Increase horsepower with steam in piston gasoline engine?

[mikeholcombe]

In a gasoline piston engine, it seems that rather than waste energy out the exhaust, it would be better to inject a tiny bit of water during the expansion phase to produce steam that would raise the pressure against the piston and provide more power with the same amount of fuel.

 

[Baluncore]

Welcome to PF.

If there is spare capacity, would it not be easier to increase the compression ratio or the inlet boost pressure?

If not present during the combustion, to flash evaporate water part way through the expansion, you will need to inject that water as a mist. Will that evaporation not cool the combustion products and reduce the power?

 

[Lnewqban]

Welcome!

Please, see:
https://en.wikipedia.org/wiki/Water_injection_(engine)

 

[mikeholcombe]

As the combusted gas expands in the cylinder from its max temperature at top dead center, the pressure has decreased at 90 degrees of the power stroke because an increase in the volume of the combusted gas decreases the pressure of the gas. At that point, the injected water mist will further cool the combusted gas, but the steam produced by the injection of the mist of water would possibly increase the pressure. So, will the result be an increase or decrease in pressure? One must take into account that the heat to produce the steam comes not only from the hot gas, but also from the hot piston and cylinder walls of the engine. This could result in a total increase in gas pressure of the engine at that point in the combustion cycle. The question is does the production of steam increase or decrease the pressure in the cylinder.

 

[Averagesupernova]

Have you heard of the crower 6 stroke engine?

 

[Baluncore]

At that point, the injected water mist will further cool the combusted gas, but the steam produced by the injection of the mist of water would possibly increase the pressure. So, will the result be an increase or decrease in pressure?

A decrease, because the water requires energy to undergo a phase change from liquid to gas before it can expand. The combustion gasses will therefore be cooled more than the steam will increase.

Having more molecules in the final mix, will give greater pressure, but the water must be injected into the high pressure environment at a cost in energy.

 

[Bystander]

https://en.wikipedia.org/wiki/Water_injection_(engine)