Increase horsepower with steam in piston gasoline engine?

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Discussion Overview

The discussion revolves around the concept of enhancing horsepower in gasoline piston engines by injecting water during the expansion phase to produce steam, potentially increasing pressure against the piston. The scope includes theoretical considerations, technical explanations, and exploratory reasoning regarding engine performance and efficiency.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that injecting a small amount of water during the expansion phase could produce steam, thereby increasing pressure and power without additional fuel.
  • Others question whether increasing the compression ratio or inlet boost pressure might be a more effective approach if spare capacity exists.
  • It is suggested that injecting water as a mist is necessary for effective evaporation, but this could cool the combustion products and potentially reduce power.
  • One participant discusses the dynamics of gas expansion and the potential effects of water injection on pressure, noting that the heat required to produce steam comes from both the combusted gas and the engine components.
  • Another participant argues that while steam could increase pressure, the energy required for the phase change of water from liquid to gas might lead to a net decrease in pressure due to cooling effects.
  • The mention of the Crower 6-stroke engine introduces an alternative concept related to engine design and efficiency.

Areas of Agreement / Disagreement

Participants express differing views on the effects of water injection on engine pressure and performance, with no consensus reached on whether it would ultimately increase or decrease pressure in the cylinder.

Contextual Notes

The discussion includes assumptions about the behavior of gases and the thermodynamics of water injection, but these assumptions are not universally accepted or resolved among participants.

mikeholcombe
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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.
 
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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?
 
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.
 
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Have you heard of the crower 6 stroke engine?
 
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mikeholcombe said:
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.
 
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