> Anyone know what this is about?
I doubt any of us here is chemist-enough to fully understand it.
Straight Nitrogen is pretty inert.
But the PR says "Nitrogen is a key element of the active cleaning molecule.."... it's not just straight Nitrogen (would not stay in the liquid anyway).
Nitrogen compounds run from NOx which irritate the lungs, to Ammonia NH3 which is good for cleaning glass, also tobacco stain, to ammonium nitrate NH4NO3 which aside from being good fertilizer can be used in a formula to "clean" rock and buildings (coal-mining, Oklahoma City bomb).
So where did they stick that N? Is it an actual change in engine fuel? Or did the PR department take a small riff and blow it up into a fugue?
One particular point: Pure Nitrogen is quite inert at normal temperature but DOES get active at high temperature, and specifically at engine combustion temperature. The "NOx" in your smog-ticket is just atmospheric N and O plus about 1,400 deg heat. Since NOx was a major problem in Los Angeles circa 1960, engine controls seek to limit peak combustion temperature. Even though a heat-engine should peak as hot as the pistons can stand, NOx production limits what we can accept. Conversely, maybe Shell has found an N-molecule which is passive until it meets the combustion.
> I wonder what it will do to older car engines and cats
Not real worried. Surely Shell chemists (some of the world's best) know what they are doing. Shell would not offer it so generally if there was risk of real harm.
"tested ... more than a half-million miles ... newer vehicles with low mileage, and older vehicles with high mileage."
> i just think it's another marketing gimmick really.
Yes. You take a little feature like olive-oil coupling-caps, and blow it up into an Audio Revolution. Hey, most products ARE awful dull, change little from one year to the next. Those PR guys have to find excitement where they can.
> I've never actually seen an engine with those crazy carbon deposits
I have. But I've never seen enough carbon in the chamber to increase compression ratio significantly, although that was a problem in the 1920s. You can have a flake of carbon initiate pinging; but with modern fuels on older engines, a few full-bore bursts usually burns it off. Never seen so much carbon on a valve that it would reduce airflow. I sure have seen 1960s engines so full of OIL sludge that they had major problems... but that's not really a gasoline thing.
Apparently it can happen that fuel injectors lose capacity. On any modern ECU car, up to a point, this is corrected by the ECU applying longer injection pulses to get a happy tailpipe mix. When the nozzle gets real-clogged, the ECU can't make happy-mix at full throttle high RPM... then it will set the Check Engine light and you will fail your next smog-inspection.
But seems to me that clogged injectors are the Gas Company's Problem. Actually the way they make gasoline now the stuff is probably very-very-clean at the refinery. But crud sneaks in throughout the distribution process. Heck, I've seen used oil poured into the gasoline tanks; even done it myself. So gasoline company detergents are self-defense against their own distribution problems.
I would not cross the street to buy, or not-buy, Shell.
I do try to buy where the station appears to be tightly controlled by a major oil company. Sloppy dirty may be a little more likely at the no-name stations.