Introduction to Agricultural Mechanization

 

🧑‍🌾 I. Introduction to Agricultural Mechanization

Agricultural mechanization improves productivity and reduces labor.

Divided into:         

Tractive Work – pulling-type operations (plowing, planting, hauling)

Stationary Work – uses power transmission via belts, gears, PTO (e.g., threshing, milling)

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🔋 II. Sources of Farm Power

1. Human Power

- Average continuous output: 0.10 hp

- Suitable for tasks requiring judgment and skill

2. Animal Power

Power output: 0.7 to 1.3 hp

Still used in areas with:

1. Small farms

2. Steep terrains

3. High labor availability

4. Crops not suited for mechanization

3. Wind Power

• Theoretical power:

  $$P = \frac{1}{2} \rho A V^3$$

• Horizontal or vertical axis types; low reliability for farm use

4. Water Power

• Two types: falling streams (hydraulic head) and tides

• Power (hp):

  $$P = \frac{Q \times H}{33,000}$$

  where Q = mass flow rate, H = head

5. Electric Power

• Formula: Power (W) = Voltage × Current

• Advantages:

  • Smooth, quiet operation

  • Easy to maintain

  • High efficiency

• Limitation: 3-phase line availability

6. Solar Energy

• Types:

  • Thermal: heating, drying, mechanical conversion

  • Photovoltaic: converts light into electricity (16% efficiency for silicon cells)

• Solar constant: 1353 W/m² (outer atmosphere); ~690 W/m² (earth)

7. Biomass Energy

• Sources: crop residues, manure, fuelwood, etc.

• Conversion methods:

  • Thermochemical: combustion, pyrolysis, gasification

  • Biochemical: biogas, ethanol

8. Heat Engines

a. External Combustion (ECE)

• Examples: steam engines, Stirling engines

• Can use various fuels

• Low noise, high emissions control

b. Internal Combustion (ICE)

• Fuel burns inside engine

• 4-Stroke and 2-Stroke types

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⚙️ III. Power and Its Measurement

Definitions:

• Work = Force × Distance

• Power = Work ÷ Time (hp or kW)

• 1 hp = 550 ft-lb/s = 746 W

• Torque = force × distance (turning effect)

Engine Horsepower:

• Indicated HP (ihp): power generated in cylinders

  $$\text{ihp} = \frac{PLANn}{33,000 \times 2} \text{ for 4-stroke}$$

• Brake HP (bhp): output at pulley shaft

• Friction HP (fhp): power lost to engine’s internal operation

• Drawbar HP: at hitch for pulling loads

  $$\text{Drawbar HP} = \frac{\text{pull} \times \text{speed}}{33,000}$$

• PTO HP: output at PTO shaft

• Hydraulic HP:

  $$P = \frac{Q \times P}{1714}$$

Efficiencies:

• Volumetric Efficiency: ratio of actual intake to piston displacement

• Thermal Efficiency: BHP ÷ fuel energy input

• Mechanical Efficiency: BHP ÷ IHP

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🔁 IV. Engine Cycles and Operation

4-Stroke Cycle:

1. Intake

2. Compression

3. Power

4. Exhaust

2-Stroke Cycle:

• Simpler, one power stroke every revolution

• Less efficient, higher emissions

Firing Order: e.g., 1-3-2 for 3-cyl
Firing Interval:

• 4-stroke: 720° ÷ cylinders

• 2-stroke: 360° ÷ cylinders

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🚜 V. Tractors

• Types:

  • Wheel (2WD, 4WD)

  • Crawler (track-type)

• Standard class: >32 hp

• Compact class: ≤32 hp

• Key Components:

  • Clutch, Gearbox, PTO, Differential, ROPS, Brakes

• Implements connected via:

  • Drawbar (fixed, swinging)

  • 3-point linkage

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⛽ VI. Fuels and Combustion

Fuel Types:

• Gasoline: high volatility, uses spark ignition

• Diesel: high cetane number (e.g., 40)

• Alcohol (ethanol, methanol): cleaner burn but lower heating value

Important Terms:

• Pre-ignition: premature ignition due to heat

• Detonation: knock due to uncontrolled combustion

• Octane Rating: antiknock property of gasoline

• Cetane Rating: ignition quality of diesel

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🛠️ VII. Valves and Mechanism

• Valve types: poppet (45° face, sometimes 30° for intake)

• Parts: camshaft, tappet, push rod, rocker arm

• Valve timing is based on piston position and crank angle

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🔩 VIII. Fuel Supply and Carburetion

• Carburetor: mixes air and fuel

• Fuel Pump: high or low pressure delivery

• Choke Plate: enriches mixture during start

• Turbocharger/Supercharger: increases air intake

Euro Emission Standards:

• Euro 4: CO = 1.0g/km (gasoline)

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🌡️ IX. Cooling Systems

1. Air Cooling:

• Lightweight, simpler

• Heat dissipated via fins and flywheel fan

2. Liquid Cooling:

• Uses radiator, water pump, thermostat

• More efficient and stable

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⚡ X. Ignition and Electrical

• Spark ignition: 25,000–40,000 V needed

• Diesel: ignition via compression

• Battery: lead-acid, 2.2V/cell

• Sulfation: lead sulfate buildup from delayed charging

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🛢️ XI. Lubricants and Lubrication

• Types: engine oil, gear oil, greases

• SAE grades: SAE 10W-30 (multi-grade)

• API classes: SA, SB, SC... (gasoline); CA, CB... (diesel)

• Additives:

  • Detergents, dispersants, oxidation inhibitors, EP agents

Lubrication Systems:

1. Splash

2. Pressure-feed and splash

3. Full-pressure

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