General Engine Design

4.1.

For an engine to operate normally, its cylinders must be supplied with a homogeneous mixture of fuel and air in definite proportions (in carburetor engines) or with metered-out charges of fuel injected under a high pressure at strictly defined moments (in diesel engines). To reduce the amount of work done in overcoming friction, to withdraw heat, and to prevent scuffing and premature wear, all the rubbing parts of the engine are lubricated with oil. The engine must be cooled in order to create normal temperature conditions in the cylinders. The high compression ratio of diesel engines prevents the possibility of their being started by hand, and so these engines are provided with a starting device. All engines used to power tractors, combine harvesters, and automobiles are arranged similarly and include mechanisms and systems performing similar functions.

Diesel engines powering tractors or self-propelled combine harvesters consist of the following mechanisms and systems.

The crank mechanism converts the straight line motion of the pistons into the rotary motion of the crankshaft, which is most convenient for transmitting mechanical energy to rotate the driving wheels or sprockets of tractors or self-propelled combine harvesters and to drive the live attachments of combines and other farm machines.

The timing gear controls the operation of the valves, making it possible to let air into the engine cylinders, compress it to a certain pressure, and purge the exhaust gases from the cylinders at definite positions of the pistons.

The fuel feed system provides for the delivery into the cylinders of metered-out charges of finely atomized fuel at definite moments.

The lubricating system ensures continuous delivery of oil to rubbing components and removal of heat from them.

The cooling system prevents the combustion chamber walls of the engine from overheating and maintains normal temperature conditions in the cylinders.

The starting system is necessary to crank the engine during starting.

The arrangement of component parts of the various systems of a tractor diesel engine is shown in Fig. 7.

Fig.7. The Д-240 Model tractor diesel engine

(a) right-hand side view,

(b) left-hand side view;
l - oil level dipstick;

2 - timing pin;

3 - oil filler;

4 - oil filter;

5 - primary fuel filter;

6 - exhaust manifold;

7 - air cleaner;

8 - fan;

9 - generator;

10 - hydraulic servo steering pump;

11 - engine front support;

12 - hand priming pump;

13 - fuel injection pump;

14 - compressor;

15 - fuel injector;

16 - secondary fuel filter;

17 - emergency engine shutdown air throttle lever;

18 - fuel system air vent valve;

19 - starter motor;

20 - starting engine;

21 - starting reduction gear

4.2. THE ENGINES OF COMBINE MODIFICATIONS, i.e., those intended primarily for use on combine harvesters, are brought into line with the base tractor engine models of the same power output.

In contrast to tractor engines, the engines of self-propelled grain combine harvesters are equipped with belt pulleys instead of power takeoff shafts. The front end of the crankshaft carries the drive pulley of the combine driving axle. This pulley is also used to drive the generator, water pump, fan, and hydraulic pumps. The rear end of the crankshaft is connected through a clutch to another shaft which carries a belt pulley for driving the live combine attachments. The operation of the attachments is controlled by means of a lever installed in the combine cab.

All grain combine harvesters are equipped with turbo-charged diesel engines. The engines are started with the aid of an electric starter motor or a starting engine.

In combine harvesters, the engine is mounted on a frame held to the threshing mechanism housing. The engine support cushions used to isolate the threshing mechanism housing from engine vibrations are installed either between the frame and the housing or between the engine supports and the frame.

The mechanisms and systems of AUTOMOBILE CARBURETTOR ENGINES are similar to those of tractor diesel engines. The differences between the former and the latter are as follows:

(a) the fuel feed system of automobile engines is intended to supply the engine cylinders with a homogeneous air-fuel mixture prepared in a special device – the carburetor;

(b) to ignite the combustible charge in the cylinders of carburetor engines, use is made of the ignition system.

The arrangement of component parts of an automobile engine is shown in Fig. 8.

Date: 2015-12-24; view: 1160