21SE05
First, Eric- I agree completely. We could cut the oil consumption of cars and light trucks in half with today's technology. i.e. Double fuel economy. No sweat. But we can't do it while driving Tahoe's, Durango, Expeditions, and Land Bruisers... For me, step one is diesel. Instant 30% improvement with no sacrifice or downside for Joe American. Europe is now 50%+, US is <1%. I can tell you diesels are finally coming to the States. The fuel will be 30ppm sulfer I think in '06 or was it '07. That allows the diesel catalysts to live. Get ready for a gradual 20 year roll-in to reach 40 or 50% penetration. I don't know anything special about fuel cells, but I'm optimistic they will eventually make them economical. They've only scratched the surface compared to the millions and millions of man-hours invested in getting IC engines to work well.

Andrew- good guestion. You're making think, which has it's pro's and con's most days. Wish I could draw you a P-V Diagram. (Pressure vs Volume as a four stroke completes one cycle) Pulling the connectors on four injectors would certainly make things worse. The throttle blade would be open a bit more, as on a deac engine, but the non-firing cylinders would be wasting more energy pulling air in against the manifold vacuum and then pushing it out against the exhaust back pressure. It's a loser in both directions. These losses would be worse than the slight gain in the firing cylinders.

If you've heard it said that an engine is just a big air pump- well, that may be true but it's sure an inefficient one cuz the first thing you come to is a nearly closed off throttle valve. At highway cruise it's only open 10%. 90% blocked off, which is proven by the huge vacuum in the manifold. My 914 pulled 14.5psi vacuum at idle when I tested it this fall. That's a measure of how inefficient a motor is, not the opposite. One of the reasons diesels are more efficient is because they don't need a throttle valve, so there's no vacuum in the manifold. i.e., it's very easy for the pistions to suck in the next gulp of air. So, controlling a gas engine by throttling the air (both at the throttle valve and at the intake valves- don't forget) is inherently worse than controlling a diesel by the amount of fuel injected.

Charge density helps but it's not more efficient, it just has more air and fuel cuz it's denser. That's why intercoolers help. Cool air is denser (more) air, to which it's easy to add a smidge of extra fuel, and so get more power. Remember, you need to stay very close to the optimal 14.7:1 ratio. Burn rate and burn completion is mostly due to fuel atomization (droplet size), and local air/fuel ratio (how homogenious is it in there really?) and the degree of turbulence created by the intake velocity and direction and the shape of the upwardly rushing piston against the chamber shape.

Time to put the cookie-munchers to bed.
Jim N.