Recently - there has been a big push in the auto industry, onsite power generation and utility scale mutli-MW gas turbine industry towards the development of internal combustion engines and turbines operating on 100% hydrogen. Over the past 8 years we have developed numerous engines - both Otto and Brayton cycle - single piston and multi-piston engines from 1200 Watts portable generator, onsite 10KW generator to 350 small block Chevy dual fuel engine and a multi-fuel turbine jet engine that also operates on 100% hydrogen.
Along this diverse pathway of approaching different engines - there were many technical hurtles to overcome from air fuel ratios, engineering fuel feeder systems, combustion issues, mechanical failures, timing adjustments, detonation issues and of course sometimes I was filled with dread to turn the key on or push the button for fear of an intense explosion and engine shrapnel flying all over either maiming me or worse. The purpose of these engine projects was to prove out the ability of using hydrogen in an ICE and applications such as power generation and propulsion. Since - at the time - there was really no where to turn to for factual data on ICEs operating on hydrogen nor was there a "Hydrogen YouTube channel":-) - much of the beginning was hit or miss - trial and error. At times I felt like a Test Pilot from the 60s not really certain of the outcome. Many times I had to rely on my still to this day common saying "Lets just try this and see how it goes". Eventually - I had all successes on all the engines. They all ran perfectly on hydrogen.
The hydrogen engine is capable of operating over a wide range of equivalence ratio: from ultra-lean mode to stoichiometric conditions. However, it has been observed that the engine gives maximum thermal efficiency and minimum NOx emissions and without any problems of backfire if operated within a definite range of lean operation. Fuel induction technique has been found to be very crucial to hydrogen engine development. This type of engine is simply a modified version of the traditional gasoline-powered internal combustion engine. The absence of carbon means that no CO2 is produced, which eliminates the main greenhouse gas emission of a conventional petroleum engine.
Hydrogen has a wide flammability range in comparison with other fuels. As a result, it can be combusted in an internal combustion engine over a wide range of fuel-air mixtures. An advantage here is it can thus be on a lean fuel-air mixture. Such a mixture is one in which the amount of fuel is less than the theoretical, stoichiometric or chemically ideal amount needed for combustion with a given amount of air. Fuel economy is then greater and the combustion reaction is more complete. Also, the combustion temperature is usually lower, which reduces the amount of pollutants (nitrogen oxides, ...) emitted through the exhaust. With this "wide range of AF ratios" hydrogen is easily adaptable to the Brayton cycle as well. Matter of fact - hydrogen loves rotating devices. Which is why Mazda is developing its own H2ICE mobile.
My jet turbine engine screams at 133,000 rpm. It spins up and runs on 100% hydrogen. I keep the rpm down around 40,000 or I have to wear ear protectors. It'll blow my ear drums out. Apart from the loud scream of the turbine and the roar of the combustion of the hydrogen - there is literally ZERO smoke or emissions detected - other than the thermal waves coming out of the exhaust. I have to spin up the turbine to 4000 rpm before I "light it up" with the assistance of the APU (auxiliary power unit) I built just like any other jet engine has to be "spun up" before ignition sequence can commence. The EGT (exhaust gas temperature) runs around 1200º F.
What most people fail to grasp is the lack of understanding of the flame speed and combustion temperature drop when using hydrogen that is counterintuitive considering the higher flame temperature of 100% hydrogen combusting with air. Running hydrogen in my piston engines I'll see a 100º temperature drop in EGTs. A hydrogen flame has a vary narrow ambient temperature window. e.g. you stack wood for a bon fire 4 feet tall. That a sizable fire. Once it ignites all the wood - you will be about 15 feet away. With a hydrogen fire of the same size - you can walk right up to the fire, vert little radiant heat and put your hand a couple of inches away without getting burned. This is due to the fact hydrogen is so light - it doesn't hang around much due to its light weight - it shoots straight up. People will say - "burning hydrogen in an ICE creates NOx emissions. Yes - that's true - but very little compared to gasoline - as stated above. BMW offered a version of the 2005-2007 BMW 7-Series, called the Hydrogen 7, with a 6.0-liter V-12 that could run on gasoline or hydrogen. It claimed an efficiency of about 40 percent on hydrogen—versus considerably less than that for most gasoline engines.
The properties that contribute to hydrogen's use as a combustible fuel are its:
- wide range of flammability
- low ignition energy
- small quenching distance
- high autoignition temperature
- high flame speed at stoichiometric ratios
- high diffusivity
- very low density
Hydrogen internal combustion engine development has been receiving more interest recently, particularly for heavy duty commercial vehicles. Part of the motivation for this is as a bridging technology to meet future climate CO2 emission goals, and as technology more compatible with existing automotive knowledge and manufacturing. In May 2021, Toyota Corolla Sport, which is equipped with hydrogen engine entered the Super Taikyu Series race round 3 "NAPAC Fuji Super TEC 24 Hours", and completed the 24 hours race. Toyota intends to apply its safety technologies and know-how that it has accumulated through the development of fuel cell vehicles and the commercialization of the Mirai. In November 2021, five automotive manufacturers in Japan (Kawasaki Heavy Industries, Toyota, Mazda and Yamaha Motor) jointly announced that they will take on the challenge of expanding fuel options through the use of internal combustion engines to achieve carbon neutrality at the (three-hour) Super Taikyu race Round 6 held at Okayama International Circuit. Their common view is that the enemy is not internal combustion engines, and we need diverse solutions toward challenging carbon neutrality. At the event, Yamaha Motor unveiled 5.0-liter V8 Hydrogen engine which is based on Lexus 2UR engine.
Here is our own special project. Its my Porsche Cayman S. It's being built as a tri-fuel car. Hydrogen, Hythanol and gasoline. When completed it will be the fastest, cleanest 
burning, most powerful street legal Porsche on the planet. It will have 3 gas tanks running on 130 octane fuel pushing about 600 hp and forced air induction powered by the TPC Stage II turbo with methanol injection system. But it wont be methanol I'm injecting - that's a secret:-) A year and a half ago Porsche Magazine wanted to do a story on my car. (I have the emails). Then after a couple of meetings and I turned over the specs (but no all) of the final build 
and then the emails between me and Porsche magazine editor stopped. I sent more emails - no reply. Two months later Porsche German announced a new Porsche 911 dual fuel running on eFuels AND announced Porsche is building a fuel factory in Peru Chile after they hooked up with Siemens. Mmmmmmm.....:-( But wait till they see my Cayman S whomp their 911. AAahaahahaahhaaaaaa..... Challenge on!!!!
Below is a list of other H2ICE projects and developments.
Keyou
TOYOTA and Subaru
https://global.toyota/en/newsroom/corporate/36328304.html
Mazda
https://www.mazda.com/en/innovation/technology/env/hre/
BMW
https://www.bmwblog.com/2016/08/17/bmw-stop-making-hydrogen-7-model/
Kwasaki and Yamaha
https://energynews.biz/yamaha-kawasaki-to-develop-hydrogen-engines/
Caterpillar
Jenbacher
https://www.innio.com/en/solutions/power-generation/hydrogen-fired-power-generation
https://www.innio.com/en/solutions/power-generation/hydrogen-fired-power-generation?utmcampaign=NAM-General-BMM-D2Hydrogen&utmsource=google&utmmedium=cpc&utmterm=power%20generation%20hydrogen&utmcontent=adgroup-130208101877creative-564744389642network-gplacement-adposition-matchtype-pdevice-c&gclid=EAIaIQobChMI-pqxtZv99gIVJj2tBh2cfwWREAAYAiAAEgIaAfDBwE
MAN
https://www.man-es.com/marine/strategic-expertise/future-fuels/hydrogen
Cummins
https://www.cummins.com/news/2022/01/27/hydrogen-internal-combustion-engines-and-hydrogen-fuel-cells
https://www.cummins.com/news/2022/01/13/making-splash-hydrogen-internal-combustion-engines
Airbus
Boeing
https://airinsight.com/boeing-remains-cautious-about-hydrogen/
FORD