REGENERATIVE BRAKING SYSTEM

Every time we step on our car's brakes, we are wasting energy.So when your car slows down, the kinetic energy that was propelling it forward has to go somewhere. Most of it simply dissipates as heat and becomes useless. That energy, which could have been used to do work, is essentially wasted.

Regenerative braking is used on automobiles to recoup some of the energy that is lost while the vehicle is stopping. This technology is used on hybrid vehicles that use both gas and electricity as sources of power. The energy that is recouped during braking is saved in a storage battery and used later to power the motor whenever the vehicle is using its electric power source.Hybrids and all-electric vehicles create their own power for battery recharging through a process known as regenerative braking (regen mode).Simply it means means capturing the vehicle's momentum (kinetic energy) and turning it into electricity that recharges (regenerates) the onboard battery as the vehicle is slowing down and/or stopping. It is this charged battery that in turn powers the vehicle's electric traction motor.

At present, these kinds of brakes are primarily found in hybrid vehicles like the Toyota Prius, and in fully electric cars, like the Tesla Roadster.However, the technology was first used in trolley cars and has subsequently found its way into such unlikely places as electric bicycles and even Formula One race cars.

How does it work?

In braking systems on conventional vehicles, friction is used to counteract the forward momentum of a moving vehicle.This friction is what turns the car's kinetic energy into heat. With regenerative brakes, on the other hand, the system that drives the vehicle does the majority of the braking. It uses completely different method of braking at slower speeds. Hybrid vehicles still use conventional brake pads at highway speeds, but electric motors help the vehicle brake during stop-and-go driving at slower speeds. As the driver applies the brakes by pressing down on a conventional brake pedal, the electric motors reverse direction. The torque created by this reversal counteracts the forward momentum and eventually stops the car.In simple words,when the driver steps on the brake pedal of an electric or hybrid vehicle, these types of brakes put the vehicle's electric motor into reverse mode, causing it to run backwards, thus slowing the car's wheels. While running backwards, the motor also acts as an electric generator, producing electricity that's then fed into the vehicle's batteries.

Advantages of regenerative braking system:-

>Increase of overall energy efficiency of a vehicle.

>—Increases vehicle range.

>—Cuts down on pollution related to electricity generation.

>Increases the lifespan of friction braking systems.

>—Less use of traditional mechanical brakes leads to less wear over time.

CNG ENGINE

CNG engine uses compressed natural gas to power the car. CNG is a substitute for gas and diesel fuel, and is considered to be much cheaper and cleaner than gas or diesel. Natural-gas-powered vehicles burn compressed natural gas (CNG) instead of conventional gasoline.

Why Use Compressed Natural Gas?

The benefits of CNG are lower operating costs, lower fuel costs, improved gasoline-gallon fuel economy, and almost zero smog-forming emissions. One example of a vehicle that uses CNG for its fuel is the Honda Civic Natural Gas Sedan.In addition, the CNG engine is considered to be more environmentally friendly. There are considerably less pollutants associated with compressed natural gas being ignited, and studies show that it gives off 40 percent less greenhouse gas.

The CNG Engine:-

The CNG engine uses a second fuel tank which has to be attached to the car, and is usually placed in the trunk (or other place where there is suitable room). This tank is usually very large, as it has to keep the gas used compressed. The amount of pressure may vary from engine to engine, but it is usually compressed to around 3,600 pounds per square inch. The driver can then decide which of the fuels they wish to use by simply pressing a switch on the dashboard. This means that the car can alternate between the different tanks, drawing fuel from either.Having a dual fuel system will ensure adequate fuel reserves in between natural gas fills. Compared to having only a gasoline engine, this additional fuel reserve will extend the vehicle’s driving range. Drivers can switch from CNG to gasoline even while driving, idling or parked. Some CNG systems will automatically switch to gasoline when the natural gas level reaches a preset low pressure setting.

How the CNG Engine works?

Once the driver selects the CNG tank, CNG is fed into the high pressure cylinders through the natural gas receptacle.The compressed gas in the tank is pulled through a series of highly pressurized lines until it reaches the regulator.Inside the regulator, the pressure on the gas is lessened until it matches the amount needed by the fuel injection system of the car's engine. Once the gas has reached an acceptable pressure, the solenoid valve allows the gas to move into the fuel injection system and from there into the engine.Just as with gasoline, once the engine has received the gas, it is ignited in the combustion chamber, and this provides the energy to power the car forward.

You can also convert your gas engine to CNG, a diesel conversion though doesn’t have problems with predetonation or need knock sensors like a gas conversion. Diesel engines is built for heavy duty use, exploding diesel with heat and combustion not spark. This all makes diesel engines the ideal CNG conversion candidate. 

VARIOUS COMPONENTS OF AN ENGINE

Internal combustion engines are made from various parts.Each part has its own location and function for proper working of engine.. There are hundreds of components which have to perform their functions satisfactorily to produce output power. The major components of the engine and their functions are briefly described below:-

1.)Cylinder Block:

The cylinder block is the largest part of the engine. Its upper section carries the cylinders and pistons. Normally, the lower section forms the crankcase, and supports the crankshaft.It is the main supporting structure for the various components. The cylinders of a multicylinder engine are cast as a single unit, called cylinder block.It is the portion of the engine between the cylinder head and sump (oil pan)and is the supporting structure for the entire engine. All the engine parts are mounted on it or in it and this holds the parts in alignment.Cylinder blocks made of aluminum are lighter than cast-iron blocks of the same size. They usually have cast-iron liners which provide a hard-wearing surface for pistons and piston rings.
 

Function- In the bore of cylinder the fresh charge of air-fuel mixture is ignited,compressed by piston and expanded to give power to piston.

2.)Cylinder Head:

It carries inlet and exhaust valve.Fresh charge is admitted through inlet valve and burnt gases are exhausted from exhaust valve.In case of petrol engine,a spark plug and in case of diesel engine,a injector is also mounted on cylinder head.

3.)Cylinder: 

As the name implies it is a cylindrical vessel or space in which the piston makes a reciprocating motion.The varying volume created in the cylinder during the operation of the engine is filled with the working fluid and subjected to different thermodynamic processes. The cylinder is supported in the cylinder block.

4.)Piston:

This is a pressure-tight cylindrical plunger which is subjected to the expanding gas pressure.It is fitted into the cylinder forming the moving boundary of the combustion system. It fits perfectly into the cylinder providing a gas-tight space with the piston rings and the lubricant. It forms the first link in transmitting the gas forces to the output shaft.

Function-During suction stroke,it sucks the fresh charge of air-fuel mixture through inlet valve and compresses during the compression stroke inside the cylinder.This way piston receives power from the expanding gases after ignition in cylinder.Also forces the burnt exhaust gases out of the cylinder through exhaust valve.

5.)Piston rings:

 These are circular rings which seal the gaps made between the piston and the cylinder, their object being to prevent gas escaping and to control the amount of lubricant which is allowed to reach the top of the cylinder.

Function-It prevents the compressed charge of fuel-air mixture from leaking to the other side of the piston.Oil rings,is used for removing lubricating oil from the cylinder after lubrication.This ring prevents the excess oil to mix with charge.

5.)Connecting Rod: 

It interconnects the piston and the crankshaft and transmits the gas forces from the piston to the crankshaft. The two ends of the connecting rod are called as small end and the big end. Small end is connected to the piston by gudgeon pin and the big end is connected to the crankshaft by crankpin.

Function-It changes the reciprocating motion of piston into rotary motion at crankshaft.This way connecting rod transmits the power produced at piston to crankshaft.

6.)Crankshaft:

It converts the reciprocating motion of the piston into useful rotary motion of the output shaft. In the crankshaft of a single cylinder engine there are a pair of crank arms and balance weights.A simple crankshaft consists of a circular-sectioned shaft which is bent or cranked to form two perpendicular crank-arms and an offset big-end journal. The unbent part of the shaft provides the main journals. The crankshaft is indirectly linked by the connecting-rod to the piston - this enables the straight-line motion of the piston to be transformed into a rotary motion at the crankshaft about the main-journal axis.

Function-Receives oscillating motion from connecting rod and gives a rotary motion to the main shaft.It also drives the camshaft which actuate the valves of the engine

7.)Camshaft:

The camshaft and its associated parts control the opening and closing of the two valves. The associated parts are push rods, rocker arms, valve springs and tappets. This shaft also provides the drive to the ignition system. The camshaft is driven by the crankshaft through timing gears.

Function-It takes driving force from crankshaft through gear train or chain and operates the inlet valve as well as exhaust valve with the help of cam followers,push rod and rocker arms.

8.)Spark Plug

Function-This device is used in petrol engine only and ignite the charge of fuel for combustion.

9.) Fuel Injector

Function-This device is used in diesel engine only and delivers fuel in fine spray under pressure

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DISC BRAKE

Disc brakes use a flat, disk-shaped metal rotor that spins with the wheel. When the brakes are applied, a caliper squeezes the brake pads against the disc (just as you would stop a spinning disc by squeezing it between your fingers), slowing the wheel.

Disc brakes use the same principle as bicycle handbrakes, but on a bike the brake pads press against the wheel itself. On a car, the disc is part of the hub to which the wheel is mounted. The disc, technically called a rotor, is clearly visible through spoked wheels.Disc brakes generate amazing stopping power even in the worst conditions because they utilize rotors (photo) attached to the wheel hubs, and calipers attached to the frame containing specially designed pads 

The main components of a disc brake are:

• The brake pads
• The caliper, which contains a piston
• The rotor, which is mounted to the hub

How Disc Brakes Work?

On a disc brake, the fluid from the master cylinder is forced into a caliper where it presses against a piston. The piston, in turn, squeezes two brake pads against the disc (rotor) which is attached to the wheel, forcing it to slow down or stop. 

This process is similar to a bicycle brake where two rubber pads rub against the wheel rim to create stopping friction.

Why do disc brake have holes in them?

Due to following reasons :-

>These holes significantly increasing the grab or friction of the brake caliper pads. 

>Reduce the weight of whole assembly.

>For proper heat dissipation generated during braking.

>The holes are spaced in such a way that the calipers used in the brake wear out uniformly, to ensure maximum longevity.

PELTON TURBINE

A turbine converts energy in the form of falling water into rotating shaft power. The selection of the best turbine for any particular hydro site depends on the site characteristics, the dominant ones being the head and flow available.

The Pelton type turbine is usually the preferred turbine for hydropower, when the available water source has relatively high hydraulic head at low flow rates.They have the advantages such as compact structure, small size, high efficiency, low operation maintenance cost, low cost because of less excavation and less investments, etc. and disadvantages like inadequate energy recovery and lower efficiency than other types of turbines.In a Pelton Turbine or Pelton Wheel water jets impact on the blades of the turbine making the wheel rotate, producing torque and power. 

Pelton Turbine – The Basic Working Principle

Working principle of Pelton turbine is simple. When a high speed water jet injected through a nozzle hits buckets of Pelton wheel; it induces an impulsive force. This force makes the turbine rotate. The rotating shaft runs a generator and produces electricity.

In large scale hydro installation Pelton turbines are normally only considered for heads above 150 m, but for micro-hydro applications Pelton turbines can be used effectively at heads down to about 20 m. Pelton turbines are not used at lower heads because their rotational speeds becomes very slow and the runner required is very large and unwieldy. If runner size and low speed do not pose a problem for a particular installation, then a Pelton turbine can be used efficiently with fairly low heads.

VERY IMPORTANT INTERVIEW QUESTION:- Q:-Difference between internal combustion engines and external combustion engines?

VERY IMPORTANT INTERVIEW QUESTION:-

Q:-Difference between internal combustion engines and external combustion engines? 

Answer:- In an *Internal Combustion Engine*, the Fuel is burnt in the cylinder or vessel eg. Diesel or Petrol engine used in Cars.
In an *External Combustion Engine*, the internal working fuel is not burnt. Here the fluid is being heated from an external source. The fuel is heated and expanded through the internal mechanism of the engine resulting in work. eg. Steam Turbine, Steam engine Trains.
* Internal engine has its energy ignited in the cylinder. like 99.9% of engines today.
* An external combustion example is a steam engine where the heating process is done in an boiler out side the engine.

So in fact we can define internal combustion engine develops its operating pressure by burning fuel directly in the engine. Gasoline engines, Wankel engines, diesels, gas turbines are all internal combustion. External combustion engines burn the fuel outside the engine and use it to heat an operating fluid which then is used to operate the engine. Steam locomotives, steam turbines, and Stirling engines are external combustion

PROPERTIES OF SYSTEM

PROPERTIES OF SYSTEM:

A property of a system is a characteristic of the system which depends upon its state, but not upon how the state is reached. There are two sorts of property :

1. Intensive properties.These properties do not depend on the mass of the system.Examples: Temperature and pressure.

2. Extensive properties.These properties depend on the mass of the system. Example:Volume. Extensive properties are often divided by mass associated with them to obtain the intensive properties. For example, if the volume of a system of mass m is V, then the specific volume of matter within the system is V/m= v which is an intensive property.