1. Four Stroke Cycle In 1892 Rudolph Diesel invented the compression ignition engine named after him. The first engine was built at Augsburg Maschinenfabrik (now part of MAN-B&W group) in 1897.The single cylinder engine was used to power stationery machinery. It weighed 5 tons and produced 20 horse power at 172 rpm. The engine operated at 26.2% efficiency, a significant improvement upon 20% efficiency of best petrol engine of its time.

2. The four stroke cycle is so called because it takes four stroke of the piston to complete the processes needed to convert the energy in the fuel to work. Because the engine is reciprocating, this means that the piston must move up and down the cylinder twice, therefore the crankshaft must revolve twice. The four stroke of the piston are induction stroke, compression stroke, power stroke and exhaust stroke.

3. 1. Induction The crankshaft is rotating clockwise and the piston is moving downwards. The inlet valve is open and the air is being drawn in or being pushed into the cylinder by the turbocharger.

4. 2. Compression The inlet valve has closed and the charged air is compressed as the piston is moving up. Because the energy is being transferred to the air, its temperature and pressure increases. By the time the piston approaches the top of the cylinder (known as top dead centre or TDC), its pressure is over 100 bar and temperature is over 500 degree C.

5. 3. Power Just before TDC, fuel is injected into the cylinder by fuel injector. The fuel is atomized into small droplets. Because they are very small, these droplets are heated very quickly and their temperature is above its self ignition temperature. The fuel starts to burn as the piston is passing over TDC. This raises the pressure and temperature of the air above the piston. This forces the piston down the cylinder and forces the crankshaft to rotate. It is during this stroke that work energy is being given to the engine, in the other three strokes of the piston, the engine has to do the work.

6. 4. Exhaust As the piston approaches the bottom of the cylinder (known as Bottom Dead Centre or BDC), the exhaust valve starts to open. As the piston starts to go up the cylinder, the hot gases (mainly consisting of nitrogen, carbon di-oxide, water vapour and unused oxygen) are pushed out into the exhaust manifold. As the piston approaches TDC again, the inlet valve opens again and the cycle repeats itself.