Principles of Engine Operation

Engines operate on cycles. There are four strokes of the piston in one cycle of engine operation. There are two outward strokes toward the crankshaft and two inward strokes away from the crankshaft.

When the pistons is at the end of the stroke away from the crankshaft (inward stroke) this is top dead centre (TDC). When the piston is at the end of the out ward stroke (toward the crankshaft) this is bottom dead centre (BDC). The piston movement from TDC to BDC is an engine stroke.

The four strokes in a cycle of the internal combustion engine are: intake, compression, power and exhaust.

Intake. During the intake stroke the piston moves to BDC and the intake valve opens. This movement of the piston draws a mixture of air and fuel into the cylinder (in a diesel this movement of the piston draws in air only).

Compression. When the piston reaches BDC it moves toward the cylinder head (inward motion). The valves do not open and the piston compresses the fuel mixture between the piston and the cylinder head (in a diesel the piston compresses air only).

Power. When the piston reaches TDC, an electric spark ignites the fuel mixture in the combustion chamber of the gasoline engine (in a diesel engine the heat of the highly compressed air ignites the fuel).

When the air-fuel mixture burns it moves the piston with great force.

There are higher pressures in the diesel engines and because of these pressures the diesel engines have heavier piston pins, connecting rods and crankshafts than the gasoline engines.

Exhaust. The exhaust stroke takes place when the piston moves up. The exhaust valve opens and the piston forces out the gases. The new cycle will begin in the cylinder.

Because of the four strokes we call this engine a four stroke-cycle engine. The four-stroke-cycle engine with spark ignition is the most common type of the internal combustion engine.

Combine Harvesters

Combine harvesters are used to harvest various crops. The combine cuts the crop, threshes it, and separates the grain from the straw and chaff.

The mechanism of a combine harvester can be divided into three sections. They are cutting, threshing and finally separating the grain from the straw and chaff.

To cut the crop a reciprocating type cutter bar is used. There is a divider at each side ' of the cutter bar. It separates the crop to be cut from that which will be left for the next round. The crop is cut while held against the cutter bar by the reel. After the crop is cut, the reel directs it to the cutter bar platform. The reel is one of the main parts of a combine.

It has tines which can be angled to provide better cutting of the crops. A large auger moves the crop to the centre of the platform. By means of tines the auger directs the crop to the main elevator which lifts the crop to the threshing mechanism.

The threshing mechanism consists of a front beater, a heavy rotating drum, a concave.

The main elevator is used to lift the crop to the front beater. It delivers the crop to the drum and concave. The front beater increases the speed of the crop as it moves to the drum. Some combines do not have a front beater. In these combines the work of the front beater can be done by the main elevator. Threshing takes place between the drum and concave. There are spaces between the concave bars, so the threshed grain is allowed to fall through on to the grain pan. To reduce the speed of the crop as it leaves the cylinder is the task of the rear beater. The rear beater is the part of the threshing mechanism which both reduces the speed of the crop and directs it to the separating mechanism. To separate the grain from the straw is the main function of this mechanism. The separating mechanism consists of two parts: the straw walkers and the grain sieves. The harvested grain is directed to the grain tank. Big combines have an auger in the grain tank to provide the proper flow of the grain.

Grain tank capacities vary from 1 to 50 tones. A high capacity auger is used to deliver the threshed grain from the grain into a trailer.

Harrows

Harrows are used for various purposes, such as preparation of seedbeds, covering of seeds, destruction of weeds and aeration of soil. Many types and sizes are in use today. The most common type is that with a zigzag frame and rigid tines.

Seed harrows are light implements with closely fitted tines, about 4 in (100 mm) long. They are used for the final preparation of seedbeds and for covering seeds after the drill. They are mounted on small tractors.

Medium tractor harrows have various functions: the preparation of seedbeds, mixing of fertilizers with soil and spring cultivation of autumn-sown corn. The wider the implement, the more important it is to have good arrangements for transport. Mounted implements up to 8 m wide may be used with tractors of 40 - 50 kw. Heavier and wider harrows for use with tractors or about 75 km may be semi-mounted. One type provides for lifting of the harrow sections to a wheeled frame, the wings of which can be manually rolled behind the centre sections.

Disc harrows cut and consolidate the soil. Two or more sets of discs are fitted on a frame which may be mounted or semi-mounted. Some heavy discs are trailed and have hydraulically operated transport wheels. Discs are supported by bearings. Disc harrows working widths vary from 1,5 to 6 m.

Adjustments of disc angle. A hand operated lever on the harrow is used to vary the cutting angle of the discs. Discs being fitted at the widest angle, the soil movement will be the greatest. When discs are set straight, they will not move the soil very much and have a consolidating effect.

 

Geodesy, Cartography and Land Management

What Is Surveying

The role of a surveyor is now extremely significant. A growing number of disciplines including mapping, navigation, and Global Positioning Systems concern the modern surveyor. Advanced surveying techniques are more accurate, faster, and reliable than traditional methods, with new technologies emerging. So, what is surveying?

In the broadest sense, surveying is gathering information about a topic. With regard to geography, surveying is the field of gathering information about land - such as boundaries, areas and elevations - using geometric measurements. Surveying is typically in reference to earth landforms and structures, but is also valid for lunar surfaces and other terrestrial planets.

Surveying is an essential science for the fields of design and construction. Boundary surveys apprise people regarding the geographical location and limits of their property, and title surveys are an important part of the real estate business. Land topography maps are required for the preparation of detailed engineering designs. The plotting of river foundations is necessary for dredging. Delineation of corridors through survey techniques precedes the construction of roads, tunnels, airports, and pipelines.

History of Surveying

Surveying has been an important factor in human civilization since ancient history. The surveyors of ancient Egypt, also called “rope stretchers,” measured distances by using ropes at appropriate intervals. They also made measurements with chains with standard length links, pulled firmly to minimize slack. Compasses that provided the deflection measurements measured angles. These survey instruments improved over time by incorporating accurately engraved discs with improved angular resolution.

Surveying was also important in Greece. As the Greeks explored the science of geometry, they put it into practice to divide land precisely. The Greeks also developed the first surveying instrument, called a Diopter.

During the industrial revolution, the development of roads, railroads, and canals demanded more precise surveying techniques and surveying technologies advanced. This era saw the development of geodetic and plane surveying.

Modern surveying techniques- Global Positioning Systems, Geomatics, Geodesy and Remote Sensing-have replaced the older surveying techniques. Today, surveying has many purposes. In addition to establishing boundaries between plots of land, it is necessary for mapping the globe, both above and below sea level, and devising land, air- and water navigation routes. It is also necessary for gathering engineering data for constructing roads, bridges, and buildings. Surveying is also essential for acquiring databases for natural resources management.

Geomatics

Geomatics has redefined the surveying technology of the last quarter of the twentieth century, and it is still undergoing revolutionary progress. This science encompasses a large variety of earth mapping techniques, including Global Navigation Satellite Systems, remote sensing, and photogrammetry. Geomatics is a progressive field that integrates acquirement, modeling, study and managing of data. It uses global, maritime, aerial and satellite based sensors to obtain data. It then transforms the data obtained from different resources into selected information systems. The associated field of hydrogeomatics involves geomatics for surveying on, below, or above the sea surface or other water bodies.

The fast progression and extensive operation of geomatics is due to the advancement in computer technology, software engineering, and computer science. Space sensing technologies have also contributed immensely in the growth of geomatics. Several universities have gone so far as to replace the names of their survey departments with geomatics or geomatic engineering.

The major disciplines of geomatics include:

· Mapping · Navigation · Geodesy · Remote Sensing · Global Positioning System

· Photogrammetry · Airborne Laser Scanning · Geospatial · Digital Terrain Modeling · Hydrography

 

Future of Surveying

With advancements in technology, new surveying equipment and techniques are developing. Current advancements are making the science of surveying more valuable, accurate, and comprehensive than ever. For example, the use of GPS in modern surveying methods is one of the radical changes influencing land measurements. GPS is a breakthrough technology in surveying because it is extremely precise, fast, and reliable.

Furthermore, the role of the surveyor is changing as technology expands and geospatial data becomes available to anyone through programs such as Google Earth. A surveyor is no longer necessary for many basic data acquisition tasks … because the data already exists. Instead, the modern surveyor needs skills in geospatial data management and analysis.