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Figure 1-22 Composition of the BFM1013 diesel engine single pump fuel system 1-Fuel tank; 2-Fuel inlet pipe; 3-Fuel pump; 4-Diesel pipe; 5-Diesel filter; 6-Fuel inlet pipe; 7-Single pump; 8-High-pressure oil pipe; 9-Injector; 10-Injector return pipe; 11-Return oil overflow valve; 12-Return oil pipe; 13-Distance between the inlet and outlet pipes of the fuel tank
(1) Composition of the single pump diesel engine fuel system ① Function Like the ordinary fuel system, the function of the single pump fuel system is to deliver a certain amount of fuel to the combustion chamber of the diesel engine at a certain pressure. ② Composition of the low-pressure oil circuit As shown in Figure 1-22, the single pump fuel system consists of a diesel tank, a low-pressure oil pump, a fuel filter (coarse filter, fine filter), and corresponding oil and other components. Diesel fuel flows from the fuel tank 1, passes through the fuel transfer pump 3, and enters the diesel filter 5. After filtration, it enters the low-pressure oil chamber cast in the cylinder block in non-electronically controlled models. The return fuel also flows into this chamber. The pressure in the low-pressure oil chamber is 0.5 MPa. If the diesel engine experiences insufficient power, the pressure in the low-pressure oil circuit should be measured first. The measurement location is at the external connection of the low-pressure oil circuit. At a diesel engine speed of 2300 rpm, p ≥ 0.45 MPa. ③ High-pressure Oil Circuit: The fuel in the low-pressure oil circuit flows from the unit pump through a short high-pressure oil pipe to the injector. When the pressure reaches 25.0 MPa, the injector opens, spraying the fuel into the combustion chamber in a mist form, where it mixes with air to form a combustible mixture. The oil pressure in the oil circuit from the diesel tank to the low-pressure fuel chamber joint is established by the fuel transfer pump. The oil pressure of the fuel transfer pump at the rated speed of the diesel engine is generally about 0.5MPa. Therefore, this section of the oil circuit is called the low-pressure oil circuit and is only used to supply oil to the single pump. The oil pressure in the oil circuit from the single pump to the injector is established by the single pump and is about 160MPa. ④ Fuel return Since the fuel supply of the fuel transfer pump is more than 10 times greater than the oil output of the single pump, a large amount of excess fuel flows back to the diesel tank through the pressure limiting valve 11 and the return pipe 12 (see Figure 1-22). The large amount of return fuel is used to carry away the air in the oil circuit, which has an automatic exhaust function. (2) Use and maintenance of the low-pressure oil circuit system The BFM1013 mechanical single pump diesel engine has two low-pressure oil circuit pressure systems: 0.3MPa and 0.5MPa. ① Low-pressure Oil Line Pressure Testing: Stable pressure in the low-pressure oil line is crucial to the diesel engine's power output. If the diesel engine experiences underpower, first check (measure) the pressure in the low-pressure oil line, controlled by the pressure-limiting valve 11 (see Figure 1-22). The primary cause of injector leakage is insufficient low-pressure oil line pressure, leading to cavitation of the injector components. Therefore, ensure the low-pressure oil line pressure and replace or clean the diesel filter promptly. The low-pressure oil line pressure measurement location is shown in Figure 1-23.
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Figure 1-23: Low-pressure Oil Line Pressure Measurement Low-pressure oil line pressure limits: 0.3MPa system, p ≥ 0.20MPa (n = 2200 rpm); 0.5MPa system, p ≥ 0.45MPa (n = 2300 rpm). Because the single-pump system requires a high pre-pressure for the fuel, it is necessary to test the fuel system pressure. If the measured pressure is lower than the specified value, the fuel pump and return oil relief valve must be inspected. ② Fuel Pump Flow Check: The fuel pump (Figure 1-24) not only supplies fuel to the injection pump but also cools the fuel system. Therefore, the fuel pump's fuel flow rate is significantly greater than the injection pump's needs. For this reason, this engine uses a diaphragmless rotor-type fuel pump with a fuel flow rate of 12 L/min at a supply pressure of 0.5 MPa. To verify the fuel flow rate, at the return oil line (the oil line after the return oil relief valve), a minimum of 8 L/min of return oil should be observed at maximum idling speed. If the return oil flow rate is lower than this value, the fuel pump must be replaced. ③ Checking the Return Oil Relief Valve: The return oil relief valve (shown in Figure 1-25) establishes a minimum pressure in the low-pressure oil circuit to meet the instantaneous fuel delivery requirements of the injection pump. If the measured pressure is lower than the above value, the return oil relief valve should be replaced, provided that the fuel delivery pump is not faulty. Note: The low-pressure oil circuit pressure of the unit pump is higher, and conventional fuel supply system return oil check valves may not be able to meet the pressure buildup requirements. Therefore, a dedicated unit pump fuel system return oil relief valve must be used.
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