Text 5. Diesel Engines Compared to other Prime Movers

Why are diesel engines used so much? Not merely because they can produce power — there are many other ways of producing power. Besides diesel engines, there are gasoline engines, steam engines, steam turbines, and water wheels (also known as hydraulic turbines), to name some though not all such examples. These machines are known as prime movers. Also, you can often buy power in the form of electricity which has come over wires; this is power which first has been produced by a prime mover and then converted into electricity. So it is a fair question – why, with all these different sources of power are diesel engines often preferred to the others? Sometimes the- question is easily answered; sometimes it demands professional engineering study.

Advantages of Diesel Engines. – It's not the purpose of this chapter to explain the work of professional engineers, so lot's just list the main advantages that diesel engines have over other forms of power for certain kinds of uses.

1. Small Consumption of Fuel. The diesel engine is one of the most highly efficient heat-engines; that is, it gets more power out of the fuel it burns than any other ordinary prime mover, except the largest and most efficient steam turbines. Its fuel consumption is much less than that of a gasoline engine. It is an engine of high economy.

2. Cheap Fuel. The diesel engine uses fuels costing less than half as much as gasoline.

3. Economy at Light Loads. The diesel engine is not only efficient when it is fully loaded, but also when it is only partly loaded (which is the way engines run most of the time). When running at half load, the diesel engine consumes only about 10 percent more fuel per unit of power produced than it does at full load. The efficiency of other engines drops off greatly when the load is reduced.

4. Greater Safety. Diesel fuel is nonexplosive and is far less inflammable than gasoline. In fact, it requires special effort to make it start to burn, much like hard coal does. This feature, alone, makes the diesel attractive in the motorboat field. Also, diesel exhaust gases are less poisonous than those from gasoline engines, because they contain little carbon monoxide.

5. Economy in Small Sizes. In great contrast to a steam- power plant, a small diesel engine has nearly as good an economy as a large one. This makes it possible to build an efficient power plant just large enough to meet present needs, and to enlarge it with additional units as the load grows. At all stages of growth, the efficiency is high.

6. Sustained Economy in Service. Again in contrast to a steam power plant, diesel efficiency falls off little during thousands of hours of use between overhauls. Steam-plant efficiency depends on continuous control of the furnace conditions and gradually falls off as boiler tubes become fouled. These factors are not present with diesel engines – as long as the exhaust gases are clear, the fuel economy must be good.

7. Independence of Water Supply. An efficient steam plant requires great quantities of condensing water, and must generally be located near a large body of water. A diesel engine requires little water, and can be successfully used in the most arid regions.

8. Lightness and Compactness. The diesel engine is a complete power plant in itself; it can be made light in weight and takes up a small amount of space. It is therefore well suited to portable and mobile installations.

9. Quick Starting. A cold diesel engine can be started instantly and made to carry its full load in a few minutes. It is therefore ideal for supplying emergency power.

10. Easily Reversible. By adding an extra set of cams, a diesel engine can be made to run at full power in either direction. This is important in marine applications.

11. Economy in Labor. No fireroom force is needed.

12. Freedom from Nuisance. There are no ashes to be disposed of, no noisy and dusty coal-handling and pulverizing equipment to maintain, no smoke, and noise can be easily eliminated.

Disadvantages of Diesel Engines.—We have just learned the-main advantages that diesel engines have over other forms of power producers. But diesel engines also have certain disadvantages, and you might as well learn right now what they are, so that you will understand why such engines do not fit into many applications.

1. Cost. Diesel engines, because of the higher pressures at which they work, require sturdier construction, better materials, and closer fits than gasoline engines. Therefore, they cost more to build.

2. Weight. Because of the sturdier construction, mentioned above, diesel engines weigh more than gasoline engines of the same power.

3. Attendance. A diesel engine requires more attention than an electric motor running on purchased current. It also requires more attention per unit of power produced than a large steam turbine or water wheel.

4. Fuel Cost. The type of oil which most diesel engines use for fuel is often more costly than coal when compared on a heat-value basis. A dollar's worth of coal contains more heat units than a dollar's worth of diesel oil. Ordinarily, this difference in fuel ргіce is more than offset by the small amount of oil consumed by the diesel compared with the amount of coal burned in a steam-power plant of the same power. But if coal is unusually cheap compared to oil, a steam-power plant may produce power at a lower cost for fuel than a diesel could.

A steam-power plant may also be able to cut its fuel cost below that of a diesel if its exhaust steam (which contains most of the heat) can be fully utilized for some heating process (as in a laundry).

Of course, no fuel at all is needed to drive a water wheel in a water-power plant. (The main items of cost in a water-power plant are the charges on the investment.)

5. Space. For large power outputs, diesel engines occupy much more space than steam turbines.

You can now see why, for one or more of the above reasons, other forms of power are preferred for such uses as:

1. Airplanes. Gasoline engines are lighter.

2. Ordinary automobiles. Gasoline engines are cheaper to build.

3. Electric-power plants in large cities. Large steam turbines occupy less space, require less attendance, and can use cheap coal efficiently.

Notes

hydraulic – гідравлічний

to sustain – підтримувати, витримувати

to foul – забруднювати

arid – посушливий

portable – складний; розбірний

instantly – відразу, негайно

emergency – крайність; непередбачений випадок

nuisance – прикрість, неприємність

to dispose – розміщати; використовувати

sturdy – стійкий; сильний

attendance – обслуговування; догляд

to consume – споживати, марнувати

offset – відвід(труби)

output – продуктивність; випуск; результати