Tubeless tires

Tubeless tires :
Tubeless tires or tyres (in some Commonwealth Nations) are pneumatic tires that do not require a separate inner tube.
Unlike traditional pneumatic tires which use a separate inner tube, tubeless tires have continuous ribs molded integrally into the bead of the tire so that they are forced by the pressure of the air inside the tire to seal with the flanges of the metal rim of the wheel.
 

FIRE TUBE BOILERS

FIRE TUBE BOILERS :
In fire tube boiler, hot gases pass through the tubes and boiler feed water in the shell side is converted into steam. Fire tube boilers are generally used for relatively small steam capacities and low to medium steam pressures. As a guideline, fire tube boilers are competitive for steam rates up to 12,000 kg/hour and pressures up to 18 kg/cm2. Fire tube boilers are available for operation with oil, gas or solid fuels. For economic reasons, most fire tube boilers are nowadays of “packaged” construction (i.e. manufacturers shop erected) for all fuels. 

Direct injection

Direct injection:-

With direct injection, the fuel is injected directly into the combustion chamber which is usually formed by a cavity in the piston crown.

This cavity is carefully shaped to promote air swirl and the direction of the injector nozzle ensures that rapid mixing of the fuel and air assists complete combustion.

Advantages - It is claimed that direct injection gives higher thermal efficiency with lower fuel consumption. This is bought about by the fact that no heat is lost or power wasted in pumping air through a restricted opening into the separate chamber or in discharging the gases from the chamber. This gives easier starting and generally this type of engine does not require a starting aid device, such as glow plugs.

Disadvantages - This kind of injection is prone to “diesel knock”.
 

Stress Concentration

A stress concentration (often called stress raisers or stress risers) is a location in an object where stress is concentrated. An object is strongest when force is evenly distributed over its area, so a reduction in area, e.g., caused by a crack, results in a localized increase in stress. A material can fail, via a propagating crack, when a concentrated stress exceeds the material's theoretical cohesive strength. The real fracture strength of a material is always lower than the theoretical value because most materials contain small cracks or contaminants (especially foreign particles) that concentrate stress. Fatigue cracks always start at stress raisers, so removing such defects increases the fatigue strength.

MECHANICAL ENGINEERING JOB INTERVIEW QUESTIONS

MECHANICAL ENGINEERING JOB INTERVIEW QUESTIONS:-

1.)How many governors are needed for safe turbine operation? Why?

Ans.-Two independent governors are needed for safe turbine operation. One is an over speed or emergency trip that shuts off the steam at 10 percent above running speed (maximum speed). The second, or main governor, usually controls speed at a constant rate; however, many applications have variable speed control.

2.)How is a fly ball governor used with a hydraulic control?

Ans.-As the turbine speeds up, the weights are moved outward by centrifugal force, causing linkage to open a pilot valve that admits and releases oil on either side of a piston or on one side of a spring-loaded piston. The movement of the piston controls the steam valves.

3.)What is meant by critical speed?

Ans.-It is the speed at which the machine vibrates most violently. It is due to many causes, such as imbalance or harmonic vibrations set up by the entire machine. To minimize damage, the turbine should be hurried through the known critical speed as rapidly as possible. (Caution, be sure the vibration is caused by critical speed and not by some other trouble).

An Actuator

An actuator is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, typically electric current, hydraulic fluid pressure, or pneumatic pressure, and converts that energy into motion. An actuator is the mechanism by which a control system acts upon an environment. The control system can be simple (a fixed mechanical or electronic system), software-based (e.g. a printer driver, robot control system), or a human or other agent.
 

VALVE TIMING DIAGRAM

VALVE TIMING DIAGRAM :-

The above diagram is for a Caterpillar series 3600 turbo charged after cooled engine. As can be seen from the timing diagram, the induction stroke commences when the inlet valve opens 10° before TDC when air is drawn into the cylinder as the piston moves down. The inlet valve closes 1° before BDC.

The air is now trapped in the cylinder and as the piston rises on the compression stroke, the air is compressed. As the air is compressed, it rises in temperature. When the piston reaches 19° before TDC, the injection of fuel commences and continues until 73° after TDC.

The heat in the compressed air ignites the fuel and combustion takes place. The gases expand forcing the piston down on the power stroke.

The exhaust valves opens at 26° before BDC and the exhaust gases commence and are discharged as the piston rises on the exhaust stroke. Most of the exhaust gases have been discharged as the piston nears TDC. However, at 10° before TDC, the inlet valve opens and air enters the cylinder and helps discharge any remaining exhaust gases until the exhaust valve closes at 3° after TDC.

The whole cycle is then repeated.

Both the exhaust valve and inlet valve are open from 10° before TDC to 3° after TDC, an overlap of 13°. This is referred to as “valve overlap” and ensures that all the exhaust gases are discharged from the cylinder and the cylinder receives a fresh charge of air to make it more efficient when combustion next takes place.

Therefore there is one power stroke for every cycle or two revolutions of the crankshaft.

Funny Facts About Engineers: [A MUST READ]

Funny Facts About Engineers: [A MUST READ]

1. For engineers every course apart from engineering is easy.
2. An engineer has the power of getting up at 9.25 am and reaching the class at 9.30 am.
3. T-shirt and jeans are engineer's national dress and Maggi is the national food.
4. A normal person will fix the broken things but an engineer will first break a thing and then he would fix it.
5. An engineer can build a car, spaceship and they even can make time machine. However, he just can’t build a relationship with a girl.
6. An engineer doesn't care for the rise in price of petrol or gold but he gets mad when cigarette costs Rs.5.50 instead of 5.20.

P.S: Add your own facts and tag your friends who can relate to this.

Heat Treatment

Heat Treatment:-

Heat Treatment is the controlled heating and cooling of metals to alter their physical and mechanical properties without changing the product shape. Heat treatment is sometimes done inadvertently due to manufacturing processes that either heat or cool the metal such as welding or forming.

Heat Treatment is often associated with increasing the strength of material, but it can also be used to alter certain manufacturability objectives such as improve machining, improve formability, restore ductility after a cold working operation.Thus it is a very enabling manufacturing process that can not only help other manufacturing process, but can also improve product performance by increasing strength or other desirable characteristics.

Traction control system

Traction control system :-

A traction control system (TCS), is typically (but not necessarily) a secondary function of the anti-lock braking system (ABS) on production motor vehicles, designed to prevent loss of traction of driven road wheels. When invoked it therefore enhances driver control as throttle input applied is mis-matched to road surface conditions (due to varying factors) being unable to manage applied torque.

Intervention consists of one or more of the following:

>Reduces or suppress spark sequence to one or more cylinders
>Reduce fuel supply to one or more cylinders
>Brake force applied at one or more wheels
>Close the throttle, if the vehicle is fitted with drive by wire throttle
>In turbo-charged vehicles, a boost control solenoid can be actuated to reduce boost and therefore engine power.