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Old 01-10-2014, 02:33 PM   #149 (permalink)
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It is good reasoning.

Originally Posted by P-hack View Post
Thanks for investing in a pressure spark plug Rusty (and bringing such a device to my awareness). Would love to see the experiment in any event and I enjoy thinking about this stuff in more detail than I had previously. I do have one other operational caveat to theorize though, P&G hypermilers already target bsfc, which is on the low side of rpm and the high side of load, where ignition timing is fairly close to tdcc. I don't see how hho will help peak bsfc(would hurt it a tiny bit actually), or help a driver who's operating the vehicle with bsfc in mind since there is minimal, if any, area under the curve left of tdcc under those conditions. Am I missing something there, or is that fair speculation? Gasoline engine assumed.
There is always some wasted pressure, but under certain conditions, these areas are minimized as you have pointed out. But, just as long as the RPM is low enough (ie, there is enough time ) there can exist, pre-combustion, some of the combustion products as found pre-detonation. Combustion is not a simple one step release of heat energy as many believe but a series of complex steps of endothermic decomposition and re-organization and then a final fall to the lowest entropy and the final exothermic release of the heat energy. That is why there is a flame front. And that flame front is robbed of some of it's energy to provide the energy to start the hydrocarbon oxidation decomposition and so forth. This explains why pure hydrogen has a flame front roughly an order of magnitude faster than hydrocarbons - it doesn't "waste time and energy" in side reactions since it is the simplest of oxidation examples as you can get. This is also one of the reasons HCCI engines, as mentioned before, can reach and exceed 50% thermal efficiency. The rapid oxidation across the entire combustion mixture means minimal energy losses to transfer heat across the "thermoclines". This is part of the irreversible combustion losses you often hear about. These losses can approach 20% of thermal potential depending on variables. Also, concentration of heat release around the classical 14 degree after top-dead-center results in maximum pressure build with minimal heat loss since the combustion chamber area is at a minimum.

The addition of HHO aids the decomposition of the classical fuel C8H18 by the fact that hydrogen needs relatively low energy to dissociate into H+ and to form OH radicals. These highly reactive radicals rob more hydrogen from the carbon chain to form HOOH radicals (very short lived) reducing the carbon chain to shorter and simpler chains such as C6H6 (benzene) down to C2H2 (acetylene). The release of hydrogen atoms is the first thing that happens in thermal decomposition of the carbon chain, but the fact that it is already present in the combustion mix accelerates the release in a domino effect. The results are not as dramatic as the HCCI combustion regimes, but with added enthalpy, our non-HCCI engines can reap some of the benefits in a small way with the addition of HHO.

This is all of course highly simplified to the point of being incorrect on some details, but it does drive home the point - in a gasoline engine, a small amount of HHO can tip a sub-critical detonation engine into faster more efficient combustion.
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