In this report: Why fuel cells beat internal combustion of hydrogen gas - and why carmakers like BMW ran away from internally combusted hydrogen.

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  / mike-sinclair-9867758  

In this report - hydrogen: Potentially a fairly sustainable future fuel, but mentally retarded for internal combustion. The top 10 reasons why internal combustion hydrogen is a very bad idea, is next.

Thankfully, you don’t need to be a particular genius to understand why hydrogen and internal combustion will forever be the ‘square-peg, round hole’ future mobility solution, compared with fuel cells. Or conventional liquid fuels.

HYDROGEN FACTS:

Fact 1: Most common ELEMENT - but a very rare gas (0.000055%) - call it 0.6ppm

Fact 2: Filthy to manufacture - mainly made from methane. And doing it this way makes it a dud fuel.

Fact 3: Hard to store: Boils at -253 C (20 K)
Resists Liquefaction - must be below 33 degrees absolute (-240 C) (You need a pressurized cryonic storage vessel - James Dewar - and even then it boils away.) Expansion rate: 1:851
Low density (as a gas) - problematic in the combustion chamber and in storage terms

Fact 4: Wide range of flammability 4-74% (gasoline 1.4-7.6%)

Fact 5: High flame speed (10x higher than gasoline at stoichiometric ratios)

Fact 6: High autoignition temp (think: Octane rating) 500C or 930F (isoOctane - 220; gasoline ~280)

Fact 7: Low ignition energy (gasoline is 10x higher) - premature ignition / flashback (or backfire)

Fact 8: Small quenching distance

Fact 9: High diffusivity

Fact 10: Ideal A/F ratio (by mass) = 34.3:1 (but can be as high as 180:1, ultra-lean)
By volume: 2.4:1
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FUNDAMENTAL PROBLEMS WITH HYDROGEN ICE:

Problem 1: Engines are limited by AIR. Hydrogen is a gas and displaces about 30% of the air in the chamber (compared to about 1-2% for gasoline) at ideal ratios. Therefore: port injection is off the table.

Problem 2: Hydrogen needs direct injection. It also needs PCV & EGR.

Intake tract management to prevent clogging by atomised oil: very important)

Problem 3: Pre-ignition (maybe even backfire) - low ignition energy, hot spots, overlap, pyrolysis (partly solved by direct injection - but not entirely - and direct injection leads to non-homogeneity of the F-A mix, and bumps up NOx thanks to reduced mixing times).

Problem 4: Needs EGR (25-30% mix) + H2O injection also helps (thermal dilution)

Problem 5: Complete engine redesign: large bore/stroke ratio and disk-shaped combustion chamber, and possibly even two spark plugs (for super lean operation, with reduced flame front speeds). Can’t use ‘waste spark systems (TDC exh stroke). (So forget about modifying your existing engine.) Plus, you can’t use platinum spark plugs, since platinum is a catalyst that helps hydrogen oxidise in air (and it’s already too good at that.)

Problem 6: Zero emissions is bullshit. Some marketing arsehole dreamed that up. NOx goes through the roof for Phi greater than 0.5-6. Also traces of CO and CO2 from burnt oil. Phi = Soich/act (less than 1 = lean)

Problem 7: Crankcase ventilation. Super-important because unburned fuel in the crankcase is a fire hazard, thanks to hydrogen’s low ignition energy. Plus, you need to build a pressure relief valve into the crankcase, just in case.

Problem 8: Oil dilution with water.

Problem 9: Power output. 85% of gasoline engine (for the same size, port injection). Or 15% greater (direct injection). But this is at shoichiometric ratios (NOx through the roof thanks to high combustion temp)

Typically, hydrogen engines use phi ~ 0.5 to manage this and therefore the power output is about half of an equivalent gasoline engine, for the same engine size. So a four-litre hydrogen engine is about the same as a two-litre gasoline engine, or a two-litre turbo hydrogen engine goes the same as a two-litre atmo engine.

Problem 10: Efficiency. Fuel cells are about twice as efficient, going from the fuel tank to the wheels. Call it 25% for ICE and 50% for fuel cell.

So there you have it - despite the potential for clever engineering subversion of some of the operational limitations, I hope you can see why hydrogen for internal combustion is a fool’s errand, fundamentally. Existing engines will never be efficiently retrofitted for burning hydrogen, and fuel cells will always smash internally combusted hydrogen on efficiency - certainly no need for the video referee there, any time soon. Fuel cells are miles ahead.