EARLY FIRE-CRACKERS !

It's not really known when and where firecrackers originated. Although both the Ramayana & the Mahabharata mention the bursting of firecrackers to celebrate victories, the common consensus is that to the use of firecrackers originated in the human province of China in 200 BC when the Han dynasty was in power .

         A villager from Human threw chunks of green bamboo into the fire because he did not have sufficient dry fuel. The bamboo chunks sizzled, blackened & then exploded with a deafening sound, startling the man but giving him the idea of getting rid of evil spirits by exploding bamboos. It wasn't  long before most people in China began to burn bamboo to keep evil spirits away.
         In 600 AD, alchemist Sun Si Miao developed a gun-powder like mixture by mixing saltpetre, honey, sulphur and arsenic disulphide, which produced a hot, bright flame when heated over fire.
         However, the first to use the mixture as firecracker was a chinese monk named Li Tian. When Prime -minister Wei Zhou of the Tang dynasty was plagued by the ghost of an evil dragon he had killed, Li Tian filled a bamboo with the gun powder like mixture and set it on fire. The loud explosion is said to have so frightened the ghost that it stopped haunting him. Li Tian came to be known as the 'father of the firecracker' in China and during the song dynasty, a temple was built to honor him. On 18 April every year, people offer sacrifices at the temple to commemorate the invention of the firecracker.
         The bamboo was replaced by paper rolls after paper was invented. The firecracker or baozhu was made by rolling sheets of paper into small tube, stuffing it with gun powder and fixing it with a fuse.
         Since the 18th century, the Human province has been the center of firecracker production in China. The world's largest manufacturer of fireworks today is China.

         Fire crackers were so popular in Britain that Queen Elizabeth I is said to have created a position for a fire master. King James II was so fascinated with the display of fireworks at his coronation that he knighted his fie master.

     
         

How does a 'four-stroke' automobile engine work ?

In an automobile, the engine's task is to burn fuel so that fuel energy is converted into motion . A for-stroke engine gets its name because it does this conversion in four stages called strokes- the intake stroke, the compression stroke, the combustion stroke and the exhaust stroke .

    To understand the strokes, we must first know the structure of the engine. The engine consists of a hallow metal cylinder inside which fuel (petrol or diesel) is burned. The cylinder is fitted with a piston - a piece of metal that slides in and out of the cylinder like a plunger. The piston is attached to a rotating rod called the crankshaft which powers gears that turn the wheels of the automobile.
     The cylinder is sealed except for two openings (called valves) at the top. One is the 'inlet valve' and the other is called 'outlet/exhaust valve'. At the top of the cylinder, there is an electrical device called spark plug that sets fire to the fuel.

      The four strokes work in the following manner :-
1.Intake : The crankshaft rotates as the piston pushes downwards inside the cylinder. The inlet valve opens and lets in a mixture of air fuel.
2.Compression : The inlet valve closes and seals the cylinder, trapping the fuel and air mixture.As the piston is move upwards, the crankshaft and it squeezes(compresses) the mixture, making it more inflammable. As soon as the piston reaches the top of the cylinder, the spark plug fires.
3.Combustion : The spark ignites the fuel-air mixture causing it to burn rapidly. This creates hot gases that push the piston downwards with force & turn the crankshaft, causing the wheels(and the car, of course) to move.
4.Exhaust : The outlet valve opens. As the crankshaft continues its rotation, the piston moves upwards again, driving out the gases as exhaust.