Guide to Diesel Generator Power Analysis & Efficiency

In the industrial and commercial fields, diesel generators are indispensable backup power equipment. However, many users in the process of use will encounter a common problem: the power output of the generator does not seem to reach expectations. This not only affects the use efficiency of the equipment, but may also cause damage to the service life of the equipment. This article will deeply discuss the principle of diesel generator power output, influencing factors, and how to ensure efficient operation of equipment through maintenance and management.

Basic Principle of Power Output

The power output of a diesel generator is mainly determined by two factors: the power of the diesel engine and the efficiency of the generator. Taking as an example a generator driven by a 1000-horsepower diesel engine with an efficiency of 95%, 1000 horsepower is equivalent to 745.7 kilowatts, which is the shaft power provided to the generator. Considering the efficiency factor, the maximum output power is 708.4 kilowatts. However, this is not all of the generator power. The maximum kilovolt-ampere (kVA) depends on the rated voltage and current of the generator.

There are two ways for the genset to be overloaded: if the load connected to the generator exceeds the rated kilowatt, it will overload the engine; if the load exceeds the rated kVA, it will overload the generator windings. Even if the load kilowatt is lower than the rated value, the generator may also be overloaded in kilovolt-ampere. Therefore, it is crucial to understand the concept of Power Factor (PF). Power factor is the ratio of actual power to apparent power in the power system, usually expressed as a percentage. For example, if a building consumes 1000 kW and 1100 kVA, the power factor will increase to 91%, but will not exceed the generator capacity. However, if the generator operates at 1100 kW and 1250 kVA, the power factor only increases to 88%, but the diesel engine is already overloaded.

Influence of Power Factor

Power factor has a profound influence on the operation of diesel generators. If only a resistor is connected to the generator and voltage and current are measured, their AC waveforms will match when displayed on a digital meter. In this case, the power factor of the load is 1.0 or 100%. However, most equipment in buildings does not have a power factor of 100%, which means that their voltage and current will shift relative to each other. If the AC voltage peak leads the current peak, the load has a lagging power factor; if the current leads the voltage, the load has a leading power factor.

Most buildings have more inductive loads than capacitive loads, which means that the overall power factor is usually lagging. Diesel gensets are designed for such loads. However, if a building has many capacitive loads, the owner must be careful, because the generator voltage will become unstable as the power factor leads. This will trigger automatic protection and disconnect the equipment from the building.

Power Classification and Usage Recommendations

The power classification of diesel generators includes prime power, continuous power, maximum power, and economic power. Prime power is the nominal power of the genset; continuous power refers to the maximum power that can be continuously used within 24 hours; maximum power is 1.1 times the rated power, but it is only allowed to be used for 1 hour within 12 hours; economic power is 0.5~0.75 times the rated power, which is the output power of diesel gensets that can be used for long-term operation without time limitation.

In actual use, users need to select the appropriate power classification according to their needs. For example, if purchasing a prime 400 kW genset, then within 12 hours there is 1 hour that can run up to 440 kW. But if purchasing a standby 400 kW genset, usually running at 400 kW, in fact this genset has always been running in an overloaded state, which is very unfavorable to the genset, will shorten the service life of the genset and cause the failure rate to increase.

Reasons for Diesel Generator Power Decline

After being used for a period of time, the power of the genset will decline, which is usually a normal phenomenon. However, if the power declines too quickly or too low, attention is required. The main reasons leading to power decline are as follows.

1. Fuel System Problems

Fuel is the energy basis for the genset to do work. Any blockage, leakage, or parameter deviation in the supply chain will directly lead to "insufficient power." The use of inferior diesel or oxidized diesel stored for a long time will form sludge that clogs injectors, causing poor atomization. In winter, if the corresponding grade of diesel is not replaced in time, wax will clog the fuel filter and pipeline. Injector wear or leakage, fuel pump performance degradation, fuel filter clogging and other problems will all lead to power decline.

2. Intake System Problems

Diesel combustion requires sufficient clean air. Blockage or leakage of the intake system will lead to "air-fuel ratio imbalance." If the genset is used in a dusty environment, the air filter will quickly accumulate impurities, and intake resistance will increase. Aging and cracking of the intake hose, loose clamps, will cause unfiltered "dirty air" to enter the cylinder directly. The core role of turbocharged gensets is "compressing air and increasing intake." If the turbocharger blades wear, bearings seize, or the boost pressure sensor fails, it will lead to insufficient boost pressure.

3. Exhaust System Problems

Blockage of the exhaust system will cause "residual exhaust gas cannot be discharged" in the cylinder, occupying the intake space and at the same time increasing the exhaust resistance of the engine. After long-term use, carbon deposits and soot generated by combustion will accumulate inside the muffler. The bolts connecting the exhaust manifold and the cylinder head loosen, and gasket damage will cause high-temperature exhaust gas leakage.

4. Engine Component Wear

The piston, cylinder, valve and other core moving parts of the engine, after long-term use, will cause "decline of sealing performance" and "insufficient compression pressure" due to wear. After long-term friction of cylinder liners and piston rings, the clearance increases, and the "airtightness" of the cylinder decreases. Piston rings stuck due to carbon deposits will further aggravate cylinder leakage. Valves and valve seats, after long-term impact and high-temperature corrosion, will cause wear on the sealing surface and pits.

5. Lubrication and Cooling System Problems

Although the lubrication and cooling systems do not directly participate in work, they are responsible for ensuring the normal operating environment of the engine. Insufficient oil, inappropriate oil viscosity, or clogged oil filters will cause poor lubrication of various moving parts of the engine. Insufficient coolant, clogged radiators, and water pump failure will cause the engine to "overheat."

6. External Environment and Improper Load Matching

For every 1000 meters increase in altitude, atmospheric pressure decreases by about 10%, and air density decreases accordingly. In summer high temperatures, intake air temperature increases, density decreases, and at the same time the pressure on the cooling system increases. High humidity environments will increase the moisture content of the air, reducing the actual effective intake. If the genset is in "overload operation" for a long time, the engine will be in a high-load state for a long time, aggravating component wear.

Maintenance and Management Recommendations

To ensure the efficient operation of diesel generators, regular maintenance and management are essential. Below are some practical recommendations.

Regular Inspection and Replacement of Fuel System Components: Regularly inspect the condition of fuel filters, injectors, and fuel pumps. Replace worn or clogged components in time. Use high-quality fuel and avoid inferior or long-stored diesel. In winter, switch to the appropriate grade of diesel to ensure smooth fuel system operation.

Maintenance of the Air Intake System: Clean or replace the air filter element regularly to ensure smooth airflow. Check the condition of intake hoses and the turbocharger, repairing or replacing damaged parts promptly. When operating in dusty or high-dust environments, increase the cleaning frequency of the air filter.

Inspection of the Exhaust System: Regularly check the condition of exhaust silencers, exhaust manifolds, and cylinder head bolts. Remove carbon deposits and soot in time. Ensure the exhaust system remains clear to prevent leakage of high-temperature exhaust gases.

Monitoring Engine Component Wear: Inspect key moving components such as pistons, cylinders, and valves regularly for wear. Repair or replace severely worn parts promptly. Maintain engine sealing performance and compression pressure to ensure combustion efficiency and power output.

Maintenance of the Lubrication and Cooling Systems: Regularly check engine oil level and viscosity, and replace oil and oil filters in time. Ensure sufficient coolant supply, clean the radiator periodically, and check the operation of the water pump. Maintain proper functioning of the lubrication and cooling systems to avoid engine overheating.

Proper Load Matching: Select the appropriate power rating according to actual demand, and avoid prolonged overload operation. For impact loads, adopt suitable buffering measures to reduce stress on the engine. When operating in high-altitude, high-temperature, or high-humidity environments, appropriately reduce the generator load to ensure normal operation.

Conclusion

The power output of diesel generators is a complex system project, affected by many factors. By understanding the basic principles of power output, the influence of power factor, power classification and usage recommendations, as well as the reasons leading to power decline, users can better manage and maintain gensets. Regular maintenance and management can not only improve the reliability of diesel generators, but also extend their service life. In actual use, users need to select and use gensets reasonably according to their needs and environmental conditions, to ensure efficient operation of equipment.

In short, diesel generators are indispensable backup power equipment in modern industry and commerce. Through scientific management and maintenance, users can maximize the performance of the equipment and ensure that stable power supply can be provided at critical moments.