Posted tagged ‘stroke’

AUTOMOBILE ENGINES

September 10, 2011

The working of an automobile engine follows the same principle as an internal combustion engine. Air, from outside, enters the engine through the air cleaner and reaches the throttle plate.
The pedal in your car is the control for the amount of air that you would want to be taken in, and you control it by pressing on this gas pedal.
The air is then distributed through the intake manifold of the cylinders.

At some point fuel is injected into the air stream, and the mixture vaporizes and is drawn into the cylinders as they start their intake stroke.

This way, when the cylinder has reached its bottom, it has drawn in sufficient mixture. As it moves up, compressing the mixture, the spark plug ignites the mixture, and as the powerful gas formed expands, it pushes the cylinder to the bottom with the cylinder once again drawing in the mixture.

In designing automobile engines, you need to be a specialist in automobile engineering.
The consideration that is taken while designing such an engine is whether it should be a carburetor or a diesel one. carburetor engines are most commonly found in passenger cars and low capacity trucks, while trucks with a capacity over two tons are fitted with diesel engines, including dump trucks, trailer tractors and bus.

Increasingly the medium and low-capacity vehicles are being fitted with diesel engines, since the fuel consumption of these engines are 30% to 50% lower than the carburetor engines.
Diesel engines not only cost more, but maintenance is much more expensive than the other type of engine. Diesels require more metal parts per kilowatt.
The critical parts of diesel engines are made of alloy steel, and the fuel injection system is much more expensive than carburetor engines.

However, the cost of manufacturing carburetor engines has increased with the use of higher mechanical grade components, considering the thermal loads of the material used. At the same time the use of high alloys and increase in production costs have contributed to the higher price of such engines.

There is a sharp rise in using aluminum alloys in design of carburetor engines in passenger cars, and with the use of high octane petrol, the cost of operation of these cars have come down extensively. Using alloy steel in constructing the engine body and other parts of the engine, makes the car lighter and hence fuel consumption goes down substantially.

The main parts that are made of high steel alloy are the main casting of the engine, the cylinder head, water and oil pumps, oil filter housing, end covers of the generator and starter, and the intake pipes. It has been observed that by using high steel alloys, the weight of the car is reduced by 35%.

The power per liter, per unit of piston area, and the brake effective pressure are 6% to 8% lower in air-cooled engines, compared to engines having liquid cooling mechanism. This is due to the fact that in engines with liquid cooling there are great losses in cylinder charging caused by the high temperature in pipes, ducts in the head, cylinder walls and head, etc.

The size of air cooled engines are much bigger than the engines with liquid cooling having the same capacity, and this is because the cylinder axes difference is larger in air-cooled engines. Taking account of the radiator dimensions, if both engines are compared, the air-cooled engine will vary slightly with its height a little longer than or approximately the same length as the water-cooled engine. As far as the width and the height is concerned both engines are about the same.

The auxiliary units of the feed and ignition, and generator and starter systems are a bit difficult to fit on the body of the air-cooled engines, because of the presence of hoods and having a danger of over-heating.

Fuel Injectors

September 8, 2011
Each cylinder has a fuel injector designed to meter and inject fuel into the cylinder at the proper instant. To accomplish this function, the injectors are actuated by the engine’s camshaft. The camshaft provides the timing and pumping action used by the injector to inject the fuel. The injectors meter the amount of fuel injected into the cylinder on each stroke. The amount of fuel to be injected by each injector is set by a mechanical linkage called the fuel rack. The fuel rack position is controlled by the engine’s governor. The governor determines the amount of fuel required to maintain the desired engine speed and adjusts the amount to be injected by adjusting
the position of the fuel rack.

Each injector operates in the following manner. As illustrated in Figure 26, fuel under pressure enters the injector through the injector’s filter cap and filter element. From the filter element the fuel travels down into the supply chamber (that area between the plunger bushing and the spill deflector). The plunger operates up and down in the bushing, the bore of which is open to the fuel supply in the supply chamber by two funnel-shaped ports in the plunger bushing.


Figure 26 Fuel Injector Cutway

The motion of the injector rocker arm (not shown) is transmitted to the plunger by the injector follower which bears against the follower spring. As the plunger moves downward under pressure of the injector rocker arm, a portion of the fuel trapped under the plunger is displaced into the supply chamber through the lower port until the port is closed off by the lower end of the plunger. The fuel trapped below the plunger is then forced up through the central bore of the plunger and back out the upper port until the upper port is closed off by the downward motion of the plunger.

With the upper and lower ports both closed off, the remaining fuel under the plunger is subjected to an increase in pressure by the downward motion of the plunger.
When sufficient pressure has built up, the injector valve is lifted off its seat and the fuel is forced through small orifices in the spray tip and atomized into the combustion chamber. A check valve, mounted in the spray tip, prevents air in the combustion chamber from flowing back into the fuel injector. The plunger is then returned back to its original position by the injector follower spring.

On the return upward movement of the plunger, the high pressure cylinder within the bushing is again filled with fresh fuel oil through the ports. The constant circulation of fresh, cool fuel through the injector renews the fuel supply in the chamber and helps cool the injector. The fuel flow also effectively removes all traces of air that might otherwise accumulate in the system.

The fuel injector outlet opening, through which the excess fuel returns to the fuel return manifold and then back to the fuel tank, is adjacent to the inlet opening and contains a filter element exactly the same as the one on the fuel inlet side. In addition to the reciprocating motion of the plunger, the plunger can be rotated during operation around its axis by the gear which meshes with the fuel rack. For metering the fuel, an upper helix and a lower helix are machined in the lower part of the plunger. The relation of the helices to the two ports in the injector bushing changes with the rotation of the plunger.

Changing the position of the helices, by rotating the plunger, retards or advances the closing of the ports and the beginning and ending of the injection period. At the same time, it increases or decreases the amount of fuel injected into the cylinder. Figure 27 illustrates the various plunger positions from NO LOAD to FULL LOAD. With the control rack pulled all the way (no injection), the upper port is not closed by the helix until after the lower port is uncovered.

Consequently, with the rack in this position, all of the fuel is forced back into the supply chamber and no injection of fuel takes place. With the control rack pushed all the way in (full injection), the upper port is closed shortly after the lower port has been covered, thus producing a maximum effective stroke and maximum fuel injection. From this no-injection position to the full-injection position (full rack movement), the contour of the upper helix advances the closing of the ports and the beginning of injection.


Fig 27 Fuel Injector Plunger

 

HYDRATION SYSTEM

August 23, 2011

04-The Future Of Bicycling Hydration, Bicycle Mounted Hydration System, Hydration System Mounts On The Bicycle Rear

Is it possible to drink too much water during ride without stop the vehicle?

Adequate hydration is as important as calorie replacement to an athlete’s performance, yet dehydration continues to be a condition many experience. This is especially true in cycling where evaporative losses are significant and can go unnoticed. Sweat production and losses through breathing can exceed 2 quarts per hour. To maximize your performance pre-hydration is important, and it is essential that fluid replacement begin early and continue throughout a ride.

Approximately 75% of the energy your body produces is converted to heat rather than being delivered to your muscles to power your pedal stroke. Keeping your body cool and re-hydrated during exertion will result in greater efficiency, higher power output, extended endurance, and a quicker, more thorough recovery. Say good-bye to the Wet Spot!


Individual fluid and electrolyte needs are widely variable during physical exercise due to differences in metabolic rate, body mass and size, environmental conditions (e.g. temperature, humidity, wind, solar load, clothing worn), heat acclimatization status, physical fitness, activity duration, and genetic variability. Sweat rates can vary from 0.5L/hr to more than 3 L/hr. Similarly, sodium concentration may vary from less than 460 mg/L to more than 1840 mg/L

03-The Future Of Bicycling Hydration, Bicycle Mounted Hydration System, Hydration System Mounts On The Bicycle Rear

Technology:

Why use a perfectly good water bottle on your bike when you could use a complex, expensive and awkward to use “hydration system” instead? That’s the promise of the VelEau Bicycle Mounted Hydration System.

01-The Future Of Bicycling Hydration, Bicycle Mounted Hydration System, Hydration System Mounts On The Bicycle Rear

The VelEau comes in several parts. First, there’s a saddlebag which holds 42 ounces (1.4 liters) of water. Then there’s a tube through which you drink, much like those found on CamelBak water bags. This runs from under the seat, along the top-tube to the handlebars, where it is secured to a retracting cord on the stem. This cord pulls the mouthpiece back into place when you’re done drinking, where it is secured by magnets.

02-The Future Of Bicycling Hydration, Bicycle Mounted Hydration System, Hydration System Mounts On The Bicycle Rear

If that seems like it’s complex, unnecessarily heavy and annoying to use, that’s because it probably is. However, there is at least a compartment to carry a multi tool in the same bag, which adds some utility.

HYDRATION SYSTEM

August 23, 2011

04-The Future Of Bicycling Hydration, Bicycle Mounted Hydration System, Hydration System Mounts On The Bicycle Rear

Is it possible to drink too much water during ride without stop the vehicle?

Adequate hydration is as important as calorie replacement to an athlete’s performance, yet dehydration continues to be a condition many experience. This is especially true in cycling where evaporative losses are significant and can go unnoticed. Sweat production and losses through breathing can exceed 2 quarts per hour. To maximize your performance pre-hydration is important, and it is essential that fluid replacement begin early and continue throughout a ride.

Approximately 75% of the energy your body produces is converted to heat rather than being delivered to your muscles to power your pedal stroke. Keeping your body cool and re-hydrated during exertion will result in greater efficiency, higher power output, extended endurance, and a quicker, more thorough recovery. Say good-bye to the Wet Spot!


Individual fluid and electrolyte needs are widely variable during physical exercise due to differences in metabolic rate, body mass and size, environmental conditions (e.g. temperature, humidity, wind, solar load, clothing worn), heat acclimatization status, physical fitness, activity duration, and genetic variability. Sweat rates can vary from 0.5L/hr to more than 3 L/hr. Similarly, sodium concentration may vary from less than 460 mg/L to more than 1840 mg/L

03-The Future Of Bicycling Hydration, Bicycle Mounted Hydration System, Hydration System Mounts On The Bicycle Rear

Technology:

Why use a perfectly good water bottle on your bike when you could use a complex, expensive and awkward to use “hydration system” instead? That’s the promise of the VelEau Bicycle Mounted Hydration System.

01-The Future Of Bicycling Hydration, Bicycle Mounted Hydration System, Hydration System Mounts On The Bicycle Rear

The VelEau comes in several parts. First, there’s a saddlebag which holds 42 ounces (1.4 liters) of water. Then there’s a tube through which you drink, much like those found on CamelBak water bags. This runs from under the seat, along the top-tube to the handlebars, where it is secured to a retracting cord on the stem. This cord pulls the mouthpiece back into place when you’re done drinking, where it is secured by magnets.

02-The Future Of Bicycling Hydration, Bicycle Mounted Hydration System, Hydration System Mounts On The Bicycle Rear

If that seems like it’s complex, unnecessarily heavy and annoying to use, that’s because it probably is. However, there is at least a compartment to carry a multi tool in the same bag, which adds some utility.

INTERVIEW QUESTIONS:GERNAL:

August 22, 2011
  • Explain the Second Law of Thermodynamics.
    The entropy of the universe increases over time and moves towards a maximum value.

 

  • How do you measure temperature in a Wet Bulb Thermometer?
    Wet bulb temperature is measured in a wet bulb thermometer by covering the bulb with a wick and wetting it with water. It corresponds to the dew point temperature and relative humidity.

 

  • What is Bending moment?
    When a moment is applied to bend an element, a bending moment exists in the element

 

  • What are the points in the Stress Strain curve for Steel?
    Proportional limit, elastic limit or yield point, ultimate stress and stress at failure.

 

  • Define Reynolds number.
    Reynolds number is the ratio of inertial force and viscous force. It is a dimensionless number. It determines the type of fluid flow.

 

  • What is a Newtonian fluid?
    A Newtonian fluid possesses a linear stress strain relationship curve and it passes through the origin. The fluid properties of a Newtonian fluid do not change when any force acts upon it.

 

  • How many Joules is 1 BTU?
    1 BTU is equal to 1055.056 joules.

 

  • What is PS?
    PS is Pferdestarke, the German unit for Horsepower.

 

  • Explain Otto cycle.
    Otto cycle can be explained by a pressure volume relationship diagram. It shows the functioning cycle of a four stroke engine. The cycle starts with an intake stroke, closing the intake and moving to the compression stroke, starting of combustion, power stroke, heat exchange stroke where heat is rejected and the exhaust stroke. It was designed by Nicolas Otto, a German engineer.

 

  • Explain the nomenclature of a 6203-ZZ bearing.
    6 is the type code, which shows it is a single-row ball bearing, 2 is the series, means light, 03 is the bore, which is 17 mm and ZZ is the suffix meaning double shielded bearing.

 

  • What is Gear ratio?
    It is the ratio of the number of revolutions of the pinion gear to one revolution of the idler gear.

 

  • What is Annealing?
    It is a process of heating a material above the re-crystallization temperature and cooling after a specific time interval. This increases the hardness and strength if the material.

 

  • Define Torque.
    Torque is defined as a force applied to an object that results in rotational motion.

 

  • What is Ductile-Brittle Transition Temperature?
    It is the temperature below which the tendency of a material to fracture increases rather than forming. Below this temperature the material loses its ductility. It is also called Nil Ductility Temperature.