Lesson 2. Derangements likely to occur in operation of engines

Notes:

Upon first sight the Diesel engine is apt to create the impression that it is a very complicated mechanism, but a little analysis will reveal that it is actually more simple than the steam plant. Comparing the two it should be born in mind that the steam engine alone is not a usable machine; to be able to use it we must have a boiler and all the attendant mechanisms, including pumps, piping, water tanks, condenser, etc., and the complete steam plant becomes quite a complicated thing. The Diesel engine, on the other hand, may be arranged so that all of the apparatus required in its operation as a power plant may be attached directly to the engine itself.

Perhaps the most striking difference in the problem of maintenance of the Diesel engine as compared to steam engine maintenance arises from the fact that the steam engine can be allowed to fall, more or less gradually, into a very bad state of disrepair and will continue to run but the Diesel engine must be pretty nearly right or it will not run at all.

DERANGEMENTS AND ADJUSTMENTS

 

The derangements likely to occur in operation and the adjustments required to correct them may be grouped into the following general classes:

a) Wrong fits and clearances, looseness and tightness of parts.

b) Mechanical defects.

c) Fuel system defects.

d) Combustion defects.

e) Cooling water system defects.

f) Lubricating system defects.

g) Air system defects.

h) Starting difficulties.

i) Operating troubles in general.

 

Exercise 1. Answer the following questions.

1) What impression is the Diesel engine apt to create upon first sight?

2) What should be born in mind when comparing the Diesel engine and the steam engine?

3) What is the most striking difference in the problem of maintenance of the Diesel as compared to steam engine maintenance?

4) What conditions are necessary to make the Diesel run at all? 5) What kinds of mechanical defects do you know? 6) What kinds of fuel system defects do you know? 7) What kinds of combustion defects do you know? 8) What kinds of cooling water system defects do you know? 9) What kinds of lubricating system defects do you know? 10) What kinds of air system defects do you know? 11) What kinds of starting difficulties are familiar to you? 12) How can you characterize operating troubles in general?

 

Exercise 2. Give the equivalents of the following.

In Russian: starting difficulties; wrong fits; combustion defects; lubricating system; to create the impression; attendant mechanisms; the most striking difference; exceeds limit marked on boiler front; adjustment of excess air; main propulsion system; the generator trips off the line; hose coupling; watertight doors; carbon dioxide cylinder storage room

In English: действующие технические средства, неполадки в работе технических средств, вахтенный моторист, выполнять распоряжения, неисправности, которые чаще всего встречаются в эксплуатации, принять необходимые меры по устранению неисправностей, неправильные зазоры, мощность на валу, вспомогательный котел, поддерживать чистоту и порядок, создавать впечатление, с другой стороны, снимать показания, вспомогательные механизмы.

 

Exercise 4. Translate into English.

1) На первый взгляд дизель может показаться очень сложным механизмом, но небольшой анализ покажет, что в действительности он значительно проще, чем паровая машина с котлом, вспомогательными механизмами, конденсаторами и т. д.

2) Неисправности, которые чаще всего встречаются в эксплуатации, могут быть классифицированы следующим образом:

а) механические дефекты;

b) неправильные зазоры;

с) плохая пригонка и т. д.

3) Если возникнут неисправности во время эксплуатации, следует принять необходимые меры по их устранению.

4) С одной стороны, дизельный двигатель может быть собран таким образом, что все инструменты, необходимые для его работы, такие как силовая установка, могут быть прикреплены непосредственно к самому двигателю.

5) Необходимо помнить, что паровой двигатель сам по себе не является полезным механизмом, чтобы мы могли его использовать нам нужен паровой котел и все сопутствующие устройства, включая насосы, трубы, конденсаторы и т.д.

 

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

THE ENGINE

 

A.: What is the power available at the shaft called and how is it measured?

В.: Shaft horsepower, or brake horsepower. It is usually meas­ured by attaching some form of brake to the shaft and measuring the amount of power absorbed by the brake when the engine is running. A second method is to attach an electric generator to the shaft and measure the electrical output of the generator.

A.: Is the mechanical efficiency, or the ratio between brake horsepower and indicated horsepower, the same at all loads?

В.: No. The power absorbed in friction in the engine is the same at all loads and as the engine load decreases the ratio of B.H.P. to I.H.P. decreases.

A.: What auxiliary machinery is usually found in the engine-room of a motorship?

В.: Jacket cooling water pumps, raw water pump, piston cool­ing pumps, lubricating oil pumps, fuel oil service pumps, bilge and ballast pumps, engine-room bilge pumps, fresh water pump, auxiliary air compressor. Diesel electric generating sets, donkey boiler, evaporator and distiller, boiler and evaporator feed pumps, emergency compressor, ice machine and oil separator.

A.: What auxiliary machinery is used on deck?

В.: Deck winches, anchor windlass, capstans, steering engine, air whistle and lighting system.

A.: How are Diesel engines started?

В.: By running as air motors, on compressed air at medium pressure, until ignition of fuel occurs and operation as a combus­tion motor starts,

A.: How is the starting air obtained and where is it stored?

В.: By means of a compressor attached to the engine or an auxiliary air compressor driven by a Diesel engine, electric motor or steam engine. It is stored in large tanks, usually suspended under the deck in the engine-room.

A.: From what other source can air for filling the starting tanks be obtained?

В.: On engines of the air injection type the injection air com­pressor attached to the engine usually has a capacity greater than that required for supplying injection air. The excess air may be by-passed to the starting tanks through a connection provided for that purpose.

Lesson 3. WRONG FITS AND CLEARANCES

Notes:

The principal source of trouble from this cause is the large bearings of the main shaft, cranks and crossheads. In general the bearing pressures are higher in the Diesel than in the steam engine and more careful and accurate fitting is required, so that the maximum bearing surface will be obtained. All bearings must be relieved at the sides enough to prevent gripping and to assist the spread of the lubricating oil around the bearing but not enough to reduce the bearing surface too much when they expand with the heat. All of the bearings, large and small, about the engine are subject to wear and looseness may develop in any of them in service but the large bearings just mentioned have the most severe duty to perform and require adjustment more often than the others.

Mechanical defects

Mechanical defects resulting in failure of parts in service may be due to errors in design, errors in machining or defects in the material itself. Errors in design have been too numerous to catalog but in the case of most well established builders such errors have been eliminated by experience in operation. Errors in machining are not the rule in any engine, if the manufacturer has an efficient inspection department, but they do occur and sometimes cause a great deal of trouble. Such errors are usually difficult to discover because they are not expected and the troubles resulting are assigned to other causes.

Sometimes careful investigation and analysis will reveal that a breakage that was apparently caused by a mechanical defect was due to bad work or neglect on the part of the engineers.

 

Exercise 1. Answer the following questions.

1) What is the principal source of trouble from wrong fits and clearances?

2) Why may looseness develop in any of the bearings in service?

3) What are the sources of mechanical defects?

4) What errors are usually difficult to discover?

5) What will sometimes careful investigation and analysis reveal?

 

Exercise 2. Give the equivalents of the following.

In Russian: To perform severe duty, accurate fitting, require adjustment, efficient inspection department, careful investigation, to prevent gripping, errors in machining, main shaft, cranks and crossheads, to assist the spread of the lubricating oil, expand with the heat, parts in service, cause a great deal of trouble.

In English: главный вал, кривошипы, крейцкопф, подвержены износу, требуют пригонки, иметь в виду, вследствие небрежной эксплуатации, конструктивный дефект, аккуратная подгонка, предотвратить заедание, дефекты устранены, погрешности при механической обработке деталей, тщательное расследование, сократить поверхность подшипника.

Exercise 4. Translate into English.

1) Большие подшипники главного вала, кривошипов, крейцкопфов являются основными источниками аварий.

2) Все подшипники подвержены износу в процессе эксплуатации двигателя и поэтому требуют периодической пригонки

3) Механические дефекты возникают вследствие конструктив­ных ошибок, погрешности при механической обработке деталей, дефектов в самом материале.

4) Это следует иметь в виду во время работы двигателя.

5) Такие погрешности трудно обнаружить, потому что на них не рассчитывают, и возникшие неисправности приписывают другим причинам.

6) Иногда тщательное расследование и анализ аварии показывает, что она произошла вследствие небрежной эксплуата­ции, хотя на первый взгляд кажется, что авария была вызва­на конструктивным дефектом.

 

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

THE ENGINE

 

A.: If all the stored air is lost how can the engines be started?

В.: In most cases a small emergency compressor is provided, driven by a very small oil engine that can be started by hand After a small amount of air is pumped up an auxiliary engine can be started and air pumped up to start the main engine.

A.: How much starting air capacity should the tanks have?

В.: The usual requirement is enough to start the engine 12 times. A better rule is to provide at least 35 times the volume swept through by one piston for each main engine.

A.: Describe the preparations for starting the engine.

В.: Jack the engine to see that it is clear for running, start lubricating oil pump and see that oil reaches all bearings, open by-pass valves in fuel oil lines to injection valves and pump oil through by hand to clear out all air and fill the pipes with oil, open stop valves in starting air and injection air lines, give cyl­inder lubricators a number of turns by hand to get some oil into the cylinders, start jacket cooling water pump and see that the propellers are clear. If means for heating the cylinders are avail­able and the weather is cold, warming up should be started in time to have all the cylinders hot before starting.

A.: Why should the bearings of a new engine be gone over after 800 to 900 hours of running?

В.: То take up looseness due to the initial wearing in.

A.: Why will a piston sometimes run without trouble at nor­mal load and drag or stick if the load is increased?

В.: Because the clearance in the cylinder may be sufficient at normal load but when overload causes all parts to become hotter the increased temperature of the piston causes it to expand more and reduce the clearance.

A.: What is the effect of too much or too little clearance be­tween a cam and its roller?

В.: Too much clearance causes late valve opening, early clo­sure, decreased lift and noisy operation. Too little clearance causes early opening, late closure, increased valve lift and may pre­vent complete closure.

A.: What are some of the common troubles experienced with fuel measuring pumps?

В.: Leaky suction and discharge valves, due to grit in the oil or to particles of dirt or lint becoming caught under the valves; pump becoming air bound; incorrect clearance between suction valve stems and tappets; leaky plungers, and change in timing, due to looseness in the operating gear.

A.: Why is it desirable to have thermometers so located that separate temperature readings of the cooling water discharge from the cylinders can be taken?

В.: If merely the temperature of the common discharge from all cylinders is taken, a single cylinder jacket may become air bound and the flow of cooling water through it stopped altogether without giving any indication at the common outlet.

A.: What are the effects of too many or incorrectly placed oil grooves in a bearing?

В.: The bearing surface is reduced and the oil escapes from the bearing without spreading over its surface.

A.: What is a common trouble with the cylinder lubricating system?

В.: Excessive feed of lubricating oil into the system, causing collection of gum and carbon in the ring slots and leakage of black oil into the crank pits.

 

Exercise 6. Speak on the following.

1) Derangements likely to occur in connection with wrong fits and clearances.

2) Derangements likely to occur in connection with mechanical defects.