Diesel engine terminology

Piston stroke:

• The distance travelled by the piston from top dead centre to bottom dead centre or from bottom dead centre to top dead centre is called piston stroke.

Swept volume:

• Swept volume is product of stroke and piston area. It is the volume swept by piston in one stroke.

Clearance volume:

• This is the volume left on top of cylinder when piston reaches top dead centre. This area inturn become the combution chamber.

Compression ratio:

• It is the collective volume of swept and clearance volume divided by clearance volume.
• Compression ratio= (swept volume + clearance volume)/ clearance volume.

Scavenging: 

• Blowing out exhaust gases from the system with the help of charged fresh air is termed as scavenging.

Supercharging/ turbocharging

• If additional air is forced into the system than the system could naturally aspirate after the working stroke then the cylinder is called called supercharged cylinder and process is called super charging.
• In modern marine engine ( two / four stroke) they use Rotary air compressor driven by turbine that uses the exhaust gas energy. This in turn increase the power with very low increase in fuel consumption.

Naturally aspirating engine:

• Engine that charge air by themselves without any additional support to charge air are called as naturally aspirating engine.

Four stroke cycle:

• The four piston stroke in four stroke cycle are
• Suction
• Compression 
• Expansion
• Exhaust

The engine has inlet and exhaust valves. These valves are provided as to draw and expell out combution product. The proper opening and closing of exhaust valves ensure this.

Suction/induction stroke: The inlet valve is open and as the piston moves downward the fresh charge of air is pulled into the system along with the support of turbo charger.

Compression stroke : The inlet and exhaust valves are closed as the piston moves upward the chargeair in the cylinder starts to compress the energy is transferd to air and thus increasing its pressure and temperature.

Expansion/working stroke: The inlet and exhaust valves are closed as the piston is about to reach TDC atomotised fuel is given in the system the heat and pressure result in spontaneous burning of fuel and this in turn gives the power stroke to the engine.

Exhaust stroke: As the piston reaches BDC the exhaust valve starts to open. As the piston moves up the exhaust gases created by the combustion process is pushed out of the system and new charge of air is given in and the cycle repeat itself.