Keith Addison wrote:
>People keep talking about and writing about and asking me about and
>offering me H2 generators for gasoline engines, and making wondrous
>claims for their effectiveness, eg:
>
>
>
>> On my 92 Ford F-150 with the 5.0 ( 302 CU ) engine, the truck at it's best
>> mileage without the H2 generator was 17.9 mpg. with the 1st H2gen it went
>> to 22.5 miles and modifying it I was getting 25 mpg.
>>
>>
While this sounds like a reasonable improvement, I have doubts about
H2 boost working to that degree on a computer-controlled, fuel-injected
engine. (My Ranger is a 1993, and I installed a custom-built computer
that replaced the factory one when I put the supercharger on. The
process of learning how to tune the engine gave me DEEP respect for the
Ford engineers!) Zeke mentioned that there isn't a lot of room for
improvement in terms of unburned fuel in a modern engine, and he's got a
good point.
Sir Harry Ricardo experimented with this sort of thing long ago and
DID improve the combustion characteristics of engines using H2 boost,
but he was using carbureted engines that lacked the O2 feedback
mechanism that's characteristic of modern fuel management systems. The
people who are touting this sort of thing are certainly standing on the
shoulders of a giant (Sir Ricardo was a very intelligent man!), but I'm
confident most of them lack his engineering credentials and the rigor of
his measurement methods.
>Are they deluded? Or does strapping a couple of magnets to the fuel
>line also turn out to work?
>
>
Think of the engine fuel like a big block of wood. It will
certainly burn, but it will ignite better if you douse it in gasoline
first. Hydrogen has extremely low flammability limits and ignites
easily. The idea behind H2 boost is that it will ignite the air / fuel
charge faster. Since 90% of engine power is produced in the first third
of engine stroke (I may be incorrect about the percentage, but it is
certainly the majority), H2 boost is theorized to move more of the
combustion energy into the first third of the engine stroke.
Does that work? Perhaps, but I'm skeptical. The fuel pressure in
my truck's injection system is high enough that whatever gasoline is
injected should be well atomized when it enters the intake manifold.
Combustion is a very dynamic process, yet even with the onboard computer
monitoring air / fuel ratio and O2 in the exhaust several times per
second, a catalytic converter is still necessary to clean up the exhaust.
Here's why:
Let's pretend I'm sitting at a light in my truck, waiting for it to
change. The injection pulses at that point are very brief--almost to
the extent that the injectors themselves barely open fully. In order to
keep the engine idling, the onboard computer has been programmed to run
it slightly rich (13.8 - 14: 1 air to fuel) so that it won't stall.
Because there is no load on the engine, a very small portion of the fuel
injected into the manifold will condense on the metal surfaces while it
waits for the intake valve to open. If the percentage of fuel to air
exceeds what is programmed, the feedback loop I've programmed in to the
computer will shorten the injection pulses. This happens constantly,
but there is still a tiny portion of unburned fuel that still has to be
cleaned up when it leaves the engine.
Now, when I crack open the throttle to move, there's an acceleration
enrichment algorithm that kicks in according to manifold vacuum and
throttle position. In order to maximize power, it runs the engine a wee
bit rich. Some of that fuel will escape without being burned, and it's
oxidized in the catalytic converter. If I move into boost because I'm
carrying a load or climbing a hill, the fuel map is programmed to
sustain a 12.5 - 13:1 air / fuel ratio so that I won't burn a valve
under high load from a lean condition. (My exhaust header gets red hot
after being under boost for a few minutes!) Of course, not all of that
fuel is going to burn, and that's why I've got to have a catalytic
converter.
When I start coasting downhill and there is no load on the engine,
the injectors shut off completely as long as the rpms remain about 1 200
or so. Under those circumstances, I'm not burning any fuel at all!
So the idea of H2 boost seems like it might address those situations
(like idle and acceleration) where an excess of fuel exists in the
system. Perhaps it does. But the vast majority of my driving occurs at
cruise, where the onboard computer does an excellent job of keeping the
air / fuel ratio stoichometric. The fact that even with a supercharger
installed and well over 230 000 km on the engine, it still easily passes
the semi-annual emissions test here in BC, testifies that the system
works well. It MIGHT improve under certain conditions with H2 boost,
but the constant drag induced by load on the alternator to drive an
onboard electrolyzer represents a loss that must be made up by burning
fuel. (This is one reason why my fuel economy is slightly worse with
the supercharger installed.) So, do these homemade units work? They
might, but anyone who has shelled out money for the plans would have a
fairly strong incentive to see an improvement. I'd like to see a more
rigorous testing regimen before I affirm its efficacy.
robert luis rabello
"The Edge of Justice"
"The Long Journey"
New Adventure for Your Mind
http://www.newadventure.ca
Ranger Supercharger Project Page
http://www.members.shaw.ca/rabello/
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