Load Characteristics of Diesel Engine

The load of the diesel engine usually refers to the size of the resistance torque of the diesel engine. Since the mean effective pressure is proportional to the torque, the mean effective pressure is often used to represent the load. The working condition of the diesel engine is determined by the speed and load. The so-called load characteristic refers to the relationship between other main performance parameters (fuel consumption rate ge, fuel consumption Gf and exhaust temperature tr, etc.) that change with the load when the speed of the diesel engine is constant. At this time, since the rotational speed is constant, the effective power can be used as a metric load. In the process of engine debugging, the load characteristic is often used as the standard for comparing its performance.

In addition, the load characteristic gives the relationship between the engine load and the fuel consumption rate under the condition of constant speed. Therefore, the load can be changed in a wide range, and the speed of the stationary engine is basically unchanged (such as the generator set engine) has a special meaning. If the load characteristic curve at a series of different speeds is measured from the engine, the most economical operating condition of the stationary or transport engine can be selected.

During the operation of the diesel engine, the amount of charge does not change much, mainly by changing the fuel supply per cycle to change the concentration of the mixture (ie the excess air coefficient), thereby adjusting the load of the diesel engine (called quality regulation). In other words, the diesel engine The load is mainly changed by increasing or decreasing the fuel supply by changing the position of the adjustment rod of the fuel injection pump.

Increasing the load of the diesel engine means increasing the fuel supply per cycle, so the fuel consumption Gf increases with the increase of the load, while the excess air coefficient a decreases with the increase of the load. The air temperature tr increases with the increase of the load. At no load, Ne=0, Pi=Pm, and m=0 at this time, so ge is infinite.

As the load increases, m increases rapidly, while ge decreases. When the load increases to point A, ge reaches a minimum value. Continue to increase the load, because the excess air coefficient a decreases, the mixture formation and combustion deteriorate, and ge increases instead. The exhaust smoke increases with the increase of load, but increases slowly at low load, and the smoke at low load is very small and invisible to the naked eye, and is usually considered to be smokeless in the exhaust. At high loads, smoke levels increase rapidly. When approaching the maximum power, due to the reduction of a, the formation and combustion of the mixture deteriorates, the combustion is incomplete, and the exhaust smoke increases sharply (point B in the figure), and the fuel consumption rate ge also increases rapidly at this time.

The thermal load on parts such as piston and cylinder head also increases rapidly. If you continue to increase the fuel supply, the exhaust of the diesel engine will emit a lot of black smoke, and the power will decrease instead, so there is a smoke limit for the diesel engine. In order to ensure the safe and reliable operation of the diesel engine, the diesel engine is not allowed to work under the smoke limit.

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