Quote:
Originally Posted by photon
What efficiency from using it in a combustion device? Burning it is really inefficient unless you're just after the heat (i.e. heating a home).
In a car, burning hydrogen is horribly inefficient, you're far better off going wind turbine -> battery -> move car than wind turbine -> generate hydrogen -> burn hydrogen -> move car.
Fuel cells are far better to use with the hydrogen, and that's still not as good as a battery.
Where hydrogen really has an advantage is in energy density. Batteries are big and heavy, takes a lot of batteries to store the same amount of energy as a few kg of hydrogen.
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I would be interested in hearing why you feel using hydrogen as the fuel in a car engine would be "horribly inefficient". In fact, hydrogen has the largest efficiency gains in reciprocating engines, where combustion residence times are shortest. Hydorgen has some really unique and amazing properties, such as the widest flammability limits of any fuel as well as the fastest flame speeds (nearly a full order of magnitude faster than natural gas or gasoline). One reason why recip engines are inefficient is because much of the combustion is still occurring during the power/expansion stroke, when pressures and temperatures are decreasing and reactions are being quenched as a result. Hydrogen is able to complete those reactions closer to the top of the piston stroke. Moreover, because of its wide flammability limits, the parts of the fuel/gas mixture that would be mixed inadequately in a natural gas or gasoline engine would continue to combust in a hydrogen engine.
You don't have to take my word on it. There is literally a century of research on the use of hydrogen in internal combustion engines. As long as there have been combustion devices, scientists have been studying using hydrogen as a fuel in these devices. A quick google search will bear this out.
The problem with using hydrogen in mobile/transportation applications is that hydrogen has an extremely low energy density by volume (but an extremely high energy density by mass) so we would need incredible compression pressures to provide any reasonable range. And because of its unique combustion characteristics (wide flammability range and fast flame speeds), it poses fire and explosion risks (e.g. the Hindenburg). That has limited its use in mobile applications. It's use in stationary applications is more limited, mostly because the gains in efficiencies are smaller because furnaces and boilers have longer combustion residence times.
I do believe hydrogen will find a place in a carbonless future. Lots of focus are being put into wind, solar and batteries because they are the low hanging fruit. But I think in a decade or so when the pace of innovation for these technologies slow and the growth of their implementation flattens, you will see more work going towards hydrogen. Hydrogen supply is limitless, and it can be considered renewable because water would be the feedstock and after combustion, it reverts it back to water. The problem that needs to be solved is for hydrogen to be generated with a much lower net loss in energy.
I also found a couple of videos that are pretty interesting about their efficiency gains: