Quote:
Originally Posted by mort
Hi drmiller100,
So traveling back in time...
OK, for some numbers, imagine a 2.5 liter Otto cycle at 1500 rpm cruise, the air consumed is about 625 l/m and the volume swept by the pistons is 1875 l/m. To eliminate pumping across the throttle requires 1250 l/m of steam. The saturated steam table says that at 100 C. we can just get to 1.7 l/g. That gives us 735 g/m. The mass of air, 625 l/m is about 590 g/m. The fuel consumption is about 40 g/m. Without testing I can tell that adding 18 times more water than fuel will prevent ignition. If you deliver only as much water as fuel ignition will be difficult, and at that point you only reduce pumping by about 5% Water injection systems used to cool high boost engines often start misfiring at about 20% of fuel flow.
Anybody with a big water tank can try it, but I'm not hopeful that reducing pumping is achievable.
Also on this:
Lower peak temperature reduces thermodynamic efficiency faster than it reduces heat loses through the cylinder walls. Higher compression ratios are more efficient, even though heat through the cylinder increases.
-mort
|
Hi Mort,
Again, THANK YOU. At least now I have some idea how to go about figuring out some of this stuff.
And not to pick nits, but now that I have your numbers, I'm seeing 1.2 grams per liter for air, and you look like you are calculating 1.2 liters per gram? Which obviously makes the numbers even worse.
An interesting thing to consider is we are not adding 14 times as much WATER - we are adding 14 times as much STEAM.
Steam is an inert gas, already vaporized, just like exhaust gas in EGR systems is an inert gas.
I don't understand why the extra water/vapor would hurt anything?
Also, FWIW, no one said this has to be a total loss system, and as you pointed out earlier, burning gasoline produces water.
The water tank might not be nearly as big as you are thinking!