IC Engine Terminology & Abbreviations

✳️ Internal Combustion Engine Terminology & Abreviations 

🔸️IC ➖ Internal Combustion

🔸️SI ➖ Spark Ignition

An engine in which the combustion process in each cycle is started by use of a spark plug.

🔸️CI ➖ Compression Ignition

An engine in which the combustion process starts when the air-fuel mixture self ignites due to high temperature in the combustion chamber caused by high compression. CI engines are often called Diesel engines, especially in the non-technical community.

🔸️TDC ➖ Top-Dead-Center

Top Dead Center (TDC), When the piston farthest from the crankshaft (for vertical engine). In a horizontal engine, it is called inner dead canter (IDC).

🔸️BDC ➖ Bottom Dead Centre 

Bottom Dead Center (BDC), When the piston is nearest to the crankshaft. In a horizontal engine, it is equivalent to outer dead center (ODC).

🔸️Stroke ➖  Movement distance of the piston from one extreme position to the other:

(TDC to BDC) or (BDC to TDC) .

🔸️Bore ➖ Diameter of the cylinder.

🔸️Maximum or total volume of cylinder ➖V_total

It is the volume of cylinder when the piston is at bottom dead center(BDC). Generally, it is measure in centimeter cube (c.c.).

🔸️Minimum or clearance volume of cylinder ➖(Vclearance)

It is the volume of cylinder when the piston is at top dead center(TDC).

🔸️CR ➖ Compression Ratio

The compression ratio (CR) of an engine is a measure of how much the air/air-fuel mixture is 

compressed in the cylinder.  It's the ratio of maximum volume to minimum volume of cylinder.

It is 8 to 12 for spark ignition engine and 12 to 24 for compression ignition engine.

▶️Compression ratio = Total volume / Clearance volume

🔸️Combustion Chamber ➖

The end of the cylinder between the head and the piston face where combustion occurs. 

The size of the combustion chamber continuously changes from a minimum volume when the piston is at TDC to a maximum when the piston is at BDC.

🔸️Displacement volume or Swept volume (Vs)

➖ It is the volume swept by the piston when moving from one dead centre to the other dead centre. Swept volume usually expressed in cubic centimetre (cc).

➡️ Vs = (π/4) * (Bore)^2 * (Stroke)

Or ➡️  Vs = Total Volume - Clearance Volume

🔸️CC ➖ Cubic Centimeters (cm³) 

The term “cc” stands for Cubic Centimeters or simply cm³ which is a metric unit to measure the Engine's Capacity or its volume.

🔸️Engine Capacity ➖

Engine capacity refers to the volume swept by all the pistons of an engine, within their bores, from the top to the bottom of their travel. Measured in litres, cubic centimetres (cc)

☑️ Engines with greater capacities are usually more powerful and provide greater torque at lower rpms but also consume more fuel.

➡️ Engine capacity = Swept volume × Number of cylinder

🔸️HP ➖ Horsepower

In essence, HP, BHP, PS, CV and kW all refer to the amount of power that an engine produces. Or, in less technical terms, how much ‘work’ it can do. As a rule of thumb, the higher the horsepower, the faster a car can ultimately go. Power is important measure of engine performance. 

🔸️Torque ➖

Like power, torque is another important measure of engine performance. Torque is a rotating force produced by an engine’s crankshaft. The more torque an engine produces, the greater its ability to perform work.

🔸️MBT ➖ Maximum Brake Torque

Maximum Brake Torque (MBT) is the use of optimal ignition timing to take advantage of an internal combustion engines maximum power and efficiency.

There is always an optimal spark timing for all operating conditions of an engine. MBT is most ideal at wide-open throttle (WOT), but not desirable when the engine is at idle. Although MBT is desired at WOT, it is wise to retard timing slightly to prevent knocking that may occur and to create a small safety margin. 

🔸️AFR or AF ➖ Air Fuel Ratio

Air-fuel ratio (AF or AFR) is the ratio between the mass of air and mass fuel, used by the engine when running.

🔸️Stroke to bore ratio ➖

Stroke to bore ratio is an important parameter in the classification of engine size.

It is the ratio of the stroke of engine (L) to its cylinder bore (d).

➡️ Stroke to bore ratio = L/d

▫️If L/d = 1, or d=L  then engine called square engine.

▫️If L/d > 1, or d<L then engine called under-square engine.

▫️If L/d < 1, or d>L then engine called over-square engine.

Over-square engines have shorter stroke length and it allows to engine operates at high speed.

➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖