Diesel Cycle – Process with P-V and T-S Diagram

Diesel cycle was invented by Rudolph Diesel in 1893. He put forward an idea by which we can attain higher thermal efficiency, with a high compression ratio. All diesel engine works on this cycle. Diesel is used as fuel in this cycle as it can be compressed at higher compression ratio. It is also known as constant pressure cycle because heat is added in it at constant pressure. It has high thermal efficiency and compression ratio (11:1 to 22:1)as compared with Otto cycle.

The engine that is put forward by Rudolph consists of an enclosed air in the cylinder. The cylinder walls are perfectly non-conductors of heat, but the bottom is a perfect conductor of heat. It has a hot body, cold body and an insulating cap, which are alternately brought in contact with the cylinder.

The ideal Diesel cycle consist of 4 process, two isentropic processes, one constant pressure and one constant volume process. 

 Processes


The 4 process are as follows
1. Isentropic (reversible adiabatic) Compression
2. Constant pressure heat addition
3. Isentropic Expansion
4. Constant volume heat rejection

Also Read: Difference Between Otto Cycle and Diesel Cycle

The working of these four processes of Diesel cycle can be easily grasped with the help of P-V and T-S diagram. 


Diesel cycle – Process with P-V and T-S diagram


diesel cycle process -  piston position

Note: for better understanding the process, watch the P-V and T-S diagram wherever necessary.

Process 1-2: Isentropic Compression 


In this process the piston moves from BDC to TDC and compression of air takes place isentropically. It means that during compression the entropy remains constant and there is no flow of heat out of the cylinder walls (non-conductors) happens. Here the air is compressed so the pressure increases from P1 to P2, volume decreases from V1 to V2, Temperature increases from T1 to T2 and entropy remains constant ( i.e. S1= S2).

Process 2-3: Constant Volume Heat Addition


In this process the, the hot body is kept in contact with the cylinder and heat addition to the air takes place at constant pressure. During this process, the piston rest for a moment at TDC. The pressure remains constant (i.e. P2 = P3), volume increases from V2 to V3, temperature increases from T2 to T3, entropy increases from S2 to S3.

Process 3-4: Isentropic Expansion


In this process, after heat addition, the expansion of air takes place isentropically and work is obtained from the system. The piston moves downward during this process and reaches to BDC. The pressure falls from P3 to P4, Volume increases from V3 to V4, temperature falls from T3 to T4 and entropy remains constant (i.e. S3=S4).

Process 4-1: Constant Volume Heat Rejection


In this process, the piston rest at BDC for a moment and the cold body is brought in contact with the cylinder and the heat rejection takes place at constant volume. The pressure decreases from P4 to P1, temperature decreases from T4 to T1, entropy decreases from S4 to S1 and volume remains constant (i.e.V4 = V1).

This is the four working process of diesel cycle engine that we have discussed. Now we will discuss how this cycle is implemented in the 4 stroke diesel engine. When this cycle is used in 4 stoke Diesel engine than we have 2 extra processes. One is suction process and other one is exhaust process. For heat addition diesel is used as fuel which burns and adds heat. 

Let’s discuss all the process in detail

0-1: Suction process (Suction stroke)
1-2: Isentropic compression process (compression stroke)
2-3: Constant volume heat addition (ignition and combustion of fuel)
3-4: Isentropic Expansion (power stroke)
4-1: Constant volume heat rejection (coolant comes in contact with cylinder walls)
1-0: Exhaust process (Exhaust stroke)

Also Read: Difference Between Petrol and Diesel Engine

Process 0-1: Suction process


In this process, the inlet valve opens and suction of air takes place at atmospheric pressure. It is called as suction stroke.

Process 1-2: Isentropic Compression


The air sucked is now compressed isentropically. Due to the compression, the temperature of the air increases to such level at which the diesel gets ignites. It is called as compression stroke.

Process 2-3: Constant Pressure Heat Addition


At the end of the compression, the piston is at TDC and at this time, the diesel fuel is injected into the cylinder through fuel injector in atomized form. As this atomized diesel fuel comes in contact with the hot compressed air, it gets ignited and combustion process starts. The combustion of fuel adds heats to the engine.

Process 3-4: Isentropic Expansion


The combustion process adds a large amount of heat and this creates a large force on the piston head and it moves downward from TDC to BDC. It is the power stroke.

Process: 4-1 Constant Volume Heat Rejection


The piston is at BDC and the coolant comes in contact with the cylinder walls and takes away heat from the engine and makes it cool. After that piston moves upward.

Process: 1-0: Exhaust Process


In this process, the piston moves from BDC to TDC and exhaust valve opens. All the burnt gases left in the cylinder escapes out through exhaust valve. It is the exhaust stroke.

This is how a four stroke compression engine works.

Summary


Summary of Diesel cycle with operation, position of piston and changes in different parameters are given below:

S.no
Process
Operation
Position of piston
Change in parameter
1.
1-2: Isentropic compression
Compression of air.
BDC to TDC
V: Decreases from V1 To V2
T: Increases from T1 to T2
P: Increases from P1 to P2
S: Entropy remains constant (S1=S2)
2.
2-3: Constant Pressure heat addition
Heat is added from an external source (hot body)
At TDC for a moment and moves slightly downward.
V: Increases from V2 To V3
T: Increases from T2 to T3
P: Remains constant  (P2 = P3)
S: Increases from S2 to S3
3.
3-4: Isentropic expansion
Expansion of air takes place due to heat addition.
TDC to BDC
V: Increases from V3 to V4
T: Decreases from T3 to T4
P: Decreases from P3 to P4
S: Entropy remains constant (S3=S4)
4.
4-1: Constant volume heat rejection
 Heat is rejected to a sink.
At BDC for a moment
V: Volume remains constant(V4 = V1 )
T: Decreases form T4 to T1
P: Decreases from P4 to P1
S: Decreases from Sto S1

Application

Diesel cycle is used where more power is needed with less amount of fuel. Mainly it is used in two stroke and 4 stroke diesel engines.

If you find anything missing or incorrect than lets us know through your valuable comments. And if you found this article informative than don't forget to comment, like and share.

What is Otto Cycle - P-V and T-S Diagram Easiest Explanation?

The Otto cycle was given by Dr. Nikolaus August Otto. It is a gas power cycle that is used in spark ignition engine (i.e. petrol engine) for its working. The entire modern petrol engine works on Otto cycle. It consist of four processes, Two isentropic (reversible adiabatic) processes and two isochoric (constant volume) processes. It has low compression ratio ranges from 7:1 to 10:1. Here we will try to understand this cycle with help of its P-V and T-S diagram.

The four processes of this cycle is as follows:

1. Isentropic ( reversible adiabatic) compression
2. Constant volume (Isochoric) heat addition
3. Isentropic (reversible adiabatic) Expansion
4. Constant volume heat rejection.

Before starting to understand these four processes, lets us first understand about isentropic and isochoric process.
  1. Isentropic Process: It is a thermodynamic process in which the entropy of the system remains unchanged (i.e. entropy remains constant). There is no dissipation of heat takes place during isentropic process, so sometime isentropic process called as reversible adiabatic process.
  2. Isochoric Process: The process which takes place at constant volume is called isochoric process.

How Otto Cycle Works?

Now, with the help of P-V and T-S diagram, we can easily understand all the process of Otto cycle.

P-V and T-S diagram of Otto Cycle

Note: For better explanation, while reading watch the P-V and T-S diagram everytime.

1. Process  1-2: Isentropic Compression

This process involves the motion of piston from TDC to BDC. The air that is sucked into cylinder during suction stroke undergoes reversible adiabatic (isentropic) compression. Since the air is compressed, the pressure increases from P1 to P2, the volume decreases from V1 to V2, temperature rises from T1 to T2, and entropy remains constant.

2. Process 2-3: Constant Volume Heat Addition

This process is an isochoric process i.e. the heat is added to the air at constant volume. The piston in this process rest for a moment at TDC and during this time heat is added to the air through external source. Due to the heat addition, the pressure increases from P2 to P3, pressure, volume remains constant(i.e. V2=V3), temperature increases from T2 to T3 and entropy increases from S2 to S3.
The amount of heat added is given by

3. Process 3-4: Isentropic Expansion

In this process, the isentropic (reversible adiabatic) expansion of air takes place. The piston moves from TDC to BDC. Power is obtained in this process which is used to do some work. Since this process involves expansion of air, so the pressure decreases from P3 to P4, volume increases from V3 to V4, temperature falls from T3 to T4 and entropy remains unchanged (i.e. S3=S4).

4. Constant Volume Heat Rejection

In this process, the piston rest for a moment at BDC and rejection of heat takes place at constant volume. The pressure decreases from P4 to P1, Volume remains constant (i.e. V4=V1), temperature falls from T4 to T1.

The amount of heat rejected in this process is given by
When this cycle is used in four stroke petrol engine than two process increases. one is suction of  air fuel mixture inside the cylinder which takes place at constant atmospheric pressure and other one is exhaust of gases out of the engine cylinder at constant atmospheric pressure. These two process are not shown in ideal otto cycle that we have discussed above. 

Summary in Tabular Form

S.no
Process
Operation
Position of piston
Change in parameter
1.
1-2: Isentropic Compression
Compression of air.
BDC to TDC
V: Decreases from V1 To V2
T: Increases from T1 to T2
P: Increases from P1 to P2
S: Entropy remains constant (S1=S2)
2.
2-3: Constant Volume Heat Addition
Heat is added in the form of spark and combustion occurs.
At TDC for a moment
V: Remains constant (V2 = V3 )
T: Increases from T2 to T3
P: Increases from  P2 to P3
S: Increases from S2 to S3
3.
3-4: Isentropic Expansion
Expansion of air takes place due to heat addition.
TDC to BDC
V: Increases from V3 to V4
T: Decreases from T3 to T4
P: Decreases from P3 to P4
S: Entropy remains constant (S3=S4)
4.
4-1: Constant Volume Heat Rejection
 Heat is rejected to a sink.
At BDC for a moment
V: Volume remains constant(V4 = V1 )
T: Decreases from T4 to T1
P: Decreases from P4 to P1
S: Decreases from S4 to S1

Thermal Efficiency

The efficiency of Otto cycle is given by

thermal efficiency of otto cycle

Application 

It is used in all  two stroke and four stroke petrol engines of motorcycles, cars, and other light duty vehicles.

If you find anything missing or incorrect than lets us know through your valuable comments. And if you found this topic informative than don,t forget to like and share it on social networks. Thanks in advance.

Compression Ignition Engine - Definition, Main Components, Working with Application

What is Compression Ignition (CI) Engine?

Compression ignition engine or CI engine is an internal combustion engine in which ignition of the fuel takes place with the help of hot compressed air. As the air is compressed, it gets hot and its heat is used for the ignition and burning of the fuel. In this engine the air is sucked during suction stroke and then this air is compressed while compression stroke. At the end of the compression stroke, fuel is injected into the cylinder and it gets ignited from the heat of compressed air and burning process begins. Diesel is used as fuel for the working of this engine. It works on the principle of Diesel Cycle. The compression ratio of this type of engine is usually ranges from 14:1 to 22:1. It is used in heavy duty vehicles like buses, trucks, ships, etc.

Main Components of Compression Ignition Engine


Compression ignition engine or CI engine

The main components of compression ignition (CI) engine are
  1. Injector: It is used to inject the fuel into the cylinder during compression of air.
  2. Inlet valve: The air inside the cylinder is sucked through inlet valve during suction stroke.
  3. Exhaust Valve: The whole burnt or exhaust from the cylinder thrown out through exhaust valve.
  4. Combustion chamber: It is a chamber where the combustion of fuel takes place.
  5. Piston: It is reciprocating part of CI engine which  does reciprocating motion inside the cylinder. Its main function is to transmit the thrust force generated during power stroke to the crankshaft through connecting rod.
  6. Connecting rod: It connects piston to the crankshaft.
  7. Crankshaft: It is used to convert the reciprocating motion of the piston into rotary motion.

Working 

Same as spark ignition engine, compression ignition engine also works. Its working is also divided into 4 strokes. Here we are discussing the working of four stroke CI engine.

1. Suction stroke: Suction of air into the cylinder takes place.
2. Compression stroke: The compression of air happens in this stroke.
3. Power stroke: Ignition and combustion of fuel.
4. Exhaust stroke: Escaping of burnt or exhaust gases.

Compression ignition engine or CI engine

Lets discuss these strokes in detail.

1. Suction Stroke

In this stroke the piston moves from TDC to BDC ( i.e downward) and the suction of air takes place through the inlet valve.

2. Compression Stroke

This stroke compresses the air that is taken into the cylinder in the suction stroke. As the air gets compressed, the temperature of the air increases and reaches upto that level where the combustion of the diesel takes place.

3. Power Stroke

At just before the end of compression stroke, the injector injects the fuel into the cylinder. Due to the heat of the air, the ignition of the fuel begins and combustion takes place. Due to the combustion of the fuel, hot exhaust gases produced that puts a very high thrust force on the piston and it moves downward. The piston rotates the crankshaft with the help of connecting rod. It is called as power stroke because power is produced in this stroke.

4. Exhaust Stroke

In this stroke the piston moves upward (i.e. BDC to TDC) and pushes the burnt gases out of the engine cylinder through exhaust valve.

After Exhaust stroke, again all the strokes repeats itself. In two stroke engine we get one power stroke in every single rotation of the crankshaft. But in four stroke engine, we get one power stroke, in every two rotation of the crankshaft.

The position of valve, and various operation performed in four stroke of a compression Ignition engine is given below.

S.no
Stroke
Inlet Valve
Exhaust valve
Operation performed
1.
Suction stroke
Open
Closed
Suction of air
2.
Compression stroke
Closed
Closed
Compression of air
3.
Power stroke
Closed
Closed
Fuel injection, ignition and combustion
4.
Exhaust stroke
Closed
Open
Escaping of burnt gases

For better explanation watch the video given below:


Application

CI engine is used in heavy duty vehicle where more power is required. They are used in automobiles ( like cars, buses, trucks etc), Aircraft, marine, and in various production industries.

If you find anything missing or incorrect than comment us. If this articles has added some information in your knowledge than don't forget to like and share it.

How Spark Ignition Engine Works?

What is Spark Ignition Engine ?

It is an internal combustion engine in which the ignition of the air-fuel mixture takes place by the spark. The spark is generated with the help of spark plug. Since in this engine, the spark is responsible for the ignition of the fuel, it is named as spark ignition engine (SI engine). This engine uses petrol as a fuel for its working. It works on the principle of otto cycle. The fuel in this engine is injected through carburetor during suction stroke. The compression ratio of this engine is usually 6 to 10. It has light weight engine and used in light duty vehicles like motorcycle, cars etc.

Main Components

Spark Ignition Engine (Si Engine)

The main components of spark ignition engine are as follows
  1. Inlet Valve: Air-fuel mixture enters into cylinder through inlet valve.
  2. Exhaust Valve: The burnt or exhaust gases produced in the power stroke escapes out through exhaust valve.
  3. Spark Plug: It produces spark at the end of the compression stroke, which ignites the compressed air-fuel mixture.
  4. Cylinder: It is a hollow cylinder in which the piston reciprocates.
  5. Piston: It is moving part of the engine that performs reciprocating motion and transmits the power generated during power stroke to the crankshaft through connecting rod.
  6. Connecting Rod: It is that part of the engine which connects the piston to the crankshaft.
  7. Crankshaft: It is used to convert the reciprocating motion of the engine into rotary motion.

Working 

Here we will discuss the working four stroke engine. The working of 4 stroke SI engine can be divided into four strokes.

1. Suction Stroke: Air-fuel mixture enters into the cylinder.
2. Compression Stroke: Compression of air fuel mixture takes place.
3. Power Stroke: Combustion of Fuel and Power Generation.
4. Exhaust Stroke: Escaping of burnt gases out of the engine.

How Spark Ignition Engine Works?


Lets us discuss each stroke in detail.

1. Suction Stroke

In this stroke, the piston moves downward and the air-fuel mixture from the carburetor enters into the cylinder through inlet valve. During this stroke inlet valve opens and exhaust valve remains closed.

2. Compression Stroke

In this stroke, the piston moves upward and compresses the air-fuel mixture. The compression strokes completes as the piston moves at TDC. During this stroke Both the inlet and exhaust valve remains closed.

3. Power Stroke

At the end of compression stroke, a spark is produced by the spark plug. This spark ignites the air-fuel mixture and combustion takes place in the combustion chamber. Due to combustion, a very high thrust force is generated which pushes the piston downward rapidly and makes the crankshaft to rotate. This stroke is called as power stroke because we get power in it. Both inlet and exhaust valve remains closed in this stroke.

4. Exhaust Stroke

In this stroke, the piston moves upward and burnt or exhaust gases produced in the power stroke escapes out of the cylinder through exhaust valve. In this stroke, the exhaust valve gets open and inlet valve remains closed.

After the completion of exhaust stroke, again all the four stroke repeats itself. The most commonly used spark ignition engine are of two stroke engine and four stroke engine. In two stroke engine we have inlet and exhaust port instead of valve.

Also Read: Difference Between Turbocharger and Supercharger

The position of inlet and exhaust valve and operation performed during all the four strokes of the SI engine are given in the table below:

S.no
Stroke
Inlet Valve
Exhaust Valve
Operation Performed
1.
Suction stroke
Open
Closed
Suction of fuel
2.
Compression stroke
Closed
Closed
Compression of fuel
3.
Power stroke
Closed
Closed
Combustion of fuel
4.
Exhaust stroke
Closed
Open
Escaping of burnt gases

Application 

The spark ignition engine are used in automobiles (motorcycle, Scooters, cars etc), aircraft, motorboats and in small engines such as chainsaws, lawn mowers etc.

If you find this article informative than don't forget to share it. And if you find anything missing in it than let us know through your valuable comments.