Exercise 5. Read dialogues and reproduce them then make up your own dialogues based on topics given below.
A.: What type of injection valve is used on modern engines?
В.: Modern engines use mechanical fuel injection and the valve is simply a spring loaded check valve with a nozzle on inner end containing one or more fine holes. When the pressure from the pump overcomes the tension of the spring the valve lifts and oil at high pressure is forced through the nozzle as a mist.
A.: What are some of the troubles experienced with injection valves?
В.: Leaks, due to grit or scale, burning of valve or seat, sticking of stem in its guide, bending of stem, leaky packing, clogging of atomizer plates and plugging of holes in flame plates or nozzles.
A.: How is a leaky injection valve repaired?
В.: Small leaks can be stopped by grinding the valve on its seat with very fine ground glass, carborundum, or prepared grinding compound, finishing up with polishing paste. If seat and valve are badly scored, the valve should be refinished by grinding in the lathe with a tool post grinder and the seat should be reamed, finished up by grinding.
A.: What precaution should be observed in cleaning injection valve stems?
В.: Cleaning should be done with kerosene, emery cloth should be used sparingly, or not at all, as it wears away the metal and increases the clearance between stem and guide. If this clearance becomes too great, it offers an easy place for gummy oil and carbon to accumulate and the tendency of the stem to stick in the guide is increased.
A.: Why does the exhaust valve require more attention than the inlet valve?
В.: Because it is exposed to the action of the very hot gases that flow through it during the exhaust period. These gases may carry solids (hard carbon, grit or scale) which tend to cut the valve and seat and the heat tends to warp and burn the valve. The inlet valve passes no hot gas and is cooled by the inflowing clean air during each suction stroke.
Comprehensive reading. Read, translate into Russian and discuss the following text
Common causes of marine diesel engines overheating
Overheating is a common symptom of marine diesel engine blockage. Marine diesels should run at 180 degrees Fahrenheit. When the temperature goes above 200, start getting worried. Dialing down the RPM may allow the engine to recover and run well at a more leisurely pace. Overheating is difficult to diagnose, and the only real way to solve the problem is a systemic examination of every engine element, i.e. trial and error. Here is a starter list of parts to examine: 1) Raw Water Impeller – the most common source. A spoke of the plastic impeller breaks off and clogs the raw water flow. Easy fix: buy a new impeller. 2) Mixing Elbow – Corrosion here blocks the flow. Solution is a new or boiled out elbow. 3) Heat Exchanger – Scale builds up in the heat exchanger. Solution is to snake with a wire and dip in acid. 4) Thermostat Sensor/Receiver – Is the thermostat stuck? Or is the engine even overheating? Check the exhaust temperature. How hot is the water? Shoot a heat sensor on the water reservoir. 5) Fresh Water Tank – Is it leaking? 6) Hoses – Delamination inside engine hoses restricts the flow, causing the engine to overheat. 7) Fresh Water Pump – An aluminum impeller inside the pump can corrode and limit flow. 8) Oil Cooler – Similar to the heat exchanger. You cannot shake her out because the tubes narrow at the ends but dipping the cooler in an acid bath does the job. 9) Over-propelled – Too large a diameter or too much pitch can cause an engine to overheat prematurely. 10) Aeration – Air getting in from a leak in the line anywhere can lead to overheating.
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Exercise 6. Discuss the following topics:
1. What is normal/abnormal temperature of marine diesel engine?
2. What should be done in order to prevent engine overheat?
3. Why is it difficult to diagnose the engine overheating?
4. What parts of the engine should be examined?
5. What other advice can you give in order to prevent engine overheat?
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