Hydrogen-Enriched Fuel Technologies in Internal Combustion Engines

Hydrogen-enriched fuel technologies encompass the addition of hydrogen or hydrogen-based gases into the intake or direct injection systems of spark ignition and compression ignition engines to enhance combustion characteristics, reduce fuel consumption and mitigate pollutant emissions. Hydrogen’s high flame speed and wide flammability limits accelerate combustion, leading to more complete oxidation of the primary fuel and lower unburned hydrocarbons and carbon monoxide. In dual-fuel configurations, hydrogen is generated onboard through water electrolysis or supplied from external tanks, blending with conventional fuels such as gasoline, diesel or compressed natural gas. Recent advances in generator design, catalyst selection and flow-rate control have improved hydrogen yield and system reliability. Within compression ignition engines, low-level hydrogen enrichment can raise in-cylinder pressure and heat-release rate, thereby increasing brake thermal efficiency even under high load. In spark ignition engines, controlled hydrogen addition has been shown to reduce knock tendency and expand lean-burn limits. Economic analyses indicate that, despite the additional electrical energy demand for hydrogen production, net operational costs may decline through fuel savings and emissions-related penalties avoided. As global regulatory frameworks tighten, hydrogen enrichment offers a transitional pathway towards decarbonisation of road transport while leveraging existing engine platforms.

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Hydrogen-Enriched Fuel Technologies in Internal Combustion Engines publication trend

The graph below shows the total number of articles in hydrogen-enriched fuel technologies in internal combustion engines across all publications each year (not limited to Nature Index journals).

Technical terms

Oxyhydrogen (HHO): A stoichiometric mixture of hydrogen and oxygen gases produced by water electrolysis, used as a combustible additive.

Brake Thermal Efficiency (BTE): The ratio of engine output power to the energy content of fuel consumed, indicating combustion effectiveness.

Brake Specific Fuel Consumption (BSFC): The mass of fuel required to produce one unit of engine power per hour, a key metric of fuel economy.

Spark Ignition (SI) Engine: An internal combustion engine where the air–fuel mixture is ignited by an electrical spark.

Compression Ignition (CI) Engine: An engine where fuel auto-ignites under high pressure and temperature without a spark plug.

Response Surface Methodology (RSM): A statistical technique for optimizing experimental conditions by fitting predictive models to response variables.

References

1. Enviro-Economic Assessment of HHO–CNG Mixture Utilization in Spark Ignition Engine for Performance and Environmental Sustainability. Energies (2022).
2. Response Surface Methodology Routed Optimization of Performance of Hydroxy Gas Enriched Diesel Fuel in Compression Ignition Engines. Processes (2021).
3. Influence of Ethanol Blended Diesel Enriched with Hydroxy Gas in Dual-Fuel Mode on Common Rail Direct Injection Engine. Energies (2023).
4. Investigation of Performance and Emission Parameters of Hydroxygen (HHO)-Enriched Diesel Fuel with Water Injection in the Compression Ignition Engine. Clean Technologies (2021).