Nitrous oxide is known by several names - "nitrous", "spray", "the bottle" , "giggle juice", "laughing gas", "N-O-S" (just please dignify yourself and don't refer to it as "nawz") - but yet it's also perhaps the least understood piece of technology that is available to a modern hot rodder. Considering that it's one of the most economical ways to add 50% or more power to an internal combustion engine, this seems like a topic ripe for a technical discussion.
The Germans discovered the effects of nitrous oxide on internal combustion engines and applied it to their Luftwaffe fighters and bombers in the form of the GM-1 high-altitude performance system. Like so much of hot rodding's early days, nitrous resulted from the post-war "peace dividend", and savvy mechanics started using it for improved performance at the drag strip and during top-speed attempts on dry lake beds and salt flats. Its popularity has continued to rise since then, driven by a combination of its cost effectiveness, its compatibility with modern engines and engine controls, and of course, its mythology. Along the way, the technology has become ever easier to use, thanks to some dedicated vendors and a growing knowledge base in the high-performance world.
So, what is nitrous oxide? Simply stated, it's a compound consisting of two parts nitrogen and one part oxygen. At room temperature and atmospheric pressure, it's a gas, but it can be condensed to a liquid at 75 degrees F by applying approximately 780 PSI. When heated to approximately 570 degrees F, it will break down and release the oxygen, giving the resultant gas mixture an oxygen concentration of approximately 35%, compared to about 21% for atmospheric air. This gas is also denser than air, so the oxygen content by volume is more than twice that of the air we (and our engines) breathe. More oxygen equals more power - if it can be controlled. Since the potential for substance abuse is substantial, the stuff that's purchased at the local speed shop includes a small amount of noxious sulfur dioxide. This has no effect on an engine, but will quickly deter any deadheads who are looking for a cheap buzz.
Not only does nitrous oxide bring along extra oxygen, but the evaporative cooling effects of the liquid-gas conversion (nitrous boils at -128 degrees F) also drops the temperature and thus increases the density of any atmospheric air in the engine's induction path. This often referred to as "chemical intercooling", and while the nomenclature may not be all that accurate, the effect itself makes nitrous oxide a great companion for high-compression naturally-aspirated engines, forced-induction powerplants, and diesels. The combination of these two effects can bring an theoretical power increase of over 100%, although this is rarely achieved in practice for a variety of reasons.
In our next post, we'll take more of an in-depth look at the hardware and control strategies that are required to safely and effectively implement nitrous oxide in a typical gasoline internal combustion engine application.