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Old 06-12-2015, 07:16 PM   #1 (permalink)
Isaac Zackary
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Suzy - '13 Toyota Avalon Hybrid XLE
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Cooled EGR vs Water Injection vs Super Lean

So I'm increasing my CR from 7.5:1 to 9.5:1 in my 72 VW Bug. I'm going to try to use cooled EGR to control detonation for now. I'm making the valve so that it operates with the throttle so that it opens as much as the throttle valve does only it's about 10% the size of the throttle valve. I'm pulling it off further down the exhaust so that there's less pressure in an attempt to get around 10% to 15% EGR even at full throttle. I also have a fully adjustable digital CB Magnaspark distributor.

I was also contemplating water injection. But it seems WI usually decreases fuel economy. I suspect that it has to be finely metered on a gasoline engine in order to increase fuel economy.

One problem with both EGR and WI is that they can reduce fuel combustion increasing CO and HC emissions while decreasing fuel economy. One thought that I had was that if I used enough, then I could run lean, even at WOT. But that would likely cause even less fuel to actually burn, perhaps even causing misfires.

But then it ocured to me. EGR and water can be used because they are inert. An enriched AFR can also do the same thing since fuel without oxygen is inert and so boils off and lowers combustion temps. So why can't a very lean AFR be used. The excess air without fuel would be inert just like EGR only that a very lean AFR would provide more than enough oxygen for complete combustion. I've read where after a certain point (about a 16:1 AFR) combustion temps and NOx production are reduced dramatically. Since a gasoline engine can run on as low as an 18:1 AFR why not use that to reduce detonation? Of course that might not be enough, so it might have to be used along with water injection at WOT.

Any comments will be appreciated.

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