Low quality fuel oil is generally referred to as low quality, difficult to use and low cost of Marine fuel oil.
Usually, low-quality fuel refers to the aforementioned "intermediate fuel oil" and "residual oil".
The low quality fuel (heavy oil) used in Marine diesel engines is mostly "intermediate fuel oil", and the most viscous quality of the diesel engine is called heavy fuel oil.
At present, with the development of petroleum refining process, the quality of low quality fuel is decreasing year by year, and the demand for diesel engine is becoming more and more stringent.
 

Low quality fuel has the following characteristics of low quality fuel.
 

(1) high density.
Low quality oil density can be as high as 0.94g/cm3 ~ 1.06g/cm3.
Therefore, fuel purification and atomization are difficult, and the oil droplets are prone to heat crack when burning, resulting in more carbon.
 

(2) high viscosity.
The viscosity of low oil is about 50mm2/s ~ 2000mm2 /s.
This causes the difficulty of fuel storage, transportation, purification and atomization.
 

(3) complex composition.
Low quality oil contains more water, ash and sulfur, vanadium, sodium, silicon, residue and other impurities.
The impurities in the oil aggravate the corrosion and wear of the components and components of the diesel engine combustion chamber.
 

(4) poor firing.
Low - quality oil has a low CN value (usually around 25).
The combustion duration is long, the combustion duration is long, the tr value of the exhaust temperature is high, and because of the incomplete combustion, both the be and the smoke are increased.
 

Use of low quality fuel.

1.Use low quality fuel.

The use of low quality fuel is an important technical achievement in the development of Marine diesel engines.
The use of this fuel can greatly reduce the operating costs of ships and can reasonably use petroleum resources.
Since the 70 s, because of the sharp price increases the diesel engine fuel, fuel costs about 50% of the cost of shipping business, the Marine diesel engine using poor quality fuel become a widely used technology.
At present, low quality fuel is used not only for Marine low-speed diesel engines, but also for medium-speed diesel engines (mainframes and generators).
 

2.When a diesel engine USES a low-quality fuel after using a low-quality fuel, the following adverse consequences can be caused if it is not properly handled:

(1) affect the normal operation of the oil injection equipment.
Increase the mechanical load and heat load of the oil injection equipment, and cause the excessive wear, corrosion, carbon, deformation and other faults of the oil spray equipment.
 

(2) deterioration of combustion performance.
Low quality fuel oil atomization difficulty, self-ignition difference, aggravate combustion performance, the highest explosion pressure drop: after burning serious, exhaust temperature increase, exhaust smoke increase, inside the cylinder is serious.
 

(3) damage main parts.
Low-quality fuel ash content, mechanical impurities, and used coal and fuel oil cracking catalyst containing silicon, aluminum, etc., will make the cylinder and the piston parts occur abnormal particles wear: poor quality fuel oil in the high sulfur content and high sodium and vanadium content produced by the low temperature corrosion and high temperature corrosion will make the cylinder liner, bearing, exhaust valve and valve seat, turbocharger, such as serious corrosion wear, increased damage of components.
 

(4) accelerate oil deterioration in crankcase.
The gas containing the sulfur oxide will leak into the crankcase, which will quickly deteriorate the crankcase oil and corrode the bearing.
 

3. Management techniques for using low quality fuel.

1.
Pretreatment of low quality fuel refers to the preheating, purification and addition of additives and other technical measures before entering the fuel injection pump.
The purpose of pretreatment is to improve the storage, transfer and use of low-quality fuel to meet the needs of diesel engines.
 

1) preheating

The different application requirements of low quality fuel oil in transportation, purification and atomization are guaranteed by the graded preheating scheme.
The preheating temperature should be subject to the viscosity requirement, so the preheating temperature is different for low quality fuel with different viscosity.
Table 5-2 shows the preheating temperature of each part of the fuel system.
If the preheating temperature in the heavy oil storage cabinet is about 30 to 38, the temperature of the pump is about 30 to 38.
In order to guarantee the quality of atomization, the fuel viscosity of the fuel injection pump should be 12 mm2/S ~ 25 mm2/S, which can be used to find the corresponding preheating temperature value from the viscous temperature curve of heavy oil.
According to the relevant regulations of our country, fuel preheating should use saturated steam (vapor pressure should not exceed 0.8mpa) as the preheating heat source to prevent the precipitation of coke in heavy oil in the heater.
Electric heating can also be used on small ships.
The Marine diesel engine using poor quality fuel its atomization temperature up to 150 ℃.
In order to prevent the high preheating temperature, the fuel vaporization is interrupted and the oil supply is used. In the modern Marine diesel engine, the pressurized fuel system (increase the fuel delivery pump pressure up to 1.6mpa) is adopted.
 

2) purification of purifying fuel includes precipitation, filtration and separation.
Sedimentation should be deposited in the settling cabinet for 12h, and at the bottom of the container, it should be discharged regularly for the purpose of preliminary purification.
Filtering is an important part of fuel purification, which is accomplished by coarse and fine filters distributed in the fuel system.
High pressure slit filter can be set at the entrance of the injector to filter the fuel.
Centrifugal separation is the main effective means of purifying fuel when purifying low-quality fuel should use two sets of oil purifier series arrangement (the first level for the purifier, secondary clarifier), and correct selection of proportion of ring, oil temperature, discharge time, and the best points of oil (30% ~ 50% calibration points of oil), to ensure the oil quality.
For low-quality fuel with a density greater than 991kg/m, it is recommended to separate the fuel separation system with the a-laval FOPX.
 

3) additives are added to low quality fuel to improve the performance of low-quality fuel. As shown in table 5-3.
 

4) emulsifying the emulsified oil and making it into the emulsified liquid of oil and water, can improve the combustion performance of the low-quality fuel and reduce the carbon in the cylinder.
Fuel emulsification can use homogenizer, which can refine and homogenize water and impurity particles in oil to improve combustion and reduce wear.
However, this homogenization technique is not widely used because of the polymerization of various impurity particles in combustion.
 

2.Operation and management of diesel engines.

1) fuel management to strengthen the inspection of low-quality fuel quality (such as gas retention samples, inspection, etc.), especially should guard against different type of fuel, or the same brand but different port fuel mix tank, in order to avoid two kinds of suspension in petroleum asphalt points together and generate sludge sediment, the so-called fuel oil were reviewed.
At this time, the oil can produce a large amount of oil sludge, which will affect the normal operation of diesel engine, such as the blockage of oil supply pipeline, excessive oil of oil separation, the death of oil injection equipment, and black smoke exhaust.
When maneuvering the ship, diesel should be replaced.
 

2) adjust the oil injection equipment appropriately to increase the advance Angle of oil injection, and ensure that the number and phase of the ignition and maximum explosion pressure near the upper stop point are normal;
Properly improve the valve pressure of the injector to ensure the atomization quality;
Pay attention to the atomization quality of the injector.
 

3) use alkaline cylinder oil to neutralize sulfuric acid.
The total base value (TBN) of cylinder oil should be adapted to the sulfur content of fuel and increase the oil filling rate of cylinder as appropriate.
 

4) adjust the cooling water temperature and control the cooling temperature of each cooling part.
To prevent high temperature corrosion due to overheating and low temperature corrosion due to too cold.
The inlet temperature and the fresh water cooling temperature should be improved properly at low load operation.
 

5) pressurization system, the management of ventilation system, exhaust valve and valve seat quickly due to high temperature corrosion damage easily, exhaust gas turbocharger nozzle ring, work and pressure jet impeller impeller carbon jams easily occurs, damage, corrosion, should be regular inspection and cleaning;
Air cooler, scavenging box and air port are prone to contamination and blockage and should be checked and cleaned regularly.
 

3.Improved the structure of components, improve the work performance of friction surface using such as plating chromium, nitriding process improve hardness on the surface of the cylinder liner, piston ring, piston ring groove, in order to improve the wear resistance, improving the structure of fuel injector head knot carbon around the strengthening cooling effect to prevent the nozzle.
The lower part of the cross head diesel cylinder is fitted with a transverse diaphragm, which improves the structure of the piston rod stuffing box and strengthens the management to prevent the combustion products from falling into the crankcase and causing the oil to deteriorate.

4. Slow down operation and optimize adjustment.

In recent 20 years, most of the operation of a ship (such as oil, ore ship, bulk carrier and other large vessels) for shipping market and shipping considering various factors such as operating costs, mostly USES the drop speed operation energy saving measures (oil).
Select (75-80) %nb (calibration speed) according to different ship and source conditions (rated speed) as the long-term running speed (the corresponding operating power is about (40-50) % Pb).
At this time, the ship speed is reduced, but the reduction is not great, and the main engine fuel consumption decreases greatly.
As in the above example, the speed reduction is about 20% and the engine oil consumption is reduced by 50%.
Therefore, it is an effective technical measure to reduce the operating cost by adopting slow running.
However, due to the long-term low load operation of the diesel engine, it deviates from its optimal working conditions, which will inevitably aggravate the combustion of the diesel engine, with more faults, such as increased wear, and large amount of carbon in the cylinder.
The effective fuel consumption rate of diesel engine is increased and the reliability is reduced.
To improve the low load operation in the operation of diesel engine performance, so as to further perfect speed down operation energy saving technology and often, when to slow down operation, carries on the corresponding optimization adjustment measures on diesel engine.

These adjustment measures mainly include:

1.Increase the compression ratio of the cylinder properly, such as adjusting the gasket at the big end of the ship.
Ensure a good thermal state of compression finish.
 

2.Appropriately increase the injection advance Angle to ensure the maximum explosion pressure high enough.
 

3.Small orifice fuel injector is used to improve the atomization quality by increasing the valve pressure and so on.
 

4.In addition to reducing the consumption of cylinder oil, it can reduce the carbon and coking in cylinder.
 

5.Ensure the normal cooling of cylinder liner and injector, adjust the air temperature after air cooler, and prevent the low temperature corrosion caused by excessive cooling.
 

6.Improve the charging and scavenging system.
If properly reduce the flow area of the nozzle, to improve the speed of the supercharger, adjust the valve timing, etc.
 

7.Strengthen the maintenance and management of diesel engines, such as shortening the hoisting cycle as appropriate, and strengthening the maintenance and maintenance of supercharger.