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4-stroke engine vs 6-stroke engine-Difference between 4-stroke engine and 6-stroke engine

This page compares 4-stroke engine vs 6-stroke engine and describes basic difference between 4-stroke engine and 6-stroke engine types.

Heat engine converts thermal energy into mechanical energy. There are various types of heat engines based on different criterias. Based on working cycles heat engines are categorized into 2-stroke, 4-stroke and 6-stroke engines.

4-Stroke Engine

4 stroke engine

In 4-stroke engine, four events take place inside engine cylinder viz. suction, compression, power and exhaust. All these events are completed in four strokes of the piston or in two revolutions of the crank shaft. Hence it is known as four-stroke engine. The four cycles are shown in the figure-1.

In 2-stroke engine, the whole sequence of events i.e. suction, compression, power and exhaust are completed in two strokes of piston i.e. one revolution of crankshaft.

6-Stroke Engine

6 stroke engine

It is developed by modifying 4-stroke design to improve efficiency and reduce emissions. It is type of internal combustion engine based on 4-stroke engine with additional complexity. There are two power strokes viz. one with fuel and other with steam or air.

The 6-stroke engines are categorized into single piston type and opposed piston type. The single piston uses one piston in the cylinder. Opposed piston design use two pistons per cylinder operating at different rates with detonation occurring between the pistons. Single piston designs include Griffin 6-stroke engine, Bajulaz 6-stroke engine, Crower 6-stroke engine and Velozeta 6-stroke engine etc. Opposed piston designs include Beare head, M4+2 etc. Other two piston designs are also available.

Following are the six stages in 6-stroke engine having four valves viz. suction valve, air inlet valve, exhaust valve and air exhaust valve.
• Suction• Compression• Ignition• Exhaust• Air Suction• Air Exhaust.

The first 4 strokes are same as either Otto or diesel cycle. The energy is produced in power stroke. After the end of 4 strokes, the bore will be still hot which is hot enough to expand water. Hence after the end of fourth stroke, when piston is moving towards BDC (Bottom Dead Center), water is inserted inside the cylinder, the water is expanded by the addition of heat to it. It is considered to be the fifth stroke. This stroke also produces power. Hence in a cycle, power is produced twice. After the fifth stroke, the piston is reciprocated back towards TDC (Top Dead Center), which is considered to be the sixth stroke. The figure-1 depicts the working of 6-stroke engine. As shown water is injected at the end of exhaust, so that an extra power and exhaust stroke is added.

Following table summarizes difference between 4-stroke engine and 6-stroke with respect to various features.

Features 4-stroke engine 6-stroke engine
Number of cycles 4 cycles, •Suction •Compression •Ignition •Exhaust 6 cycles, •Suction •Compression •Ignition •Exhaust •Air Suction •Air Exhaust.
Number of power strokes One Two
Output torque Lower Higher
Output Power Lower Higher
Efficiency Low High
Emission High Low
Air pollution Higher Lower
Fuel consumption High Low
Cooling System Good Better due to more air intake.


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