Reasons for Diesel Fuel in Diesel Engine Water Tank and Engine Oil

In the case of the NT855-C280 Cummins diesel engine, it was found that diesel oil flowed out from the overflow hole of the water tank when the diesel engine stopped working. When the water tank lid was opened, about 10 L of diesel flowed out; the oil level in the oil pan continued to rise during the operation of the diesel engine. The viscosity of the oil drops, the pressure decreases, and the oil needs to be replaced in almost one week; the temperature of the diesel engine is high and the work is weak. Analysis believes that the cause of this failure are: (1) The cylinder head has air holes or cracks. Cummins diesel engine PT fuel pump-type fuel supply system, the diesel fuel tank in the cylinder head, the cylinder head on both the organic oil and waterways, and diesel road. When working, the diesel pressure in the diesel channel on the cylinder head is 0.8～1.2MPa, the pressure of water is less than 0.6MPa, the pressure of diesel is higher than the pressure of water. Once air holes, trachoma or cracks appear on the cylinder head, the water channel and the diesel channel will be connected. Diesel will enter the waterway. (2) Seal failure or mechanism failure. For example, the oil seal of the PT pump spindle fails, and the diesel oil enters the timing gear box to reach the oil pan. The shut-off valve at the diesel outlet of the PT pump is not closed tightly. Although the diesel engine has been shut down, due to the higher position of the diesel fuel tank, the diesel Still can follow the following route to enter the oil pan: fuel tank → tubing → PT gear pump → shutoff valve (when lax close) → tubing → fuel injector (injector in the oil return and fuel flow, the nozzle cavity The diesel fuel tank and the diesel tank communicate with each other. Under the influence of the atmospheric pressure, diesel oil drips into the combustion chamber through the injection hole) → Combustion chamber → Oil sump; Injector hole is too large, damage or two O-ring seals on the injector When it is damaged, the diesel will enter the combustion chamber and then infiltrate into the oil pan; when the check valve on the return manifold of the PT fuel system fails, the diesel will flow through it to the injector and infiltrate into the oil pan flat; There is a manual shut-off valve at the exit of the tank. If the spool is damaged and the shut-off is not strict, diesel will flow into the combustion chamber and enter the oil pan; a certain cylinder pressure is too low, causing the cylinder to not work, allowing diesel to flow into the oil. Bottom hull; insufficient intake of diesel engine, unsafe combustion, The oil flows into the oil pan along the cylinder wall. When inspecting the diesel engine, it was found that there were a lot of blisters around the injectors of the No. 2 and No. V cylinders. Since the diesel pressure was higher than the water pressure when the engine was working, the water could not flow into the diesel channels around the injectors, so the diesel entered. The water tank; the top of the II cylinder injector push rod is broken and the push rod of the V cylinder injector is bent, causing the lift of the II, V cylinder injector push rod to change, and the fuel oil cannot be supplied accurately, resulting in incomplete diesel Combustion flowed into the oil pan; in addition, after removing the oil outlet pipe on the PT pump shutoff valve, it was found that diesel oil still flowed from the cutoff valve port. After the valve core is cleaned, the diesel will no longer seep out; at the same time, after the replacement of the new cylinder head and push rod, the fault phenomenon is eliminated.