Lesson 4. Fuel system defects

 

Notes:

Derangements in the fuel system are most likely to occur at the fuel measuring pumps. These pumps must handle a very small amount of oil at high pressure on each stroke and in order to do this the suction and discharge valves must be kept in perfect condition. A frequent source of trouble with these valves is dirt or grit in the oil. A small particle of sand or a thread qf waste under a valve will cause it to leak. Good strainers should be provided in the fuel oil supply line to the pumps and the strainers should be cleaned frequently. The pump plungers should be very carefully packed to prevent leakage of oil outward and air inward. Accumu­lation of air in the pumps will cause either irregular supply of fuel to the engine or stoppage. Stoppage of fuel supply to any one cylinder throws extra load on the other cylinders when the governor acts to increase the pumps discharge. Repeated regrinding of the pump suction valves will require careful checking of the pump timing.

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. Give the equivalents of the following.

In Russian: Pump timing, incomplete burning, sea injection valve, well designed ships, sea suction, discharge valves, good strainers, pump plunger, insufficient breaking up of the oil, clogged fuel nozzles, incorrect timing, jacket supply of a sea water cooling system, auxiliary pump, air pocket in the supply line, loss of injection air, bleeder valve, properly adjusted.

In English: скопление воздуха, сгорание топлива, всасывающий клапан, низкая компрессия, приемные патрубки забортной воды, выпускной клапан, скалка насоса, длительность накачки, забитые форсунки, входной воздухопровод, предназначенные для плавания на мелководье, корпус двигателя, возможность взрыва, всасывание компрессора.

 

Exercise 3. Use the correct words from the text.

1) The pump plungers should be very carefully packed to prevent …

2) Repeated regrinding of the pump suction valves will require …

3) Normally the combustion in each power cylinder should be …

4) The high suction is used in …

5) All Diesel engines today are lubricated by …

6) The most serious derangement that can occur in the air system of an air injection engine is …

 

Exercise 4. 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 5. Make up a dialogue of your own based on the one given below.

THE ENGINE

 

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.

 

Exercise 6. Speak on the following.

 

1) Derangements likely to occur in connection with the fuel system.

2) Derangements likely to occur in connection with combustion.

3) Derangements likely to occur in connection with the cooling water system.

4) Derangements likely to occur in connection with the lubricat­ing system.

5) Derangements likely to occur in connection with the air sys­tem.