# What equation would be used to estimate the temperature?

1. Jan 26, 2004

### jlmac2001

Can someone help me get started on this question?:

In a Diesel engine, atmospheric air is quickly compressed to about 1/20 of its original volume. Estimate the temperature of the air after compresion and explain why a Diesel engine does not require spark plugs.

What equation would be used to estimate the temperature?

2. Jan 26, 2004

### chroot

Staff Emeritus
Use the adiabatic condition $\left(PV^\gamma = \textit{constant}\right)$ to find the pressure in the cylinder after the volume has been reduced to 1/20 of its initial volume.

Next, use the ideal gas law $\left(PV = nRT\right)$ to calculate the temperature.

- Warren

3. Jan 27, 2004

### turin

chroot, how do you know it's adiabatic? Is this an approximation? I don't see how heat is prevented from transfer to the cylinder wall.

4. Jan 27, 2004

### chroot

Staff Emeritus
The key word is "quickly." Given that the compression happens quickly, not enough time is available for significant heat transfer to occur.

- Warren

5. Jan 28, 2004

### turin

Thanks chroot. That's exactly the kind of clarification I was looking for, and it makes sense to me now.