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Hi Gord,
Not so much on us automotive engineers today... A lot of modern automotive engines are run right along the knock limit for efficiency, with knock control constantly operating. To do this, there has to be a knock event every now and then for the knock control to be able to detect the limit. (Knock control just detects knock events and retards the ignition. When there is no knock, ignition is advanced again until the next knock occurs.) This normally works fine. However on some (not all) engine types, on high load testbed runs this has recently led to very rare statistical occurence of "super-knock" events, with disastrous results. Yes, that's quite interesting to me, and it backs my opinion of using low test fuel in my cars...I never use high test fuel at all, mind you, I only use standard domestic vehicles but I consider high test wasteful in modern engines with 'knock control'. Well, it depends... Normally you won't damage an engine with knock control by using lower grade fuel than recommended, however within limits. If you use very low octane fuel on a high compression or a turbocharged engine, ignition might occur before the spark just from the compression, as we discussed. There is nothing knock control can do about that. Also, depending on your driving profile, you might find that fuel consumption increases with the lower grade fuel, as retarded ignition reduces engine efficiency. This is especially valid at high engine loads and low engine speed, where the biggest retard is neccessary. Wether the increase in consumption will eat up the price advantage of the lower grade can only be determined by experiment. Yes, I understand that, another good system that GAMI is looking at is their accurate fuel injectors to enable automobile engines to be run lean. Now that is a new one to me! I know about GAMIs injectors for GA piston engines and all the LOP-operation stuff, wich are around for a while now, and which I think are a big improvement. I didn't know that they are planning on entering the automotive market and I'm quite surprised. Automotive engines, different from aviation, run stoechiometric basically anywhere on the map exept full load. (stoechiometric mixture is more or less peak EGT). Due to their design, mostly liquid cooled, temperatures are not a problem. Of course you could run such an engine lean (LOP), but you won't pass any emissions test for sure. I don't think you really need special injectors to do it, but you would need to retune the ECU. And the fuel savings compared to running stoechiometric are only a fraction of what you save if otherwise you have to run rich. The Japanese car makers had lean running engines on the market for a while, and some of the direct injection gaoline engines being developed now also run lean by creating a stratified charge. But that's far beyond an aftermarket improvement. We run (perhaps ran might be more accurate) large recip aircraft engines at '10% lean from best power' (by manually leaning them during cruise) for many thousands of hours and they worked fine in that condition, matter of fact they'll continue to run fine as much as about 30% lean before they get unstable, they seem to love lean mixtures!... Do you by chance know whether these had direct injection (injecting the fuel into the cylinder instead of the manifold)? To my knowledge there have been direct injection piston engines among the big radials, but I haven't found any further information about it so far. regards, Friedrich -- for personal email please remove "entfernen" from my adress |
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