Exercise 1. Before you start working with the materials of this Unit, study the following words that we have chosen for you from the text

Before you start working with the materials of this Unit, study the following words that we have chosen for you from the text.

1) vaporizing oil - керосин;

2) compression ratio - степень сжатия;

3) calorific value - показатель теплотворности (энергетическая ценность);

4) efficiency - эффективность; коэффициент полезного действия (КПД);

5) brake (indicated) power - эффективная (индикаторная) мощность;

6) volatile - летучий (о химических веществах);

7) (to) load - нагружать; нагрузка;

8) pollution - загрязнение;

9) spare parts (spares) - запасные части;

Exercise 2

Consult the textbook and other reference materials you have at your disposal, in order to repeat the use and Russian translation of the verb “to be”.

Grammar Note: You are recommended to take it into consideration that verb to be can occur in the language practice as a notional verb, an auxiliary verb, a modal verb, and Participle I.

Read the text, paying attention to the meanings of the sentences containing the verb “to be” in different forms and functions.

Text 7

Three main types of internal-combustion engines are commonly installed on farm and industrial tractors: 1. petrol engines; 2. paraffin (vaporizing oil) engines; 3. diesel ones. There are few differences between engines which employ petrol alone as a fuel and those which start on petrol and then run on vaporizing oil. But there are considerable differences between these two types and diesel engines.

The tractor fuel that is still often called paraffin is, in fact, a specially prepared mixturecontaining a proportion of volatile aromatic constituents which confer “anti-knock” properties not possessed by true paraffin or lamp oil. Aromatics must be excluded from the latter, because they cause smocking and danger of explosion. “Detonation”, or “knocking”, is an important factor limiting engine output, and anti-knocking properties are important in vaporizing oil, as well as in petrol. The better the anti-knock properties of the fuel, the higher is the compression ratio that can be employed, and the higher is the possible efficiency. Tractor vaporizing oil normally has a higher calorific value than petrol; but because lower compression ratios are to be employed with vaporizing oil, petrol engines tend to give a slightly better performance in terms of kW hours per liter. Typical optimum figures for petrol and vaporizing oil tractor engines are 1.9-2.1 kW hours per liter, being about 2.8 kW hours per liter for typical diesel engines.

Engine and tractor test reports indicate engine efficiency by the “specific fuel consumption”, which is expressed by the weight of fuel used per kW hour, or weight of fuel consumed by the tractor or automobile covering 100 mile distance. Typical optimum specific fuel consumption for modern diesel engined tractors are 240-300 g gas oil per kW hour available at PTO. Experience shows that the specific fuel consumption is higher at light loads. It is a design purpose of mechanical engineers to find ways to increase the brake power and the indicated powerand to decrease the specific fuel consumption. These technical measures could allow to make the exploitation of farm tractors more economic and even profitable for their owners.

Oil-based fuels cost many times more than electric power, and farmers should therefore exploit the largest possible amount of this cheap driving force. Another beneficial factor is that power engineering takes about 20 per cent of the primary energy resources. Oil and gas are the most convenient fuels for agricultural power engineering, but they are non-renewable resources. The tendency now is for farm machinery to be designed for electrical operation with the motors built in as a part of the machine.

Electric motors are the simplest and the best reliable machines out of types of farm power equipment used. Among the principle advantages that motors boast if compared to internal-combustion engines it is worth mentioning their ease of starting and control, operational durability, little need in spares, time-saving features, and power supply being provided without exhaust fumes, noise and many other environmental pollutions. Moreover, the electric motor is a highly efficient power unit, since at full load it converts 90 per cent of the electricity it takes into usable mechanical power.