
NEWTON, Ask A Scientist!

Name: Jacob
Status: student
Grade: 9-12
Location: TN
Country: USA
Date: Fall 2011

I am trying to figure out several things: 1) How many O2 molecules could fit into 1 psi? 2) How many psi could a 3in thick 4 cubic feet steel container safely hold? 3) How much would that weigh? You may of guessed what I am getting at: an O2 tank in cars to promote complete combustion. My idea has been discouraged, but without proof as to why.

Hi Jacob,

Your first question "1) How many O2 molecules could fit into 1 psi?" is not logical. "PSI" is a unit of pressure, and molecules do not fit into a "pressure". There is no possible answer.

What IS possible to determine is "how many 02 molecules does a container of a given size, and pressurized to a given pressure, contain". First, understand that 1 Mole of O2 (that is, a mere 16 grams) contains 6.022 x 10^22 molecules of this gas. This is an unimaginatively HUGE number! From there, it would be possible to figure out how many O2 molecules would fit in your 4 cubic foot container, if you knew the pressure. But as you will see below, to use any of this in the field of automotive combustion, is unfortunately quite pointless.

Your second question, "2) How many psi could a 3in thick 4 cubic feet steel container safely hold" cannot be answered without a lot more detail from you. The cubic volume isn't enough, because the container could be round or square, long and skinny or short and fat. All of these have a huge bearing on a container's ability to withstand pressure. One thing for sure: such a container would be extremely heavy!

Your third question "3) How much would that weigh?" is likewise impossible to answer without the actual dimensions.

But stepping back and looking at the big picture, I can say that a 4 cubic foot container pressurized to even extreme pressures (say, 10,000 psi), and supplying oxygen to a car engine instead of air, will not even get the car to the end of the block! Engines use a LOT of oxygen!

It is also important to understand that supplying an engine with pure oxygen will NOT promote more complete combustion. Today's cars, with their modern fuel injection systems, and their use of O2 sensors in the exhaust to feed back combustion data to the fuel injection computer, already burn their gasoline almost perfectly, with almost nothing but water vapor and CO2 emerging from the exhaust. To illustrate this, a modern car when operating in smoggy conditions, has such complete combustion that it actually has LESS pollution in its exhaust, than in the surrounding (smoggy) air! Regards,

Bob Wilson

Click here to return to the Engineering Archives



Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory