Multi-objective prediction and optimization of alcohol–gasoline SI engines using a hybrid gradient boosting and evolutionary algorithm framework

Thermodynamic trade-offs of methane–hydrogen fuel blends in a spark-ignition engine: Effects of compression ratio and fuel hydrogen fraction under fixed ignition timing

Lubricant formulation effects on ultra-fine particles emissions from gas fuelled engines: experimental investigation using machine learning in data analysis

Mitigating carbon emissions in a legacy spark-ignition engine via ammonia supplementation: An efficiency-NOx trade-off study

Effects of air-fuel ratio, ammonia blending ratio and operating parameters on performance, combustion and emission characteristics of an ammonia-gasoline spark-ignition engine

Hydrogen-fueled internal combustion engines (H 2 -ICEs) hold strong potential as a pathway toward CO 2 -neutral propulsion. To reduce emissions, H 2 -ICEs are usually operated under fuel-lean conditions, where the flames are prone to thermo-diffusive instabilities (TDIs). These TDIs govern both local and global flame propagation, but their impact on full-scale engine combustion remains an open question. In this study, high-fidelity three-dimensional large-eddy simulations (LES) are performed at multiple mesh resolutions, with the finest grid sufficiently resolved to directly characterize flame front dynamics relevant to engine-scale combustion. The simulations reveal cellular and finger-like flame structures characteristic of TDIs throughout the entire combustion process. Analysis of the local thermo-chemical state demonstrates that differential diffusion induces pronounced mixture stratification and elevates reaction rates, resulting in super-adiabatic temperatures that strongly correlate with flame curvature. Building on these findings, the performance of the baseline artificially thickened flame (ATF) model and a recently developed thermo-diffusive (TD)-aware extension is assessed. Unlike the state-of-the-art ATF model, which suffers from grid dependence and underestimates the experimental pressure trace, the TD-aware formulation captures experimental trends more accurately and provides consistent, grid-independent integrated heat-release (IHR) traces. For the operating condition considered here, the results show that TD effects represent sub-grid-scale contributions that need to be accounted for to obtain consistent predictions of global combustion behavior under the investigated lean H 2 -ICE conditions. • LES captured cellular and finger-like thermo-diffusive flame structures. • Coarser grids suppressed fine-scale instabilities resolved at high resolution. • Local mixture stratification enhanced reactivity and caused super-adiabatic states. • ATF model showed grid bias from missing thermo-diffusive instability treatment. • Thermo-diffusive-aware ATF model reduced grid bias and improved predictive accuracy.

Illustrative overview of CNG engine performance, emissions behavior, and operation challenges. The graphic highlights key trends identified in the systematic review, including typical 10–20% power and torque losses; reductions in CO, HC, PM, and CO 2 emissions; methane-slip escalation with mileage; and the dual effect of cleaner combustion but accelerated lubricant oxidation. The figure synthesizes evidence from 22 studies to show how engine architecture, retrofit quality, and accumulated mileage shape real-world CNG outcomes • Provides the first systematic, strata-based synthesis of CNG performance, emissions, and durability in aged and retrofitted SI and CI engines. • Demonstrates that performance and emissions outcomes under CNG are governed by engine design, retrofit quality, calibration strategy, and accumulated degradation rather than fuel properties alone. • Shows that retrofitted SI fleet engines commonly experience power loss and methane slip, while optimized dedicated SI engines achieve higher efficiency through compression ratio and combustion phasing control. • Identifies dual-fuel CI engines as offering strong particulate reduction but requiring careful pilot-injection and EGR management to avoid CO and HC drawbacks at low load. • Highlights durability and lubrication trade-offs under CNG, with reduced soot contamination but increased thermo-oxidative oil stress, emphasizing the need for robust maintenance and calibration practices. Compressed natural gas (CNG) offers significant emissions advantages over gasoline and diesel, yet most literature focuses on new or laboratory-optimized engines rather than the aged, retrofitted vehicles common in developing countries. With addition of other studies, the review followed PRISMA 2020 guidelines and a prospectively registered protocol (OSF) − https://osf.io/c8u7f/ . Searches across Scopus, IEEE Xplore, and Google Scholar identified 816 records, of which 26 studies met inclusion criteria. CNG consistently lowered CO, HC, PM, and CO 2 emissions, but retrofitted SI engines experienced 10–20% losses in power and torque due to methane’s low volumetric energy density and age-related declines in efficiency. High-mileage fleets showed methane-slip increases, catalyst deterioration, and lubricant oxidation, whereas optimized or dedicated CNG engines demonstrated improved thermal efficiency and fuel economy. Retrofit quality and calibration accuracy proved decisive in determining real-world outcomes. The findings highlight that CNG’s environmental and efficiency benefits are achievable but depend on proper engine design, maintenance, and regulatory support, especially in regions dominated by older vehicle fleets. This review provides the first systematic synthesis focused on aged, high-mileage, and retrofitted spark ignition (SI) and compression ignition (CI) engines operating on CNG, integrating evidence on performance, emissions, combustion behavior, methane slip, lubricant degradation, and catalyst aging. By comparing retrofitted and dedicated CNG engines against real-world aged engine across diverse regions, it reveals how engine architecture, retrofit quality, and accumulated mileage shape CNG outcomes and identifies the operational challenges and research priorities needed for durable, efficient, and low-emission operation.

Strategies for improving premixed oxy-fuel combustion in spark-ignition engines

Influence of passive prechamber orifice diameter on hydrogen combustion dynamics in a spark-ignition optical engine

Performance and emission analysis of spark ignition engine powered by premium gasoline-ethanol blends with partial addition of amyl alcohol, iso-butanol and hydrogen

Optimization of the gas exchange process in a H2 V8 6.6 ℓ 2-stroke heavy-duty spark ignition engine

Variable valve timing strategies for ammonia-hydrogen fuelled spark ignition engine combustion

Design and performance analysis of an 8.7-liter E100-fuelled SI engine integrated with an ORC waste heat recovery system for genset applications

The article presents a detailed analysis of operational repair costs for vehicles with mileage of 30,000, 60,000, 90,000, and 120,000 kilometers. The study focused on selected automotive groups that offer at least three vehicle models within the same market segment, with the condition that these vehicles were equipped with identical powertrains-both spark ignition and compression ignition engines. The analysis was conducted in the context of repairs carried out at both authorized service stations and independent repair workshops. The aim of the study was to assess whether the operational repair costs for premium segment vehicles differ significantly from those of mass-market vehicles within the same automotive group. Furthermore, the study examined whether there is a relationship between the duration of individual brands' participation in the automotive group structure and the reduction of differences in operational repair costs. The research employed a numerical experimentation method using the AUDATEX system, which enabled the precise determination of repair costs. The differences in service costs for cars considered more prestigious compared to popular cars ranged from -20% to nearly 120%. This was most often to the detriment of cars considered prestigious, which is interesting given that they used the same engines. Service availability and market presence are important considerations, as younger brands tended to show greater differences.

This study experimentally investigates the effects of n-butanol/gasoline blends on combustion, exhaust emissions, and sustainability indicators in a single-cylinder, air-cooled spark-ignition engine. Two fuel mixtures containing 5% and 15% n-butanol by volume (NB5 and NB15) were tested under full load at engine speeds of 1500, 2000, 2500, and 3000 rpm. Results show that the addition of n-butanol improves combustion quality and significantly reduces CO emissions by up to 50% at high speeds, while CO₂ emissions increase slightly at low-to-medium speeds due to more complete combustion. HC emissions decreased with the NB5 blend but increased with NB15, particularly at lower speeds, due to reduced volatility and mixture inhomogeneity. An integrated energy–exergy–exergoenvironmental–exergoenviroeconomic analysis was performed to evaluate thermodynamic efficiency, environmental cost, and sustainability performance. Exergy loss exhibited a logarithmic increase with engine speed, while the exergoenvironmental impact showed a logarithmic decrease. The exergoenviroeconomic index (Ψ) demonstrated a logarithmic growth pattern, indicating improved sustainability with n-butanol addition. Among the tested fuels, NB15 achieved the lowest exergy destruction (≈9.6 MJ/s at 3000 rpm) and the highest sustainability index (Ψ ≈ 3019), demonstrating a 10–15% improvement in thermodynamic and environmental performance compared with gasoline. These findings confirm that n-butanol, due to its oxygenated nature and high-octane rating, enhances combustion efficiency and offers a viable pathway toward cleaner and more sustainable spark-ignition engine operation.

Abstract The progressive exhaustion of conventional fossil-fuel reserves, combined with increasingly stringent emission legislation under Euro 6 and Bharat Stage VI (BS-VI) norms, has created an urgent imperative to develop and validate alternative fuel pathways for spark-ignition (SI) engines. This paper presents a rigorous experimental investigation of the performance and emission characteristics of a four-stroke, four-cylinder water-cooled petrol engine fuelled with four configurations: neat gasoline (baseline), 10% ethanol–gasoline blend (E10), 20% ethanol–gasoline blend (E20), and a compressed natural gas (CNG) pilot blend. Dynamometer tests were conducted at 1500 rpm across four discrete load conditions (25%, 50%, 75%, and 100% of rated load). Measured performance parameters include Brake Thermal Efficiency (BTE), Brake Specific Fuel Consumption (BSFC), Mechanical Efficiency, and Volumetric Efficiency. Exhaust emission constituents—HC, CO, CO₂, and NOₓ—were quantified using a calibrated five-gas analyser in accordance with ISO 8178. The Morse test was used to determine Indicated Power independently for each cylinder. Results demonstrate that E20 achieves the highest BTE of 33.2% at full load, a 10.3% relative improvement over the petrol baseline (30.1%), with BSFC concurrently reduced from 275 g/kWh to 245 g/kWh. HC emissions decrease by 27.6% and CO by 31.6% with E20, while NOₓ rises marginally by 7.2%. CNG blend delivers the lowest CO (1.68% vol) and NOₓ (810 ppm) but at a volumetric efficiency penalty. Uncertainty analysis confirms BTE values within ±1.32% at 95% confidence. E20 is substantiated as a viable drop-in alternative fuel requiring no hardware modification, aligned with India's EBP 2025 mandate. Index Terms alternate fuels, brake thermal efficiency, BSFC, CNG, ethanol blends, exhaust emissions, four-cylinder engine, SI engine.

In-cylinder pressure is a key parameter for evaluating combustion processes and engine performance in spark-ignition engines. However, acquiring high-resolution pressure data over a wide range of operating conditions, particularly under varying spark advance (SA), is costly and technically challenging, which limits its practical application. To address this issue, this study proposes two artificial neural network (ANN)-based methods for in-cylinder pressure reconstruction using data from a three-cylinder gasoline engine under different spark advance conditions. Both methods employ crank angle and spark advance as input features. The first method (ANN-P) directly predicts the in-cylinder pressure profile, achieving a coefficient of determination (R2) exceeding 0.99 on both training and validation datasets, with a root mean square error (RMSE) below 0.13 bar. The model accurately reproduces the pressure evolution throughout the compression, combustion, and expansion processes and enables reliable estimation of indicated mean effective pressure (IMEP). The second method (ANN-HRR) adopts an indirect strategy by first predicting the heat release rate (HRR) and subsequently reconstructing the pressure trace through thermodynamic integration based on a single-zone model. This approach avoids error amplification associated with numerical differentiation and demonstrates improved accuracy in predicting combustion phasing metrics, such as CA10 and CA50. The results indicate that both methods effectively capture the influence of spark timing on combustion characteristics and peak pressure. While ANN-P provides higher accuracy in pressure reconstruction, ANN-HRR offers superior performance in characterizing combustion features. Overall, this study presents a cost-effective and accurate framework for combustion diagnostics, performance calibration, and control optimization of gasoline engines.

This study investigated the performance and emission behavior of a spark-ignition (SI) engine fueled with a novel four-component hybrid blend comprising 40% gasoline, 20% ethanol, 20% biogas, and 20% hydrogen, and optimized the operating parameters using a cubic Response Surface Methodology (RSM) framework. Unlike earlier works limited to binary or ternary blends, this research introduced a synergistic fuel mixture that combined the high flame speed of hydrogen, the oxygenated combustion of ethanol, and the renewable carbon fraction of biogas. Experimental tests were conducted on a spark ignition engine across a wide range of inlet pressures (0.75–1.5 bar), compression ratios (8–11), and engine speeds (1000–4000 rpm). Performance (BP, BTE, BSFC) and emission parameters (CO, CO 2 , NO x , HC) were modeled using RSM, and all regression models exhibited excellent adequacy ( R 2 > 0.97), confirming strong predictive strength. The best working conditions were 1.5 bar inlet pressure, 10.9 compression ratio and 3330 rpm. These conditions provided the maximum brake power (35.37 kW), brake thermal efficiency (25.89%), and the minimum BSFC (0.33 kg/kWh). Oxidation occurred at a faster pace with hydrogen and ethanol, and the speed at which flames propagated also increased, which reduced the emissions of CO and HC significantly. Nevertheless, the increase in the NO emissions increased slightly at higher temperatures. The integrated optimization produced a desirability index of 0.779, which showed that it was a good balance between improving efficiency and controlling emissions. The study showed that a hydrogen-assisted gasoline–ethanol–biogas blend burned steadily and without knocking, with better performance and less pollution. This showed that there is a way to run SI engines cleaner and more sustainably.

A variational mode decomposition based statistical approach for knock detection in spark ignition engines using engine block vibrations

Abstract Hydrogen is widely recognized as an effective combustion enhancer in internal combustion engines due to its high reactivity and wide flammability range. Although numerous studies have reported qualitative improvements in efficiency, combustion stability, and lean-burn capability through hydrogen addition, the quantitative identification of combustion stability limits and minimum hydrogen requirements under ultra-lean operating conditions remains insufficiently addressed. This study experimentally investigates a spark-ignition engine operating on a hydrogen–gasoline dual-fuel concept with port fuel injection of hydrogen and direct injection of gasoline. The engine was tested over a wide air excess ratio range from λ = 1.0 to 2.6 and hydrogen energy shares from 0% to 40%, with the objective of identifying threshold hydrogen concentrations required to maintain stable and efficient combustion. Combustion behavior was evaluated using brake thermal efficiency, in-cylinder pressure analysis, coefficient of variation of indicated mean effective pressure, and gaseous emission measurements.The results reveal the existence of a critical hydrogen energy share between 20% and 30%, beyond which combustion stability is preserved even under ultra-lean conditions. Hydrogen shares of 30–40% enable a substantial extension of the operable lean range while maintaining acceptable efficiency and pressure stability, whereas lower hydrogen fractions provide only marginal stabilization. These findings provide experimentally derived threshold values that support the practical design and control of hydrogen-assisted combustion systems.