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Comparison of Two and Four Stroke Cycle Diesel Engine

Internal Combustion Engine
Engine Components
Four-Stroke-Cycle Spark-ignition (Petrol) Engine
Valve Timing Diagrams
Two Stroke Spark Ignition Engine
Difference Between Two & Four Stroke Cycle Petrol Engines
Four Stroke Cycle Compression Ignition (Diesel) Engine
History of Diesel Engine
Two Stroke Cycle Diesel Engine
Comparison of Two and Four Stroke Cycle Diesel Engine
Comparison of S.I. and C.I. Engine
Piston Displacement or Swept Volume
Engine Torque & Engine Power
Compression Ratio

A brief but critical comparison of two and four stroke diesel engine is made below:

a) Theoretically, almost twice the power can be developed with a two-stroke engine compared with a four-stroke engine.

b) A comparison between a typical 12 liter four-stroke engine and a 7 liter two-stroke engine having the same speed range would show that they would develop similar torque and power ratings. The ratio of engine capacities for equivalent performance for these four-stroke and two-stroke engines would be 1.7:1.

c) In a four-stroke engine, the same parts generate power and empty and fill the cylinders. With the two-stroke engine, the emptying and filling can be carried out by light rotary components.

d) With a two-stroke engine, 40–50% more air consumption is necessary for the same power output; therefore the air-pumping work done will be proportionally greater.

e) About 10–20% of the upward stroke of a two-stroke engine must be sacrificed to emptying and filling the cylinder.

f) The time available for emptying and filling a cylinder is considerably less in a two-stroke-cycle engine – something like 33% of the completed cycle as compared to 50% in a four-stroke engine. Therefore more power will be needed to force a greater mass of air into the cylinder in a shorter time.

g) Compared with a two-stroke engine, more power is needed by the piston for emptying and filling the cylinder in a four-stroke engine, due to pumping and friction losses at low speeds. At higher engine speeds the situation is reversed, and the two-stroke’s Rootes blower will consume proportionally more engine power – this could be up to 15% of the developed power at maximum speed.

h) With reduced engine load for a given speed, a two-stroke engine blower will consume proportionally more of the power developed by the engine.

i) A two-stroke engine runs smoother and relatively quietly, due to the absence of reversals of loading on bearings as compared with a four-stroke engine.