What Causes Increased Oil Levels in Diesel Generator Engine

 
The so-called oil increase refers to the unburned or incomplete combustion of diesel oil in the diesel generator engine through the gap between the cylinder and the piston into the crankcase and the oil pan, which cannot be volatilized in time, resulting in the oil being polluted and diluted, and the liquid level scale rising. This problem has an adverse effect on the normal operation and life of the diesel generator engine, and needs to be analyzed and dealt with in detail. In the following parts, we will mainly talk about the factors for such a problem.
 

How a Diesel Engine Works

 
Before analyzing the oil increase issue of diesel generator engine, we get to understand the principle of a diesel engine. Diesel generators push the engine piston down to generate power through the expansive force generated by the rapid combustion of fuel at high temperature and pressure. In the engine design, the piston diameter is usually slightly smaller than the cylinder diameter, and the small gap is reserved in the cold state, and the gap will gradually become smaller after the engine is heated up. In order to improve the sealing, a piston ring is installed on the piston, but because the piston ring has a more significant thermal expansion and contraction characteristic than the piston, a cold gap is reserved, that is, the piston ring three gaps. The engine combustion chamber is not completely sealed due to the gap between the piston, piston ring and cylinder. In the cold state, combustible mixture and incomplete combustion exhaust may enter the crankcase through the gap, and contact with the oil, resulting in oil deterioration and dilution.
 

Causes of Oil Increase in Diesel Generator Engine

 
During the operation of the diesel generator set, there will occasionally be an increase in oil. This situation not only affects the normal operation of the engine, but also shortens its service life. The following is the analysis of the main reasons for the increase of engine oil in the generator set.
 

1. Wet Stacking in Cylinder Direct Injection Engine

The phenomenon of wet stacking produced in the injection process of direct injection engine is an important reason for the increase of oil. Diesel engine fuel injection mainly has intake manifold injection and direct injection in the cylinder two ways.
 

Intake Manifold Injection

The oil injection nozzle is installed on the intake manifold, diesel injection to the outside of the cylinder, with the intake valve opened into the cylinder, diesel and air are fully mixed, but the controllability of the injection is poor, and the precise control of the injection amount is insufficient.
 

Cylinder Direct Injection

The injection nozzle is installed on the cylinder head, and the diesel fuel is injected directly into the cylinder, which is quickly mixed with the air through the very high oil pressure, which is 30 ~ 40 times that of the intake manifold injection. The engine can precisely control the injection amount according to the intake volume to achieve thin mixture combustion and achieve higher economy. However, during the injection process, the fuel that is not completely atomized contacts the cylinder or piston, forms small liquid particles when it is cold, and is mixed into the oil through the gap in the compression stroke, resulting in oil dilution.
 
Not all direct injection engines will have a wet stacking phenomenon. The overhead nozzle design can inject fuel directly onto the piston, greatly reducing the wet stacking phenomenon, but this requires the placement of valves, spark plugs, and fuel injection nozzles above the combustion chamber, increasing the design complexity and manufacturing cost of the cylinder head. Therefore, most in-cylinder direct injection engines still use side-mounted nozzle structure.
 

2. Influence of Turbocharging Technology

Although non-turbocharged engines do not suffer from the wet stacking problem, turbocharging technology is an important factor. Turbocharged engines have obvious power and economic advantages over naturally aspirated engines. The turbocharging system uses active air intake, which greatly increases the intake volume and cylinder pressure at the same compression ratio, making the fuel more flammable when mixed with air. However, under high temperature conditions, the piston and piston ring need to reserve expansion clearance to avoid excessive expansion at high temperature, and the clearance is further enlarged in the cold machine state. Under high pressure, more mixture and incomplete combustion exhaust gas are more likely to enter the crankcase through the gap, resulting in oil increase. Therefore, the diesel engine oil increase problem is relatively more frequent.
 

3. Special Case of Hybrid Generator Set

The engine of the hybrid power generator set uses a mixed injection structure of manifold injection and direct injection in the cylinder, and uses a naturally aspirated rather than a turbocharged structure, but there is still a problem of oil increase. This is closely related to the non-continuous operation of the engine of the hybrid generator set and the long-term cooling condition. The hybrid generator set works alternately by the motor and the engine, which leads to the engine cooling condition being prolonged, and eventually leads to the problem of oil increase.
 
In short, there are many factors that lead to the increase of diesel engine oil, mainly including engine design problems, fuel injection technology, turbocharging system and hybrid structure. In view of these problems, some effective measures can be taken to reduce the occurrence of this problem, so as to ensure the efficient operation of diesel generators and extend their service life.