It can't - hydrogen is an energy storage mechanism.

What it does allow us to do is use electricity, generated from coal or renewable resources, to power our cars.

 

Electrolysis is about 70% efficient, so right off the bat you're losing 30% of the energy.

Incorrect. In a modern engine, the fuel is almost completely burned (think high 90%). The 35% efficiency of a gasoline energy means that while the fuel is almost fully combusted, the remaining 65% of the energy is lost mostly through friction and heat in the exhaust and cooling system. So there's not a lot to be gained through improvements to the combustion process itself.

As to the Gazette's fuel economy test, pretty much any vehicle driven conservatively will surpass its Transport Canada mileage rating. Like the EPA's ratings, they apply a factor that makes them very conservative. Improving that Grand Cherokee's mileage by 10% is absolutely nothing to brag about.

 

How about the decrease in emissions? Is that theoretically possible by injecting the hydrogen? Even without the fuel savings, if the emissions decrease a lot it may still be worthwhile.

 

I don't see it. Modern engines have closed-loop systems that monitor oxygen content in the exhaust. So if an engine is running rich or lean enough to affect emissions, the computer will compensate by adjusting the mixture. Adding hydrogen will just cause the computer to back off the fuel to keep things in check.

In theory you can reduce carbon output to the extent that you're burning more pure hydrogen, but by the time you pay for the 50% efficiency of the alternator and the 70% efficiency of the electrolysis process, you're not gaining anything. It's similar to the oxygenated fuels many states mandate in the guise of improving emissions. While it might work on carbureted cars, a FI car will sense the additional oxygen in the exhaust stream and add more fuel. For all practical purposes, a modern gasoline engine is pretty much emissions-free once warmed up.

 

Bingo. In fact, hydrogen unfortunately tends to be worse for emissions, since its higher combustion temps lead to increased NOx production.

 

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Run away. It can't work any better than a perpetual motion machine can. If you use eight pounds of gasoline your engine emits about 120 pounds of carbon dioxide, nitrogen, and water vapor, and that's if it's burning cleanly.

Last I checked, CO2 is a Kyoto protocol emitted greenhouse gas.

 

I agree with this 100%. I think you can be put on life-support with the fumes coming from a modern Impala or FiveHundred. Seriously, there are studies that show the new cars have less toxic fumes than are found in common air in most cities.

To add to the heat/efficiency thing, I would like to add another case...
There are actually engines running today with all the friction-producing components made of ceramics (or coated with them in some cases).

I can't recall here at my desk, but the coefficients of thermal expansion for ceramics is orders of magnitude less than for steels. Since ceramics don't expand as much as steels or iron, they are more thermally stable and able to hold tighter tolerances across the range of temps seen by IC engines. By reducing the tolerances, you can actually make an IC engine that has no compression or oil-scraping rings - reducing the heat generated by friction tremendously. Add in ceramic bearings and cam components, and you can basically run the engine without oil or need for lubrication - external cooling becomes optional depending on the size of the engine, the # of cylinders, and their proximity to each other. I have seen and studied these engines back in the mid-90's, and their efficiency was far better than conventional steel and iron units because more of the heat was used in the process instead of being carried away by antifreeze and oil. These ceramic engines can run much hotter than conventional engines, especially ones using hypereutectic aluminum pistons. Emissions was also improved because (as the guys said above) the engine was able to burn hotter - burning out more of the NOx and *** components.

The problem was mass-producing the ceramic parts... the cost was exhorbitant, and at the time no major carmakers or engine companies could justify the expense of tooling for ceramic parts - much less modifying assembly lines to assemble them. Even today, I doubt the gain in efficiency is sufficient to offset the cost of developing the tooling and processing of the ceramic components alone. Think about all the aftermarket and downstream issues... from the original manufacture and handling to the tools in a mechanic's toolbox required to work on them. There's a lot to overcome.
Some of this technology has begun to make it's way into industry though - ceramic bearings is just one venue making large inroads into machine design today.

Interestingly enough, I still see the infrastructure change as THE major hurdle to finally killing the gasoline/diesel engines as we know them. For our nation to go Hydrogen, Fuel cell, or any other alternate fuel will take $Billion$ in private investments from companies and individuals, and it won't happen overnight. (Although I think the $3.50/gal prices we saw a few weeks ago got a few people's attention!)

Other alternatives to try to eliminate friction and wear found in the traditional reciprocating piston-type engine with rings include the Wankel or the Grunstra engines - and there are several more.

Bottom line is, the first technology to give the desired power output at a cost that competes with gas, and with a minimal amount of infrastructure investment - THAT will be the next fuel system for our vehicles. If any of us knew which fuel/system it would be, we would soon be VERY stinking wealthy!