A Reciprocating Engine is a classification of the internal combustion engines in which the piston moves up and down. The top portion of the piston where valves are located is called Top dead center, and the opposite extreme down portion of the piston is called Bottom dead center
The air or air-fuel mixture is drawn into the cylinder through the Intake valve and the combustion products are expelled from the cylinder through the Exhaust valve.
This is the powerhouse of the vast majority of automobiles such as trucks, aircraft, ships, electric power, generator and so on.
The piston reciprocates in the cylinder between the Top Dead Center (TDC) and Bottom Dear Center (BDC).
The largest distance in one direction traveled by the piston from TDC TO BDC is called a Stroke of the engine.
The diameter of the piston is called BORE.
The minimum volume formed in the cylinder when the piston is at TDC is called Clearance volume.
The volume displaced by the piston as its move between TDC to BDC is called Displacement volume.
The ratio of the maximum volume formed in the cylinder to the minimum (Clearance) volume is called the Compression Ratio.
This compression ratio= (Vmax or BDC ) / (Vmin or TDC )
The below figure shown of a Reciprocating Engine which describes the complete term and Overview of an engine:
Types of Reciprocating Engine:
The reciprocating engine classification has been categorized into various category:
1. According to the thermodynamic cycle:
- OTTO or Constant Volume Cycle (In this the energy released during the combustion of a fuel occurs at constant volume.)
- DIESEL or Constant Pressure Cycle (In this the energy released during the combustion of a fuel occurs at constant pressure.)
- DUAL or Limited Pressure Cycle (In this the energy released by combustion of a fuel partly at constant volume and pressure.)
2. Number of Stroke Per Cycle:
- 4 Stroke engine (In 4 stroke the cycle of engine complete 4 strokes of piston whereas)
- 2 Stroke engine (In 2 stroke the cycle of engine completes 2 strokes of the piston)
3. Ignition System:
- Spark Ignition (SI) Engine (A homogenous mixture of air and fuel vapor is supplied to the engine and the combustion is initiated by spark plug)
- Compression-Ignition (CI) Engine (Air sucked inside the cylinder is compressed to a higher pressure and temperature, This temperature exceeds the self-ignition temperature of the fuel.)
The engine cycle of both SI and CI engines can be completed in 2 strokes or 4 strokes of the piston.
4. Fuel Used:
- Petrol (The engine works on Petrol fuel such as Motorcycle )
- Oil or Diesel (engine works on Diesel)
- Gas (CNG, LPG, PRODUCER GAS)
- Multi-Fuel Engine (Use gasoline or diesel oil for starting the engine and kerosene as there primary fuel)
5. Cooling System:
- Water Cooling (Engine cooled by circulating water)
- Air Cooling (Engine cooled by blowing atmospheric air over the hot surface)
6. Multicylinder Engine:
- The power output of an engine is directly proportional to its speed.
Parts of a Reciprocating Engine:
A reciprocating Engine consist of the following parts:
- Piston Cylinder
- Connecting Rod
- Valves (Inlet and Outlet) or Port (Inlet and Outlet)
- Spark Plug or Fuel Injector
- Piston Ring
- Cooling jackets
A piston is circular in shape and it is the moving component of a reciprocating engine. The piston is connected with the connecting rod and transfer power from the engine to the crankshaft.
In a 2-stoke engine piston also work as a valve by closing and opening inlet and outlet port.
Here is how a piston looks:
It is also circular in shape, and in which the piston is move. It is made by the same material as of piston.
The main function of the connecting rod is to convert the reciprocating motion of the piston to the rotary motion. One end of the connecting rod is connected with a piston with the help of a gudgeon pin or piston pin and another end is connected with the crankshaft.
Here is the piston-cylinder arrangement:
Valves (Inlet and Outlet) or Port (Inlet and Outlet):
Valves are used in Four-Stroke Engine, and Ports are Used in Two-Stroke Engine.
When the engine in the suction condition then charges are entering through the inlet valve and after burning of charge the burned gas goes out of the cylinder with the help of the outlet valve.
Spark Plug or Fuel Injector:
Spark plug used for igniting the charge in a petrol engine and the fuel injector is used in diesel engines where high-pressure fuel is sprayed by the injector, however, fuel injector also controls the timing and quantity of fuel sprayed inside the cylinder.
Here I mentioned the brief differences between Spark Plug vs Fuel Injector, you may check this guide too.
Piston rings are used for:
- To save the piston and cylinder from wear out due to direct contact.
- To clean the surface of the piston, and also it scratches down extra the lubrication oil from the cylinder surface to the sump.
- It provides a tight seal so that charges inside the cylinder can not get out of the cylinder.
It fits inside or outside of the cylinder to save the engine cylinder from excessive heating, we may use water or coolant inside the cooling jacket and it’s continuously circulating.
How does a Reciprocating engine work?
As I already introduced the parts of the reciprocating engine, let’s discuss on the working principle of a reciprocation engine.
The reciprocating engine has four types of strokes.
- Suction Stroke
- Compression Stroke
- Power Stroke
- Exhaust Stroke
In suction stroke, fuel goes to the engine cylinder via inlet valve or port, when the piston goes from TDC to BDC then there is pressure difference between atmosphere and vacuum is created inside the cylinder, due to this vacuum fuel is in through the inlet valve, at this stage the outlet valve is in closed condition.
In compression stroke, the charge (Fuel or air+fuel) is compressed due to this its pressure and temperature gets higher and higher, and at this time spark plug (for petrol engine) give the spark and the whole the charge gets burned
At this stage, a high thrust produced by the burned gas to the piston, so that the piston shifted to the BDC, and the piston is connected with the crankshaft via a connecting rod, so the crankshaft is started rotating. This stroke is called a power stroke.
And at exhaust stroke again piston comes from the BDC to TDC and pushes the burned gases out of the cylinder.
So this is how a reciprocating engine work, by the way, in a 2-stroke engine Suction and Compression happens in one movement of the piston, i.e. from BDC to TDC and Power stroke and Exhaust stoke happen in another movement of the piston, i.e. from TDC to BDC.
I will highly recommend you to check out these article for complete knowledge about engines.
Still, if you have any doubts regarding the reciprocating engine do mention in the comment section, I reply to all comments.
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What is a Reciprocating Engine?
How does a Reciprocating Engine Works?
1. Suction Stroke (Where charge (Air+Fuel/Fuel) get inside the cylinder)
2. Compression Stroke (Charge are compressed and burned)
3. Power Stroke (The burned gas push the piston down words)
4. Exhaust Stroke (The burned gas is removed from the cylinder)
What are the Parts of a Reciprocating Engine?
2. Piston Cylinder
3. Connecting Rod
4. Valves (Inlet and Outlet) or Port (Inlet and Outlet)
5. Spark Plug or Fuel Injector
6. Piston Ring
7. Cooling jackets