The IC engines or “Diesel Engines” as they are referred to, are named after Rudolf Diesel, who invented these engines in 1893.
The first working engine was built in 1897. It weighed 5 tonnes and produced 20 hp at 172 rpm with an efficiency of about 26%. (Modern low speed diesel engines can have thermal efficiency that exceeds 50%).
In 1912 the first ocean going ship to have installed diesel engines was “Selandia” which was powered by twin, 1010 BHP B&W, 8 cylinder, 4 stroke engines, which were direct coupled.
The worlds largest diesel engine is Wartsilla Sulzer RTA96-C common rail marine diesel of about 113,210 hp @ 102 rpm output.
Modern Diesel engines operate on Dual Combustion Cycle which is a combination of Constant Volume (Otto) and Constant Pressure (Diesel) cycle is shown in the sketch.
The area of the diagram represents the work done on the piston during one cycle.
Starting from point C, the air is compressed adiabatically to a point D.
Fuel injection begins at D, and heat is added to the cycle partly at constant volume (shown by vertical line DP), and partly at constant pressure ( shown by horizontal line PE).
At point E expansion begins. This proceeds adiabatically to point F when the heat is rejected to exhaust at constant volume.
The exhaust and suction strokes are shown by horizontal line at C, and this as no effect on cycle.
This theoretical cycle deviates from practical cycle due to
> Unavoidable thermal, hydraulic and mechanical losses.
> The manner in which, and the rate at which, heat is added to the compressed air is a complex function of fuel injection equipment.
> The compression and expansion strokes are not truly adiabatic. Heat is lost to the cylinder walls to an extent which is influenced by coolant temperature and by design of the heat paths to the coolant.
> Some of the useful work is expended to perform the induction and exhaust process. Greater losses are involved during exhaust as the unused energy is lost by compressed hot gases when the exhaust valve opens before the piston arrives.
> Action arising out of reciprocating, rotating and rubbing components also contribute to losses.
> Some energy is used to drive auxiliaries like lub oil pumps, jacket water pumps, etc.
4 STROKE CYCLE
Nickolaus Otto invented the 4 stroke cycle in 1862.In 1893 Rudolph Diesel invented the compression ignition engine, now named after him.
The four stroke cycle is so called because it takes four strokes of the piston to complete the process needed to convert the energy in the fuel to work. Because the engine is reciprocating, this means the piston has to move up and down the cylinder twice, and therefore the crankshaft must revolve twice.
The four stroke of the piston are known as induction stroke, compression stroke, power stroke and the exhaust stroke.
Induction Stroke : The crankshaft is rotating clockwise and the piston is moving down the cylinder. The inlet valve is open and the fresh charge of air is drawn inside the cylinder at a pressure existing in the intake manifold. The inlet valve closes at the end of the stroke.
Compression Stroke : Both inlet and exhaust valves are closed and air is compressed by the piston as it moves up in the cylinder. Because energy is transferred into air the pressure and temperature of the air increases.
Power stroke : Just before piston is reaching the TDC ( top dead centre) fuel is injected into the cylinder by fuel injector. Fuel is ignited by the high temperature produced at the end of compression and the expanding gases forces the piston down the cylinder. The gases expand until at the end of the stroke when exhaust valve opens.
Exhaust Stroke : As the piston is approaching the BDC ( bottom dead centre) , the exhaust valve opens. As the piston moves up the cylinder the exhaust gases are expelled from the cylinder.
As the piston approached the TDC again the inlet valve starts to open and the cycle repeats itself.
1.AIR INDUCTION VALVE OPENS 15 BTDC
2. EXHAUST VALVE CLOSES 10 ATDC
3. INDUCTION IS IN PROGRESS
4.INDUCTION VALVE CLOSES 35 ABDC
5. COMPRESSION IS IN PROGRESS
6.FUEL INJECTION STARTS 10 BTDC
7. FUEL INJECTION CONTINUES 35 ATDC
8. EXPANSION OR POWER STROKE
9. EXHAUST VALVE OPENS 40 BBDC
10. EXHAUST VALVE CLOSES 10 ATDC
2 STROKE CYCLE
Two stroke cycle was invented by Sir Dugald Clerk in 1881.
The two stroke cycle is so called because it takes two strokes of the piston to complete the process needed to convert the energy in the fuel to work. i.e. to complete one working cycle. Unlike the four stroke engine there are no inlet and exhaust valves but there are inlet (scavenge) ports and the exhaust ports which get covered and uncovered during the upward and downward stroke of the piston respectively. (please note the modern two stoke diesel engine has a separate exhaust valve mounted on the top of the cylinder instead of the exhaust ports)
The working of two stroke cycle engine differs from that of four stroke cycle engine because of complete absence of two distinct strokes of induction and exhaust. Every downward stroke is a power stroke and every upward stroke is a compression stroke.
Every downward stroke causes the exhaust ports to uncover first causing the escape of the exhaust which lowers the pressure in the cylinder. The further downward travel of the piston then uncovers the scavenge ports so as to admit the scavenge air a little above the atmospheric pressure.
Compression Stroke and firing:
The cylinder is filled up with the charge of fresh air at the beginning of compression. The air is compressed by the piston moving upwards in the cylinder after closing both scavenge and the exhaust ports and pressure and temperature of air is increased. Fuel is injected towards end of compression and heat is added to the mass of air and fuel starts to burn as piston is passing over TDC
Expansion and Exhaust and scavenging :.
The expanding gases push the piston downwards.
At the end of the expansion stroke the exhaust is opened first , the pressure drops below the scavenge manifold pressure and fresh air is admitted through scavenge ports. The cylinder is cleansed of residual products of combustion by incoming air and the cycle is repeated.
1 SCAVENGE PORTS CLOSED 35 ABDC
2. EXHAUST PORT CLOSED 50 ABDC
3. COMPRESSION IS IN PROGRESS
4. FUEL INJECTION STATRTS 10 BTDC
5. FUEL INJECTION CONTINUES 30 ATDC
6. EXPANSION OR POWER STROKE
7.EXHAUST PORTS OPEN 50 BBDC
8. SCAVENGE PORTS OPEN 35BBDC
9. EXHAUST AND SCAVENGING TAKING PLACE
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