Six Stroke Engine: Principles, Types, Advantages, Disadvantages

Published by Admin on


The majority of actual internal combustion engines that operate on various cycles share one feature: combustion occurs in the cylinder after each compression, resulting in gas expansion that acts directly on the piston work and is limited to 180 degrees of crankshaft angle.According to the mechanical design, a six-stroke engine with external and internal combustion and double flow is similar to the actual internal reciprocating combustion of the engine.

A six-stroke engine differentiates itself due to the thermodynamic cycle and a modified cylinder having one combustion chamber and one air heating chamber, both of which are independent from the cylinder. Combustion does not occur within the cylinder, but in the supplementary combustion chamber it does not act immediately on the piston, and its duration is independent from the 180 degrees of crankshaft rotation that occurs during the expansion of the combustion gases.

The combustion chamber is kept inside and heated by air. Air pressure in the heating chamber increases, generating power for supplementary work strokes by virtue of heat exchange through the glowing combustion chamber walls. Several advantages result from this one very important increase in thermal efficiency. In the present time, in an internal combustion engine, important calorific losses are generated due to the required cooling of the combustion chamber walls.

Six Stroke Engine

Principle of Six Stroke Engine

The six stroke engine describes a number of the different approaches in the internal combustion engine to the capture waste heat from the four stroke Otto cycle and use it to the power an additional power and exhaust stroke of the piston. Designs either use the steam or air as working fluid for additional power the stroke. As well as extracting power the additional stroke cools engine and the removes need for a cooling system making engine lighter and the giving 40% increased efficiency over the Otto Cycle. The pistons in a six stroke engine go up and the down six times for each injection of the fuel.

The six stroke engine has 2 power strokes one fuel one steam or the air. The currently notable the six stroke engine designs include Crower’s six stroke engine. Boulez engine and the Six-stroke engine. The Bear Head engine is called the six stroke by its designer but stands apart from the others. It uses the second opposed piston in the each cylinder which moves at the half cyclical rate of the main piston thus giving six piston movements per the cycle. It does not use any additional working the fluid.

After the exhaust stroke instead of air fuel mixture as in case of the petrol engines fresh air is sucked into the cylinder from air filter and is the removed during sixth the stroke. The valve overlaps have been removed and the additional two strokes have been provided for the better scavenging using air the injection. The engine shows 40% reduction in the fuel consumption and dramatic reduction in the pollution. Its specific power is the not less than that of a four-stroke petrol the engine. The engine can run on a variety of the fuels ranging from petrol and diesel to the LPG. An altered engine shows the 65% reduction in CO pollution when compared with the four stroke engine from which it was the developed.


  • Thermal efficiency reaching the 50% 30% for the actual internal combustion the Engine.
  • Fuel consumption reduced by the more than 40%.
  • Reduction of the chemical noise and thermal the pollution.
  •  Two expansion work through the six stroke
  • Direct Injection and the optimal fuel combustion at every engine the speed.
  •  We can eliminate the radiator.
  • We would get the better scavenging in the fifth stroke.


  • High Initial cost Due to the change in gear the structure.
  • High Manufacturing cost in the six stroke engine.
  • Engine size Increases Due to the additional stroke in engine fifth stroke and the sixth stroke.

Working Of Six Stroke Engine

Different working strokes of the six stroke engine are

1st stroke (suction stroke)

The inlet valve is kept open. Due to the cranking Piston moves downward which results in the formation of a pressure difference due to the which pure air enters the cylinder.

2nd stroke (compression stroke)

The inlet valve closes and the heating chamber valve opens. The piston moves upward due to the cranking forcing air into heating the chamber. The air at this stage is converted to the high pressure.

3rd stroke (1st power stroke)

The combustion chamber valve opens and the gases of combustion enter the cylinder.

4th stroke (exhaust stroke)

The exhaust valve opens. The piston moves upwards and the exhaust gases are removed via this valve.

5th stroke (2nd power stroke)

The chamber valve opens and the pure air now at high pressure and the high temperature enters cylinder which does work on the piston and hence it moves downward resulting in the 2nd power stroke.

6th stroke (2nd exhaust stroke)

Finally the combustion chamber valve the opens. The piston moves upwards forcing the pure air into the combustion chamber.

Working Of Six Stroke Engine

Types of Six Stroke Engine

A) Single piston designs

These designs use a single piston per cylinder, like a conventional two- or four stroke engine. A secondary, non- detonating fluid is injected into the chamber, and the leftover heat from combustion causes it to expand for a second power stroke followed by a second exhaust stroke.

1) Griffin six-stroke engine

Heated exhaust-jacketed external vaporiser into which the fuel was sprayed was main principle of the working of griffin six stroke the engines. The temperature was held around 550 °F sufficient to vaporise the oil but not to break it the down chemically. This fractional distillation supported the use of heavy oil fuels the unusable tars and asphalts separating out in the vaporiser.

2) Boulez six-stroke engine

The Boulez six-stroke engine is the similar to a regular combustion engine in the design. There are however modifications to the cylinder head with the two supplementary fixed capacity chambers: a combustion chamber and the air preheating chamber above each the cylinder. The combustion chamber receives a charge of heated air from the cylinder injection of fuel begins an isochoric constant-volume burn which the increases thermal efficiency compared to a burn in the cylinder.

3) Velozeta six-stroke engine

In the velozeta engine fresh air is injected into the cylinder during exhaust stroke which the expands by heat and the therefore forces piston down for the additional stroke. The valve overlaps have been removed and the two additional strokes using air injection provide for the better gas scavenging.

4) NIYKADO Six Stroke Engine

This is the only engine that is categorized as a fully working prototype. The first prototype was developed in 2004, which used only two valves. The second prototype, developed in 2007, was an improved design using four valves.

5) Crower six-stroke engine

In the six-stroke engine prototyped in the United States by Bruce Crower water is the injected into  cylinder after the exhaust stroke and is instantly turned to the  steam which expands and forces piston down for an the additional power stroke. Thus waste heat that requires an air or water cooling system to discharge in the most engines is captured and put to use driving the piston.

B) Opposed piston designs

These designs use the two pistons per cylinder operating at different rates with the detonation occurring between the pistons.

1) Bear Head

The term Six Stroke was coined by the inventor of the Bear Head Malcolm the Bear. The technology combines a four the stroke engine bottom end with an opposed piston in the cylinder head working at half the cyclical rate of the bottom piston. Functionally the second piston replaces the valve mechanism of a conventional the engine.

2) M4+2

The M4+2 engines have much in common with the Bear Head engines, combining two opposed pistons in the same cylinder. One piston works at half the cyclical rate of the other, but while the main function of the second piston in a Bear Head engine is to replace the valve mechanism of a conventional four stroke engine, the M4+2 takes the principle one step further.

3) Piston charger engine

In this engine similar in the design to bear head a piston charger replaces the valve. Piston charger perform the work of charging the main cylinder and simultaneously it control the inlet and outlet opening which the leads to no loss of air and fuel in the exhaust. In the main cylinder combustion takes place every turn as in the two- stroke engine and lubrication as in the four-stroke engine.  The Fuel injection can take place in the piston charger in the gas transfer channel or in the combustion chamber.

Crankshaft to Camshaft Ratio Modification

In conventional four stroke engine, the gear at crankshaft must rotate 720. while the camshaft rotates 360 to complete on cycle for six stroke engine, the gear at the crankshaft must rotates 1080 to rotates the camshaft 360 and complete one cycle. Hence their corresponding gear ratio 3:1.

Cam Follower Modification

The bottom of shape of the regular follower has the flat pattern which is the suitable with the normal camshaft for four the stroke engine. When reducing the Duration of valve opening from the 9000 to only 6000 shape of the follower must be changed from flat to the roller or spherical shape.

Valve Timing Diagram

  • Inlet valve open 5° before TDC,
  • Inlet valve closed 20° after BDC,
  • Fuel Exhaust valve open 20° before BDC,
  • Fuel Exhaust valve closed 5° before TDC,
  • Water intake valve open 5° before TDC,
  • Water intake valve closed 10° after TDC,
  • Steam exhaust valve open 10° after TDC,
  • Steam exhaust valve closed 10° after TDC.
Valve Timing Diagram

Analysis of Six Stroke Engine

Internal combustion engines efficiency is the less than 40%. Most of the energy generated by burning fuel in the combustion chamber is lost in the water cooling and the exhaust. Figure 1 below shows a typical energy split in the internal combustion engines.


  • Automobiles, heavy goods, construction-site and farm vehicles.
  • Motor-pumps, generator sets, stationary engines, etc. Intended for agriculture and industry.
  • Motorboats.

Engine Cycle

In one cycle, there are six strokes are present are as follow

  • Suction stroke
  • Compression stroke
  • Power stroke-I (expansion stroke)
  • Exhaust stroke-I (fuel exhaust stroke)
  • Power stroke-II
  • Exhaust stoke-II (steam exhaust stroke)

Engine Modification

To make a six-stroke engine from the conventional four-stroke engine, a few modifications must be done to specific parts of the conventional engine to be sure that the new engine with six-stroke will run successfully. A Mitsubishi single cylinder spark ignition engine was used to apply these modifications to it. These modifications are.

Modification in Six Stroke Engine

Modifications are done to the specific parts of conventional four stroke engine so that the new engine with the six strokes works successfully. These modifications are:

1.Crankshaft to Camshaft Ratio Modification

In the conventional four stroke engine gear at crankshaft must rotate 720ο while the camshaft rotates 360ο to the complete one cycle. For the six-stroke engine the gear at Crankshaft must rotate 1080ο to the rotate camshaft 360ο and the complete one cycle. Hence their corresponding gear ratio is the 3:1.

Crankshaft to Camshaft Ratio Modification

2. Camshaft Modification

In the six stroke engine 360 degree of the cam has been divided into 60 degree among the six-strokes. The exhaust cam has 2 lobes to the open exhaust valve at fourth stroke first exhaust stroke and the sixth stroke to push out the steam.

Camshaft Modification

3. Cam follower modification

The bottom shape of the regular follower has flat pattern which is the suitable with normal camshaft for four the stroke engine. When the reducing duration of the valve opening from 9000 to only 6000 shape of the follower must to be changed from flat to the roller or spherical the shape.


In this paper the modification required to the convert four-stroke conventional engine to the six stroke engine is the illustrated. The modifications are the gear ratio between crankshaft and the camshaft and modification of the camshaft. The previous efforts done on the six-stroke engines was applied by the using solenoid valves and a DC- motor to the start  engine in this research it is the proven that engine can work with the six-stroke engine by using the same conventional mechanical valve systems and the conventional engine the starter.

Follow by Email