Mechanical Engineering Lecture Notes: IC Engines and Compressors

• IC ENGINES AND COMPRESSORS:

Internal Combustion Engines are the basis of human transportation and without them human civilization will come to halt. The main characteristics of an IC engines is its combustion chamber where fuel is burnt at elevated temperature and pressure to develop rotational kinetic energy.

IC engines, or internal combustion engines, are a type of heat engine that convert the heat generated by the combustion of fuel into mechanical energy. This mechanical energy is used to power a vehicle or machine. IC engines can be categorized into two types: spark ignition engines and compression ignition engines. In spark ignition engines, a spark is used to ignite the fuel-air mixture, while in compression ignition engines, the fuel-air mixture is compressed until it spontaneously ignites.

Compressors, on the other hand, are mechanical devices that are used to increase the pressure of a gas. They are commonly used in a variety of applications, such as in air conditioning and refrigeration systems, as well as in the compression of natural gas and other gases for transport or storage. There are several types of compressors, including positive displacement compressors and dynamic compressors. Positive displacement compressors work by trapping a fixed amount of gas and then compressing it, while dynamic compressors use a rotating impeller to increase the velocity of the gas and then convert that velocity into pressure.

While IC engines and compressors have some similarities in terms of their use of internal combustion, they are fundamentally different types of devices with different applications and operating principles.

Compressors are mechanical devices that are used to increase the pressure of a gas. There are several types of compressors, each with its own unique characteristics and applications. Here are some of the most common types of compressors and their functions:

• Types of Compressors and Functions:

Reciprocating compressors: This type of compressor uses a piston and cylinder to compress the gas. The piston moves back and forth within the cylinder, creating a vacuum that draws in the gas, which is then compressed as the piston moves back up.

Rotary screw compressors: These compressors use two interlocking screws to compress the gas. The screws rotate in opposite directions, drawing in the gas and compressing it as it moves through the screw threads.

Centrifugal compressors: Centrifugal compressors use a rotating impeller to increase the velocity of the gas, which is then converted into pressure by a diffuser. This type of compressor is commonly used in high-flow, low-pressure applications.

Axial compressors: Axial compressors use a series of rotating blades to compress the gas. The blades are arranged in a row, with each row of blades increasing the pressure of the gas as it moves through the compressor.

Scroll compressors: Scroll compressors use two interleaved spirals to compress the gas. One spiral remains stationary while the other moves in a circular motion, trapping and compressing the gas as it moves through the spirals.

The function of a compressor is to increase the pressure of a gas, which can then be used for a variety of purposes, such as powering tools and machinery, refrigeration, air conditioning, and gas transport and storage. Compressors are used in a wide range of industries, including manufacturing, healthcare, energy, and transportation.

• Reciprocating compressors: and its functions:

Reciprocating compressors are a type of positive displacement compressor that use a piston and cylinder to compress a gas. The piston moves back and forth within the cylinder, creating a vacuum that draws in the gas, which is then compressed as the piston moves back up. Reciprocating compressors are commonly used in applications where a high-pressure output is required, such as in natural gas processing, petroleum refining, and chemical processing.

The functions of reciprocating compressors include:

Compression of gas: The primary function of a reciprocating compressor is to compress a gas to a higher pressure, which can then be used for various industrial processes.

Gas transport: Reciprocating compressors can be used to transport gases through pipelines or other systems. The compressed gas can be moved over long distances without losing pressure, making it an efficient method of transport.

Storage: Compressed gas can be stored in tanks or other vessels for later use, and reciprocating compressors can be used to fill these storage containers.

Power generation: Reciprocating compressors can be used to generate power by compressing gas and then using that compressed gas to power a turbine or other type of engine.

Refrigeration: Reciprocating compressors can be used in refrigeration systems to compress refrigerant gases and remove heat from a space or product.

Overall, reciprocating compressors are a versatile type of compressor that can be used for a wide range of industrial applications where high-pressure gas output is required.

• Components of a reciprocating compressors:

A reciprocating compressor is a complex machine made up of several components that work together to compress a gas. The main components of a reciprocating compressor include:

Cylinder: The cylinder is the main body of the compressor where the piston moves back and forth to compress the gas.

Piston: The piston is a cylindrical component that moves back and forth within the cylinder to compress the gas. The piston is typically made of a metal alloy and is attached to a connecting rod.

Connecting rod: The connecting rod connects the piston to the crankshaft and converts the linear motion of the piston into rotational motion of the crankshaft.

Crankshaft: The crankshaft is a shaft that rotates to convert the linear motion of the connecting rod into rotational motion. The crankshaft is typically driven by an electric motor or a combustion engine.

Valves: The compressor has two sets of valves, intake and discharge, that control the flow of gas into and out of the cylinder. The intake valve opens to allow gas to enter the cylinder, and the discharge valve opens to allow compressed gas to exit the cylinder.

Crankcase: The crankcase is a compartment in the compressor that houses the crankshaft and connecting rods. It is typically filled with oil to lubricate the moving parts and reduce wear and tear.

Pressure relief valve: The pressure relief valve is a safety feature that opens when the pressure in the compressor exceeds a certain threshold. This prevents the compressor from being damaged or exploding due to excess pressure.

Overall, each component of a reciprocating compressor plays a critical role in the compressing process and must be designed and maintained to ensure reliable and efficient operation.

• Efficiency of a reciprocating compressor:

The efficiency of a reciprocating compressor is a measure of how effectively it can compress gas while consuming the least amount of energy. The efficiency of a reciprocating compressor can be affected by several factors, including the compressor design, operating conditions, and maintenance practices.

The following are some of the factors that can affect the efficiency of a reciprocating compressor:

Compression ratio: The compression ratio is the ratio of the discharge pressure to the suction pressure. The higher the compression ratio, the lower the compressor efficiency.

Clearance volume: The clearance volume is the volume of gas remaining in the cylinder after the piston has reached the end of its stroke. A larger clearance volume can decrease the efficiency of the compressor.

Gas properties: The physical properties of the gas being compressed, such as its molecular weight, specific heat ratio, and heat capacity, can affect the efficiency of the compressor.

Operating conditions: The operating conditions of the compressor, such as the suction and discharge pressures and temperatures, can also affect its efficiency.

Maintenance: Proper maintenance practices, such as keeping the compressor clean and lubricated, can help maintain its efficiency over time.

To improve the efficiency of a reciprocating compressor, it is important to properly size and design the compressor for the specific application and operating conditions. Proper maintenance practices, such as regular cleaning, lubrication, and inspection, can also help to maintain the efficiency of the compressor over time.