Friday 30 December 2016

MECHANICAL PROPERTIES OF MATERIALS

Why are heat addition processes in a petrol and diesel engine modelled as constant volume and constant pressure processes respectively?

The combustion process in a petrol engine is instantaneous. Hence approximated in the Otto cycle as constant volume heat addition.

While the combustion process in a diesel engine takes comparitively longer time and hence approximated as constant pressure process in idealised Diesel cycle.

The often made assumptions that the SI or Otto engine is best approximated by the constant-volume cycle, and the CI or diesel engine is best approximated by the constant-pressure cyle are not necessarily correct.

MULTIPLE CHOICE QUESTIONS ON INDUSTRIAL ENGINEERING

1-In the Deming’s quality cycle, ‘P’ stands for

(A) Product

(B) Productivity

(D) Plan

2-Poka Yoke is a concept of

(A) mistake proofing systems

(B) rework of jobs

(D) tool for production planning control

3-Simplex method is used for

(A) Linear programming

(B) Queuing theory

(D) Value engineering

4-Break even analysis consists of

(A) fixed cost

(B) variable cost

(D) operations cost

5-In micro motion study, therblig is described by

(A) a symbol

(B) an activity

(D) standard symbol and colour

6-Work study is concerned with

(A) improving present method and finding standard time

(B) motivation of workers

(D) improving production planning and control

7-Hungarian method of solving the Assignment problems involves

(A) Covering Maximum number of zeroes and maximum number of lines

(B) Covering Minimum number of zeroes with maximum number of lines

(D) Covering maximum number of zeroes with minimum number of lines

8-Which one of the following would normally be considered as one of the costs of quality?

(A) Appraisal costs

(B) Marketing costs

(D) Transaction costs

9-Which of the following would most commentators regard as one of the ‘quality gurus’?

(A) Joseph Juran

(B) Charles Handy

(D) Joe Rine

10-Queuing theory is associated with

(A) Inventory

(B) Sales

(D) Production time

11-Predetermined motion time systems include

(A) Method Time Measurement

(B) Work factor systems

(D) All of above

12-Critical path method requires

(A) Single point estimation

(B) Double point estimation

(D) None of the above

13-Gantt chart gives information about

(A) Scheduling and Rating

(B) Sales

(D) Machine utilization

14-In break even analysis, total cost consists of

(A) Fixed cost + Sales revenue

(B) Variable cost + Sales revenue

(D) Fixed cost + Variable cost + Profit

ANSWERS:

1-(D), 2-(A), 3-(A), 4-(C), 5-(A), 6-(A), 7-(C), 8-(A), 9-(A), 10-(C), 11-(D), 12-(C), 13-(C), 14-(C)

THERMODYNAMIC PROCESSES

When any of the properties of the system such as temperature, pressure, volume etc change, the system is said to have undergone thermodynamic process. Various types of thermodynamic processes are: isothermal process, adiabatic process, ischoric process, isobaric process, and reversible process.

Introduction
Before going into the thermodynamic process and types of thermodynamic processes, let us see what the meaning of the thermodynamic state of system is. The system has certain properties like temperature, pressure, volume, etc. The present values of the properties of the system are called as thermodynamic state of system. Say for instance in a thermos flask there is 250 ml of water at 50 degree Celsius, this is the state of the system, thermos flask. If the values of the properties of the system changes, the state of the system also changes. Suppose we pour out 100 ml of water and its temperature also reduces, the state of this system is also said to have changed.
Thermodynamic Process
When the system undergoes change from one thermodynamic state to final state due change in properties like temperature, pressure, volume etc, the system is said to have undergone thermodynamic process. Various types of thermodynamic processes are: isothermal process, adiabatic process, isochoric process, isobaric process and reversible process. These have been described below:

1) Isothermal process: When the system undergoes change from one state to the other, but its temperature remains constant, the system is said to have undergone isothermal process. For instance, in our example of hot water in thermos flask, if we remove certain quantity of water from the flask, but keep its temperature constant at 50 degree Celsius, the process is said to be isothermal process.

Another example of isothermal process is latent heat of vaporization of water. When we heat water to 100 degree Celsius, it will not start boiling instantly. It will keep on absorbing heat at constant temperature; this heat is called latent heat of vaporization. Only after absorbing this heat water at constant temperature, water will get converted into steam.

2) Adiabatic process: The process, during which the heat content of the system or certain quantity of the matter remains constant, is called as adiabatic process. Thus in adiabatic process no transfer of heat between the system and its surroundings takes place. The wall of the system which does not allows the flow of heat through it, is called as adiabatic wall, while the wall which allows the flow of heat is called as diathermic wall.

3) Isochoric process: The process, during which the volume of the system remains constant, is called as isochoric process. Heating of gas in a closed cylinder is an example of isochoric process.

4) Isobaric process: The process during which the pressure of the system remains constant is called as isobaric process. Example: Suppose there is a fuel in piston and cylinder arrangement. When this fuel is burnt the pressure of the gases is generated inside the engine and as more fuel burns more pressure is created. But if the gases are allowed to expand by allowing the piston to move outside, the pressure of the system can be kept constant.

The constant pressure and volume processes are very important. The Otto and diesel cycle, which are used in the petrol and diesel engine respectively, have constant volume and constant pressure processes. In practical situations ideal constant pressure and constant pressure processes cannot be achieved.

5) Reversible process: In simple words the process which can be revered back completely is called a reversible process. This means that the final properties of the system can be perfectly reversed back to the original properties. The process can be perfectly reversible only if the changes in the process are infinitesimally small. In practical situations it is not possible to trace these extremely small changes in extremely small time, hence the reversible process is also an ideal process. The changes which occur during reversible process are in equilibrium with each other.

Thursday 29 December 2016

CHECK OUT WHY DIESEL ENGINES ARE NOT USED IN BIKES

Why diesel engine is not used in bikes?

We use bike many times in a day. Usually bike is run on petrol. The price of petrol is higher than diesel in many countries. Sometimes we think, why bike is not run by diesel. If there is a diesel bike than we can save some money. Actually,we do have diesel engines for two wheelers, but not in the scale the petrol engines are. There is only one type of bike with a diesel engine in India and that is the Royal Enfield Taurus.This is shown in figure below :-

The main reasons for not using diesel engines in two-wheelers are as follows:

1. Diesel engine has a compression ratio 24:1, which is higher than petrol engine compression ratio of 11:1. Diesel engine must be bigger and of heavy metal in order to handle this high compression ratio. That's why the diesel engine is heavier than petrol engine and not suitable for small vehicle like motorcycle.

2. Due to high compression ratio, diesel engine produces more vibration and noise as compared to the petrol engine. It is not possible for a light vehicle to handle this high vibration and noise.That's why diesel engines are not used in motorcycle.

3. Due to high compression ratio and heavy engine, initial price of the diesel engine is more than the petrol engine. And this initial price difference is about 50,000 rupees, which is not suitable for small vehicle.

4. Diesel engine produces approximately 13% more carbon-di-oxide per gallon as compared to the petrol engine. So it makes greater pollution than petrol engine and it is not good to use for environment.

5. Diesel engine works on high pressure, so wear and tear is high in diesel engines. To reduce this wear and tear oil change are frequently required at every 5,000 kilometer instead of 10,000 kilometer in the case of petrol engine.

6. Diesel engine produces more torque but low rpm than petrol engine. So in bikes where we need high speed, it is not suitable.

7. Diesel has high energy per gallon as compare with the petrol. When diesel burns, it produces a large amount of heat which can destroy walls of the cylinder and other parts of the engine. So to reduce this heat, we need a greater surface area and proper cooling system. In order to achieve this greater surface area, the engines are made slightly bigger.

8. Diesel engine uses turbocharger or supercharger to pump more air into the cylinder, which increases its price and size.

9. In diesel engines, injector technology is used to inject fuel into the combustion chamber, which is more expensive than spark plug technology of petrol engine.

10. Diesel engine is very big as compared with the petrol engine and it uses high power starting motor to crank the engine, which is not suitable for motorcycles.

CHECK OUT WHY BUBBLES ARE DANGEROUS IN HYDRAULIC BRAKING SYSTEM !!

Why are air bubbles dangerous in a hydraulic brake system?

One of the most necessary conditions for a hydraulic system to function properly is that the hydraulic fluid must be incompressible.

Effect of air bubbles on a hydraulic system:-

Loss of bulk modulus -Air is a compressible fluid. When air bubbles get into a hydraulic system, the force does not get transmitted properly.Also,free or entrained air in the hydraulic system reduces substantially the effective bulk modulus of the system. That is, an air-oil mixture appears to increase the compressibility of the fluid, making the system spongy.
Loss of horsepower — When an air pocket is present in an actuator, it is alternately compressed and relaxed as the actuator is cycled. Since the air pocket must first be compressed before the fluid can cause the actuator to move, power is consumed. Upon relaxation, the air pocket expands and rives fluid out. The stored power, therefore, is expended in driving fluid back into the reservoir and not in moving the actuator.
Spongy control — Because fluids are considered to be basically incompressible, we expect great stiffness in a hydraulic system. That is, the positioning of an actuator should be immediate (rapid response) and precise. The larger the amount of free or entrained air, the spongier (softer, less stiff) the system.
Loss of system fluid — One of the most serious conditions that can occur in a hydraulic system is the loss of reservoir fluid. The fluid level must be kept high enough to insure enough fluid for the pump intake, otherwise cavitation begins.

In that case, on pressing the brake pedal, one would feel the pedal like a jello. It would be as if you are pressing a sponge. The wheels would not lock instantly and the car would travel considerably long distance before the required braking effect is obtained.

9 BASIC THINGS EVERY MECHANICAL ENGINEER MUST KNOW

1. What does CC mean in Car engine?

Now, cc stands for cubic centimetres - It is a unit to measure the engine's displacement.

This is the measurement of the volume of the engine's cylinders or "compartments".

Now, when you read 200 cc it means the volume of the cylinder is 200 cubic centimeters.

CC can also be expressed in the form of litres. So, 200 cc = 0.2 L engine.

Remember that: 1 cubic centimeter = 0.001 liters = 1 milli liter.

With that you can understand that more cc does not mean more power. So, that brings to the most asked question: Does more cc mean more fuel consumption?

From what I've read, it is generally true that a vehicle with more displacement will have more fuel consumption.

However, there are very many other factors that affect fuel efficiency.

Therefore, by minimizing engine displacement, you will not ensure increased fuel efficiency.

2. What is meant by 'wheelbase' and 'ground clearance' in a car?

Wheelbase:

In a car, there are two rods used to connect the center of the wheels, one on the front and another on the rear.

The distance between these two rods or axles of a vehicle is known as its wheelbase.

This term is generally checked while buying a car to see how much large the cabin is. The longer the wheelbase, the more the interior room in the car's cabin.

Ground Clearance:

It means the distance between the ground (the point where the tire meets the ground) and the under side of the chassis i.e. any parts that aren't designed to touch the ground. The manufacturers generally mention this distance in millimetres or inches in the list of specifications.

High Ground Clearance Vs. Low Ground Clearance:

More the ground clearance, more is the vehicle capable of moving on off-road, bumpy, rough terrains. For this reason, you will generally find that SUVs are designed with high ground clearance.

If the vehicles has low ground clearance will have low center of gravity and that leads to better handling and performance.

A balance between a high and low ground clearance is needed and you'll find this being achieved in the most executive sedans.

3.What does air-cooled engine mean?

As is apparent from the term we are looking at, Air-cooled engines have air circulating over the hot parts of the engine to cool it. Now I can't put a diagrammatic explanation here, but it is pretty clear even with just the theory.

Most cars we use today have modern internal combustion engines.

A great percentage of the heat generated through these engines is released through the exhaust.

The remaining is handled traditionally by using a liquid coolant that is passed through a closed circuit over the cylinder head and engine block.

The liquid coolant absorbs heat and when it reaches the heat exchanger or radiator of the car, it released the heat into air.

Now you may feel that isn't the engine being ultimately cooled by air. Well yes, but because a liquid-coolant circuit was used, this system is called water-cooled engine.

In contrast, the air-cooled engines have the heat generated released directly into the air. Natural air flow plays a big part in this.

4.What is the difference between Multi Utility Vehicle (MUV) and Sports Utility Vehicle (SUV)?

SUV is a term used to denote any vehicle that looks like a station wagon.

They are equipped with four-wheel drive or all-wheel drive.

Their design aims to display superior off-road and towing capabilities and bigger seating capacity.

Example: Mahindra Scorpio, Ford Ecosport, Renault Duster, Toyota Fortuner etc.

MUV is a type of vehicle designed in a shape of van.

They typically allow easy conversion between multiple combinations of passenger and luggage capacity.

Example: Toyota Innova, Maruti Ertiga, Renaulta Lodgy, Honda Mobilio etc.

5. What is the difference between Automatic transmission and Manual transmission?

Automatic transmission have only few select options, like forward, neutral and reverse. Where manual transmission will have complete gear selector.

For buyers, Automatic means a vehicle will select a appropriate Gear by itself as 1st, 2nd or .... as per the vehicle speed and load. where in Manual a driver has to decide and put vehicle in correct gear to move in desired form.

Automatic may have solenoid gear selector or a complex mechanism of overdrive and clutches which we see in luxurious vehicles only.

6. Front and Rear suspension - What do they mean and why are they needed?

First why suspension, between you vehicle body and wheels suspension are the main medium which holds vehicle and make moving when moving wheels. second suspension is for absorbing sudden shocks from round terrain. Each wheel have separate suspension for independent work( minds its for cars only, trucks may have different arrangements)

in every cars there are two axles front and rear. each axles will get two suspension of same type on both the wheels.

For buyers, Front suspension has some difference bcoz front suspension has to modify and adjust as per the turning on front wheel in corners. whereas rear wheels has to Go straight only.

7. What is the difference between 4-cylinder engine and 3-cylinder engine?

4 or 3 cylinder engine - it implies number of cylinder and piston you have in your engine. More number of cylinder means more CC and more power. and also it increases size of the engine.

8. What is drivetrain and powertrain and why is it important?

Powertrain

The powertrain is composed of everything that makes the vehicle move. These components include the engine which generates the initial energy, the transmission that distributes it and produces torque and all the other components of the drivetrain that help to propel the body forward. It can be expressed in terms of a mathematical equation for simpler understanding:

Powertrain = [Engine] + [Drivetrain]

The output from the power sources are controlled by a transmission system and the driveline to deliver torque to the wheels. The circular motion of the crankshaft is transmitted to the rear wheels through the gearbox, clutch, universal joints, drive shafts or propeller shafts, the differential and the axles connected to the wheels.

The application of engine power to the driving wheels through the collaborative effort of each of these components is called the power transmission. All wheel drive vehicles have two sets of these components to distribute the power almost equally to the front and the rear.

Drivetrain

The drivetrain is the part of a motorized carriage that connects the engine and transmission to the wheel axles through a number of other components. Drivetrain consists of all components after the transmission.

9. What is the difference between All-wheel drive and four-wheel drive?

All wheel drive - means the power as explained in power goes from engine to all wheels of a vehicle basically the term uses for multi axle heavy duty trucks or trailer tractors.

Four Wheel Drive- as it says power goes to 4 wheel drive only.

4×4 (also, four-wheel drive and 4WD)

Reflecting two axles with both wheels on each capable of being powered.

6×6 (also, six-wheel drive and 6WD)

Reflecting three axles with both wheels on each capable of being powered.

8×8 (also, eight-wheel drive and 8WD)

Reflecting four axles with both wheels on each capable of being powered.

PISTON AND PISTON RINGS

PISTON :-
A piston is a cylindrical engine component that slides back and forth in the cylinder bore by forces produced during the combustion process. The piston acts as a movable end of the combustion chamber. The stationary end of the combustion chamber is the cylinder head. Pistons are commonly made of a cast aluminum alloy for excellent and lightweight thermal conductivity. Thermal conductivity is the ability of a material to conduct and transfer heat. Aluminum expands when heated, and proper clearance must be provided to maintain free piston movement in the cylinder bore. Insufficient clearance can cause the piston to seize in the cylinder. Excessive clearance can cause a loss of compression and an increase in piston noise.

Piston features include the piston head, piston pin bore, piston pin, skirt, ring grooves, ring lands, and piston rings. The piston head is the top surface (closest to the cylinder head) of the piston which is subjected to tremendous forces and heat during normal engine operation.

A piston pin bore is a through hole in the side of the piston perpendicular to piston travel that receives the piston pin. A piston pin is a hollow shaft that connects the small end of the connecting rod to the piston. The skirt of a piston is the portion of the piston closest to the crankshaft that helps align the piston as it moves in the cylinder bore. Some skirts have profiles cut into them to reduce piston mass and to provide clearance for the rotating crankshaft counterweights.

A ring groove is a recessed area located around the perimeter of the piston that is used to retain a piston ring. Ring lands are the two parallel surfaces of the ring groove which function as the sealing surface for the piston ring. A piston ring is an expandable split ring used to provide a seal between the piston an the cylinder wall. Piston rings are commonly made from cast iron. Cast iron retains the integrity of its original shape under heat, load, and other dynamic forces. Piston rings seal the combustion chamber, conduct heat from the piston to the cylinder wall, and return oil to the crankcase. Piston ring size and configuration vary depending on engine design and cylinder material.

PISTON RING:-

Piston rings commonly used on small engines include the compression ring, wiper ring, and oil ring. A compression ring is the piston ring located in the ring groove closest to the piston head. The compression ring seals the combustion chamber from any leakage during the combustion process. When the air-fuel mixture is ignited, pressure from combustion gases is applied to the piston head, forcing the piston toward the crankshaft. The pressurized gases travel through the gap between the cylinder wall and the piston and into the piston ring groove. Combustion gas pressure forces the piston ring against the cylinder wall to form a seal. Pressure applied to the piston ring is approximately proportional to the combustion gas pressure.

A wiper ring is the piston ring with a tapered face located in the ring groove between the compression ring and the oil ring. The wiper ring is used to further seal the combustion chamber and to wipe the cylinder wall clean of excess oil. Combustion gases that pass by the compression ring are stopped by the wiper ring.

An oil ring is the piston ring located in the ring groove closest to the crankcase. The oil ring is used to wipe excess oil from the cylinder wall during piston movement. Excess oil is returned through ring openings to the oil reservoir in the engine block. Two-stroke cycle engines do not require oil rings because lubrication is supplied by mixing oil in the gasoline, and an oil reservoir is not required.

Piston rings seal the combustion chamber, transferring heat to the cylinder wall and controlling oil consumption. A piston ring seals the combustion chamber through inherent and applied pressure. Inherent pressure is the internal spring force that expands a piston ring based on the design and properties of the material used. Inherent pressure requires a significant force needed to compress a piston ring to a smaller diameter. Inherent pressure is determined by the uncompressed or free piston ring gap. Free piston ring gap is the distance between the two ends of a piston ring in an uncompressed state. Typically, the greater the free piston ring gap, the more force the piston ring applies when compressed in the cylinder bore.

A piston ring must provide a predictable and positive radial fit between the cylinder wall and the running surface of the piston ring for an efficient seal. The radial fit is achieved by the inherent pressure of the piston ring. The piston ring must also maintain a seal on the piston ring lands.

In addition to inherent pressure, a piston ring seals the combustion chamber through applied pressure. Applied pressure is pressure applied from combustion gases to the piston ring, causing it to expand. Some piston rings have a chamfered edge opposite the running surface. This chamfered edge causes the piston ring to twist when not affected by combustion gas pressures.

Friday 30 December 2016

Why are heat addition processes in a petrol and diesel engine modelled as constant volume and constant pressure processes respectively?

Introduction

Thermodynamic Process

Thursday 29 December 2016

Why diesel engine is not used in bikes?