David Megginson writes: > For the record, I fly lean of peak, wide-open throttle regularly in cruise > -- my engine runs cooler, I burn a lot less gas to produce the same power > (about 8.5 gph instead of 10 gph), my spark plugs don't foul, and the risk > of CO poisoning virtually vanishes, so there's not much to dislike about it. >
>From a non-pilot engineer's point of view this makes perfect sense. At wide-open >throttle you've reduced the pumping losses, and by running lean of peak you increase >the engine's thermal efficiency. The key is not to go so lean that combustion >becomes unstable. This is effectively how diesel engines are controlled (without the >lean combustion stability limits inherent in homogenous-charge gasoline engines), and >is one of the reasons why they are more efficient than their gasoline cousins. >Diesels are much more popular in private cars in Europe than in the States - my wife >drives a small, 1.4litre diesel hatchback, and this is regarded as perfectly normal. >Of course, it's possible that my perception of the States as diesel-hating gasoline >guzzlers is out of date by now! The reason for the lack of lean-burn cruise in most current automotive gasoline engines is entirely due to emissions regulations. Of the three main pollutants legislated against, two (unburned hydrocarbons [HC] and CO) must be oxidised (to H2O and CO2) and one (NOx) must be reduced (to N2). Running the engine at a stoichiometric (just the correct amount of oxygen for complete combustion) air-fuel ratio and using a 3-way catalyst allows an order of magnitude reduction of these pollutants post catalyst. Running lean and trying to reduce NOx in an oxygen rich exhaust stream has been likened to drying one's washing in a rainstorm. An effective lean NOx trap is one of the 'holy grails' of aftertreatment engineering, and would probably allow an immediate reduction of at least 10% in fuel consumption from new gasoline engines calibrated for lean cruise if available, and probably more in the future since lean-burn stability would inevitably receive more design focus. I'm not entirely sure what the current and future legislative landscape looks like as far as general aviation is concerned - are you likely to face emissions regulations in the near future? I'm pretty sure they're starting on the bikers now. Cheers - Dave _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
