INTRODUCTION
The internal
combustion engine is a heat engine that convert chemical energy in a fuel into mechanical
energy, usually
made available on a rotating output
shaft.
Chemical energy of the fuel is first converted to thermal energy by means of com-
bustion or oxidation with air inside the engine.This
thermal energy raises the
temperature and pressure of the gases within the engine, and the high-pressure gas then expands
against
the mechanical mechanisms of the engine.
This expansion is converted by the mechanical
linkages of the engine
to a rotating crankshaft,
which is the output of the engine. The crankshaft, in turn,
is connected
to a transmission and/or power
train
to transmit the rotating
mechanical
energy
to the desired final use.
EARLY HISTORY
During 19th century,different internal combustion engines were built and tested.The first fairly practical engine was invented by J.J.E. Lenoir (1822-1900) and appeared about in 1860.
 |
| lenoir Engine |
During the next decade,Engines were built with power up to about 4.5 kW (6 hp) and mechanical efficiency up to 5 %.In 1867 the Otto-Langen engine, with efficiency improved to about 11%, was first introduced, and several thousand of these were produced during the next decade. This was a type of atmospheric engine with the power stroke propelled by atmospheric pressure acting against a vacuum. Nicolaus A. Otto (1832-1891) and Eugen Langen (1833-1895) were two of many engine inventors of this period. During this time, engines operating on the same basic four-stroke cycle as the modern automobile engine began to evolve as the best design. Although many people were working on four-stroke cycle design, Otto was given credit when his prototype engine was built in 1876. In the 1880s the internal combustion engine first appeared in automobiles. Also in this decade the two-stroke cycle engine became practical and was manufactured in large numbers. By 1892, Rudolf Diesel (1858-1913) had perfected his compression ignition engine into basically the same diesel engine known today. This was after years of development work which included the use of solid fuel in his early experimental engines. Early compression ignition engines were noisy, large, slow, single-cylinder engines. They were, however, generally more efficient than spark ignition engines. It wasn't until the 1920s that multi-cylinder compression ignition engines were made small enough to be used with automobiles and trucks.
Classification of Engine.
Internal combustion engines can be classified in a number of different ways:
(b) Compression Ignition:The combustion process in a SI engine
starts when the air-fuel mixture self-ignites due to high pressure in the
combustion chamber caused by high compression.
2. Engine Cycle.
a) Four-Stroke Cycle:A four-stroke cycle experiences four piston movements over two engine revolutions for each cycle.
(b) Two-Stroke Cycle:A two-stroke cycle has two piston movements over one revolution for each cycle.
3. Valve Location
(a) Valves in head (overhead valve), also called I Head engine.
(b) 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.
4. Basic Design
(a) Reciprocating Engine has one or more cylinders in which pistons reciprocate back and forth. The combustion chamber is located in the closed end of each cylinder. Power is delivered to a rotating output crankshaft by mechanical linkage with the pistons.
(b) Rotary Engine is made of a block (stator) built around a large non-con- centric rotor and crankshaft. The combustion chambers are built into the non rotating block.
5. Position and Number of Cylinders of Reciprocating Engines
(a) Single Cylinder. Engine has one cylinder and piston connected to the crankshaft.
(b) 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 automo- bile 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).
(c) V Engine. Two banks of cylinders at an angle with each other along a sin- gle crankshaft. The angle between the banks of cylinders can be anywhere from 15° to 120°, with 60°-90° being common. V engines have even num- bers of cylinders from 2 to 20 or more. V6s and V8s are common automobile engines, with V12s and V16s (historic) found in some luxury and high-performance vehicles.
(d) Opposed Cylinder Engine. Two banks of cylinders opposite each other on a single crankshaft (a V engine with a 180° 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).
(e) W Engine. Same as a V engine except with three banks of cylinders on the same crankshaft. Not common, but some have been developed for racing automobiles, both modern and historic. Usually 12 cylinders with about a 60° angle between each bank.
(f) 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 complex mechanical linkage.
(g) Radial Engine. Engine with pistons positioned in a circular plane around the central crankshaft. The connecting rods of the pistons are connected to a master rod which, in turn, is connected to the crankshaft. A bank of cylin- ders on a radial engine always has an odd number of cylinders ranging from 3 to 13 or more. Operating on a four-stroke cycle, every other cylin- der 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. For large aircraft, two or more banks of cylinders are mounted together, one behind the other on a single crankshaft, making one powerful, smooth engine. Very large ship engines exist with up to 54 cylinders, six banks of 9 cylinders each.
6. Air Intake Process
(a) Naturally Aspirated. No intake air pressure boost system.
(b) Supercharged. Intake air pressure increased with the compressor driven off of the engine crankshaft .
(c) Turbocharged. Intake air pressure increased with the turbine-compressor driven by the engine exhaust gases .
(d) 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 crankcase compression.
7. Method of Fuel Input for SI Engines
(a) Carbureted.
(b) Multipoint Port Fuel Injection. One or more injectors at each cylinder intake.
(c) Throttle Body Fuel Injection. Injectors upstream in intake manifold.
8. Fuel Used
(a) Gasoline.
(b) Diesel Oil or Fuel Oil.
(c) Gas, Natural Gas, Methane.
(d) LPG. (e) Alcohol-Ethyl, Methyl.
(f) Dual Fuel. There are a number of engines that use a combination of two or more fuels. Some, usually large, CI engines use a combination of methane and diesel fuel. These are attractive in developing third-world countries because of the high cost of diesel fuel. Combined gasoline-alcohol fuel sare becoming more common as an alternative to straight gasoline automobile engine fuel.
(g) Gasohol. Common fuel consisting of 90% gasoline and 10% alcohol.
9. Application
(a) Automobile, Truck, Bus.
(b) Locomotive.
(c) Stationary.
(d) Marine.
(e) Aircraft.
(f) Small Portable, Chain Saw, Model Airplane.
1O. Type of Cooling
(a) Air Cooled.
(b) Liquid Cooled, Water Cooled.
No comments:
Post a Comment