Combustion defects

Normally the combustion in each power cylinder should be smokeless and complete and occur early in the stroke. Insufficient breaking up of the oil during injection will cause slow and incomplete burning and may be the result of clogged fuel nozzles, oil too cold or incorrect timing. Other causes of incomplete burning are compression too low, injection valves not correctly timed and air inlet pipes clogged.

Cooling water system defects

Complete stoppage of the cooling water supply can hardly occur unless the circulating pump breaks down or the ship grounds in shoal water where mud may plug up the sea injection valve, thus stopping the supply of raw water to the coolers of a closed fresh water system or the jacket supply of a sea water cooling system. In the event of the rare occurrence of pump breakage there is always an auxiliary pump available. Most well designed ships, especially when designed to operate in shoal water, have high and low sea suctions. The high suction is used in shallow water where mud might be drawn in through the low suction. The low suction should always be used at sea as the rolling of the ship is likely to throw the high suction out of the water and admit air into the sys­tem. It not infrequently happens when ships anchor in tropical harbors that the sea suction becomes clogged with jellyfish. When this happens it can be cleared by blowing out, if a steam or air con­nection on the body of the sea valve is available.

Failure of the water supply to any individual cylinder or piston may be caused by an air pocket in the supply line to that point or in the upper part of the cylinder head. Where all of the cooling water is passed through the coolers on the air compressor before reaching the engine jackets a leak in a cooler will allow air to blow into the water and stop the supply to all cylinders.

Lubricating system defects

All Diesel engines today are lubricated by the forced feed method and no hand oiling of any part is required. This requires that the engine housings be closed in, to prevent loss of oil through splashing, and the oil piping, with the oil circulating pump, forms a closed circuit through which the same oil circulates repeatedly. Of course the most serious derangement in such a system is loss of pressure.

Air system defects

The most serious derangement that can occur in the air system of an air injection engine, aside from the remote possibility of an explosion, is loss of injection air. Assuming that the compressor suction is open and the bleeder valve in the first stage properly adjusted, a falling off in the air pressure may be due to leaky, broken or stuck compressor valves, an injection valve sticking open, leaky air valve stem packing, leaky joints in the air piping or failure of the cooling water supply. If the air pressure falls to somewhere near the compression pressure in the power cylinders, unless the trouble can be located immediately, the engine should be stopped. If the engine is kept running, there will be a possibility of an explosion inside the injection valve body.

Exercise 1. Answer the following questions.

1) What derangements in the fuel system are most likely to occur?

2) What will cause the valve of the fuel measuring pump to leak?

3) What must be done to avoid it?

4) When should combustion occur in each power cylinder?

5) What are the causes of incomplete burning?

6) When can complete stoppage of the cooling water supply occur?

7) What sea suctions do most well-designed ships have?

8) When is the high suction used?

9) When should the low suction be used?

10) Which sea suction is used in shallow water?

11) How are all Diesel engines lubricated today?

12) What is the most serious derangement that can occur in the air system of an air injection engine?

13) What should be done if the air pressure falls and the trouble cannot be located immediately?

Exercise 2. Translate into English.

1. Неисправности топливной системы чаще всего встречаются в клапанах топливных насосов. 2. Скопление воздуха в насосах либо нарушит регулярную подачу топлива к двигателю, либо совсем прекратит ее. 3. Повторные притирки всасывающих клапанов требуют внимательной проверки. 4. Как правило, сгорание топлива в цилиндре должно быть полным, бездымным. 5. Неполное сгорание может происходить вследствие очень низкой компрессии. 6. Большинство судов, предназначенных для плавания на мел­ководье, имеют нижние и верхние приемные патрубки забортной воды.

Exercise 3. Make up a dialogue of your own based on the one given below.

A.: What are some of the causes of loss of injection air pres­sure?

В.: Leaky, broken or stuck compressor valves, injection air valve sticking open, leaky spray air valve stem packing, leaky joints in air piping, loss of cooling water.

A.: How can a start be had if there is no compressor avail­able?

В.: Procure a bottle of CO₂ gas and connect it to the starting air line. This gas is non-explosive and safe to use for this purpose.

A.: What are some of the causes of failure of an engine to start firing after it begins to turn on air?

В.: Fuel pumps not discharging oil, incorrect timing of fuel valves, low compression, injection air pressure too low and cylin­ders too cold.

A.: What are some of the causes of cracked cylinder heads?

В.: Unequal heating, due to poor design, air pockets in jacket, insufficient cooling water and overloading.

A.: How does wear on main bearings cause crank shaft to break?

В.: By throwing the shaft out of line and causing it to be bent in alternate directions twice in every revolution.

A.: Give the valve timing for the average large, 4-cycle engine.

В.: Injection valve opens 5 degrees before top center, injection valve closes 49 degrees past top center, exhaust valve opens 140 degrees past top center, air inlet valve opens 15 degrees before top center, exhaust valve closes 10 degrees past top center, and air inlet closes 214 degrees past top center. When in use, the air starting valve opens at top center and closes at 128 degrees past top center.

A.: What is the most important valve timing?

В.: The time of opening of the injection valve. A small change in this time may seriously affect the operation of the engine.

A.: When setting valves how to determine when the injection valve opens?

В.: Keep moving the cam roller with the fingers until it makes contact hard enough to bind, turn injection air into the valve and listen for the hiss of air through the indicator cock when the valve starts to open, or use a micrometer dial indicator to note when the valve stem starts to lift.

Lesson 5. STARTING DIFFICULTIES

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. 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 3. Make up a dialogue of your own based on the one 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 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.

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