The Harm of Poor Quality Diesel to Diesel Generators

The fuel used by diesel engines is diesel. Its main performance properties include fluidity, atomization, ignition and evaporation, etc. These properties have a great impact on the operation of diesel engines. Poor diesel performance will cause the diesel engine to start difficultly, power reduction, unstable operation, exhaust black smoke, and it is also easy to form carbon deposits on the valves, pistons, and cylinder liners, accelerating the wear of the parts. It can be seen that the performance and quality of diesel have a great impact on the performance of diesel engines. The viscosity and cleanliness of diesel also have a great impact on the operation of diesel engines. Cummins focuses on these two issues in this article.

The impact of diesel viscosity on diesel engine fuel system

Generally, the kinematic viscosity of light diesel at 20°C is 2.5~8cP. Too high or too low diesel viscosity has a great impact on the fuel supply, atomization quality, and wear of parts of the fuel system.

1.Impact on atomization quality

When the viscosity of diesel is too high, the atomization quality deteriorates: On the contrary, when the viscosity of diesel is too low, the average diameter of the oil droplets is small, and the poor atomization condition leads to uneven mixing of air and fuel, which makes it difficult to fully burn and exhaust smoke.

2.Impact on fuel supply

When the viscosity of diesel is too low, the leakage of diesel through the plunger and the piston increases, and the power is insufficient. The fuel supply of the injection pump varies with the viscosity, and the viscosity of diesel also varies with temperature and pressure. The viscosity decreases when the temperature rises, and the viscosity increases when the pressure increases.

3.Impact on wear of parts

Using diesel with too low viscosity will deteriorate lubrication. It is not easy for diesel to form an oil film in the gap between the plunger and the plunger sleeve, and the needle valve and the needle valve body, which increases the wear of precision parts.

The impact of diesel cleanliness on the fuel system

The core parts of the fuel system are the plunger pair on the fuel injection pump, the oil delivery valve pair and the needle valve pair on the fuel injector, which are called the three major precision pairs of the fuel system. The plunger pair consists of a plunger and a plunger sleeve. It is the most important pair of precision pairs and the key component for the fuel injection pump to generate high pressure. The oil delivery valve pair consists of an oil delivery valve and a seat. The oil delivery valve is inserted into the oil delivery valve seat, and the oil delivery valve spring is used on it to make the oil delivery valve and the oil delivery valve seat fit tightly. The needle valve and valve hole of the fuel injector are also extremely precise. The matching accuracy of these pairs is high. After matching grinding, the matching clearance is only 0.001~0.003 mm.

1. Hazards of mechanical impurities
If the fuel is not clean and has more impurities, the hard mechanical impurities will wash the sealing surface of the precision pair with the diesel at high speed during the fuel supply process, just like grinding, causing serious wear and tear on the surface, destroying the sealing performance. Mechanical impurities in the fuel can cause wear or jamming of three major precision parts:

   Plunger parts

• The piston and sleeve are worn, and the matching clearance increases. During the oil compression process, the fuel leaks back seriously, the oil supply pressure is reduced, the oil supply time is delayed, the oil supply amount is reduced, and the diesel engine power decreases. In severe cases, it may even fail to start;
• When the piston pair is completely stuck in the oil return or oil inlet position, the oil supply function is lost and the diesel engine automatically shuts down; when it is stuck in the stop supply position, the diesel engine cannot start; when it is stuck in the maximum oil supply position, it will cause the diesel engine to have a “flying car” accident (the Guisai and the sleeve are stuck at the bottom and cannot move. When the oil pump cam moves upward, it will break the piston or cause the camshaft to bend.

  Oil outlet valve parts

• The sealing cone surface of the oil outlet valve is not tight, which will cause the injection time to be delayed and the injection amount to be reduced.
• When the clearance between the oil outlet valve pressure relief ring and the valve hole is too large, it will cause the injector to not cut off the oil after spraying, the injector nozzle will drip, the fuel will burn poorly, and knocking and carbon deposition will occur.

   Injector parts.

• The sealing cone surface between the needle valve and the spray hole is not tight, causing the injector to drip oil, causing the diesel engine to knock, smoke and carbon deposit.
• The gap between the needle valve guide part and the valve hole is too large due to wear, which increases the internal leakage of the injector, reduces the injection volume, and delays the injection time, causing the diesel engine power to drop and start difficulty. ③ The needle valve is stuck in the open position, and the fuel is sprayed into the steam drive with a relatively large oil beam. The diesel engine exhaust smokes seriously and “explodes”. At the same time, because the needle smoke cannot be closed, the injector “backfires” and “backflow” phenomena will occur, burning the injector or cutting off the oil supply, causing the diesel engine to shut down by itself.

2. The harm of water in fuel
The water in the fuel will cause the diesel to oxidize into sludge, causing rust, wear, blockage and even seizure of fuel system parts. The floating water will also clog the diesel filter element, making the diesel pass performance worse.

In summary, this paper discusses the effects of diesel viscosity and diesel cleanliness on the operation of the fuel system, and points out measures to improve diesel cleanliness in order to improve diesel engine performance and reduce the occurrence of faults.