added on the crankshaft.
    

7) weld the crankshaft.