Dear Tom and Ray:

Is there any merit to the claim that nitrogen in gasoline has any benefit for cleaning the engine? What's the chemistry behind it? Or is this just the latest gasoline-additive scam?

-- David

TOM: Hmm. Maybe they're trying to get rid of all that excess nitrogen that they couldn't talk people into buying and using in their tires?

RAY: You're asking about Shell Oil Company's latest campaign, David, in which it claims that its gasoline is "nitrogen enhanced." And like most of the "enhancement" offers that come via e-mail these days, David, this claim probably should be ignored.

TOM: Shell claims that its new nitrogen-enhanced gasoline keeps your engine cleaner.

RAY: Here's the story. Every gasoline is required to use a certain minimum amount of deposit-control additive -- which does help keep deposits from forming on your valves and other engine components. All of these additives contain small amounts of nitrogen.

TOM: But nitrogen is only one of several ingredients in these cleaning additives. So my guess is, Shell has increased the amount of cleaning additive in its gasoline, which has "enhanced" the nitrogen component.

RAY: And more cleaning additive is good. I mean, why not? It's such a small amount of nitrogen, compared with the volume of gasoline, that it doesn't affect the amount of nitrous oxides that come out of the tailpipe. And if your engine runs cleaner, that's all the better.

TOM: But what the claim "nitrogen-enhanced" doesn't tell you is how much additive the gasoline had in the first place, and how much it has now. Maybe Shell used to add the absolute minimum necessary? Maybe it already was good, and got better? There's no way for us to know, as these are trade secrets. And by claiming its gasoline is enhanced, all we know is Shell is using more now than it was before.

RAY: Right. It would be like me and my brother claiming that our newspaper column is now "enhanced with right answers." It could mean that we really are trying harder and putting more time into answering each question. Or it could mean that we've enhanced the column to the point that we now get at least one answer right a year.