From a technical point of view, its operation is based on the use of hydrogen as primary fuel, which is a highly efficient and environmentally friendly energy source.
Hydrogen is the lightest and most abundant chemical element in the universe. Its high energy content and its ability to generate electrical energy through oxidation processes make it an attractive option for engine propulsion.
In the context of hydrogen engines, there are mainly two types of technologies: hydrogen fuel cells and hydrogen internal combustion engines.
Hydrogen fuel cells
Hydrogen fuel cells are electrochemical devices that convert the chemical energy of hydrogen and oxygen into electrical energy and water, without generating polluting emissions. These batteries work through a chemical reaction between hydrogen and oxygen in the air, in which electricity, heat and water are produced as byproducts.
This process is carried out in a structure made up of individual cells, where each cell contains an anode, a cathode and an electrolyte. Hydrogen comes into contact with the anode, while oxygen from the air reacts at the cathode, generating electrons that are directed through an external circuit, producing electricity that powers the vehicle's electric motor.
Vehicles that use hydrogen fuel cell engines are considered electric cars.
Comparison with conventional electric vehicles
Battery electric cars store electricity in a rechargeable battery, which is charged by connecting it to an external electricity source, such as a plug or charging station.
On the other hand, hydrogen fuel cell cars do not store electricity directly in a battery, but instead produce electricity on board from the hydrogen stored in the vehicle, through the electrochemical reaction in the fuel cell.
Hydrogen internal combustion engines
On the other hand, hydrogen internal combustion engines operate similarly to conventional internal combustion engines, but instead of using gasoline or diesel as fuel, they use hydrogen.
These engines burn hydrogen in the presence of oxygen in the air, generating heat and expanding the resulting gases to drive a piston. Unlike conventional combustion engines, hydrogen engines do not emit greenhouse gases, since the only byproduct of the reaction is water.
Brayton cycle
Hydrogen internal combustion engines use a similar thermodynamic cycle to conventional internal combustion engines, such as gasoline or diesel engines.
This cycle is known as the Brayton cycle, also called the ideal gas cycle, and consists of four main processes: intake, compression, combustion/expansion, and exhaust. However, in the case of hydrogen engines, some significant differences occur due to the unique properties of hydrogen as a fuel.
- Intake: In this first step, a mixture of hydrogen and air is introduced into the engine cylinder. Unlike gasoline engines, where air is mixed with a liquid fuel, in hydrogen engines, gaseous hydrogen is injected directly into the cylinder. Hydrogen is mixed with air in proper proportions to allow efficient combustion.
- Compression: Once the hydrogen and air mixture has entered the cylinder, the piston moves upward, compressing the mixture. This process increases the temperature and pressure inside the cylinder, preparing the mixture for combustion.
- Combustion/Expansion: In this stage, the combustion of hydrogen and compressed air begins using a spark generated by the engine spark plugs. The chemical reaction between hydrogen and oxygen in the air produces heat and expands the resulting gases, pushing down the piston and generating mechanical energy. Unlike gasoline engines, where carbon dioxide and water vapor are produced as combustion products, in hydrogen engines, the only combustion product is water.
- Exhaust: Once the expansion process has been completed and the piston has reached its lowest point, exhaust gases are expelled from the cylinder into the vehicle's exhaust system. These gases consist mainly of water vapor, along with small amounts of other combustion products, such as nitrogen oxides (NOx) in very low quantities.
Hydrogen storage and distribution
Regardless of the type of technology used, hydrogen storage and distribution are critical aspects to consider in the operation of a hydrogen engine. Since hydrogen is a highly flammable and low-density gas in its natural form, its storage and transportation require specific technologies, such as compression or cryogenization.
In addition, the recharging infrastructure must be adequately developed to guarantee an efficient and safe supply of hydrogen to vehicles equipped with this type of engine.
Energy efficiency
In terms of efficiency, hydrogen engines have the potential to outperform conventional internal combustion engines and, in some cases, even battery electric vehicles.
This is because the specific energy of hydrogen is considerably higher than that of fossil fuels, allowing for higher energy density and therefore longer driving range.