September 2010 Issue 102

by Colin Fisher

In the past, this column has addressed “air” and “water”; the subject for this month is “fire.” Certainly, man’s ability to make and use fire has contributed greatly to the success of our kind for over hundreds of thousands of years.

What is fire? Fire is a high temperature gas that, in a wood fire for example, is sufficiently hot enough to heat its fuel to a temperature that causes more combustible gas to be released from the burning wood. The combustible gas is a hydrocarbon that, upon burning, produces tiny “soot” particles of carbon that are heated to an incandescent temperature whereupon they radiate a yellow or orange light, giving the flame its characteristic color. The radiant heat that we feel coming from the flame is principally radiant heat transfer from these incandescent carbon particles.

An open fire, such as with wood or paper, has no shortage of air available; there is actually a surplus of air compared with that required for complete combustion. In a gas appliance, such as a furnace or stovetop, the amount of air that mixes with the gas is adjustable so that a proper flame may be obtained. A proper flame has a high temperature, produces little or no soot and, more importantly, produces little or no carbon monoxide, a poisonous gas.

The design of internal combustion engines, including your car both petrol and diesel as well as the gas turbines that generate electrical power and propel your jetliner, all have a flame produced somewhere in the engine when it is operating. The engineers who design these engines spend quite a bit of their time studying the flames produced in test model engines. The flames are evaluated for temperature, pressure and the timing of the flame relative to the other moving parts of an engine. These studies are used to optimize the design for economy, smoothness of operation and durability of metal parts that may be exposed to the flames. It is not surprising that the two automotive companies that also design and manufacture motorcycles, where optimum performance is required, also produce automobiles that are outstanding for their performance (BMW and Honda).

Then there is gunpowder. When a cartridge in a firearm is fired, the speed of burning of the powder has a large effect on the performance of the gun. The gunpowder we use today is quite slow-burning in comparison with the old “black powder” of antiquity. If the gunpowder used today were to burn too rapidly, it would destroy the gun before there was time for the bullet to be accelerated up to the design muzzle velocity. Then the owner would be a “one-shot Charlie.”

An important application of fire is that used by your electrical utility company to produce the electricity that we all depend upon for the “modern life.” In recent times there has been research programs aimed at reducing the pollution caused by these power plants, especially those burning coal. To date, most of these programs have not gotten beyond the use of “scrubbers” to remove particulate from the stack gas of power plants.

There has been much talk of “sequestering carbon dioxide” in the effluent of these furnaces. Sequestering includes storing it underground in impervious geological deposits. So far, none of these programs has been very promising. Coal from many sources in the world contains radioactive uranium and thorium as well as mercury. These are important environmental pollutants. A typical coal-fired power plant in the USA will emit more radioactivity than any normal nuclear power station. The world’s oceans and fresh water lakes are producing fish that contain high levels of mercury.

Perhaps, we have flamed out!

© Colin Fisher, 2009

This entry was posted by cfisher on Sunday, November 1st, 2009 at 12:00 am and is filed under Science Stuff. You can be notified of any comments on this entry through the RSS 2.0 feed. You can leave a comment in the box at the bottom of the post.

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