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Increasing Energy Efficiency of Internal Combustion Engines by Replacing Fossil Fuel With Hydrogen
* Corresponding author: Prof. Dr. Moussa Said, Faculty of Automotive Engineering Technology, saxony Egypt University for Applied Science and Technology, Cairo, Egypt. moussa.said@seu.edu.eg
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Received: ,
Accepted: ,
How to cite this article: Said M. Increasing Energy Efficiency of Internal Combustion Engines by Replacing Fossil Fuel With Hydrogen. Sci Technol Nex 2025;1:67-0. doi: 10.25259/STN_6_2025
Abstract
Objective
This study uses Computational Fluid Dynamics (CFD) to assess hydrogen as a fossil fuel alternative in internal combustion engines.
Material and Methods
Simulations tested various air-fuel ratios and spark timings with pure hydrogen and hydrogen-fossil fuel blends via port injection, identifying optimal conditions for each fuel.
Results
While hydrogen-fossil fuel blends improved efficiency and reduced emissions, pure hydrogen yielded the best results, consuming 28% less fuel and producing 20% more power than gasoline.
Conclusion
Pure hydrogen also minimises carbon monoxide emissions (9.2 × 10-⁸ grams) under stoichiometric and lean conditions.
Keywords
ANSYS-CFD
Emissions
Energy efficiency
Engine performance
Hydrogen
Natural gas.
1. INTRODUCTION
Evaluation of vehicle energy efficiency is commonly used to manage and control tasks in intelligent transport fleets. The smart world fleet features an increased share of vehicles with alternative power sources, such as hybrid, electric, and hydrogen fuel cells. However, vehicles powered by Internal Combustion Engines (ICE) still constitute a significant portion of such fleets.[1]
One method for evaluating the Energy Efficiency of vehicles powered by ICE is to measure the fuel consumption under specific operating conditions.[2] The most used efficiency measure for engines is the Specific Fuel Consumption (SFC). SFC is calculated as the mass flow rate of fuel divided by the power output. In contrast, Indicated Specific Fuel Consumption (ISFC) is defined as the fuel consumption per unit of time divided by the indicated power of an ICE.[3]
Internal combustion engines, powered by renewable fuels like hydrogen and hydrogen blends, can significantly contribute to climate change mitigation by providing a widespread, reliable, and affordable propulsion technology.[4]
ICEs use central, port, or direct injection fuel delivery systems. Central injection (using a carburettor) introduces the fuel-air mixture at the air intake manifold inlet, while port injection injects it directly at the inlet port, both during the intake stroke. Direct injection forms the mixture within the combustion chamber after the air intake port closes.[5] Fuel injectors, which are solenoid-operated valves, spray fuel into either the intake manifold or combustion chamber.[6]
Gasoline manifold injection produces lower hydrocarbon (HC) and carbon monoxide (CO) emissions than gasoline carburetion under all operating conditions. However, gasoline port injection results in higher nitrogen oxides (NOx) emissions due to the use of leaner fuel mixtures, which it can utilise more effectively than gasoline carburetion. A key advantage of gasoline port injection is its potential for higher power output.[7]
Two-stroke engines offer high power output due to their simple design and ease of maintenance. However, they produce more smoke, carbon monoxide, hydrocarbons, and particulate matter than four-stroke engines because they burn a mixture of oil and gasoline. NOx emissions are, conversely, lower.[8]
Current research on spark-ignition (SI) engines focuses on hydrogen fuel. Studies have explored hydrogen-gasoline blends in both carburetted and port-injected SI engines.[9-12] Carbureted hydrogen engines suffer a 15% power loss and are unsuitable for hydrogen fuel due to uncontrolled combustion.[13]
Adding up to 66% hydrogen by volume (3.7% by mass) to a gasoline-fuelled spark ignition engine improved work output, reduced burn duration, and decreased cycle-to-cycle variation under lean conditions (ϕ < 0.85). Near stoichiometric conditions (ϕ > 0.85), performance differences were minimal.[14] An electronically controlled fuel injection system was developed and tested on a two-stroke gasoline engine.[15]
Compressed Natural Gas (CNG) is an attractive fuel because it is cheaper than gasoline or diesel and produces lower air pollution emissions due to its high hydrogen-to-carbon ratio, which in turn reduces greenhouse gas emissions. However, challenges remain in using CNG in internal combustion engines (ICE), particularly optimizing the balance between emissions and fuel economy and adjusting the ideal air-to-fuel ratio for varying conditions and gas properties.[16]
The impact of hydrogen addition on the early flame development of lean natural gas-air mixtures was studied through experiments and simulations. Results showed that adding hydrogen enhanced the initial combustion of these premixed mixtures, especially as the mixture leaned towards the flammability limit of natural gas.[17]
Computational simulation effectively tackles complex thermal system challenges like those in internal combustion engines (ICE). Computational Fluid Dynamics (CFD) analysis accurately replicates the combustion process and fuel spray characteristics within the ICE, including vaporisation, mixing, and fluid interactions.[18,19] Researchers often use CFD software such as Ansys Forte to optimise ICE design due to its capabilities.[20,21]
A computational fluid dynamics (CFD) analysis was performed to evaluate the performance and emissions of a single-cylinder, two-stroke spark ignition engine fuelled by different fuels. Gross ISFC (g/kWh) was used to assess energy efficiency, with lower values indicating higher efficiency.
2. MATERIAL AND METHODS
This simulation assumes the following species composition: gasoline fuel (isooctane, C8H18), natural gas (methane, CH₄), and hydrogen gas (H₂). Table 1 summarises the air-to-fuel ratios for stoichiometric, rich, and lean mixtures used.
| Fuel | Formula | Stoichiometric | Rich | Lean |
|---|---|---|---|---|
| Natural gas (Methane) | CH4 | 17.2 | 15 | 20 |
| Gasoline (Isooctane) | C8H18 | 15 | 13 | 17 |
| Hydrogen | H2 | 34 | 30 | 39 |
With complete combustion and the theoretical amount of air, exhaust gases should ideally contain only carbon dioxide, water, and nitrogen. The following balanced equation (1) will be used to calculate the mass fractions of these species in the simulations.
In this context, λ represents the air-fuel (A/F) ratio, and 3.76 is the nitrogen-to-oxygen molecular ratio (79/21). Combustion coefficients are represented by A, B, and D. Two calculation groups were established to configure the inlet composition in Ansys-Forte, ensuring accurate mass fractions for various premixed fuel and air combinations in port-injected engine fuelling scenarios.
In a port-fuel injection system, a premixed fuel-air blend is present in the intake port. This simulation features three intake ports and one exhaust port. The gas composition initialisation defines the fuel-air mixture within the intake ports, assuming perfect mixing. Subsequent sections will detail cases using both pure and blended fuels.
2.1. Refuelling with pure gasoline
Table 2 shows the inlet composition and mass fractions of premixed pure gasoline and air used in the engine for several fuel-to-air (F/A) ratios. Spark ignition timing was fixed at 320° BTDC, with a fuel injection duration of 9 degrees and a constant fuel injection pressure of 50 bar.
| Species | Stoichiometric | Rich | Lean | ||||||
|---|---|---|---|---|---|---|---|---|---|
| O2% | n2% | C8H18% | O2% | n2% | C8H18% | O2% | n2% | C8H18% | |
| 100% C8H18 | 19.7 | 74 | 6.3 | 19.5 | 73.3 | 7.2 | 19.84 | 74.6 | 5.56 |
2.2. Refuelling with pure natural gas.
Table 3 shows the inlet composition and mass fractions for premixed natural gas and air at various fuel-to-air (F/A) ratios. Spark ignition timing was varied from 320° to 370° BTDC, while other combustion conditions remained consistent with case 2.2.
| Species | Stoichiometric | Rich | Lean | ||||||
|---|---|---|---|---|---|---|---|---|---|
| O2% | n2% | CH4% | O2% | n2% | CH4% | O2% | n2% | CH4% | |
| 100% CH4320 to 100% CH4370 | 19.85 | 74.66 | 5.49 | 19.69 | 74.06 | 6.25 | 20.0 | 75.24 | 4.76 |
2.3. Pure hydrogen refueling
Table 4 details the inlet composition and mass fraction for premixed hydrogen-air mixtures at various fuel-to-air (F/A) ratios. Spark ignition timing varied between 320° and 370° BTDC. Other combustion conditions remained consistent with case 2.2.
| Species | Stoichiometric | Rich | Lean | ||||||
|---|---|---|---|---|---|---|---|---|---|
| O2% | n2% | h2% | O2% | n2% | h2% | O2% | n2% | h2% | |
| 100% H2320 to 100% H2370 | 20.5 | 76.7 | 2.8 | 20.4 | 76.3 | 3.3 | 20.5 | 77 | 2.5 |
2.4. Gasoline-hydrogen blends
Table 5 shows the Induction blend mass fractions for port- injected gasoline-hydrogen engine fueling at various air- fuel ratios. Hydrogen addition is expressed as a percentage of the inlet air. Several air-fuel ratios were tested, maintaining combustion conditions consistent with case 2.2.
| Species | Stoichiometric | Rich | Lean | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| O2% | n2% | C8H18% | H2% | O2% | n2% | C8H18% | H2% | O2% | n2% | C8H18% | H2% | |
| + 1% H2 | 19.5 | 73.2 | 6.3 | 1.0 | 19.31 | 72.6 | 7.2 | 0.95 | 19.6 | 73.9 | 5.56 | 0.94 |
| + 2% H2 | 19.3 | 72.5 | 6.3 | 1.9 | 19.11 | 71.9 | 7.2 | 1.86 | 19.44 | 73.12 | 5.56 | 1.88 |
| + 3% H2 | 19.1 | 71.8 | 6.3 | 2.8 | 18.90 | 71.1 | 7.2 | 2.86 | 19.24 | 72.38 | 5.56 | 2.82 |
2.5. Natural gas-hydrogen blends
The inlet composition and mass fractions for premixed natural gas-hydrogen blends and air entering the engine. Hydrogen addition is expressed as a percentage of the inlet air. Several air-fuel ratios were tested, maintaining combustion conditions consistent with case 2.2.
In additional composition values were included for lean mixtures. This is because lean mixtures of natural gas require higher hydrogen content to improve combustion performance. The areas in the table marked with an asterisk (*) indicate that both stoichiometric and rich air-fuel (A/F) ratios have already achieved optimal performance and do not require any further increase in hydrogen percentage; therefore, they were not further examined, these data are tabulated and provided as supplementary materials.
3. RESULTS AND DISCUSSION
3.1. CFD Simulation
A simple engine configuration was utilised in the CFD simulation software for demonstration purposes. It is a two-stroke engine, similar to the one presented by Prof. Long Liang.[22] The three-dimensional geometric model, illustrated in Figure 1, was created to simulate the operational process of the two-stroke engine. The engine’s compression ratio is 12.65, the bore measures 8.58 cm, and the stroke is 673 cm.
- Model of a single-cylinder two-stroke gasoline engine.
Mesh and Initial Boundary Condition Settings: The grid generation tool provided by Ansys Forte was utilised for pre-processing, specifically adjusting the grid size in the vicinity of the inlet and exhaust port areas, as well as the cylinder volume. The global mesh size was set to 2 mm. The relevant boundary and initial conditions for the calculations are like those in Reference.[23] Each simulation run takes approximately 20 hours on an Intel® Core™ i7-8550U CPU running at 1.80 GHz, with a 64-bit operating system and x64-based architecture.
Case Setup and Materials: This computational fluid dynamics (CFD) tool includes a gas simulation for gaseous fuels and a parcel simulation for liquid fuels. The properties of air were considered for all pure fuels and fuel blends. The fuel simulation utilises iso-octane (C8H18), methane (CH4), and hydrogen (H2) as the selected fuels. The run parameters included the minimum step time, maximum step time, simulation start time, simulation end time, and solver type. The simulation was conducted for one cycle, which spanned from 97° ATDC to 455° ATDC. The engine speed was fixed at 2000 rpm.
Combustion Model: The simulation incorporates a comprehensive chemical kinetics calculator known as “CHIMKIN.” This tool features a chemical reaction mechanism that outlines the overall reaction between the fuel and the oxidiser through a series of elementary reactions. It is possible to simulate the combustion of various fuels by modifying the mechanism and utilising different fuels, such as gasoline, natural gas, and hydrogen. Since the preparation of the air-fuel mixture is a critical aspect before the initiation of combustion, a turbulence model called the “Reynolds-Averaged Navier-Stokes” model has been integrated into the CFD simulation software.
3.2. Computational results
An example of the computational results is presented in Figure 2, while the comprehensive results for all studied cases are detailed and provided as supplementary materials. Four criteria were selected from the simulation results for discussion: two representing engine performance—gross indicated power and gross indicated specific fuel consumption (ISFC)—and two representing emissions: carbon monoxide (CO) at the exhaust valve opening (EVO) and nitrogen oxides (NOx) at the exhaust valve opening (EVO).
- Example of computational results for fueling pure gasoline, pure hydrogen, and their blends at the stoichiometric air-fuel (A/F) ratio. ISFC: Indicated specific fuel consumption.
3.3. Pure gasoline
A peak gross indicated power of 5.03 kW was observed at a rich air-fuel (A/F) ratio. The minimum gross indicated specific fuel consumption (ISFC) was 487 g/kWh at a lean A/F ratio, which also corresponded to the lowest carbon monoxide (CO) emission of 1.6 × 10-⁴ g. The minimum nitrogen oxides (NOx) emission was 7.8 × 10-⁵ g, recorded at a rich A/F ratio.
3.3.1. Fueling with pure gasoline
The engine performance and emissions of the two-stroke engine when powered by pure gasoline. As this is the standard fuel used in such engines, it will serve as the reference case.
3.3.2. Fueling with pure hydrogen
The performance and emissions associated with fueling using pure hydrogen. The examined spark start angles are 320°, 330°, 340°, 350°, 360°, and 370° before top dead centre (BTDC).
3.3.3. Fueling with pure natural gas
The engine performance and emissions when fueled with pure natural gas. The examined spark ignition timing angles are 320°, 330°, 340°, 350°, 360°, and 370° before top dead centre (BTDC).
3.3.4. Fueling with blends of gasoline and hydrogen
The performance and emissions associated with different blends of gasoline and hydrogen.
3.3.5. Fueling with natural gas and hydrogen blends
The engine performance and emissions when using various blends of natural gas and hydrogen. Additional subcases to identify the maximum Gross Indicated Power at 40%, 45%, and 50% hydrogen. The optimal power output recorded was 6.35 (kW) at 45% hydrogen.
3.4. Pure natural gas
The maximum gross indicated power, 9.29 kW, occurred at the stoichiometric air-fuel (A/F) ratio. The lowest gross indicated specific fuel consumption (ISFC) was 200 g/kWh at a lean A/F ratio. The minimum CO emission was 1.6 × 10-⁴ g at the lean A/F ratio. The lowest EINOX emission was 1.6 × 10-5 g, at the rich A/F ratio. Figure 3 illustrates the relationship between gross ISFC, the A/F ratio, and spark ignition timing.
- The relationship between the gross indicated specific fuel consumption (ISFC), the air-fuel (A/F) ratio, and the spark start angles.
3.5. Cases of pure hydrogen
The highest gross indicated power of 6 kW was achieved at the stoichiometric air-fuel (A/F) ratio, while the lowest gross ISFC of 126 g occurred at a lean A/F ratio. The minimum CO emission measured was 9.2×10-8 g at a lean A/F ratio. Additionally, the lowest EINOX record was 2.9×10-5 g at a rich A/F ratio. Figure 4 illustrates the relationship between gross ISFC, the A/F ratio, and the spark ignition timing angles.
- The relationship between gross indicated specific fuel consumption (ISFC), the air-fuel (A/F) ratio, and the spark ignition timing angles.
3.6. Cases of gasoline and hydrogen blends
The highest gross indicated power recorded was 6.93 kW, achieved at a rich air-fuel (A/F) ratio. The lowest gross ISFC was 358 (gm) at a lean A/F ratio. The minimum CO emission was 1.6x10-4 g at the lean A/F ratio. Finally, the lowest EINOX emission was 5.2x10-7 g at a rich A/F ratio, as shown in Figure 5.
- The relationship between the gross indicated specific fuel consumption (ISFC), the air-fuel (A/F) ratio, and the percentage of hydrogen for gasoline + hydrogen fuel mixture.
3.7. Cases of blends of natural gas and hydrogen
The highest gross indicated power recorded was 6.39 kW, achieved at the stoichiometric air-fuel (A/F) ratio. The lowest gross ISFC was 328 g at a lean A/F ratio. The minimum CO emission was 7.3 ×10-3 g at a lean A/F ratio. Finally, the lowest EINOX emission was 1.5 × 10-6 g at the rich A/F ratio, as shown in Figure 6.
- The relationship between the gross indicated specific fuel consumption (ISFC), the air-fuel (A/F) ratio, and hydrogen percentage for natural gas + hydrogen fuel mixture.
4. CONCLUSION
The number of licensed vehicles in Egypt reached 9.95 million by the end of 2023, with the majority powered by internal combustion engines (ICEs). Rather than replacing these substantial assets with new EV vehicles, it is more logical to convert them to use alternative fuels that offer higher energy efficiency and lower emissions. This research examines the energy efficiency and pollution levels associated with such fuels. The objective is to prevent the discrediting of ICEs within smart fleets. Table 6 summarises the optimal operating conditions necessary to enhance energy efficiency when utilising different fuels to power a single-cylinder, two-stroke spark-ignition engine under various operating conditions. The optimal operating conditions necessary to enhance energy efficiency when utilising different fuels to power a single-cylinder, two-stroke spark-ignition engine under various operating conditions are summarised and mentioned.
| Pure gasoline | Pure natural gas | Pure hydrogen | Gasoline + Hydrogen | Natural gas + hydrogen | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Gross indicated power [kW] |
Gross ISFC [g] | CO@ EVO [g] | EINOX @ EVO [g] |
Gross indicated power [kW] |
Gross ISFC [g] | CO@ EVO [g] | EINOX @ EVO [g] |
Gross indicated power [kW] |
Gross ISFC [g] | CO @ EVO [g] | EINOX @ EVO [g] | Gross indicated power [kW] | Gross ISFC [g] | CO @ EVO [g] | EINOX @ EVO [g] |
Gross indicated power [kW] |
Gross ISFC [g] | CO@ EVO [g] | EINOX @ EVO [g] | |
| Best value | 5.03 | 487 | 1.60E-04 | 7.80E-05 | 9.29 | 200 | 1.4E-04 | 1.6E-05 | 6.00 | 135 | 9.2E-08 | 2.9E-05 | 6.93 | 358 | 1.6E-04 | 5.2E-07 | 6.39 | 328 | 7.3E-03 | 1.5E-06 |
| F/A ratio | Rich | Lean | Lean | Rich | Stoich | Lean | Lean | Rich | Stoich | Stoich | Lean | Rich | Rich | Lean | Lean | Rich | Stoich | Lean | Lean | Lean |
| Spark start angle [o] | 320 | 320 | 320 | 320 | 350 | 350 | 340 | 360 | 360 | 360 | 340 | 320 | 320 | 320 | 320 | 320 | 320 | 320 | 320 | 320 |
| Blend ratio | 100% | 100% | 100% | 100% | 100% | 100% | 100% | 100% | 100% | 100% | !00% | 100% | 1% H2 | 2% H2 | 0% H2 | 3% H2 | 30% H2 | 45% H2 | 10% H2 | 50% H2 |
ISFC: Indicated specific fuel consumption, CO: Carbon monoxide, EVO: Exhaust valve opening, EINOX: Emission index nitrogen oxides, F/A: Fuel/Air.
The highest gross indicated power value of 9.29 (kW) is achieved using pure natural gas at a spark start angle of 350 (o) and the stoichiometric air-fuel (A/F) ratio. The lowest gross ISFC of 135 g, which indicates the highest energy efficiency, is achieved when using pure hydrogen at a spark start angle of 360 degrees with a stoichiometric air-fuel (A/F) ratio. The lowest CO@EVO of 9.2x10-8 g is achieved by fueling pure hydrogen at a spark start angle of 340 (o) and a lean air-fuel (A/F) ratio. The lowest EINOX@EVO of 5.2x10-7g is achieved by fueling with gasoline enriched with 3% Hydrogen at a spark start angle of 320 (o) and a rich air-fuel (A/F) ratio.
Hydrogen fuel is recommended as a gasoline replacement in internal combustion engines due to its superior energy efficiency (28% of gasoline’s ISFC), lowest carbon monoxide emissions (9.2 × 10-⁸ grams), and 20% higher gross indicated power. Increased Nitrogen Oxide emissions can be managed with a catalytic converter. This computational analysis is validated by the author’s previous experimental work and supported by recent experimental studies.
Ethical approval
Institutional Review Board approval is not required.
Declaration of patient consent
Patient’s consent not required as there are no patients in this study.
Financial support and sponsorship
Nil
Conflicts of interest
Dr. Moussa Said is on the Editorial Board of the Journal.
Use of artificial intelligence (AI)-assisted technology for manuscript preparation
The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.
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