How Does Gas Volume Change After Combustion in an Engine?

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Discussion Overview

The discussion revolves around the volume relationship between unburned air-gasoline mixtures and the resulting exhaust gases after combustion in an engine. Participants explore the implications of temperature and pressure on gas volume changes, considering both theoretical and experimental contexts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant inquires about the volume relationship between unburned and exhaust gases in a stoichiometric air-gasoline mixture at 1 bar pressure, emphasizing the importance of temperature.
  • Another participant questions the relevance of the initial inquiry, suggesting a need for clarity on its importance.
  • A different participant proposes that under quasi-static conditions, the volume ratio before and after combustion is approximately equal to the engine's compression ratio, but notes that this is a simplistic view.
  • One participant suggests that for accurate exhaust gas volume, factors like temperature, fuel type, and air-fuel ratio must be considered.
  • Another participant reiterates the question about the volume of ignited gases from a specific volume of stoichiometric mixture, proposing a lab test scenario for clarity.
  • A later reply suggests performing a mass balance and converting to volume based on the gas laws, indicating that the answer depends on specific conditions.

Areas of Agreement / Disagreement

Participants express differing views on the significance of the initial question and the methods to determine gas volumes after combustion. No consensus is reached on the volume relationship or the best approach to calculate it.

Contextual Notes

Participants highlight the need for specific conditions such as temperature and pressure, as well as the type of fuel used, which may affect the outcomes of their inquiries. The discussion remains open-ended with various assumptions and conditions not fully resolved.

CHICAGO
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Hi you all

Seaching in internet, I have not found an answer to this:

In a air-gasoline stechiometric mixture, what can be the volumen relationship between the unburned (intake gas) and final exhaust gases?.

I guess temperature is important, but let's consider a normal working temperature for that engine. And let's also consider the cylinder is filled at 1 bar.

I just only want to have an idea of how much the gas is expanded after combustion.

Thanks in advance.
 
Engineering news on Phys.org
may i ask why this is important?
 
Under quasi-static conditions, the ratio of volumes before and after combustion is approximately the compression ratio of the engine (since the volume is dictated by the geometry of the swept combustion chamber, not by the gases!). This is pretty meaningless. For an approximate "final" exhaust gas volume, just assume it's air at whatever temperature you're interested in. For an accurate "final" exhaust gas volume, you need to know the exact temperature, fuel type, and air-fuel ratio.
 
Brewnog ..you are good!
wish i said that...
 
I know what you mean, but I assume a volumen of air-gasoline stechiometric mixture at 1 bar pressure.What is the volumen at 1 bar pressure of the ignited result gases?.

We better forget this gas in a engine, and let's do the test in a lab. We have 1 cubic inch of that stech. mixture and we flame it. How many cubic inches of gas (whatever gases are those) do we get out of that combustion?

I do not know if I exposed the question properly. Sorry if it is not.

.
 
see Post titled gas pressure in internal combustion gasoline engine
in this forum a few days ago
 
CHICAGO said:
I know what you mean, but I assume a volumen of air-gasoline stechiometric mixture at 1 bar pressure.What is the volumen at 1 bar pressure of the ignited result gases?.

We better forget this gas in a engine, and let's do the test in a lab. We have 1 cubic inch of that stech. mixture and we flame it. How many cubic inches of gas (whatever gases are those) do we get out of that combustion?

I do not know if I exposed the question properly. Sorry if it is not.

.

It depends. Do a mass balance and then convert to volume at whatever temperature you're in. Just think back to the gas laws.
 

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