Quote:
Originally Posted by photon
A little more detail with basic percentages, sources, etc would aid greatly in understanding what you mean when you say "can result in efficiency gains that offsets the net energy loss from the production of hydrogen".
You lose 20-30% right off the top, and hydrogen IC engines are not that much more efficient than gasoline ones to offset that.
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Let's say a semi-trailer truck running on diesel has a fuel consumption rate of 40 L of diesel per 100 km of travel, based on a thermal efficiency of 28%.
LHV of diesel = 36 MJ/L
So mileage in terms of fuel energy input = 36 x 40 = 1440 MJ per 100 km
Let's say we want to displace 10% of that diesel fuel input with hydrogen:
1296 MJ of the chemical energy comes from diesel fuel, and 144 MJ comes from hydrogen.
Let's say for every 1 MJ of energy from the alternator used to generate the hydrogen, only 0.7 MJ of hydrogen is actually produced.
Energy used to produce 144 MJ of H2 = 144 MJ / 0.7 = 206 MJ
So about 60 MJ of fuel energy has to be consumed just to produce the hydrogen. This means 1440 - 60 MJ = 1380 MJ of fuel energy is used for mechanical energy: 1236 MJ is from diesel fuel and 144 MJ from hydrogen.
Hydrogen addition to a diesel engine is shown to improve the thermal efficiency of the engine from about 20% to as much as 50% as per figure below. But let's be conservative and say the thermal efficiency of the diesel engine increases 20%, or from from 28% thermal efficiency to 34% thermal efficiency.
(
https://library.ndsu.edu/ir/bitstrea...pdf?sequence=1)
The total km of travel now possible with that engine would be:
0.40 / 0.28 x 1380 / 1440 x 100 km = 116 km
The fuel consumption of the truck using the same amount of fuel energy has improved by (116 km - 100 km)/100 km x 100 = 16%.
This is a similar guarantee from this company, although they don't provide any details of how much hydrogen is used. Their 20% cost reduction likely also includes savings from having to perform less oil changes and particulate filter replacements so our calculation of a 16% fuel efficiency savings on 10% hydrogen addition is probably pretty close to how they come up with their numbers.
https://www.hytechpower.com/savings-calculator