After a number of years of promises that hydrogen is the clean fuel of the future, only for not much to happen, it now appears that the future may finally be almost upon us.
Automotive manufacturers, including Mazda and Toyota, are currently developing hydrogen engines to power their vehicles, and these engines could one day replace not only hydrogen fuel cell technology and traditional combustion engines, but perhaps even electric vehicles (EVs).
However, while the EV market races ahead, the use of hydrogen engine technology in commercial vehicles is still in its initial phase, and the feasibility of hydrogen gas as a useful and practical alternative is yet to be proven.
What is a Hydrogen Engine?
A hydrogen engine is an advanced version of traditional internal combustion engines that uses liquid hydrogen instead of gasoline as fuel. An automobile that runs on hydrogen engines is called a hydrogen internal combustion engine vehicle (HICEV). These are different from hydrogen fuel cell electrified vehicles (FCEVs), such as Toyota's Mirai or the Hyundai Tucson, which use a fuel cell in which hydrogen chemically reacts with oxygen in the air to produce electricity that powers an electric motor.
Hydrogen engines generate power through the combustion of hydrogen and use fuel supply and injection systems that are modified versions of those used with gasoline engines. Except for the combustion of small amounts of engine oil, which is also the case with gasoline engines, hydrogen engines emit no CO2 when in use.
Hydrogen engines emit primarily water or water vapor as a byproduct, but the process of producing the hydrogen fuel can cause greenhouse gas emissions. However, one study has found that even if hydrogen is extracted in the most inefficient manner, it is likely to cut the CO2 emissions by more than 30%, when compared with gasoline.
Difference Between HICEV and FCEV
The key difference between a HICEV and FCEV lies in the way hydrogen is utilized in these vehicles. The former involves the combustion of hydrogen while the latter performs an electrochemical reaction and uses liquid hydrogen to generate power for its electric motor.
The hydrogen internal combustion engine (HICE) technology is still in its early phases of development. Meanwhile, the global fuel cell electric vehicle market has already crossed the US $1 billion mark, and in the coming years it is expected to show annual growth of around 38%.
Origin and Evolution of Hydrogen Engine
In 1806, Francois Isaac de Rivaz created an experimental internal combustion engine that used a hydrogen and oxygen mixture as fuel. The De Rivaz engine is said to be the earliest hydrogen-powered engine in the world.
Not long after this, in 1820, the Reverend W. Cecil wrote a paper for the Cambridge Philosophical Society titled, “On the Application of Hydrogen Gas to Produce Moving Power in Machinery.” This paper described an engine operating on the vacuum principle, where the vacuum was created through the burning of hydrogen gas.
About 150 years later, Paul Dieges patented a modification to the internal combustion engine that could run on both gasoline and hydrogen. Of course, by then, gasoline-fuelled vehicles were the norm, and few manufacturers saw the need for developing hydrogen-fuelled vehicles.
In the years that followed, the harmful effects of using fossil fuels on increased air pollution, health, global warming, acid rain, and in other areas in vehicles and industries started to become widely acknolwedged, along with their impact. Scientists, activists, leaders, and researchers all began to raise concerns about the increasing CO2 emission and the environmental risks associated with the extraction and use of fossil fuels.
The rising environmental concerns and demands for clean energy alternatives led many automobile companies to focus on the development first of low-lead fuels, and then on hydrogen and electric vehicles.
In the early 2000s, the Japanese automaker, Mazda began installing Wankel engines in their RX-8 model. The Wankel engine is a type of internal combustion engine that uses an eccentric rotary design to convert pressure into rotating motion. For a given power, they are more compact and weigh less than a combustion engine. They can also be easily converted to run on hydrogen.
More recently, they have updated the design, developing the RENESIS hydrogen rotary engine, which uses an electronically-controlled hydrogen gas injector and can be adapted to run as a gasoline-hydrogen hybrid.
The work to develop an efficient hydrogen engine has not stopped there. Around 2006, BMW developed a dual fuel hydrogen-gasoline internal combustion engine for their limited production Hydrogen 7, which was designed to demonstrate that hydrogen could work as a fuel. During tests, the car managed to run at a speed of 187 mph (301 km/h), and the company also claimed that their hydrogen car achieved zero CO2 emissions.
However, the claims made by BMW were later rejected by the United States Environmental Protection Agency (EPA), which pointed out that the car still emitted carbon from the evaporation of engine oil. In addition, the efficiency of the car when running on hydrogen was extremely low, returning about 5.6 mpg (50 l/100km) on average. This was mostly due to the difference in energy density between petrol and hydrogen.
Advantages of Hydrogen-Powered Engine
There are various significant reasons why hydrogen-powered engines are considered by some to be the future of the automobile industry, and why vehicle manufacturers spending millions of dollars to create efficient hydro engines.
Energy experts and companies believe that hydrogen has the potential to serve as an endless and relatively low-carbon source of energy. It could also represent a viable alternative to the use of heavy metals in batteries — which are damaging to the environment and could become very expensive in coming years, with the growth of EVs.
Low Ignition Energy and High Efficiency
Hydrogen ICE has low ignition energy compared to conventional gasoline-powered engines, because the combustion of hydrogen in these engines uses lower flame temperatures and lower heat transfers. This allows the engine to run on very lean mixtures and still combust quickly. In addition, because of high diffusivity (hydrogen mixes with air quicker than gasoline), the use of hydrogen reduces dangers associated with possible leaks.
Carbon Free Emissions
Hydrogen engines are said to provide a greater scope of improving energy security and reducing the carbon footprint. This is because no carbon compounds are released as byproducts when these vehicles run on hydrogen.
Because hydrogen has a low volumetric energy density, it needs to be stored as a compressed gas in order to give the driving range of conventional vehicles. This requires a the use of high-pressure tanks capable of storing hydrogen at either 5,000 or 10,000 pounds per square inch (psi). Retail dispensers, which are installed at gasoline stations, can fill these tanks in about 5 minutes. This is much faster than the time it takes to recharge EVs, even with fast-charging. Although, of course, EVs can also be charged at home, and hydrogen vehicles cannot. Other storage technologies are under development, including bonding hydrogen chemically with a material such as metal hydride or low-temperature sorbent materials.
An alternative power source
Because internal combustion engines can be adapted to burn hydrogen instead of, or in addition to gasoline, a number of countries are working on intiative to increase the production of hydrogen for use as a fuel in airplane, ships and even for power generation. If the hydrogen is produced using alternative energy, this could be a cost-effective way to rapidly reduce the use of fossil fuels in a number of areas.
Disadvantages of Hydrogen-Powered Engine
Despite numerous merits to their use, hydrogen engines are still not used on a large scale, and there are numerous complications associated with hydrogen fuel. The growth of efficient battery-powered vehicles and FCEVs have also led to a loss of interest among car manufacturers and innovators for developing HICE. Apart from this, there are also a number of serious issues that will need to be overcome before this is a practical alternative to EVs.
An Expensive Technology
The process of hydrogen extraction is both costly and energy-intensive. While an FCEV running on hydrogen is considered a zero-emission vehicle, extracting the hydrogen itself is not zero-emission. Currently, the majority of hydrogen is extracted using steam reforming, which combines high-temperature steam with natural gas to extract hydrogen.
Hydrogen can also be produced from water using electrolysis. This is more energy intensive, but can be done using renewable energy, which would eliminate a great deal of the emissions. However, the cost of producing hydrogen is still higher than that of gasoline (or electricity), so will need to come down quite a bit before hydrogen engines can be cost-effective on a large scale.
Lower energy density
Hydrogen is not as energy-dense as other fuels, meaning that you need more of it to do a given amount of work. Couple that with the inherent inefficiency of a piston engine, and hydrogen engines do not offer a significant energy advantage overall.
While no carbon is emitted by hydrogen engines, because of the heat generated within the combustion chamber, nitrogen oxide can still be formed as a byproduct. This compound is harmful to the environment, meaning that while hydrogen engines have zero carbon emissions, they are not emission-free.
Vehicles that run on hydrogen internal combustion engines are equipped with pressurized hydrogen fuel tanks. These tanks are designed to be very safe but in case of a leakage, the highly flammable nature of hydrogen can cause serious damage. A solution would be installing special sensors in the vehicle to detect any such leaks, which comes at a cost.
Large Size and Reduced Power Output
For hydrogen combustion engines, the stoichiometric air/fuel ratio is 34:1. This implies that a hydrogen engine uses twice the amount of air for complete combustion.
However, this also leads to reduced power output, and therefore, a hydrogen engine tends to deliver only around half amount of power as compared to a same-sized gasoline engine. To counterbalance this power loss, hydrogen engines are made large in size and often come with a turbocharger.
Future, Fact and Trends Related to Hydrogen Power
- The automobile sector is not unanimous on the feasability of hydrogen technology for the passenger vehicle segment, and some car manufacturers, such as Volkswagon and Audi are no longer working on developing HICEVs, opting to focus on EVs instead. Other automakers, including as Toyota, Renault, and Hyundai, are more optimistic about hydrogen-fueled vehicles, and they are expected to continue their developments of hydrogen engines. The Toyota Mirai HFCV was unveiled in 2014 and has 10,300 worldwide sales since December 2019, while South Korea’s Hyundai is producing the hydrogen powered SUV Nexo.
- To accelerate hydrogen production, the European Union has set a goal of installing 40 gigawatts in capacity of electrolyzers across the continent. Spain has already announced a plan to spend $10.5 billion (8.9 billion euros) on the construction of 4 gigawatts (GW) of solar-powered hydrogen electrolyzers. Other countries, including Denmark, are setting up plants to increase hydrogen production from electricity-based electrolysis. Even OPEC leader Saudi Arabia is building a green hydrogen production facility.
- Microsoft Corporation is testing the use of hydrogen fuel cells to replace diesel generators as their backup power source. ZeroAvia, a US-based startup plans to create a hydrogen-powered aircraft by 2024.
- Israeli engine manufacturer, Aquarius Engines has developed a new 22 lb (10 kg) hydrogen engine that uses a unique internal gas exchange system, and the company claims it to be a lightweight, cost-effective, and environment-friendly alternative to traditional combustion engines.
- Asian Renewable Energy Hub is a massive sustainable energy project in Australia that is currently in progress. When fully functional, it is planned to generate more than 50 TWH of electricity from solar and wind power. The major portion of this electric power will be used for the production of ammonia and clean hydrogen.
- At present, only three hydrogen-powered vehicles are available in the US and UK, these are Honda Clarity, Toyota Mirai, and Hyundai Nexo. However, the numbers are expected to grow in the coming years since promising developments in the field of hydrogen power and engine technology are taking place globally.
While hydrogen engines still face a number of issues, the market for hydrogen as a green power source is expected to grow rapidly in the coming years, with some estimates valuing it as high as a $70 billion by 2030. According to Bloomberg New Energy Finance, there are moe than $90 billion worth of upstream, midstream, and downstream 'green' hydrogen projects in the pipeline. Whatever happens with HICE vehicles, the use of renewable hydrogen as an energy source will continue to grow.