Cummins Diesel Generator PT Pump Fuel Injection System

The PT fuel injection system of diesel generator is superior to the inline pump injection system and the distribution pump injection system in terms of power, economy, and environmental protection. The PT pump fuel injection system is a specialized fuel injection system for Cummins K series, N series and other models.

The basic principle of the Cummins diesel generator PT pump fuel injection system is a simple hydraulic principle (Pascal principle).

1. In a fluid filled system, any change in pressure is immediately and equally transmitted to the entire system.

2. The flow rate of a fluid passing through a certain section is directly proportional to the fluid pressure, allowed passage time, and the cross-sectional area passed through.

If the flow time and flow cross-section remain constant, the flow rate is proportional to the pressure; If the pressure and cross-section remain constant, the flow rate is directly proportional to time; If the pressure and time remain constant, the flow rate is directly proportional to the cross-section.

Taking tap water as an example, the amount of water collected in a bucket depends on three factors: water pressure, flow time, and channel area (valve opening).

The Cummins PT fuel system is designed based on this simple hydraulic principle.

From this, it can be concluded that the amount of oil in the oil cup depends on fuel pressure, metering time, and the size of the metering hole.

1. The size of the measuring hole: In the PT system, the size of the measuring hole depends on the fuel injector, which is determined by the CPL number. Once the CPL number is determined, the measuring hole remains fixed. In this way, during the operation of the diesel engine, the amount of fuel injected per cycle depends only on two factors: fuel pressure and metering time.

2. Measurement time: As the fuel injector is driven by the camshaft, the measurement time of the PT fuel injector is influenced by the contour of the camshaft and the speed of the camshaft. For pre manufactured diesel engines, when wear factors are not considered, the shape of the cam is fixed, so the cam angle that controls the opening time of the fuel injector metering hole remains unchanged. But when the speed changes, the metering time of the fuel injector corresponding to the same cam angle is inversely proportional to the speed, that is, the higher the speed, the shorter the metering time of the fuel injector. That is, as the diesel engine speed increases, the metering time of the PT fuel injector decreases, resulting in a decrease in fuel quantity, which is not allowed. In order to prevent a decrease in fuel injection due to an increase in engine speed, the PT fuel pump can be used to increase the inlet pressure P at the metering hole of the fuel injector, thereby maintaining the fuel supply not affected by changes in diesel engine speed. This is the basic principle of using pressure and time to control fuel supply.

3. Fuel pressure: refers to the fuel pressure output by the PT pump under various working conditions, which is related to the speed of the diesel engine.

The pressure at the measuring hole of the fuel injector, which is the supply pressure of the fuel pump or the inlet pressure of the fuel injector, depends on the opening of the throttle valve in the PT pump and the outlet pressure of the governor. When the opening of the throttle valve is constant, the supply pressure of the fuel pump increases or decreases with the increase or decrease of the outlet pressure of the governor. The oil pressure increases or decreases with the increase or decrease of centrifugal force on the governor flying block, and the magnitude of centrifugal force increases or decreases with the increase or decrease of diesel engine speed. Therefore, when the opening of the throttle valve remains constant, under different diesel engine loads, the combined effect of fuel supply pressure and time keeps the diesel engine speed basically unchanged.

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