What is drilling? | Types of drills | Drilling operation formula

Drilling is the most common process of machining. The drilling process accounts for nearly 75% of all metal cutting material removed.

Drilling is an operation to create cylindrical holes by extracting the metal from solid material or by widening existing holes using multi-tooth cutting tools called drilling. There are various cutting tools available for drilling, but the most common is the twist drill.

The Egyptians drilled holes some 3000 years ago through bow drills in 1200 B.C. The bow drills are the mother of the current drilling machine for metal cutting. There are various types of drilling machine available in the market. 

Drilling characteristics:

• The chips must exit out from the hole created by the drilling process. 
• When chips are large or continuous, existing chips can cause problems. 
• At the entrance and for deep holes, the drill can wander. 
• Coolant may need to be delivered to the cutting front through the drill shaft for deep holes in large workpieces.
• The most likely drilling on the drill press is by someone who is not a machinist in the process of powder metal cutting.

There are several apparatus needed during the drilling operation. 

• Drilling machine
• Center punch 
• Hammer
• Center drill 
• Twist drill 
• Coolant
• Vernier calliper
• Two flute drill set 
• Center drill
• Countersink drill 
• Counterbore drill
• Drill various diameter

Types of drills:

Step drill to produce a hole of two or more different diameters. 

Core drill to enlarge existing holes.

Counterboring and countersinking to produce depression on the surface to accommodate heads of screws and bolts. 

Center drill a short and stubby drill to produce holes so that workpiece can be mounted between lathe centres. 

Spot drill to start a hole. 

Spade drill to remove large and deep holes. 

Crankshaft drill for good centring. Suitable for deep holes. 

Gun drilling for deep hole making, self-centring, lubrication, and coolant passage. 

Trepanning removal of disk-shaped piece.  

Twist drills to remove the metal in large volume in a minimum period of time. 

The formula for drilling operation:

The cutting speed of the drilling operation is the peripheral speed of the cutting edge. 

Cutting speed = π D N 

Where D =  drill diameter

N = Rotational speed in rpm 

A feed is the distance the drill penetrates per revolution ( mm / rev ). 

Each cutting edge is f / 2. 

Depth of cut is taken as half the diameter of drilling. 

Depth of cut = D / 2

Drilling time is the time taken to complete the drilling operation. 

 T = L / f * N

Where, f = feed-in mm / rev

N = rotational speed ( rpm )

L = the sum of hole depth 

Material removal rate ( MMR ) is the volume of material removed by the drill per unit time. 

MMR = ( π D² / 4 ) * f * N 

Explore more information: 

1. What is the size of the drilling machine?
2. How to use a drilling machine?
3. Safety while using a drilling machine
4. The function of the drilling machine
5. Care should be taken while using a drilling machine
6. Parts of drilling machine

What is electrochemical machining | Working principle | Application | Advantages and Disadvantages

Electro-chemical machining is one of the newest and most useful processes of metal removal by the controlled dissolution of the anode of an electrolyte cell.

The process is suited to metal and alloys which are difficult or impossible to the machine by mechanical processes.

This is based on Michael Faraday's classical laws of electrolysis, requiring basically the two-electrodes, electrolytes, a gap and a source of D.C power of sufficient capacity.

Working principle of electrochemical machining

In this machining process workpiece acts as anode and tool acts like cathode and the electrodes should be placed closely with a gap of about 0.5 mm. Anode and cathodes should be immersed in an electrolyte. A potential difference is maintained in between the electrodes as a result ions existing in the electrolytes and it migrates towards the electrodes. Positively charged ions are attracted toward the cathode and negatively charged ions are attracted towards the anode and thus the flow of current is initiated in the electrolyte. The setup is kept stationary and the tool is fed linearly the desired amount of metal is removed through the electrolysis process.

To keep the tool safe from damage by a continuous supply of electrolyte is ensured by pumping at high pressure. The temperature generated is very low and no spark produced this there may not any scope of metallurgical changes in the work material. The tool and the workpiece do not come in direct contact with each other so in this machining process negligible wear and tear are observed. By using this process dimensions up to 0.05 mm can be easily machined. 

Function of electrolyte 

The electrolytes used in this machining process are sodium chloride, sodium nitrate, potassium chloride, sodium hydroxide, sodium fluoride, sulfuric acid and sodium chlorate. 

The main function of electrolyte in this process is following below. 

• To carries the current between the tool and workpiece.
• Removes products of machining and other insoluble products from the cutting region.
• To dissipates heat produced in the operation.
• To keed the reaction continuous. 

What should be the criteria for selecting Electrolyte?

• Required Machining rate
• Required Dimensional Accuracy
• Surface Texture and Integrity

The essential characteristics of Electrolytes are following below. 

• Good electrical conductivity.
• Non-toxicity and chemical stability.
• Non-corrosive property.
• Low viscosity
• High specific heat.

The properties of Electrolytes are following below. 

• High Electrical Conductivity.
• High Current Efficiency for machining.
• Good Surface finish and integrity are necessary.
• Composition of the electrolyte and structure of the material controls the final surface texture. 

Tool material for electrochemical machining 

Copper, brass, titanium, copper-tungsten and stainless steels are most commonly used electrode material when the electrolyte is made of slats of sodium or potassium. Some material such as aluminium, graphite, bronze, platinum and tungsten carbide are also used for tool material.

Requirements of the tool material in electrochemical machining are following below.

• Tool material is a conductor of electricity.
• Because of the fluid pressure, it should be rigid enough to take up the load.
• The electrolyte should be chemically inert.
• Making it in the desired shape should be easy to machine.

Accuracy of electrochemical machining

Under ideal conditions with properly designed tooling, is capable of holding a tolerance of the order of (+0.02 to -0.02 mm) and less. Internal radius is greater than 0.2 mm and  0.05 mm an external radius. The taper is of the order of 0.010 mm for 10 mm depth and side over-cut is about 0.1 to 0.2 mm. Based on the work material, the surface finish of this process varies from 0.2 to 0.8 microns.

Factors which affect the accuracy are following below. 

• Machining Voltage.
• The feed rate of the electrode. 
• The temperature of the electrode.
• The concentration of electrolyte.

Application of electrochemical machining

The main application is machining of hard heat-resisting alloys. This process also used to make an aerospace component, machining of tungsten carbide and that of nozzles in alloy steels. Almost any conducting material can be machined by this method. The main process performed by the electrochemical machining process is electrochemical cutting, broaching, and drilling. 

Typically this method is used for mass production and works with extremely hard materials that are difficult to handle using other techniques but are limited to the use of electrically conductive materials.

Advantages of electrochemical machining 

• The metal removal rate is quite high for high-strength-temperature-resistant (HSTR) materials as compared to the conventional process.
• Accurate machining.
• Residual stress is low.
• Surface finish is in the order of 0.2 to 0.8 microns.
• No direct contact between tool and workpiece.
• Negligible wear and tear of tool material.
• Environmental friendly.
• Possible to machine non-rigid and open workpiece.
• It can be a machine configuration which is beyond the capability of the conventional machining process.
• Extremely thin sheets of metal can be worked easily without distortion.
• A job with complex shapes can be machined easily and accurately.
• Several holes can be done at once during drilling.
• It is a time-saving machining process as compared to conventional machining.
• Deburring can be done in hard to access areas.
• Fragile and brittle materials can be machined easily without cracking or breaking.
• The metallic workpiece is not damaged due to thermal stresses.

Disadvantages of Electrochemical Machining :

• Power consumption is more.
• Initial tooling can be timely and costly.
• Non-conducting materials can not be machined.
• The process is costly because of expensive equipment.
• Continuous supply of electrolyte is necessary.
• Steady voltage should be maintained during the whole process.
• Corrosion and rust of the machine can be a hazard.
• If hydrogen is liberated at the tool surface then it is possible to suffer from hydrogen-embitterment of the surface.
• There may be a possibility of damages because of sparks.
• Conventional machining produced more improved fatigue properties than electrochemical machining.

Read more related posts: 

1. Advantages and disadvantages of electrochemical machining

Lathe machine | Function | Types | Operation | Cutting speed | Feed | Depth of cut

The lathe machine is one of the oldest machine tools that rotate a workpiece about an axis of rotation to perform different operations such as turning, drilling, knurling, facing and many more. In this article, you can check out the function, types, operations, cutting speed, feed, depth of cut, and machining time of the lathe machine. 

Functions of the Lathe Machine:

Removing metal from a piece of work to give it the required shape and size is the main function of a lathe.

This is done by keeping the work on the device securely and rigidly and then turning it against the cutting tool which extracts metal from the work in the form of chips.

Types of Lathe Machines:

• Speed Lathe Machine
• Engine Lathe Machine
• Bench Lathe Machine
• Toolroom Lathe Machine
• Capstan and Turret Lathe Machine
• Special-purpose Lathe Machine
• Automatic Lathe Machine

Lathe Machine

Lathe Machine parts and their function:

The lathe machine parts and their function are explained below. 

The bed

The lathe bed is the foundation of a lathe machine. The headstock and tailstock are on either end of the bed and the carriage lies on the bed and slides over it. It is the guiding member of the lathe machine so it should be rigid to prevent deflection, avoid distortion, and must be resisted to twisting. Nickel and chromium alloyed cast iron form a suitable material for lathe bed.

The headstock

The headstock is firmly fixed on the inner ways at the left end of the lathe bed consists of a hollow spindle and mechanism for driving and altering the spindle speed. 

The tailstock

The tailstock is at the right end of the bed on the inner ways. It supports the other end of the workpiece holds a tool for performing an operation. 

The carriage

The carriage consists of several parts such as saddle, cross-slide, compound slide, toolpost, and apron that serve to support, move and control the cutting tool. 

The saddle is an H-shaped casting that fits over the bed and slides along with the ways carried the cross-slide and tool post. 

The cross-slide comprises casting machined on the underside for attachment to the saddle. 

The compound rest is mounted on top of the cross-slide used for obtaining angular cuts and short tapper. 

The tool post is located on the top of the compound rest to hold the tool and enable it to be adjusted to a working position. There are different types of tool post such as single screw tool post, four-bolt tool post, open side tool post, and four-way tool post. 

The apron is linked with the saddle and hands over the front of the bed contains gears, clutches, and levers for operating the carriage by hand and power feeds. 

Feed Mechanism 

The movement of tool related to the work is called a feed. A lathe machine may have three types of feed such as longitudinal, angular and cross. 

Gearbox 

The gearbox is placed below the headstock and contains gears.

Operations performed on Lathe Machine:

Operations that are performed in a lathe either by holding the workpiece between centres or by a chuck are following below. 

• Straight turning
• Shoulder turning
• Chamfering
• Thread cutting
• Facing
• Knurling
• Filling
• Taper turning
• Eccentric turning
• Polishing
• Grooving
• Spinning
• Spring winding
• Forming

Operations that are performed by holding the work by a chuck or a faceplate or an angle plate are following below. 

• Drilling
• Reaming
• Borning
• Counterboring
• Taperboring
• Internal thread cutting
• Tapping
• Undercutting
• Parting-off

Operations that are performed by using special attachments are following below. 

• Grinding
• Milling

Lathe Machine precaution:

• Do not use your hand to support the work piece you can using the work holding device.
• Use the brush to clean the chip.
• While the machine is in operating condition no adjustment done by the operator. 
• Before starting the operation makes sure that all parts are secured tightly. 
• Not to keep a chuck handle attached by the chuck. 
• Do not touch the table to a rotating chuck. 

A lathe is one of the most flexible machine tools in the manufacturing industry today due to its versatility. 

Cutting speed of Lathe Machine:

The speed of the cutting tool at which the metal is removed by the tool from the workpiece is called the cutting speed. It is the peripheral speed of the work expressed in meters per minute. 

Cutting speed = Πdn/1000 m/min

Where, d = Diameter of the work piece 

n = RPM

A feed of Lathe Machine:

The distance the tool advances of each revolution of the work is called a feed of cutting tool. The feed is expressed in millimetres per revolution. 

Depth of cut of Lathe Machine:

The perpendicular distance measured from the machine surface to the uncut surface of the workpiece is called the depth of cut. 

Depth of cut = d1-d2/2

d1=Diameter of the work surface before machining

d2=Diameter of the machined surface 

Machining time of Lathe Machine: 

The machining of the lathe machine can be calculated for a particular operation if the speed of the job, feed and length of the job is known. It is calculated by the below formula. 

Machining time = l/s×n min 

Where, l=Length of the job 

s=Feed of the job 

n=RPM of the workpiece

Advantages and disadvantages of mass production

Mass production is the manufacture of discrete parts using a continuous process justified by a very large volume of production. In a line or product layout, the machines are arranged in this type of production system. In simple words, the manufacture of large quantities of goods using machinery and techniques such as assembly line and labour division. Let us have a deep insight into the advantages and disadvantages by using mass production in this article. 

Advantages of mass production : 

• Higher rate of production with reduced cycle time. 
• Standardization of product and process sequence. 
• Higher capacity utilization due to line balancing. 
• Less skilled operators are required so minimize labour cost. 
• Lower in process inventory. 
• Manufacturing cost per unit is low. 
• Material handling can be completely automatic. 
• Production planning and control are easy. 
• An economic process incurs fever labour costs, material costs, efficiently utilizes resources, while at the same time decreasing total expenditure per unit.
• Rate of production is fast due to automation and efficiency.  
• The quality of the product is consistent. 
• Different demands of customers can be met. 

Disadvantages of mass production : 

• Breakdown of one machine will tend to stop an entire production line. 
• High investment in production facilities. 
• Setup cost will be high.
• Identical products made very quickly. 
• The cycle time is determined by the slowest production operation. 
• Line layout needs major change with the changes in product design. 
• Labours are not very motivated because of a repetitive process. 
• As a production line is difficult to adapt, this production system is not flexible. 
• Components for different jobs may need to be stored increases costs.

There is clearly a place for mass production, primarily with companies seeking to make consistent, on-demand product while keeping costs low and ensuring quality standards. Share your experiences regarding mass production in the comments section below.

Explore more information: 

1. Batch production - Advantages and disadvantages
2. Job shop production - Advantages and disadvantages

Advantages and disadvantages of batch production

Batch production is a manufacturing process in which a job passes in lots of batches through the functional departments and each batch can have a different routing. It is common in more than just bakeries and small businesses that produce in controlled quantities. Let us have a deep insight into the advantages and disadvantages of batch production in this article. 

Advantages of batch production : 

• Products can be produced in mass quantities, reducing the overall cost per each quantity. 
• Machinery is not always on that saves the energy costs. 
• Better utilization of plant and machinery. 
• Promote functional specialization. 
• The cost per unit is lower than the production of job orders.
• Generally lower capital cost because of lower investment in plant and machinery.
• Companies only focus on a small group of products, leading to greater quality control and product expertise. 
• Smoother and more consistent production flow over time lends itself to repeat order. 
• Job satisfaction exists for operators. 
• It has the flexibility to produce a variety of different products.
• It is ideal for seasonal orders, or trial runs of a new product. 
• It reduces inventory. 
• Reducing the risk of simply concentrating on one product. 
• Labour cost reduced so the final price is lower. 
• Production is faster. 
• Begins to take advantage of economies of scale. 

Disadvantages of batch production : 

• Each batch must be tested for quality and uniformity before batches can be produced, causing ideal downtime. 
• Machine must be stopped and recalibrated between batches, also causing downtime. 
• High storage cost for large batches for the same products. 
• Work is less interesting and repetitive works can demotivate workers. 
• Material handling is complex of irregular and longer flows. 
• Production planning and control are complex. 
• If the prototype has an error all the rest of the same products will have that fault as the machine replicates exactly so the loss of material and time would be costly. 
• Labour is required to move items from one stage of batch process to another.
• If lots are small, the cost of the units will be high.
• Larger stock of raw materials must be kept. 

There is clearly a place for batch production, primarily with companies seeking to make consistent, on-demand product while keeping costs low and ensuring quality standards. Share your experiences regarding batch production in the comments section below.

Explore more information: 

1. Mass production - Advantages and disadvantages 
2. Job shop production - Advantages and disadvantages

Advantages and disadvantages of job shop production system

Job shop production is characterized by the manufacture within prefixed time and cost of one or more quality products designed and manufactured in accordance with customer specifications. This is characterized by low volume and high product variety. A workshop consists of machines for general use arranged in different departments. Let us have a deep insight into the advantages and disadvantages of job shop production in this article. 

Advantages of job shop production : 

• Low volume and high variety of products can be produced because of general-purpose machines and facilities. 
• Highly skilled operators who can take up each job as a challenge gives them a learning opportunity. 
• The full potential of operators can be utilized. 
• The opportunity exists for creative methods and innovative ideas. 
• Large inventory of material, tools and parts.
• Easy of supervision.
• High utilization of expensive machines. 

Disadvantages of job shop production :

• High cost due to frequent setup changes. 
• Large space requirements. 
• Production planning is complicated. 
• Higher inventory levels at all levels and higher inventory costs as a result.
• The conflict between resource utilization and customer service. 

There is clearly a place for job shop production, primarily with companies seeking to make consistent, on-demand product while keeping costs low and ensuring quality standards. Share your experiences regarding job shop production in the comments section below.

Explore more information: 

1. Mass production - Advantages and disadvantages
2. Batch production - Advantages and disadvantages

Difference between CAD and CAM

The terms CAD and CAM are both important in computer-aided engineering and manufacturing, but they refer to different parts of the design and production process. CAD is an abbreviation for Computer-Aided Design to use of computer technology for design, while CAM is an abbreviation for Computer-Aided Manufacturing software used for machining or prototypes and finished parts. 

Main difference:

The main difference between CAD and CAM is that CAM software is used by engineers while CAM is used by trained machinist are highly skilled and are equivalent to a computer engineer. They both are heavily dependent upon each other.  

Difference between CAD and CAM : 

• CAD make 2D technical drawings and 3D models while CAM using 3D models to design the machining process. 

CAD responsibility : 

2D and 3D design, Drafting, Detailing, All type of sheet metal and surface design.

CAM responsibility : 

Manufacturing process after a design by using G code and M code, drilling, tapping, cutting, boring, milling, turning, and multiple operation processes perform on CAM software.

• CAD is much easier more accurate and fast drafting for 2D drawing but for 3D models impossible without computers whereas CAM is automization of the machining process. 
• Require expensive software and knowledge on how to use it in both CAD and CAM. Software used by CAD and CAM is the following. 

Software used by CAD : 

Autodesk AutoCAD, Autodesk Inventor, Autodesk Fusion, SolidWorks, SolidEdge, CATIA, Creo, NX CAD

Software used by CAM : 

EdgeCAM, NX CAM, Master CAM, CAMWorks

Refrigeration and Air Conditioning important question and answer

Question 1 : 
Heat removing capacity of a one-ton refrigerator is 
Option A: 25 Kcal / sec
Option B: 50 Kcal / min
Option C: 50 Kcal / hour
Option D: 100 Kcal / hour 
Explaination: 50 Kcal/min

Question 2 : 
In SI units, one tonne of refrigeration is equivalent to  
Option A: 1.5 kW
Option B: 2.5 kW
Option C: 3.5 kW
Option D: 5 kW
Explanation: In SI units, one tonne of refrigeration is equivalent to 3.5 kW and 210 kJ/min. 

Question 3 : 
In a refrigeration system, the moisture is removed by 
Option A: Driers
Option B: Desiccants
Option C: Filter driers
Option D: All of the above
Explanation: Moisture is removed by driers, filter driers and desiccants too. 

Question 4 :
Subcooling occurs when the vapour
Option A: Has high latent heat
Option B: Has low latent heat
Option C: Removes sensible heat from the refrigerant
Option D: Has high thermal conductivity
Explanation: Subcooling occurs when the vapour removes sensible heat from the refrigerant.

Question 5: 
In the sensible cooling process, specific humidity
Option A: Increases
Option B: Decreases
Option C: Remain constant
Option D: NONE
Explanation: In a sensible cooling process, specific humidity remains constant and relative humidity increases.  

Question 6: 
The dew point temperature as compared to wet bulb temperature for unsaturated air is
Option A: Equal
Option B: Less
Option C: More 
Option D: Unpredictable
Explanation: DPT is less than WBT for unsaturated air.

Question 7:
Air conditioning means?
Option A: Cooling and Heating
Option B: Removal of air impurities
Option C: Dehumidifying
Option D: All of the above
Explanation: A system for controlling the humidity, ventilation, and temperature in a building or vehicle, typically to maintain a cool atmosphere in warm conditions. 

Question 8: 
The main parts of a vapour compression refrigeration system in a sequence are
Option A: Compressor, Condensor, Evaporator and Throttle valve
Option B: Compressor, Throttle valve, Condensor, and Evaporator
Option C: Compressor, Evaporator, Condensor, and Throttle valve
Option D: Compressor, Condensor, Throttle valve, and Evaporator
Explanation: First compressor then condenser, throttle valve and last evaporator. 

Question 9: 
If a refrigerant is having low specific heat, then co-efficient of performance will be
Option A: Lower
Option B: Higher
Option C: Same
Option D: NONE
Explanation: Higher

Question 10: 
The ratio for sensible heat factor is 
Option A: Latent heat to Sensible heat
Option B: Sensible heat to Latent heat
Option C: Latent heat to Total heat
Option D: Sensible heat to Total heat
Explanation: SHF = Sensible heat / Total Heat 
Sensible heat is the heat which increases or decreases the temperature of the body.

Question 11: 
The subcooling in the refrigeration cycle, 
Option A: Increases COP
Option B: Reduce cooling
Option C: Increases work of compression
Option D: Reduce condenser size
Explanation: The subcooling process increases the COP of the refrigeration cycle. 
The coefficient of performance or COP of a heat pump, refrigerator or air conditioning system is a ratio of useful heating or cooling provided to work required. Higher COPs equate to lower operating costs. 

Question 12: 
The phenomenon of emf developed between two dissimilar metals in contact is which of the following effect
Option A: Seeback effect
Option B: Thomson effect
Option C: Peltier effect
Option D: Thermocouple effect

Explanation: A temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference is called as seeback effect. 

Question 13: 
In a refrigeration cycle, the heat is absorbed by a refrigerant in a and heat is rejected by a refrigerant in a
Option A: Evaporator, Condensor 
Option B: Evaporator, Compressor
Option C: Condensor, Evaporator
Option D: Evaporator, Expansion valve 
Explanation: The heat is absorbed by an evaporator and rejected by the condenser. 

Question 14: 
Mass of the water vapour present in 1 kg of dry air is called, 
Option A: Relative humidity
Option B: Absolute humidity
Option C: Humidity ratio
Option D: Percentage humidity
Explanation: Humidity ratio, it is also known as specific humidity. 

Question 15: 
Mass of the water vapour present in 1 m³ of dry air is called, 
Option A: Relative humidity
Option B: Absolute humidity
Option C: Percentage of humidity
Option D: Humidity ratio
Explanation: Absolute humidity

Question 16: 
Dew point is the temperature at which, 
Option A: Ice starts melting in the presence of air without external aid
Option B: Condensation of water vapour in air starts
Option C: Vapourisation of water vapour in air starts
Option D: NONE
Explanation: The dew point is the temperature to which air must be cooled to become saturated with water vapour. Dew point temperature indicates dryness of the air, moisture content of air, condition of air. 

Question 17:
Dry bulb, wet bulb and dew point temperature are the same for, 
Option A: Dry air
Option B: Saturated air
Option C: Wet air
Option D: NONE
Explanation: Saturated air 

Question 18: 
The difference between the dry bulb and wet bulb temperature is called
Option A: Dry bulb temperature
Option B: Wet-bulb temperature
Option C: Dew point temperature
Option D: NONE
Explanation: WBT = DBT - WBT 

Question 19: 
The moisture content of air is indicated by, 
Option A: Dry bulb temperature
Option B: Wet-bulb temperature
Option C: Dew point temperature
Option D: Both A and B
Explanation: Moisture content of air is indicated by the dry bulb and wet bulb temperature. 

Question 20: 
If wet-bulb depression is zero, it indicates
Option A: Relative humidity is zero
Option B: Relative humidity is 100%
Option C: Rain is likely to occur
Option D: NONE
Explanation: If the wet-bulb depression is zero relative humidity is 100% as wet-bulb depression indicates relative humidity. 

Lenoir cycle | Working process | Thermal efficiency

The Lenoir cycle is a thermodynamic cycle that can be invented by Jean Joseph Etienne Lenoir in 1860 is often used to model a pulse jet engine. 

Process of Lenoir cycle :

All type of process individually done in a heat engine in Lenior cycle. 

The Lenoir cycle consists of four processes which are following below. 

• A constant-volume gas expansion process. From the diagram shown below the ideal gas in the system absorbs some amount of heat from the heat source at a high temperature and then expands thus the work was done on surroundings. 
• A reversible adiabatic gas expansion process. In this process, the system is thermally insulated. The gas expands continuously and does work on surrounding, which causes the system to cool to a lower temperature. 
• A reversible isothermal gas compression process. In this process, work has done surrounding gas and cause a loss of heat.
• A reversible adiabatic gas compression process. In this process, surrounding continue to do work to a gas, which causes the temperature to rise back to high temperature attain in the first process. 

Lenoir cycle PV and TS Diagram

The thermal efficiency of Lenoir cycle : 

Thermodynamically, the efficiency of Lenoir cycle is given by

ŋ_Lenoir = Work done by the system / Heat supplied to the system