6 Stroke Engine

[c0re]

I've recently become interested in the idea of injecting water into an engine in order to improve efficiency.

The 6 stroke engine cycle is effectively a 4 cycle engine with 2 added strokes: water injection and an steam exhaust stroke. The theory is of course that the water is converted to steam in endothermic process that will create an increase in pressure. This would have three effects:

1. Turning waste heat from the Otto cycle used in a 4 cycle engine into useful work, thus substantially increasing efficiency
2. Increasing peak power output of an engine due to there being 2 power strokes of six rather than one power stroke of 4
3. Eliminating the need for a cooling system

Now I'd say that designing and building a 6 stroke engine would certainly be beyond the scope of what an average person can do as whole new cams need to be designed, high pressure water injection systems must be installed in the head and the ECM software would need to be completely revamped.

That said, what do you guys think about this cycle? It seems to me that it would be a very impressive way to recover a large portion of energy that otherwise gets wasted in the Otto cycle and tossed out through the radiator. Don't forget that most engines are around 20% efficient so most of the difference is tossed.

[NeilBlanchard]

Welcome to EcoModder!

This has been done, and there is a thread here:

http://ecomodder.com/forum/showthrea...roke-3960.html

[t vago]

Eh...

Roughly speaking, in order to raise the temperature of one gram of liquid water by 1 degree C, you'd need the same amount of heat energy that would otherwise heat up 1 gram of air by 4 degrees C. Worse yet, turning that 1 gram of liquid water into steam, would require the same amount of heat energy that would otherwise heat up 1 gram of air by 2200 degrees C.

Now, whenever you raise the temperature of air inside a cylinder, pressure will increase. The same effect is observed when temperature of air is lowered inside the cylinder - its pressure will decrease.

Now, estimating that at the end of the power stroke, the exhaust gas temperature is at 600 C at a pressure of 3 atm, then if you were to inject any liquid water whatsoever into that cylinder, the air temperature inside that cylinder would immediately drop as the heat energy of the air transfers into the injected liquid water. This will cause pressure inside the cylinder to drop as well, which is counterproductive to the stated goal.

[Piwoslaw]

I'd think the 6-stroke engine would be easier to implement when the camshaft is replaced by an electrically actuated valve opening system. That way swithing between 4- and 6-stroke would be easy - just a few lines of programming in the ECU. Why would you want an efficient 6-stroker to work as a 4-stroker? Think: Warm-up times. Start the engine in 4-stroke mode and use the extra waste heat to bring it up to temp, then go into 6-stroke mode.