Engine Terminologies,

Heat Engine

             Heat Engine is a system/machine that performs the conversion of heat or thermal energy to mechanical energy (work) as a result of combustion

             Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production/libration of heat. The release of heat can result in the work.

                Fuels of interest often include organic compounds (especially hydrocarbons) in the gas, liquid or solid phase.

                These types of reactions are exothermic and significant amount of heat is evolved which increase temperature and pressure

             General case:

                Hydrocarbons (Fuel) + O2 → CO2 + H2O + energy

             Petroleum is a mixture of a very large number of different hydrocarbons; the most commonly found molecules are alkanes (linear or branched), cycloalkanes, aromatic hydrocarbons. Each petroleum variety has a unique mix of molecules, which define its physical and chemical properties, like color and viscosity etc

             The alkanes, also known as paraffins, are saturated hydrocarbons with straight or branched chains which contain only carbon and hydrogen. They generally have from 5 to 40 carbon atoms per molecule.

             The alkanes from pentane (C5H12) to octane (C8H18) are refined into petrol, the ones from no-nane (C9H20) to hexa-decane (C16H34) into diesel fuel, kerosene and jet fuel). Alkanes with more than 16 carbon atoms can be refined into lubricating oil. Octane, a hydrocarbon found in petroleum. Lines represent single bonds; black spheres represent carbon; white spheres represent hydrogen.

Petrol combustion:

2C8H18 + 25O2 → 16CO2 + 18 H2O + energy/Heat

Diesel/Petro-diesel combustion

2C16H34 + 49O2 → 32CO2 + 34H2O + energy/Heat

Natural Gas (CNG) combustion

CH4 + O2 → CO2 +  H2O + energy/Heat

Engine Terminologies

Bore (d):

The internal diameter of the cylinder

Stroke (l):

                The maximum length of travel of piston from one extreme position to other extreme position in one direction

Top dead centre (TDC):

                The position of the piston at the end of its travel when moving towards cylinder head

Bottom dead centre (BDC):

                The position of the piston at the end of its travel when moving towards the crankcase

Piston displacement (PD):

                The volume displaced or covered by the piston when it moves from TDC to BDC

Clearance volume (CV):

                The space or volume between the top of the piston and the engine cylinder head, when the piston is at the TDC. It is also called combustion chamber

Total cylinder volume (TCV):

                The volume designated by PD and Clearance volume

                TCV = PD + CV

Compression Ratio (CR):

                The ratio of total cylinder volume and the clearance volume

                CR = TCV/CV

Engine Size:

                It is the product of diameter of piston and the stroke of the engine

Heat Engine Classification

1. Internal Combustion Engine (I.C.E.)

                a. Reciprocating

                b. Rotary

 C: Crankshaft

 E: Exhaust camshaft

 I: Inlet camshaft

  P: Piston

 R: Connecting rod
  S: Spark plug

  V: Valves. Red: exhaust, Blue: intake

W: Cooling water ducts

2. External Combustion Engine (E.C.E.)

                a. Reciprocating (Old tractors, boilers)

                b. Rotary (Steam turbines, Power plants)

                Turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work. The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and impart rotational energy to the rotor

Internal Combustion Engine

It is a machine which converts the reciprocating motion into rotary motion as a result of thermal expansion caused by combustible Gases

As combustion takes place inside the engine cylinder, so the engine is called internal combustion engine

External combustion engine

An external combustion engine (EC engine) is a heat engine where an (internal) working fluid is heated by combustion of an external source, through the engine wall or a heat exchanger. The fluid then, by expanding produces motion and usable work. The working fluid can be a gas or steam as in a steam engine.

Reciprocating motion, also called reciprocation, is a repetitive up-and-down or back-and-forth motion. It is found in a wide range of mechanisms, including reciprocating engines and pumps. . The piston moves in a reciprocating motion, which is converted into circular motion of the crankshaft, which ultimately propels the vehicle or does other useful work.

Rotary motion, Rotation around a fixed axis is a special case of rotational motion.

I.C.E:

a. Reciprocating:

                a.1: C.I. Engines

                                a.1.1 Four stroke (Tractors, cars, buses)

                                a.1.2 Two stroke (Motor cycles)

                a.2: S.I. Engines

                                a.1.1 Four stroke (Tractors, cars, buses)

                                a.1.2 Two stroke (very rare)

                The SI spark plug is timed to start combustion at the ideal moment, usually some degrees before the piston reaches the top (TDC or Top Dead Centre). The burning mixture then drives the piston down for the power stroke.

The CI fuel is injected (sprayed) into the cylinder at the ideal moment - this too is usually some degrees before TDC, and the red-hot air in there then starts the fuel burning. This then drives the piston down for the power stroke.

b. Rotary Engines:

                                Airplanes, Power plants