Hydrogen

I read about this too - very interesting technology. Everybody else is trying to figure out how to make the engine burn hydrogen exclusively, which is dependent upon a national hydrogen infrastructure. I like the incremental steps taken by this company - just supply a small water tank for electrolysis and then suppliment the air/fuel mixture with the resulting hyrdogen for a nice MPG benefit along with better emissions. I would like to see this feature become standard on new vehicles.

 

It might improve emissions, but it certainly won't improve mpg.

Electricity -> Motor -> Wheels

is always going to be waaaay more efficient than....

Electricity -> Hydrogen by electrolysis -> Combustion in ICE engine -> Wheels and generator

Electrolysis will be about 70% efficient, and combustion in the ICE at best about 30% efficient, so you start with 100 units of energy and you end up with about 20. 80% of the electrical energy you started with has been frittered away when it could have been used assisting directly.

 

The point seems to be that a very small amount of hydrogen improves the combustion efficiency of diesel. Less black smoke coming out the back means more of the fuel is being burned. But this seems to be specific to diesel engines. To be practical on gas engines, the efficiency gained would have to outweigh the cost of the added components.

 

If a very small amount of hydrogen improves the combustion efficiency of diesel, how does that efficiency compare to the efficiency gain of applying the electricity through an electric motor to drive the wheels?

In the end analysis [Energy In] * [Efficiency] = [Energy Out]

I don't know the answer but, as a mechanical engineer, I'm inclined to agree with Clet's MPG conclusion.

 

I've caught myself apparently violating the law of conservation and want to clarify.
[Energy In] and [Energy Out] refer to useful energy.
The equation

[Energy In] * [Efficiency] = [Energy Out] + [Energy Lost to Entropy]

 

Internal-combustion engines are not very efficient at all. There is so much room for improvement that some counter-intuitive measures can produce remarkable results.

Example: At slow vehicle speeds the Prius runs its engine faster (closer to design rpm) than other cars, turning MG1, which produces electricity, which goes directly to MG2, which helps to move the car.

Intuitively, this should LOSE energy because of the double conversion (mechanical -> electrical -> mechanical). However, the engine is so much more efficient at its design rpm that you lose less energy from the double conversion than you lose from the slow engine speed in a conventional car moving slowly.

Likewise, apparently a very small amount of hydrogen improves the efficiency of a diesel (by burning the fuel more completely) more than the energy that is lost to inefficiency of producing that small amount of hydrogen.

Your equations above are fine. But since the numbers for efficiency are so low, there's a LOT of room for an improvement in one area to offset a loss in another.

However, the effect of hydrogen on the combustion efficiency of a diesel engine does not necessarily translate to a gasoline engine.

 

Really? The second law of thermodynamics sets some pretty firm limits on the efficiency of heat engines, and I think modern gas and diesel engines get reasonably close (like 80%) to the thermodynamic limits. Saying that "counter-intuitive measures can produce remarkable results" sounds suspicious to me.

 

actually from what ive seen, the typical ICE only tranfers about 15-18% of the power used to the wheels. even the ultra performing Prius is only about 37%.

hydrogen cars are supposed to be starting at 60% and eventually improve to 85%. i believe that when i see it.

either way, the ICE is not an efficient way to travel.

 

i don't think electrolysis would be practical

most H is extracted from natural gas

 

A tank full of hydrogen, rightly or wrongly, is going to remind too many people of the Hindenburg. Likewise with a hydrogen 'pipeline'. Electrolysis to generate hydrogen to put in your tank might work in an area of abundant hydro electric power, but even then it would be more efficient to put the electricity in your 'tank' directly, instead of turning it into hydrogen (and oxygen) first.

Or maybe we could liquefy the hydrogen and the oxygen, and have rocket power! That would be something to see. From a distance.

 

Thermodynamics sets a limit to how much work can be extracted from a heat engine of 1-T_cold/T_hot, or for gasoline at a combustion temperature of 525 Kelvin and room temperature of 300 Kelvin, 1-300/525=43%. Getting 37% when 43% is the theoretical limit is pretty darn good (though I'd be interested in a citable source for the 37% number).

A hydrogen car working on combustion would face similar theoretical limits, depending on the combustion temperature of hydrogen.

A hydrogen-powered car based on an electrochemical system (fuel cells) would not have these thermodynamic limits on efficiency, and could be much more efficient. However, if a heat engine were required to split water into hydrogen and oxygen, the efficiency of the chain of (1. energy -> 2. make hydrogen -> 3. recombine hydrogen to drive car) would probably be of low efficiency, even if step 3 were to have pretty high efficiency.

 

Actually PEM hydrogen fuel cells have a PEAK efficiency of 50% and actually average much less than that. Road-going diesel engines are already about 45% efficient and several manufacturers are aiming for 50% in the near future.

The idea that adding a little hydrogen to the mix improving the thermal efficiency of a diesel engine is just ridiculous. It assumes that in a modern diesel engine, much of the fuel is not burnt completely and gets chucked out of the exhaust.

While this may be true of a 1950's London double decker bus, or some blue-smoking tractor in Calcutta, it bears no relevance whatsoever to a modern diesel engine. Certainly, some particulates (unburnt fuel) are emitted, but nowhere near enough to add up to even 1% of the fuel going into the engine.

For example, a Toyota Avensis diesel emits 0.002 grammes of PM per km, while it burns 45 grammes of diesel per km. The unburnt fuel fraction is therefore of the order of 0.004 %.

Is it worth going to all this hassle to burn the last 0.004% of available fuel? That kind of fuel efficiency gain can be achieved by reducing the mass of the car by the equivalent of one screw. Crazy.

 

QED and that is why everyone should take physics.

 

the efficiency rate also takes into account total power created. some of which is regen from kinetic energy. something an ICE cannot do

 

Regen helps you get closer to theoretical, but can never push you beyond the theoretical limit. A hybrid helps in two ways: run the ICE at a condition closer to its efficiency peak (moderate RPMs rather than low RPMs) more of the time, and recover some of the energy that might have been thrown away as heat in the brakes. Neither of these things gets you past the fundamental efficiency limit of converting the heat energy of gasoline to work in the ICE at the outset.

Diesels can get higher numbers because they involve combustion at higher temperatures, thus helping with 1-T_cold/T_hot.