Lesson 5. Starting difficulties

 

Notes:

Failure of the engine to start on air may be due to one or more of the following causes: starting air pressure too low, incorrect timing of starting air valves, one or more starting air valves stuck, compression relief gear out of order, stop valve in air line closed, or, if starting after working on the engine, the jacking gear may still be engaged.

Operating troubles in general

Water in fuel oil. Water may get into the fuel oil by leakage through defective riveting of tanks, through alternate use of tanks for fuel oil and water ballast, or the fuel oil as delivered into the tanks may contain considerable moisture that will settle out. The degree of seriousness of the resulting troubles will vary with the amount of water in the oil, but among the possibilities are cracked heads and pistons, burned out exhaust valves, low compression due to wear of rings and liners, and irregular running of the engines.

Improperly refined oil.

Fuel oil must, during the refining process, be treated with sulphuric acid and this acid must later be neutralized with soda. If this neutralizing agent is not thoroughly washed out of the oil, its presence cannot be detected without chemical analysis nor is it removed by the filtering and straining methods ordinarily used on shipboard. When the engine is opened up after running on this insufficiently washed oil the entire surface of the combustion spaces in the cylinders will be found to have a coating of gritty material which looks and feels like sand but which is mostly sodium sulphate. It does not cause any immediate derangement of the engine but it does cause considerable wear of piston rings and cylinder liners. When such deposits are found the only remedy is to stop using the fuel from that particular refinery.

Loss of power or slowing down of engine

When this occurs the first possibility that should be investigated is hot bearings. Other causes are failure of fuel to one or more cylinders, derangement of valves of valve gear or a fall in cooling water temperature. A decided reduction of the sea water temperature will often be experienced when entering a river from the sea, passing out of the Gulf Stream or leaving tropical waters. When this occurs the cooling water supply should be cut down until the jacket water temperature is up to normal. A distinct loss in efficiency sometimes results from the idea that the jacket water should always be kept as cold as possible.

Cracked cylinders and cylinder heads

Cracks may result from unequal heating due to poor design, bad castings, air pockets in jackets, lack of cooling water and overloading. Modern practice in design and construction has greatly reduced the probability of cracking from the first two causes and watchfulness on the part of the engineers eliminates the other causes, so that cracked heads and cylinders are not nearly so common as they were in the early days of Diesel engineering.

Cracked crank shafts

During the early development period cracked crank shafts were so common that it was considered one of the inevitable hazards associated with Diesel engine operation. This trouble has become very rare, however, in modern practice.

Vibration

The amount of vibration of an engine and of the ship's hull in which it is installed will depend on how well the reciprocating and rotating masses in the engine are balanced and the position of the engine relative to a nodal point in the hull. These are both matters over which the operating engineer has no control. Normally Diesel engines, especially in the large sizes, run with very little vibration but it sometimes happens that an engine will have a critical speed, a speed at which the twisting impulses imparted to the crank shaft by the pressure acting on the pistons coincide with the natural period of vibration of the crank shaft. When the engine operates at this speed violent vibration will occur that may result in loosening nuts, shaking off small fittings, breaking pipes and even breaking of the crank shaft, if continued long enough.

 

Exercise 1. Answer the following questions.

1) Due to what causes may the engine fail to start on air?

2) How can water get into fuel oil?

3) What is the only remedy against improperly refined oil?

4) What may a distinct loss in efficiency sometimes result from?

5) Why are cracked heads and cylinders not so common as they used to be in the early days of Diesel engineering?

6) What does the amount of vibration of an engine and of the ship's hull depend on?

7) Why was a cracked crank shaft considered one of the inevita­ble hazards associated with Diesel engine operation?

8) When may violent vibration occur?

Exercise 2. Give the Russian equivalents of the following.

1) Air pocket.

2) To start on air.

3) Starting air valves.

4) Exhaust valves.

5) Unequal heating.

 

Exercise 3. Use the correct words from the text.

1) Mechanical defects may be due to errors in...

2) There are errors which are difficult to... because they are not expected.

3) A careful... revealed that the engine trouble was due to neglect on the part of the engineers.

4) A thread of waste under the valve caused it to...

5) Stoppage of fuel supply to one cylinder throws extra... on the other cylinders.

6)... of cylinder heads often results from unequal heating.

7) When... of power occurs the first possibility that should be investigated is hot bearings.

 

Exercise 4. Translate into English.

1) Неисправности в двигателе, связанные с пневмозапуском, могут быть вызваны неправильной регулировкой воздушно­го пускового клапана и другими причинами.

2) Вода может попасть в топливо вследствие переменного ис­пользования цистерн для топлива и водяного балласта.

3) Резкое снижение температуры забортной воды влияет на мощность двигателя.

4) Трещины цилиндров происходят вследствие неравномерного нагрева, из-за конструктивных недостатков, плохой отливки, воздушных пробок.

5) Самой серьезной неисправностью, которая встречается в воз­душной системе пневмозапуска, является падение давления воздуха, поступающего в цилиндр.

6) Бдительность со стороны механиков может исключить при­чины, вызывающие аварии двигателя.

 

Exercise 5. Make up a dialogue of your own based on the one given below.

THE ENGINE

 

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 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.

A.: What is the best procedure for keeping valves in good con­dition?

В.: Do not wait for trouble to develop before examining valves. Establish a regular routine for removing valves for examina­tion and overhaul. This routine procedure is facilitated, if a com­plete set of spare valves is available so that the spares can be in­stalled while in port and the used valves overhauled at leisure. The length of time between examinations of valves can be es­tablished to suit the nature of the service the ship is engaged in.

 

Exercise 6. Speak on the following.

1) Derangements likely to occur in connection with starting dif­ficulties.

2) Derangements likely to occur in connection with water in fuel oil.

3) Derangements likely to occur in connection with improperly refined oil.

4) Derangements likely to occur in connection with loss of power or slowing down the engine.

5) Derangements likely to occur in connection with cracked cylinders and cylinder heads.

6) Derangements likely to occur in connection with cracked crank shafts.

7) Derangements likely to occur in connection with vibration.