Comments on: They never met a fuel catalyst they didn't like

by: Daniel Rutter

Fri, 13 Feb 2009 11:28:48 +0000

Here, by the way, is another salutary recent example of picking the lab that'll give you the results you want. (See also The Goodies: Tim: "Nine out of every ten doctors agree that people who don't eat Sunbeam sliced bread will get squashed by elephants!?" Graeme: "That's right. Mind you, it did take us a long time to find the right nine doctors [makes "loony" gesture]. And the elephants.")

by: Tony (fuelsaving)

Sat, 31 Jan 2009 05:57:52 +0000

Actually, this isn't quite as stupid as it sounds. A significant cause of efficiency loss in gasoline (but not diesel) engines is the "pumping loss" caused by sucking intake air through a partially-closed throttle. You get a pressure drop of maybe 400 mbar (12" Hg) and the energy is just lost. If you can eliminate this, you can maybe save 5 - 10% of fuel used. BMW's Valvetronic engines pretty much eliminate pumping loss by fancy intake valve timing; lean-burn engines reduce it by opening the throttle (less pressure drop) and running with much more air per unit of fuel, but this does give very high NOx emissions. In theory I guess it is true that if you can greatly heat the intake air - maybe via a heat exchanger with the exhaust - you can also significantly cut pumping losses by making the same mass of air take up a lot more volume, so again you can open the throttle up more at part load. So maybe you really could save 5 - 10% of fuel in this way (though 30% is beyond credibility, except at idle). But (there is always a but)...this is only helpful at part load. As soon as you put your foot down, it's essential to get cold air again or performance will be crippled. Especially important is to get the air cold quickly, or else the "throttle response" will be terrible. It will be interesting to see some more details, when they appear (the cited patents only seem to cover fuel vaporisation, not air heating).

by: phrantic

Fri, 30 Jan 2009 16:45:16 +0000

This, gentlemen (presumably) is why Dan needs forums on his site.

by: Rob L

Fri, 30 Jan 2009 12:47:01 +0000

Does not necessarily involve autoignition/preignition, correct. You can have knock from spark ignition, can you not?

by: TwoHedWlf

Fri, 30 Jan 2009 12:28:43 +0000

So, what you're saying is that detonation does not involve ignition?

by: Rob L

Fri, 30 Jan 2009 09:57:41 +0000

Nope, two seperate issues.
Autoignition starts the fuel/air mixture burning, important word being *burn*
Detonation is exactly that, fuel/air mixture *explodes* =>high pressure rise rates, supersonic shockwaves in cylinders and associated nastiness.
You can have knock without autoignition and autoignition without knock.

by: TwoHedWlf

Fri, 30 Jan 2009 05:06:03 +0000

Or, I suppose I should say detonation/knock is usually autoignition...Damnit, I just pedanticed myself!:(

by: TwoHedWlf

Fri, 30 Jan 2009 04:55:52 +0000

Just because I like to be pedantic sometimes... Rob, Detonation/knock is autoignition.

But autoignition isn't necessarily detonation/knock. :P

by: Rob L

Thu, 29 Jan 2009 09:25:16 +0000

There's nothing fundamentally wrong with autoignition before TDC, the fuel needs to be burning before TDC to get nice high cylinder pressures for a hefty expansion stroke. Spark advance can run significantly before TDC, 30 degrees or more.

It's also plainly ridiculous to target diesel like economy in a petrol engine, there's a significant difference in energy density between the two fuels, you simply get more bang/kg of diesel fuel. That's without even getting into the efficiency of running a much higher compression ratio in a diseasel.

These fuel gizmos are hilariously depressing, or depressingly hilarious...

by: Rob L

Thu, 29 Jan 2009 08:29:36 +0000

Shame on you dan for saying "detonation/knock" is the same as "autoignition" http://en.wikipedia.org/wiki/Engine_knocking

Diesels DO autoignite as part of normal operation, but they can also knock/ping/detonate which is abnormal and potentially destructive.