Cooperation between Turbocharger and Diesel Engine in Generator Sets

When the turbocharger and the diesel engine in a generator set work together, there is no mechanical connection between them. They transfer energy through air or gas flow. Since different operating conditions of the diesel engine require different air - supply capacities from the compressor, the power - doing ability of the turbine comes from the reasonable organization of the exhaust gas from the diesel engine, and all the power of the turbine is consumed by the compressor. In other words, the air flow and boost ratio required for the diesel engine to generate a certain power are exactly what the compressor should provide.

To ensure a good cooperation between the turbocharger and the diesel engine and enable them to work satisfactorily under various operating conditions, two things need to be done. One is to determine the position of the diesel engine on the compressor characteristic curve according to its specific operating conditions (such as rated operating condition or maximum torque operating condition) (that is, select a suitable turbocharger model for the diesel engine). The other is to achieve a good cooperation between the diesel engine and the turbocharger in the entire operating range.

Here, selecting a good turbocharger is a prerequisite. If the turbocharger is not well - selected, the diesel engine may not achieve the expected supercharging effect. When selecting a turbocharger, based on the air flow (including scavenging air volume) and pressure ratio required by the specific operating condition of the diesel engine, the position of this operating condition on a certain compressor characteristic curve can be determined. If this point falls within the high - efficiency area of the compressor characteristic curve, the turbocharger model can be preliminarily selected.

Different from piston - type diesel engines, in blade machines such as turbines and compressors, the structural angle of the blade leading edge is determined by the airflow parameters of the design operating condition. When the operating condition changes and causes a change in the gas flow, the inflow direction of the gas will deviate from the direction of the blade leading - edge structural angle, resulting in impact losses and narrowing the high - efficiency area of the blade machine. Therefore, it is impossible to make all operating conditions of the diesel engine work in the high - efficiency area of the compressor. Only some specific operating conditions of the diesel engine can be considered.

Each turbocharger has a definite operating range. In the small - flow range, the compressor is limited by surge. In the large - flow range, the compressor is also limited due to excessive efficiency decline. In the high - speed and high - load range of the turbocharger, the turbocharger may be limited by over - speed or over - temperature because the exhaust gas energy is too high, causing the turbocharger to exceed the allowable rotational speed of the mechanical strength, or because the exhaust temperature is too high, exceeding the temperature that the turbine blades can withstand. This determines a roughly definite operating range for the turbocharger.

Within this allowable operating range, the cooperation between the turbocharger and the diesel engine can be judged according to their combined operating position.

If the combined operating line does not match the compressor characteristic curve well and local adjustment is needed, a common method is to change the outlet cross - sectional area of the turbine nozzle ring. For example, reducing the outlet cross - sectional area of the nozzle ring can move the combined operating line from the low - efficiency area of the compressor to the high - efficiency area (closer to the surge line). However, the above adjustment is limited. If the combined operating line deviates far from the optimal cooperation with the compressor, it is better to replace the turbocharger model.

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