LESSON 3. IC Engines for Farm Operations

3.1 Engine Classifications

With the advancement of technology in every sector, engine being prime mover or power house for any automobile or farm machinery, much has already been done in the development of engines for general purpose usage and special applications. So, engines can be classified in many ways depending upon their construction, operating principle, size, fuel used etc..

3.2 Types of engines depending on method of ignition

3.2.1 Spark Ignition (SI) : Spark plug is used in SI engines to initiate the combustion process in each cycle with the help of a high voltage electrical discharge between two electrodes. The air fuel mixture in the combustion chamber is ignited by the plug. Earlier the torch holes were being used to start combustion from external flame and then with the technological advancements electric spark plug replaced these torch holes.

(i) Carbureted: A device for mixing air and fuel to facilitate the combustion process

(ii) Multipoint port fuel injection: One or more injectors at each cylinder intake.

(iii) Throttle body fuel injection: Injectors upstream in intake manifold.

(iv) Gasoline direct injection: Injectors mounted in combustion chambers with injection directly into cylinders.

Module 2 Lesson 3 Fig.3.2_1 

3.2.2 Compression Ignition (CI) : The combustion process in a CI engine starts when the air-fuel mixture self-ignites due to high temperature in the combustion chamber caused by high compression.

(i) Direct injection: Fuel injected into main combustion chamber.

(ii) Indirect injection:  Fuel injected into secondary combustion chamber.

3.3. Types of engines depending on Engine cycle

3.3.1 Four-stroke cycle: A four-stroke cycle has four piston movements over two engine    revolutions for each cycle.

3.3.2 Two-stroke cycle: A two-stroke cycle has two piston movements over one revolution for each cycle.

3.4 Types of engines depending on Valve location

3.4.1 Valves in head (Overhead valve), also called I Head engine.

3.4.2 Valves in block (flat head), also called L Head engine. Some historic engines with valves in block had the intake valve on one side of the cylinder and the exhaust valve on the other side. These were called T Head engines.

3.4.3 One valve in head (usually intake) and one in block, also called F Head Engine; this is much less common.

3.5 Types of engines depending on Position and number of cylinders

3.5.1 Single Cylinder: Engine has one cylinder and piston connected to the crankshaft.

3.5.2 In-Line: Cylinders are positioned in a straight line, one behind the other along the length of the crankshaft. They can consist of 2 to 11 cylinders or possibly more. In-line four-cylinder engines are very common for automobile and other applications. In-line six and eight cylinders are historically common automobile engines In-line engines are sometimes called Straight (e.g., straight six or straight eight).

3.5.3 V Engine: Two banks of cylinders at an angle with each other along a single crankshaft, allowing for a shorter engine block. The angle between the banks of cylinders can be anywhere from 15° to 120° with 60°-90°. V engines usually have even numbers of cylinders from 2 to 20 or more.

3.5.4 Opposed Cylinder Engine: Two banks of cylinders opposite to each other on a single crankshaft (a V engine with 180 deg V). These are common on small aircraft and some automobiles with an even number of cylinders from two to eight or more. These engines are often called flat engines (e.g., flat four).

3.5.5 Opposed piston engine: Two pistons in each cylinder with the combustion chamber in the center between the pistons. A single combustion process causes two power strokes at the same time, with each piston being pushed away from the center and delivering power to a separate crankshaft at each end of the cylinder. Engine output is either on two rotating crankshafts or on one crankshaft incorporating a complex mechanical linkage. These engines are generally of large displacement, used for power plants, ships, or submarines.

3.5.6 Radial engine: Engines with pistons positioned in a circular plane around a circular crankshaft. The connecting rods of the piston are connected to a master rod, which in turn, is connected to the crankshaft. A bank of cylinders on a radial engine almost always has an odd number of cylinders ranging from 3 to 13 or more. Operating on a four-stroke cycle every other cylinder fires and has a power stroke as the crankshaft rotates, giving a smooth operation. Many medium and large size propeller driven aircraft use radial engines.

3.6 Types of engines depending on Air Intake Process

3.6.1 Naturally Aspirated: No intake air pressure boosts system.

3.6.2 Super charged: Intake air pressure increased with the compressor driven off of the engine crankshaft.

3.6.3 Turbo charged: Intake air pressure increased with the turbine compressor driven by the engine exhaust gases.

3.6.4 Crankcase compressed: Two-stroke cycle engine which uses the crankcase as the intake air compressor. Limited development work has also been done on design and construction of four-stroke cycle engines with crank case compression.

3.7 Types of engines depending on Fuel used

3.7.1 Petrol/Gasoline engines

3.7.2 Diesel engines

3.7.3 Gas, Natural gas, Methane engines

3.7.4 Alcohol-Ethyl, Methyl engines

3.7.5 Dual fuel engines: There are a number of engines that use a combination of two or more fuels. Some, Usually large, CI engines use a combination of natural gas and diesel fuel. These are attractive in developing third world countries because of the high cost of the diesel fuel. Combined  gasoline alcohol fuels are becoming more common as an alternative to straight gasoline automobile engine fuel.

 (f) Gasohol engines: Common fuel consisting of 90% gasoline and 10% alcohol.

3.8 Types of engines depending on Type of cooling

3.8.1 Air cooled : Circulating air is used to dissipate the heat from the fins on an engine. Mostly small engines are used with air cooled engines.

3.8.2 Liquid cooled, Water-cooled : Water is made to flow through the water jackets provided along the surface of cylinders or liners to absorb the heat. Further the heated water is cooled with the help of radiator.

Last modified: Monday, 27 January 2014, 11:55 AM