Fire Piston

## Rationale for this lesson

Learn useful fluid mechanics knowledge.
Learn how engineers approach design.
Have fun ==> fire pistons are cool!

## The fire piston

Fire piston: A piston/cylinder that uses compression ignition to ignite paper or other materials.

Resources:

• Buy a fire piston at Amazon
• Many website explain how to build. Here is an explanation on YouTube
• You can find many other websites that give useful information.

Applications. The ideas of the fire piston show up in many engineered products. For example

• refrigeration system work based on expansion (cooling) and compression (heating) of fluids.
• diesel engines use compression ignition
• air compressors require cooling (because the compression of gas causes the gas to heat up).

## How Engineers Approach The Design Process

A smart person with no engineering training can easily design and build a FP.

An engineer would do everything a smart layperson would do, but would approach the problem

• apply a math model to predict what will happen; to understand cause and effect
• take data on the experiment (experimental validation)
• understanding ==> why, ….

## Math Modeling

Math model = one or more equations that can be used to predict or explain occurrences in the physical world.

Math model of a fire piston ==> 2 Eqns ==>

• IGL
• Eqn. for a polytropic process

Let's start building knowledge for math modeling

## Units for Pressure

pressure is ratio of normal force of a fluid to area at a point

3 categories of units

• force/area: Pa, psi, pst
• height of a fluid column
• atmospheric pressure: atm, bar

Pressure values to memorize
1 atm = 101.3 kPa = 1.013 bar = 14.7 psi = 10.3 m (33.9 ft) of water = 760 mm (29.92 in) of mercury

## Gage Pressure, Absolute Pressure, and Vacuum Pressure

• p_abs = p_atm + p_gage (Eq. 3.3a)
• p_abs = p_atm - p_vacuum (3.3b)

## Why gas gets hot?

macroscopic description: explain w/o resorting to molecules
microscopic description: explain based on what the molecules are doing

## Temperature Units

Kelvin & Celsius
Ranking and Fahrenheit

## SWBOT

• list three categories of pressure
• covert pressure units
• convert between gage and absolute pressure
• explain what macroscopic and microscopic mean
• convert temperature units (K, deg-C, deg-F, Rankine)
• carry and cancel units using the ideal gas law
• define a mole, a lbm-mole, and a kg-mole
• define an ideal gas
• apply 3 forms of IGL in traditional and SI units
• apply the IGL to relevant calculations