Ammonia has emerged as a promising zero-carbon fuel to support carbon-neutral engine operation. However, its low flame speed and high ignition resistance often result in incomplete oxidation and unburned ammonia slip. To overcome these limitations, hydrogen was introduced in small quantities as a combustion enhancer. In this study, a water-cooled, single-cylinder diesel engine operating at constant speed was fueled with diesel as a pilot and supplemented with port-injected hydrogen and ammonia. Independent injectors were used to vary hydrogen and ammonia enrichment durations (1, 3, and 5 ms). Key combustion and performance parameters, including cylinder pressure, net heat release rate, combustion phasing, brake thermal efficiency, and emissions of CO, HC, NOx, and smoke, were systematically evaluated. Results showed that ammonia enrichment reduced HRR and delayed combustion, whereas hydrogen addition enhanced HRR, shortened combustion duration, and accelerated autoignition. With increasing hydrogen dosing, the combustion mode shifted from diesel-like diffusion combustion toward a more premixed combustion behavior. A significant reduction in CO and HC emissions confirmed improved combustion efficiency, while higher peak in-cylinder temperatures contributed to increased NOx emissions. To identify optimal operating conditions, the analytic hierarchy process multi-criteria decisionmaking method was applied. The analytic hierarchy process analysis recognized engine loads of 7 kg and 10.5 kg with 5 ms hydrogen and 3-5 ms ammonia dosing as optimal, achieving reductions in NOx and smoke emissions compared to baseline operation, albeit with a slight decrease in BTE. These findings highlight the synergistic role of hydrogen in promoting efficient and sustainable ammonia utilization in compression ignition engines. The peak of cylinder pressure and heat release rate increase up to 8-10%. maximum brake thermal efficiency increased by 33.4%, and percentage reductions in CO (38-44%), and HC (up to 52%), under optimized ammoniahydrogen operation.

This study evaluates the feasibility of California achieving a fully zero-emission light-duty vehicle (ZEV) fleet by 2035 through the exclusive adoption of hydrogen fuel cell electric vehicles (FCEVs), advancing beyond the state's ambitious goals to address the intensifying global climate crisis. While California's current regulatory framework supports a mix of battery-electric vehicles (BEVs), hydrogen FCEVs, and other technologies, this research focuses on a comprehensive hydrogen FCEV transition to fully decarbonize transportation. Forecasting models, including the autoregressive integrated moving average (ARIMA) and the seasonal autoregressive integrated moving average (SARIMA), project a shortfall of 17-22 million zero-emission vehicles under existing sales trajectories, emphasizing the need for accelerated adoption strategies. Lifecycle assessments reveal that hydrogen FCEVs emit only 141,000 tonnes of CO2 annually for a fleet of 28 million vehicles, compared to 98 million tonnes emitted by gasoline vehicles and 1.67 million tonnes by BEVs. Additionally, hydrogen FCEVs generate lower emissions of CO, NOx, and volatile organic compounds (VOCs), making them particularly suitable for long-range and high-utilization applications. However, achieving this transition requires an estimated $141 billion annually for hydrogen production, infrastructure development, and consumer incentives. This case study highlights the potential of hydrogen FCEVs to accelerate decarbonization in California, offering a scalable framework for global innovation, strategic investments, and robust climate policy.

The blending of gasoline with ammonia is increasingly recognized for its potential to enhance fuel efficiency and reduce emissions. The integration of gasoline and ammonia, along with the addition of hydrogen, presents as a viable approach for advancing sustainable fuel technologies. Experiments for laminar burning velocity (LBV) at atmospheric pressure were performed for a fuel blend involving gasoline, ammonia and hydrogen for 5 % energy fraction of ammonia (ENH3 = 0.05) on an externally heated diverging channel setup re-modified to include combined fuel mixtures of gaseous and liquid fuels and was performed for a temperature range from 350 K up to 600 K and for equivalence ratios 0.8-1.2. A mechanism consisting of hydrocarbon-ammonia interaction reactions for each surrogate component, was merged using a newly developed code, TIRAMISU, by Timoth & eacute;e Fages [31]. The reliability of merged mechanisms against laminar burning velocity experimental data taken from literature at atmospheric pressure for pure fuel at various inlet temperatures such as 358 K, 373 K, and existing literature data on TRF/NH3/air mixtures at 400 K between equivalence ratios 0.7 to 1.4 were tested. The numerical results aligned well with experimental data and satisfactory results were obtained from both the analysis with less than 10 % error. The chosen blend of gasoline-ammonia-hydrogen blends revealed a marginal decrease of about +/- 10 cm/s across the study temperature range, with reduced gasoline (similar to 34 % mole fraction) and higher ammonia concentration (similar to 46 % mole fraction). This indicates that the blend achieves comparable combustion performance to pure gasoline. Most significant reactions responsible for affecting LBV value and for existing discrepancies were identified conducting sensitivity analysis.

India is advancing the production of Dimethyl Ether (DME) as an alternative fuel for various applications. Due to its low-temperature reaction characteristics and high cetane number, DME is particularly suitable for direct use in compression ignition (CI) engines. Conversely, DME can significantly reduce emissions as an additive in spark-ignited (SI) engines. This study examines the emission reduction potential of partially replacing LPG with DME in multi-point fuel injection (MPFI) SI engines, using DME concentrations ranging from 0

This study evaluates the effect of hydrogen enrichment on the dual fuel CI engine. Experiments were conducted using port-injected hydrogen under variable load conditions. Brake thermal efficiency (BTE) increases with hydrogen addition, and achieved the maximum BTE i.e., 25.66% at full load for 8-ms hydrogen enrichment in diesel (HEID) compared to diesel (23.51%). Exergy efficiency also increased from 17.1% (diesel) to 21.7% with hydrogen enrichment at full load. A reduction in exergy destruction and entropy generation confirmed lower irreversibility in the combustion process. Hydrogen addition also lowered CO, HC, and smoke emissions due to better mixture formation, although NOx increased because of higher combustion temperature. The sustainability index showed a notable improvement with HEID. These results demonstrate that hydrogen enrichment improves thermodynamic utilization of fuel, enhances sustainability, and reduces carbon-based emissions, highlighting hydrogen-enriched diesel dual-fuel CI engine operation as a promising low-carbon engine approach.

The escalating global demand for energy has spurred a critical search for alternative fuels to power internal combustion engines (ICEs). The formulation and application of gasoline surrogates in multi-point fuel injection (MPFI) spark ignition (SI) engines have gained significant interest in assessing their viability compared to commercial gasoline. Understanding the emission profiles of these surrogates is essential for optimizing engine performance and minimizing environmental impact. In MPFI SI engines, gasoline surrogates can alter combustion dynamics, thereby influencing the production of emissions such as carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NOx). In this current study, the formulation of three gasoline surrogates and their emission analysis were carried out in an MPFI SI engine. The results demonstrated that both S-C and S-B surrogates exhibited lower CO and HC emissions compared to baseline gasoline operations. This improvement can be attributed to better combustion facilitated by the additional oxygen present in these surrogates.

CO2-assisted co-gasification has emerged as a promising thermochemical technology for sustainable energy production and waste management. This review explores the synergistic effects of combining various feedstocks, including biomass, coal, plastics, and mixed wastes, in CO2-assisted co-gasification processes. By utilizing CO2 as a gasifying agent, this approach offers dual benefits: reducing greenhouse gas emissions and enhancing syngas yields with improved energy efficiency. The literature reviewed indicates that synergistic interactions between feedstocks can lead to notable improvements in key performance metrics such as syngas yields, carbon conversion rates, process reactivity, and hydrogen-to-carbon ratios, compared to the gasification of individual feedstocks. The addition of CO2 optimizes gasification kinetics, allowing for a reduction in the formation of harmful tars and char. Advanced reactor designs, catalysts, and process optimization techniques have further improved performance, with some studies reporting calorific value enhancements of up to 10 MJ/kg in selected cases, while minimizing environmental impacts. Despite these advantages, challenges remain in terms of feedstock variability, scalability, catalyst deactivation, and process energy requirements, which may limit near-term industrial adoption. This review provides comprehensive insights into the technological advancements and prospects of CO2-assisted co-gasification, emphasizing its potential for biofuel production, chemical synthesis, and carbon-neutral energy systems. Future research focused on advanced catalysts and process integration will be crucial for bridging the gap from laboratory-scale success to industrial-scale application.

The growing global demand for sustainable energy and efficient waste management necessitates innovative conversion pathways for municipal and sanitary waste. Sanitary diaper waste, owing to its non-biodegradable composition and high disposal volume, poses a persistent environmental challenge. This study evaluates the techno-economic feasibility of producing syngas from sanitary diaper waste through CO2-assisted co-gasification, integrating both environmental and economic perspectives. The analysis considers plant-scale parameters such as fixed and operational costs, manufacturing expenses, and payback period to assess overall project viability. The techno-economic evaluation for an industrial-scale plant processing 1000 kg/day of feedstock revealed a fixed cost of INR2.7 million, an annual operating cost of INR5.33 million, and a manufacturing cost of INR32.27 per kg of syngas, with a payback period of 10.32 years. These findings demonstrate that CO2-assisted co-gasification of sanitary diaper waste is a technically feasible and economically sustainable approach for renewable syngas production, contributing to circular-economy objectives and reduced carbon emissions through decentralized waste-to-energy systems.

To enhance combustion and emission characteristics in hydrogen-powered CI engines, this study numerically examined the impact of injector hole variation using a single-cylinder model. Transitioning from diesel-only combustion to dual-fuel hydrogen–diesel operation significantly improved performance. The ISFC decreased by 11.9

The thermodynamic and sustainability potential of diesel-syngas-hydrogen (DSH) fuel blends in a Reactivity Controlled Compression Ignition (RCCI) engine was experimentally evaluated. The syngas was produced from sanitary waste offering a sustainable waste-to-energy fuel alternative. The produced syngas was used for experimental testing in the RCCI engine with hydrogen to demonstrate the practical application of waste-derived syngas in the engines. The study assessed the energy, exergy, combustion, and emission characteristics of various diesel-syngas-hydrogen blends (DS6H3, DS6H4, DS6H5, DS8H3, DS8H4, and DS8H5) were tested. The optimal blend, DS6H5, demonstrated significant improvements over baseline diesel at full load, with a 25.53 % increase in in-cylinder pressure, a 35.04 % increase in net heat release rate, and a 7.2 % increase in brake thermal efficiency. Thermodynamic analysis revealed entropy generation was reduced by 12.87 % and the highest sustainability index was 2.86 % higher than diesel, indicating reduced irreversibility and enhanced efficiency. This blend also achieved substantial reductions in CO and hydrocarbon (HC) emissions by 25.88 % and 38.82 %, respectively. However, NOx emissions rose by 19.87 % for DS6H5 due to higher in-cylinder temperatures. Overall, this study validates sanitary-waste-derived syngas with hydrogen enrichment as a promising fuel for advanced combustion engines, while highlighting the need for NOx mitigation strategies.

The global transition from fossil fuels to carbon‐free energy has accelerated interest in renewable fuels such as hydrogen and ammonia (NH 3 ). Ammonia has emerged as a promising carbon‐free energy carrier because it can be liquefied at approximately 1 MPa under ambient conditions, has a high‐octane number of about 110, and contains 17.6 wt% hydrogen, making it attractive for large‐scale energy storage and transportation. This article focuses on earlier research and recent studies on technical developments in direct injection (DI) of NH 3 ‐assisted combustion. Focus on the combustion characteristics of NH 3 DI in ICEs, as well as the spray characteristics, safety, and handling of NH 3 . This review paper develops the fundamentals of the mechanism of NH 3 combustion technology, providing new insights into the application of NH 3 in ICEs. Although NH 3 possesses favorable storage characteristics, its application in ICEs is challenged by a high autoignition temperature ( ∼ 650 °C), low laminar flame speed ( ∼ 7 cm/s), and lower heating value (18.8 MJ/kg), which contribute to combustion instability, NO x formation, and NH 3 slip. The review also explains the fundamental combustion mechanisms of ammonia and identifies key research gaps and future directions for developing efficient, low‐emission ammonia‐fueled internal combustion engines, supporting the transition towards sustainable and carbon‐free transportation.

This study presents an experimental investigation of a single-cylinder, four-stroke high-pressure direct injection CI engine operating on a diesel–hydrogen–sanitary waste-derived syngas tri-fuel blend, with the aim of improving combustion and emissions through combined optimization of engine operating parameters. The tri-fuel combination was selected to utilize the high reactivity and clean-burning characteristics of hydrogen together with the waste-to-energy potential of sanitary waste-derived syngas, thereby improving engine performance while reducing dependence on conventional fossil fuels. Experiments were conducted by varying the compression ratio (CR: 16.5, 17.5, and 18.5), injection timing (IT: 21°, 23°, and 25° bTDC), and injection pressure (IP: 500, 600, and 700 bar). Diesel was supplied via direct injection, while syngas and hydrogen were introduced through port injection. The DS6H5 configuration (diesel with 6 ms syngas and 5 ms hydrogen induction) provided the best results at CR 18.5, IT 25°, and IP 700 bar. Under these conditions, peak in-cylinder pressure and net heat release rate increased by 41.13% and 39.7%, respectively, compared to baseline diesel. The engine showed a 12.22% improvement in brake thermal efficiency (BTE) and a 20% reduction in brake specific fuel consumption (BSFC). Regarding emissions, carbon monoxide (CO), and unburned hydrocarbons (UHC) were reduced by 22%, and 38.9%, respectively. While oxides of nitrogen (NOx) emissions increased by 9.9% for DS6H5, the DS8H5 blend (diesel with 8 ms syngas and 5 ms hydrogen induction) showed a lower NOx increase of 8.26% under the same parameters. These results show that higher compression ratio, advanced injection timing, and higher injection pressure improve combustion intensity and fuel utilization in tri-fuel operation.

Hydrogen is a promising alternative fuel for internal combustion engines due to its renewable nature, low emissions, and superior combustion performance. In the current research, the effects of hydrogen enrichment were studied on the thermodynamic analysis of spark ignition engines using premium gasoline-ethanol blends. The blends were prepared with a partial addition of ethanol (10 % and 20 % by volume) in premium gasoline and hydrogen was injected during combustion for 2, 3, 4, and 5 mu s. The testing was done on the varying engine speeds at 1500, 2000, 2500, 3000, and 3500 rpm. Energy and exergy analyses, entropy generation, and sustainability index were assessed for different fuel blends and contrasted with premium gasoline. The brake thermal efficiency and exergy efficiency were found maximum at 2500 rpm engine speed for all tested fuel blends. The BTE of E10H5 fuel blend is 18 % higher than premium gasoline and the exhaust gas energy of the E10H5 fuel blend is 12 % higher than premium gasoline at 2500 rpm. Among all tested fuel blends, the E10H5 fuel blend showed prominent results. The present experimental investigation focuses on energy-exergy analyses of premium gasoline-ethanol blends with enriched hydrogen at different injection times to assess the potential fuel blends. These blends will help to reduce dependency on conventional fossil fuels by enriching hydrogen without modification of the engine.

Micromix combustion technology emerges as a promising solution to address challenges in achieving clean combustion, particularly for hydrogen utilisation. This review provides a critical analysis for the potential of micromixing by delving into its core principles, diverse applications and the factors influencing its performance. The paper focuses on injector design, flame stabilisation and NOx mitigation strategies within the micromixing framework. Key findings include innovative burner designs, optimised air distribution techniques and the crucial role of fuel properties, especially for hydrogen combustion. The review highlights significant reductions in NOx emissions achieved through micromix combustion technology. For instance, NOx emissions were lowered to 2.2 ppm at phi = 0.4, representing a 45% improvement compared to conventional design configurations. Furthermore, a reduction of 40% in NOx emissions compared to standard configurations was observed at an equivalence ratio of 0.65. The study also compares NOx emissions between hydrogen and its blended fuels, showing lower emissions for methane. By highlighting the importance of optimising fuel mixture formation and flame stability for various operating conditions, this review underscores the significance of micromix combustion for advancing sustainable combustion technologies with low NOx emissions and reduced chance of flashback in hydrogen combustion.

Internal combustion (IC) engines have contributed to global economic development in industrialized societies. Hydrocarbon fuels used for fueling the IC engines need to be replaced by sustainable and eco-friendly origins that do not adversely impact the environment locally and globally. Electro-fuels (or E-fuels) and biofuels are essential to displace fossil fuels. They are primarily produced using renewable electricity and feedstocks, respectively, and represent an emerging class of carbon-neutral drop-in fuels for the transport sector, which are becoming increasingly important with every passing day globally and have an essential role in the ‘net-zero’ future. This paper comprehensively reviews the advancements in IC engines to become more efficient in taking the fuel property advantages of various E-fuels and biofuels in existing engines. The paper focuses on several fuels, among the most studied ones in the open literature in the last decade, since their adoption might depend on factors such as the local economic considerations, cultural contexts and the application itself, storability, power requirement, and government policies. The paper covers these fuels by briefly introducing their production pathways and properties. It then focuses on their engine use to meet the future tailpipe and greenhouse gas emissions norms. Challenges regarding the modelling of engines powered by E- or bio-fuels are also included. E-fuels offer a straightforward advantage even in engine-out emissions and after-exhaust emission control technologies. It represents an opportunity to limit GHG emissions. Moreover, the E−(or Bio-) fuels powered engines can cover the same operating range (or a larger one) with similar efficiency or greater than hydrocarbon fuels. However, using these fuels still remain challenging. Retrofitting existing engines for using E−(or Bio-) fuels depends on the cost of the fuel injection system for injecting the fuel into the combustion chamber. The transition from fossil fuels can be done using liquid fuels such as methanol, ethanol, etc., by blending them with conventional fuels. In the long run, methanol, hydrogen, and ammonia are expected to significantly decarbonize the transport sector globally.

This study addresses the dual challenge of waste management and sustainable energy by investigating the utilization of sanitary-waste-derived syngas in a dual-fuel Reactivity-Controlled Compression Ignition (RCCI) engine. Sanitary waste, co-gasified with CO2, produces hydrogen-rich syngas, offering a novel route for both waste valorization and partial diesel displacement. The engine was operated under varying load conditions using different diesel-syngas injection strategies (DS2-DS10), with syngas port-injected and diesel directly injected. A combined energy and exergy analysis was performed to evaluate combustion behavior, emission characteristics, entropy generation, and the sustainability index. The results revealed that the DS2 blend (2 ms syngas injection) delivered the most balanced performance, achieving only a 4.1% reduction in exergy efficiency compared to diesel while limiting exergy destruction and entropy generation. Higher syngas fractions such as DS10 degraded performance, leading to an 18.45% drop in exergy efficiency and a 36.26% increase in entropy generation. Compared to diesel, DS2 showed minor losses in BTE (4.68%) and exhaust energy (3.72%) but enabled a net improvement in environmental sustainability metrics. The novelty of this work lies in demonstrating the viability of sanitary-waste syngas as a co-fuel in RCCI mode, supported by integrated thermodynamic and sustainability assessments, extending beyond conventional biomass syngas applications by addressing the energy-exergy trade-offs of hydrogen-rich waste-derived fuels.

This study evaluates the environmental and economic impacts of hydrogen production through traditional steam methane reforming and electrified steam methane reforming, utilizing various renewable energy systems. A life cycle assessment using greenhouse gases, regulated emissions, and energy use in technologies model software reveals significant annual carbon dioxide emissions from traditional steam methane reforming, projected to reach 14 million tonnes by 2035. In contrast, electrified steam methane reforming with carbon capture and storage shows an 82 percent reduction in carbon dioxide emissions. The system advisor model was used to design and optimize renewable energy systems, identifying concentrated solar power as producing the highest annual energy output of 1.63 million megawatt-hours and hydrogen output of 39,057 tonnes, with total revenues of $4.4 billion. While concentrated solar power is the most efficient and economically viable for hydrogen production, the horizontal wind turbine system provides a continuous energy supply, ideal for consistent energy needs. These findings highlight the importance of integrating mature technologies like steam methane reforming with renewable energy and carbon capture and storage to achieve sustainable hydrogen production.

Sustainable Aviation Fuels (SAFs) and e-fuels present a transformative opportunity to significantly decarbonize aviation. However, their widespread adoption depends on overcoming challenges such as production scalability, infrastructure expansion, and cost efficiency. This study explores the potential of integrating e-fuels into aviation by evaluating three scenarios: Scenario 0 (99 % conventional jet fuel), Scenario 1 (50 % e-fuels blend), and Scenario 2 (100 % e-fuels). Using SARIMAX modeling, we project aviation fuel demand to reach 182.4 billion gallons by 2050. Under Scenario 0, this results in 195.3 million metric tonnes (MMT) of CO2 emissions. Scenario 1 achieves a 50 % reduction to 97.7 MMT, while Scenario 2 nearly eliminates emissions, reducing them by 96 % to 2.8 MMT. To meet fuel demand, Scenario 1 requires 223 MMT of hydrogen per year and approximately 8000 Concentrated Solar Towers (CST), whereas Scenario 2 doubles these needs to 446.5 MMT of hydrogen and 16,000 CST systems. Scenario 1 provides a pragmatic near-term approach by leveraging existing infrastructure, while Scenario 2 represents a long-term, near-zero emissions pathway. This analysis highlights the essential role of green hydrogen and renewable energy systems in aviation decarbonization. Accelerated investments, policy enhancements, and technological innovations are crucial to bridging the gap between ambition and implementation, ensuring a sustainable future for air travel.