[Ken Fry]

Originally Posted by Olympiadis

Over and over I see far too many extremely knowledgeable and academically qualified individuals (perhaps armchair physicists) jump authoritatively into discussions concerning engine efficiency and the amount of fuel that is being burned during a given set of conditions in a running engine.

John Heywood, arguably the best known authority on automotive combustion is one such person. He not an arm chair kinda guy, but does real tests with real engines.

These instances pop up often in discussions concerning the ability of HHO to effect a change in engine efficiency or fuel mileage, where the supposed "debunker" points to research data showing that less than 1% of fuel remains unburned as tested before the catalytic converter.

The HHO promoter claim that prompts these rebuttals goes like this: "15% to 25% of the fuel in the combustion chamber goes right out the tailpipe. HHO improves combustion (acting like a catalyst or oxidizer) to burn all the fuel."

Of course the 15% to 25% figures are wrong. But equally wrong is the idea that HHO acts as an oxidizer in any meaningful sense. HHO, which is really 2H2 + O2, is a stoichiometric mixture that, when burned, offers no additional oxygen to the combustion mixture. The infinitesimally small amount of O2 is used up in burning the infinitesimally small amount of H2.

What counts is WHEN the fuel is burned.

And HHO has no effect on combustion rate, because the amounts used are far too small to have any effect at all.

A tuner can change the output (BSFC) of the engine drastically by simply changing the spark advance and keeping all other variables the same.
If you take the "debunker's" claims as absolute reasoning, then every engine tuner out there has somehow broken the law of conservation of energy.

Hard to know what you are trying to say here. First, given factory optimized timing, (which varies continuously under control of the ECU) a tuner cannot make "drastic" changes in either BSFC or output (which are not the same thing). There are no evil automotive engineers working to make you use more fuel. Companies spend many millions to tune for an optimized mix of fuel economy, drivability and performance. But the fact that you can make small changes in power output by altering timing has absolutely nothing to do with conservation of energy.

There are several ways to manipulate the burn-rate in the chamber, ranging from static/dynamic compression changes, fuel additives, cylinder head modifications, heat rejection rate, AFR, fuel additives, and more.
None of these violate any law of physics.

I have never seen anyone claim that any of these violate the laws of physics. Nor have I seen anyone claim that adding meaningful amounts of H2, O2 or a combination of the two would in some way violate laws of physics.

Perhaps you are confused by the often (and correctly) cited fact that no spark ignition engine car engine produces electrical energy from its alternator at better than 20% overall efficiency from fuel tank to alternator output. An ounce of gasoline consumed from the tank gives you 1/5 oz of energy equivalent at the alternator. So where the "conservation of energy" or "laws of thermodynamics" concepts come into the discussion is for those HHO promoters who claim that the H2, when burned, adds "power" or replaces fuel, etc. If this were true, in other words if the H2 energy output were equal to the additional fuel to power the alternator, then the electrolysis process would need to more than be 500% efficient which is impossible due to the universal applicability of the concepts mentioned.

I'm pretty sure that HHO is around 88% Oxygen by weight, making it a very formidable oxidizer, and theoretically very little HHO mass would be required to effect a change in burn rate at a low engine RPM and VE.

There is no theory that suggests this. First, HHO is not a "formidable oxidizer", even when employed in large quantities (e.g. 30 -100 times more than produced by an HHO unit). This is for the reason previously mentioned: there is no excess oxygen. But more important is the fact that even at low RPM and loads, the amount of HHO generated is not enough to have any measurable effect. One liter per minute of steam and oxyhydrogen is typical for a good HHO unit. Of this, 1/3 liter is O2. A 2 liter engine at 1/3 throttle and 1500 rpm takes in 500 liters of air per minute. Of that, 21% is O2, so figure 100 liters of oxygen per minute. Adding 1/3 liter of O2 to 100 liters will have no measurable effect, let alone the 30%, 50%, 75%, improvements mentioned in the adds. Even the EPA-certified $25,000/day dynos used for fuel economy measurements cannot measure such small changes reliably.

For any given combustion event a falling average RPM of 2000 RPM will have a much slower piston speed than a rising average RPM of 2000 RPM.
This is another one of those obscure facts that a tuner must know to be successful at matching burn-rate to piston speed.

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A "combustion event" in the usual parlance means one burn, taking place during the power stroke and lasting milliseconds. The ECU adapts very quickly, event by event, so that it makes little difference if the car is accelerating or pulling a constant rpm. When accelerating, the average piston speed changes almost imperceptible from one event to the next, because therre are only milliseconds between events. But during any given stroke, piston speed changes dramatically from 0 to max and back to 0.