On Mon, Jun 15, 1998 at 01:46:22PM +1000, Dennis Plunkett wrote: > 15/6/'98 > > So is water injection a black art? It would seem that all the links that > Clyde Smith-Stubbs gave point to aircraft bobing around at 10000 feet > (Things are quite different up there), as for Diesels, this is to reduce the Actually, often higher than 10,000. For example the P47C Thunderbolt had an 18 cylinder Pratt and Whitney turbosupercharged engine which developed 2000 horsepower, but optional water injection allowed short-term boost to 2300 horsepower at 27,000 feet. The The use of water injection with petrol engines seems to mainly be useful with turbo- or super-charging, and allows higher boost ratios to be used without causing detonation. So it's a means of getting more power, but it wouldn't help a normally-aspirated engine much, I suspect, and I can't see it would do anything for fuel economy. > emissions. Just form the users point of view, if you do an economy run > during the day and another at night which one is best and why (Its not I don't think it would make much difference. You might get slightly higher power output at night because the air is cooler, but that wouldn't alter the economy at all. Basically, for a given engine (or class of engine) you get power out (driving the wheels) directly proportional to the power in (as chemical energy from the fuel). The fuel economy of a car depends more on such factors as how fast you drive (air resistance increases as a power of the speed, I think it's the square theoretically, in practice it can be higher), how much energy you lose through braking, etc. Modern fuel-injection systems are very good at controlling the fuel-air mixture across variations in air temperature, pressure etc. so these things should have very little bearing on fuel economy. A carburetted engine controls the mixure less accurately, so warmer (less dense) air would result in a richer mixture, which might result in increased fuel consumption. -- Clyde Smith-Stubbs | HI-TECH Software Email: clyde@htsoft.com | Phone Fax WWW: http://www.htsoft.com/ | USA: (408) 490 2885 (408) 490 2885 PGP: finger clyde@htsoft.com | AUS: +61 7 3354 2411 +61 7 3354 2422 --------------------------------------------------------------------------- HI-TECH C: compiling the real world.