# Gas expansion in a engine

1. Nov 25, 2009

### CHICAGO

Hi you all

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 lets consider a normal working temperature for that engine. And lets 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.

2. Nov 25, 2009

### Ranger Mike

may i ask why this is important?

3. Nov 25, 2009

### brewnog

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.

4. Nov 25, 2009

### Ranger Mike

Brewnog ..you are good!!!
wish i said that...

5. Nov 25, 2009

### CHICAGO

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 lets 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.

.

6. Nov 25, 2009

### Ranger Mike

see Post titled gas pressure in internal combustion gasoline engine
in this forum a few days ago

7. Nov 25, 2009

### brewnog

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