Hydrogen Combustion Engines Are a Lousy and Desperate Attempt to Keep Them Alive

Toyota has insisted on this for quite a while already. Renault seems to have jumped on the same train with its latest concept car. It does not matter who proposes to burn hydrogen on a combustion engine: rest assured this is a desperate measure to keep combustion engines alive – in the worst way possible.
Renault and Toyota want to save the combustion engine with hydrogen. Forget about it 16 photos
Photo: Renault/Toyota
Yamaha hydrogen-oowered 5.0-liter V8 engineYamaha hydrogen-oowered 5.0-liter V8 engineYamaha hydrogen-oowered 5.0-liter V8 engine2022 Toyota Mirai2022 Toyota Mirai2022 Toyota Mirai2022 Toyota Mirai2022 Toyota Mirai2022 Toyota Mirai2022 Toyota Mirai2022 Toyota Mirai2022 Toyota Mirai2022 Toyota MiraiRenault wants to save the combustion engine with hydrogen. Forget about itRenault and Toyota want to save the combustion engine with hydrogen. Forget about it
If you have not seen the news lately, Renault promised to present a concept car in May that will burn hydrogen in a conventional internal combustion engine. Toyota and Yamaha introduced a 5-liter V8 powered by hydrogen in November 2021.

More recently, the Japanese companies said the V8 delivers 450 hp (335.6 kW) at 6,800 rpm and 540 Nm (398.3 pound-feet) at 3,600 rpm. Would burning hydrogen make them carbon neutral? Not necessarily. And they would still pollute the air.

Most of the hydrogen produced nowadays comes from decomposing natural gas. If it just separates hydrogen from carbon and releases the latter into the atmosphere, it is called grey hydrogen. If the carbon is captured, it is named blue hydrogen. Hydrogen made from electrolysis – converting water into hydrogen and oxygen – is called green, and it is the only kind of this gas that is carbon neutral. Mind you: that is only the case if the energy for electrolysis comes from renewable sources.

Hydrogen production is one of the reasons its critics think it is a ridiculous option. If you need electricity to produce the gas, why not just put it in batteries and get going? The reasons are simple: current battery packs are expensive, heavy, and take a long time to recharge. That extra weight charges a toll in commercial vehicles, reducing the payload. Hydrogen can make them lighter and faster to top up. However, burning that gas is preposterous.

Basic chemistry explains why that is the case. Although hydrogen is the most abundant element in the universe, it has curious properties. One kilogram (2.21 pounds) has an energy density of 120 MJ (megajoules). Gasoline has an energy density of 45.8 MJ/kg – or a little more than one-third of what the fossil fuel offers.

The issue is that one liter of liquid hydrogen weighs just 71 grams (0.16 lb). Consequently, it has a very low energy density: 8.5 MJ/l. A liter of gasoline weighs around 770 g or 0.77 kg (1.7 lb). That means that a liter of gas offers about 35 MJ/l – or a little more than four times what hydrogen presents. On top of that, hydrogen only remains in its liquid state if it is kept under -252.87°C (-423.17°F).

Besides providing way less energy than gasoline, hydrogen in a combustion engine has another handicap. To be fair, it is a combustion engine handicap: how inefficient they are to convert chemical energy into movement.

Most ICEs have a thermal efficiency of 20%, which means they waste 80% of the fuel energy. The most efficient ones reach 40% of thermal efficiency. For every $100 you spend, only $40 moves the wheels of your car. The other $60 becomes fumes and heat. Mazda vowed to reach an efficiency of 56%. If it manages to deliver that, you’ll only waste $44 of each $100 you spend on fuel. That’s still too much.

An electric motor turns 90% of electricity into movement. If a fuel cell generates electricity with the same hydrogen, the vehicle will travel much further with it. All that with no emissions, something you can’t say about an engine burning hydrogen.

Although it does not generate carbon directly, any oil used to lubricate the moving parts in an engine will also burn, even if in small quantities. The nitrogen in the air will generate nitrogen oxides. We can also have ozone coming from the oxygen, and the lubricant may also generate particulates. Summing up, the combustion engine is an inefficient and polluting machine, regardless of what feeds it.

BMW already tried burning hydrogen from 2005 up to 2007 with the Hydrogen 7, an E65 with the 6-liter V12 that could use gasoline or hydrogen. One hundred units were built. A V12 is undoubtedly not the most frugal example of an engine, but neither is a 5-liter V8.

The BMW V12 got 16.9 MPG (13.9 l/100 km) with gasoline. When that engine burned hydrogen, it returned 4.7 MPG (50 l/100 km). It had two fuel tanks: one for gasoline, with 73.8 liters (19.5 gallons), and one for hydrogen, with 170 liters (45 gallons). While the car could run 480 kilometers (298 miles) on the fossil fuel, hydrogen made it run only 201 km (125 mi).

Compare that with what the Toyota Mirai offers: 74 MPGe (3.2 l/100 km) and 645 km (402 mi) of range with two hydrogen tanks that together hold 122 liters (32,2 gallons) of hydrogen. Even the Hyundai Nexo Blue goes further with its worse aerodynamics and large frontal area: 61 MPGe and 612 km (380 km) for the three tanks with a combined capacity of 156 l (41.2 gallons).

If that was not enough to prove that burning hydrogen is a terrible idea, the BMW Hydrogen 7 used liquid hydrogen, which had to be kept below −253°C (20.1K or −423.4°F). When the car was not in use, hydrogen warmed up, and pressure increased.

Whenever it was above 87 psi (6 bar), the tank would release hydrogen to prevent higher pressures. After 10 to 12 days without use, the tank would get completely empty. That’s something that does not happen with hydrogen stored as a gas under high pressures.

If the combustion engine is to be saved, hydrogen is not the option. Renewable fuels offer a better alternative. Considering they capture carbon that is already in the atmosphere instead of releasing the one that was under the ground for millions of years – as fossil fuels do – they are carbon-neutral elements. However, there are several other complications involved with them.

Ethanol is already used in Brazil on a large scale. People argue that sugar cane robs space from other crops, which farmers who are specialized in them deny. Second-generation ethanol – produced from biomass – would be a better alternative, but it is still expensive. Porsche is investing in synthetic fuels to keep its classic cars running when fossil fuels are not allowed anymore.

None of these solutions address the other pollutants the combustion engine inherently produces nor its inefficiencies. Considering how well it has served mankind in the last one hundred years, it deserves an honorable retirement instead of these embarrassing attempts to keep it working. Admit it, guys: the combustion engine is already smoked.
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About the author: Gustavo Henrique Ruffo
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Motoring writer since 1998, Gustavo wants to write relevant stories about cars and their shift to a sustainable future.
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