If Hydrogen could be produced using renewable energy, “it would surely be easier simply to use this energy to charge the batteries of all-electric or plug-in hybrid vehicles.” The Los Angeles Times wrote in 2009, “Any way you look at it, Hydrogen is a lousy way to move cars.” The Washington Post asked in November 2009, “Why would you want to store energy in the form of Hydrogen and then use that Hydrogen to produce electricity for a motor, when electrical energy is already waiting to be sucked out of sockets all over America and stored in auto batteries…?”
In 2013, the Motley Fool had stated that “there are still cost-prohibitive obstacles for Hydrogen cars relating to transportation, storage, and, most importantly, production.” During the same period, Volkswagen’s Rudolf Krebs also indicated that “no matter how excellent you make the cars themselves, the laws of physics hinder their overall efficiency. The most efficient way to convert energy to mobility is electricity.” He elaborated: “Hydrogen mobility only makes sense if you use green energy, but … you need to convert it first into Hydrogen with low efficiencies where you lose about 40% of the initial energy. You then must compress the Hydrogen and store it under high pressure in tanks, which uses more energy. And then you have to convert the Hydrogen back to electricity in a fuel cell with another efficiency loss.” Krebs continued: “in the end, from your original 100 percent of electric energy, you end up with 30 to 40 percent.”
Toyota Mirai, FCV 2022 Using H2
In 2014, electric automotive and energy futurist Julian Cox8 wrote that producing Hydrogen from methane “is significantly more carbon intensive per unit of energy than coal.” While former Dept. of Energy official Joseph Romm9 concluded that renewable energy cannot economically be used to make Hydrogen for an FCV fleet “either now or in the future.” GreenTech Media’s analyst reached similar conclusions.
A 2017, an analysis published in Green Car Reports found that the best Hydrogen fuel cell vehicles consume “more than three times more electricity per mile than an electric vehicle … generate more greenhouse-gas emissions than other powertrain technologies … and have very high fuel costs. … Considering all the obstacles and requirements for new infrastructure (estimated to cost as much as $400 billion), FCEVs seem likely to be only a niche technology. In 2017, Michael Barnard, writing in Forbes, listed the continuing disadvantages of Hydrogen fuel cell cars and concluded that “by about 2008, it was very clear that Hydrogen was and would be inferior to battery technology as a storage of energy for vehicles. By 2025 the last hold outs should likely be retiring their fuel cell dreams.” A 2019 video by Real Engineering10 noted that using Hydrogen as a fuel for cars does not help to reduce carbon emissions from transportation. The 95% of present day Hydrogen is still produced from fossil fuels releases carbon dioxide, and producing Hydrogen from water is an energy-consuming process. Storing Hydrogen requires more energy either to cool it down to the liquid state or to put it into tanks under high pressure, and delivering the Hydrogen to fuelling stations requires more energy and may release more carbon. The Hydrogen needed to move a FCV a kilometer costs approximately eight times as much as the electricity needed to move a BEV the same distance. Also in 2019, Katsushi Inoue, the President of Honda Europe, stated, “Our focus is on hybrid and electric vehicles now. Maybe Hydrogen fuel cell cars will come, but that’s a technology for the next era.”
Assessments since 2020 have concluded that Hydrogen vehicles are still only 38% efficient, while battery EVs from 80% to 95% efficient. A 2021 assessment by CleanTechnica concluded that while Hydrogen cars are far less efficient than electric cars, the vast majority of Hydrogen being produced is polluting grey Hydrogen, and delivering Hydrogen would require building a vast and expensive new infrastructure, the remaining two “advantages of fuel cell vehicles – longer range and fast fueling times – are rapidly being eroded by improving battery and charging technology.” A 2022 study in Nature Electronics agreed.
Hydrogen In ICEVs As Directly Injected Fuel
The earliest attempt at developing a Hydrogen IC Engine (HICE) was reported by Reverend W. Cecil in 1820. Cecil presented his work before the Cambridge Philosophical Society in a paper entitled “On the Application of Hydrogen Gas to Produce Moving Power in Machinery.” The engine itself operated on the vacuum principle, in which atmospheric pressure drives a piston back against a vacuum to produce power. The vacuum is created by burning a Hydrogen-air mixture, allowing it to expand and then cool. Although the engine ran satisfactorily, vacuum engines never became practical. Sixty years later, during his work with combustion engines in the 1860s and 1870s, N. A. Otto (the inventor of the Otto cycle) reportedly used a synthetic gas of which Hydrogen content was more that 50% , as fuel. Otto also experimented mixing this gas with gasoline, but found it dangerous to work with, prompting him to return to using liquid fuels. Soon after, the development of the carburetor, initiated a new era in which gasoline could be used both practically and safely, and interest in other fuels subsided. Liquid Hydrogen as stated above, remained a preferred fuel for rocket engines. In recent years, the concern for cleaner air, along with stricter air pollution regulation and the desire to reduce the dependency on fossil fuels have reignited the interest in Hydrogen as a vehicular fuel. The properties that contribute to use of Hydrogen as a combustible fuel in ICEs are its wide range of flammability, low ignition energy, small quenching distance, as well as its high auto ignition temperature, high flame speed at stoichiometric ratios, high diffusivity and very low density. Due to this wide flammability range hydrogen injected fuel-air mixture can be combusted in an ICE even when the fuel mixture is lean (i.e. it has lesser fuel than the theoretical, stoichiometric value). That’s why it is fairly easy to start an ICE on Hydrogen and also it gives a better fuel economy due to better combustion reaction when a vehicle runs on such a lean mixture. Additionally, with usage of Hydrogen, the final combustion temperature is generally lower, reducing the amount of pollutants, such as nitrogen oxides, emitted in the exhaust. However, there is a limit to how lean the ICE can be run, as lean operation significantly reduces the power output due to reduction in the volumetric heating value of the air/fuel mixture.
Another advantage of using Hydrogen in ICE is that, it brings down the ignition energy enabling these modified HICEs to ignite even the lean mixtures, ensuring prompt ignition. Unfortunately, this low ignition energy Hydrogen mixed fuel has a flip side, since even the hot gases and hot spots on the cylinder can cause premature ignition and flashback. Preventing this premature ignition is one of the challenges associated with running an engine on Hydrogen. The wide flammability range of Hydrogen means that almost any mixture can be ignited by a hot spot.
Hydrogen has a much smaller quenching distance than gasoline, which means Hydrogen flames will travel closer to the cylinder wall before they extinguish making it comparatively difficult to quench a Hydrogen flame than a gasoline flame within the engine. Such smaller quenching distance can also increase the tendency for backfire since the flames from a Hydrogen-air mixture can more readily reach nearer to the closed intake valve, than a hydrocarbon-air flame. Yet with its relatively high auto ignition temperature the HICEs can be designed to have much higher compression ratio than that is being used for a hydrocarbon ICE. Apart from these, with the very high diffusivity rate, Hydrogen is somewhat advantageous when used in ICEs for two main reasons: firstly, it facilitates the formation of a uniform mixture of fuel and air and secondly, if a Hydrogen leak develops, the Hydrogen disperses rapidly. Thus, unsafe conditions can either be avoided or minimized. Not but the least, Hydrogen has very low density which results in two more problems when used in an ICE – firstly, a very large volume storage of Hydrogen is necessary for an adequate driving range & secondly, due to the lower energy density of a Hydrogen-air mixture, the power output of ICE is reduced.
Despite all these challenges, trials to run conventional ICEVs to run on Hydrogen fuel were never stopped. However, the Hydrogen can also be used Hydrogen fueled ICE, which has higher reliability and cost performance, and requires less investment for mass production than fuel cell vehicles. Rotary Engine (RE) better known as “Wankel Engines”, provide merits such as prevention of pre-ignition of Hydrogen combustion. Mazda has been developing Hydrogen vehicles driven by Hydrogen ICE from the early 1990s.
Safety Issues In Handling Hydrogen
Hydrogen, molecule is the smallest molecule (120 pm i.e. 120*10^-12 m) and hence has the greatest tendency to escape through openings. This tendency is about 1.26~2.80 times faster than a natural gas leak through the holes or joints of low-pressure pipe lines however, since Hydrogen has about 1/3rd the energy density, than natural gas, any Hydrogen leak would result in much less energy release than a natural gas leak. For very large leaks from highpressure storage tanks, where the leak rate is limited by the sonic speed, Hydrogen would escape 3 times faster than natural gas (due to higher sonic speed in Hydrogen which is ~1308 m/s compared to the sonic speed in natural gas which is ~450 m/s). Another good property of Hydrogen is its buoyancy and rapid diffusiveness (compared to that of gasoline, propane, or natural gas) due to which in any untoward incident, of its leak for whatever reason, it will disperse much faster than any other gaseous fuel, thus reducing the hazard levels associated with Hydrogen.
To be continued
Prabhat Khare holds BE (Electrical) & a Gold Medalist from IIT, Roorkee. He is an Automotive (EV) & Engineering Consultant, as well as a Technology Article Writer. He is a Certified Energy Manager (BEE) & Lead Assessor for ISO 9K, 14K, 45K & 50K. He can be reached at LinkedIn: https://www.linkedin.com/in/prabhatkhare2/.
